# Request: How to use an oscilloscope to check amp for clipping?



## ErinH (Feb 14, 2007)

I have at least 10 of these things at my work but I have no idea how to use them to test my amplifier's clipping point. It'd be nice to know so that when I adjust gains when I do my next install I have an idea of what I cannot go past. 

Rather than re-cap why one of the Techs here said I couldn't do it, I'll just let someone tell me how I can and then go do it myself.

I know this might be a large request, but I'd appreciate it.


----------



## chad (Jun 30, 2005)

You got dummy loads?


----------



## ErinH (Feb 14, 2007)

Have no idea. I'll have to ask later.


----------



## bdubs767 (Apr 4, 2006)

chad said:


> You got dummy loads?


cant you just use resistors??? or leave the loud speaker connected?


----------



## chad (Jun 30, 2005)

I really don't think you want to pin your amps full bore into mids and tweets 

Dummy loads are resistors, but ones that can handle the brunt of the amplifier.


----------



## ErinH (Feb 14, 2007)

chad said:


> I really don't think you want to pin your amps full bore into mids and tweets
> 
> Dummy loads are resistors, but ones that can handle the brunt of the amplifier.


That's pretty much why he (the tech) was saying I couldn't use an o-scope. He said that you couldn't use speakers because you would burn them up (which is right), and that there weren't any resistors he knew of that would take that much power.

I'll have to ask if he's heard of a dummy load tomorrow morning.


----------



## chad (Jun 30, 2005)

Dale makes the load resistor I Use










This is my load










never mind the missing Bananna jack, it's been replaced.

I have another load I run wet bathed in Automatic Transmission Fluid, that gets me by for home purposes.

I used a "water heater load" with a water pump and a radiator/fan when I was doing the big amps like the Crest 9001's and Crown MA10,000's


----------



## ErinH (Feb 14, 2007)

Man, you really confuse the hell out me about 90% of the time.


----------



## chad (Jun 30, 2005)

bikinpunk said:


> Man, you really confuse the hell out me about 90% of the time.


Big ****ing Resistors...... Soak power.... Make Heat..... no Blow Speakers... Speakers No Hooked Up.....


----------



## MarkZ (Dec 5, 2005)

chad said:


> I have another load I run wet bathed in Automatic Transmission Fluid, that gets me by for home purposes.
> 
> I used a "water heater load" with a water pump and a radiator/fan when I was doing the big amps like the Crest 9001's and Crown MA10,000's


Why ATF?


----------



## MarkZ (Dec 5, 2005)

bikinpunk said:


> Man, you really confuse the hell out me about 90% of the time.


That's why you shouldn't get too exotic with your gain setting! Do it the standard way.


----------



## chad (Jun 30, 2005)

MarkZ said:


> Why ATF?


Keeps it cool, does not evaproate, Dielectric, and will not burn under those conditions, ever. Works for RF too!


----------



## chad (Jun 30, 2005)

MarkZ said:


> That's why you shouldn't get too exotic with your gain setting! Do it the standard way.



Word


----------



## ErinH (Feb 14, 2007)

MarkZ said:


> That's why you shouldn't get too exotic with your gain setting! Do it the standard way.


Yea, but I kind of like learning stuff like this. Even though I have no idea wtf is going on sometimes.


----------



## xcoldricex (Apr 28, 2007)

chad said:


> This is my load


that's what she said...

wait it doesn't work :blush:


----------



## Horton Hears The Who (Nov 7, 2007)

BikinPunk, I like your attitude of wanting to learn. This forum seems cool so I'm surprised no one has helped you yet.

I just bought a used scope a couple weeks back so I'm new at using it. If I leave something out or make a mistake, someone should correct it. 
Here is one link I found.

http://www.edesignaudio.com/edv2/gains_video.php

He uses a 4 ohm resistor instead of speakers to present a load to the amp and a volt meter, but somewhere on the site he uses an oscilloscope.

An oscilloscope is actually fairly straight forward. I hope you have an analog scope. From what I understand an analog scope works better for testing clipping. 

Do you have the manual for your scope? It will tell you how to compensate the probe you are using.

You should test and set the components upstream from the amp one by one before setting the amp. 

Test the head unit first by connecting the probe to inside/female part of the preamp output and the probe ground to the shield/outside.

If the head unit is installed disconnect the interconnects at the next component in line and connect the probe there.

Play a 0 db 1khz sine wave. They can be found on test discs or downloaded and burned to CD.

Start with the head unit volume about half way. (Not critical but will save a little fiddling and looking for a waveform) You may not see a signal at first. Adjust the volts/div and time/div knobs on the scope until you can see a waveform. 

The tops and bottoms of the waveform should be rounded. Turn up the volume until you see the rounded top "Clipped" off. Now back the volume down until you don't see any clipping.

You have just found your head units clipping point. Make a note of it.

Some head units don't clip, even at full volume. My Denon DCT-Z1 is one of those. I also tested a Rockford RFX-8240 and it highest volume without clipping was 29. I believe full volume is 32 on it.

If you have one or more equalizers, adjust them the same way. When you get to the amp the scope settings will be different because the signal is now amplified. 

Start with the amp gains turned down, which is numerically high. Use the 4 ohm resistor and do the same as before. (I haven't researched on exactly what type of 4 ohm resistor to use)

I haven't tested/adjusted my amp's gain setting this way yet. The pot adjustment screw decided to quit working on channels 1/2 of my Nakamichi P504.

I think scopes are fun and cool! 

Let me know if this is helpful.


----------



## Horton Hears The Who (Nov 7, 2007)

BikinPunk, I like your attitude of wanting to learn. This forum seems cool so I'm surprised no one has helped you yet.

I just bought a used scope a couple weeks back so I'm new at using it. If I leave something out or make a mistake, someone should correct it. 
I found a video on elemental designs website. I can't post it yet because I don't have 5 posts.

He uses a 4 ohm resistor instead of speakers to present a load to the amp and a volt meter, but somewhere on the site he uses an oscilloscope.

An oscilloscope is actually fairly straight forward. I hope you have an analog scope. From what I understand an analog scope works better for testing clipping. 

Do you have the manual for your scope? It will tell you how to compensate the probe you are using.

You should test and set the components upstream from the amp one by one before setting the amp. 

Test the head unit first by connecting the probe to inside/female part of the preamp output and the probe ground to the shield/outside.

If the head unit is installed disconnect the interconnects at the next component in line and connect the probe there.

Set all tone controls to zero/off. EQ's and bass boost also get turned off. Play a 0 db 1khz sine wave. They can be found on test discs or downloaded and burned to CD.

Start with the head unit volume about 3/4. (Not critical but will save a little fiddling and looking for a waveform) You may not see a signal at first. Adjust the volts/div and time/div knobs on the scope until you can see a waveform. 

The tops and bottoms of the waveform should be rounded. Turn up the volume until you see the rounded top "Clipped" off. Now back the volume down until you don't see any clipping.

You have just found your head units clipping point. Make a note of it.

Some head units don't clip, even at full volume. My Denon DCT-Z1 is one of those. I also tested a Rockford RFX-8240 and it highest volume without clipping was 29. I believe full volume is 32 on it.

If you have one or more equalizers, adjust them the same way. When you get to the amp the scope settings will be different because the signal is now amplified. 

Start with the amp gains turned down, which is numerically high. Use the 4 ohm resistor and do the same as before. (I haven't researched on exactly what type of 4 ohm resistor to use)

I haven't tested/adjusted my amp's gain setting this way yet. The pot adjustment screw decided to quit working on channels 1/2 of my Nakamichi P504.

I think scopes are fun and cool! 

Let me know if this is helpful.


----------



## newtitan (Mar 7, 2005)

chad said:


> Dale makes the load resistor I Use
> 
> 
> 
> ...



why the need for transmission fluid versus standard water? do you amps runs that warm under heavy load?

and any details as to how you constructed this dummy load setup?


----------



## Ge0 (Jul 23, 2007)

chad said:


> Big ****ing Resistors...... Soak power.... Make Heat..... no Blow Speakers... Speakers No Hooked Up.....


OMFG I just pissed myself and spewed Vodka out my nose!

Way to dumb things down Chad  .

Ge0


----------



## Oliver (Jun 25, 2007)

Ge0 said:


> OMFG I just pissed myself and spewed Vodka out my nose!
> 
> Way to dumb things down Chad  .
> 
> Ge0


Sweet !!!!!

After Bikinpunk finds out the price of those big ass resistors  , it'll be like **** that O'scope ****  

I can set these just fine with a disc from Navone, and my ears !!


----------



## Ge0 (Jul 23, 2007)

newtitan said:


> why the need for transmission fluid versus standard water? do you amps runs that warm under heavy load?
> 
> and any details as to how you constructed this dummy load setup?


I just joined this thread and have not read through the entire thing. However, I use oils as a coolant for my high current power resistors because it handles high temp and won't evaporate. You can "love a load a long time" and not worry about the coolant disappearing.

As far as the load box, I imagine the resistors terminate to a post on the nanner jacks. You can configure a different resistance load by applying various jumpers across the resitors. He just mounted them on a bud type project enclosure you can buy through Digikey.

I did mine differently. I mounted my resistors (identical to Chads) to an extruded aluminum heat sink from an old linear power amp (lots of tall fins and high surface area for heat dissipation). I dip the heat sink fins in fluid when needed. My oil bath is housed in a metal container which is also constucted of old amp extrusions. I blow a large fan over the whole assembly to remove the heat. With this, I can run a 2KW amp full bore all day and not worry about thermal overload. Without it, these resistors tend to self destruct rather violently. I learned by experience when a wire wound resistor blew up and lodged its windings in my chest.

Keeping the amp itself cool is another story. I have a small environmental chamber with liquid nitrogen assist that can keep the amp at a cool -40 degrees.

Ge0


----------



## Ge0 (Jul 23, 2007)

Hic said:


> Sweet !!!!!
> 
> After Bikinpunk finds out the price of those big ass resistors  , it'll be like **** that O'scope ****
> 
> I can set these just fine with a disc from Navone, and my ears !!


You can buy power resistors surplus on ebay pretty cheap. Besides, you don't NEED to run an amp at its rated load to determine its clip point. For instance, you could always increase the resistance by a power of 10 or 100. These resistors are far cheaper.

Run a sinewave signal to the amps input and keep the scope on its output. Hard clipping occurs when the tips of the sine wave start to flatten out (i.e. hit the amps power supply rails). Back gain down a notch or two beyond the point to where the output signal starts flattening.

Ge0


----------



## Ge0 (Jul 23, 2007)

bikinpunk said:


> I have at least 10 of these things at my work but I have no idea how to use them to test my amplifier's clipping point. It'd be nice to know so that when I adjust gains when I do my next install I have an idea of what I cannot go past.
> 
> Rather than re-cap why one of the Techs here said I couldn't do it, I'll just let someone tell me how I can and then go do it myself.
> 
> I know this might be a large request, but I'd appreciate it.


Have the tech show you how to mehyer (measure) a sine wave using the scope. Also have him show you how to adjust the sucker to change volts per division and time per division. Once you get this down, come back and we'll discuss amp clipping.

Ge0


----------



## Oliver (Jun 25, 2007)

Ge0 said:


> I just joined this thread and have not read through the entire thing. However, I use oils as a coolant for my high current power resistors because it handles high temp and won't evaporate. You can "love a load a long time" and not worry about the coolant disappearing.
> 
> As far as the load box, I imagine the resistors terminate to a post on the nanner jacks. You can configure a different resistance load by applying various jumpers across the resitors. He just mounted them on a bud type project enclosure you can buy through Digikey.
> 
> ...


You must get some serious readings when you can cool down an amp like that!

What is the highest wattage you have seen ?


----------



## chad (Jun 30, 2005)

Ge0 said:


> I just joined this thread and have not read through the entire thing. However, I use oils as a coolant for my high current power resistors because it handles high temp and won't evaporate. You can "love a load a long time" and not worry about the coolant disappearing.
> 
> As far as the load box, I imagine the resistors terminate to a post on the nanner jacks. You can configure a different resistance load by applying various jumpers across the resitors. He just mounted them on a bud type project enclosure you can buy through Digikey.
> 
> ...


That pretty much sums it up, my oil bathed ones are completely subersed, I have 2 loads at home, well for AF then I have a couple RF loads too.



Ge0 said:


> Besides, you don't NEED to run an amp at its rated load to determine its clip point. For instance, you could always increase the resistance by a power of 10 or 100. These resistors are far cheaper.
> 
> Ge0


Oh yeah you do, you need to run at the planned impedance.

For example, put an amp on a 4 ohm load and run it just to the verge of clipping.... then half the impedance... it will now be clipping because it's under more stress. This is why amplifiers simply do not double power every time you half impedance, either the PS or the output section will eventually buckle. Contrary to many marketing department's belief.



Hic said:


> You must get some serious readings when you can cool down an amp like that!
> 
> What is the highest wattage you have seen ?



I can't remember my highest but I remember going "woah" with a Crown Macrotech 10,000... hint.... It REQUIRED a 3 phase AC input 

Back in the day at one shop we had "loadzilla" which was a modified electric hot water heater that had a water pump, a radiator and radiator fan outdoors. It was filled with a simple glycol/water mix like in your car. That sucker could take some POWER!


Chad


----------



## Ge0 (Jul 23, 2007)

Hic said:


> You must get some serious readings when you can cool down an amp like that!
> 
> What is the highest wattage you have seen ?


Mind you, this setup was developed for the purpose of testing electric heaters that are part of the product I design, not specifically for testing big, bad ass amplifiers. Although it works well for doing so .

You can't hold an amp running full tilt at -40C. It still heats up like an SOB. But, having the cool ambient air (with circulation) around it helps keep its temp from reaching nuclear melt down.

The power supply I use is limited to 200A at 15VDC. I had an old Harrison Labs Drag Queen on it at one time. It maxed the supply out at 3KW. Mind you, amps are not 100% efficient so I was only dumping about 2KW into the loads. Doesn't seem that sexy right? At least knowing that the amp was capable of delivering 10KW+ into it loads.

Our heaters are another story. We can test numerous heaters in parallel using 3 independant supplies for a total load of approximately 9KW.

Ge0


----------



## Ge0 (Jul 23, 2007)

chad said:


> Oh yeah you do, you need to run at the planned impedance.
> 
> For example, put an amp on a 4 ohm load and run it just to the verge of clipping.... then half the impedance... it will now be clipping because it's under more stress. This is why amplifiers simply do not double power every time you half impedance, either the PS or the output section will eventually buckle. Contrary to many marketing department's belief.
> Chad


My bad, I made the assumption that the power supply rails would not droop significantly between the unloaded condition and the rated load of 4 ohm. At least they shouldn't. Of course they will droop as soon as you start bridging channels or loading them down with lower resistance loads.

I'll let you explain that one to the PUNK .

Ge0


----------



## chad (Jun 30, 2005)

Ge0 said:


> The power supply I use is limited to 200A at 15VDC.
> Ge0


I'm sooo drooling right now........ I want.


----------



## Ge0 (Jul 23, 2007)

chad said:


> I'm sooo drooling right now........ I want.


It's kind of cool. My company bought 7 of these supplies from another company who had no idea what they were. We paid $5000 for all of them PLUS two environmental chambers, 5 oscilloscopes, bench top meters, etc...

I found the deal so was allowed to keep some equipment for myself. After all, I do work at home at night .

Ge0


----------



## chad (Jun 30, 2005)

Ge0 said:


> It's kind of cool. My company bought 7 of these supplies from another company who had no idea what they were. We paid $5000 for all of them PLUS two environmental chambers, 5 oscilloscopes, bench top meters, etc...
> 
> I found the deal so was allowed to keep some equipment for myself. After all, I do work at home at night .
> 
> Ge0


Isn't that great? Do you have a shop to work in at home to get away?


----------



## Horton Hears The Who (Nov 7, 2007)

The guy genuinely wants to learn something and this is how you teach him?

He asked a question about a piece of test equipment that will teach him more about electronics than reading the preceding crap. 

Instead of encouraging him, you shut him down and try to impress each other.

Very helpful, very useful, very intelligent. I'm smarter for reading it!


----------



## chad (Jun 30, 2005)

Horton Hears The Who said:


> The guy genuinely wants to learn something and this is how you teach him?
> 
> He asked a question about a piece of test equipment that will teach him more about electronics than reading the preceding crap.
> 
> ...


I have his and he has my phone number, if he's up **** creek I KNOW he will call me. When I'm home, in front of my scope, and can twist knobs, and explain to him on a hands on basis what to look for.  

Ease up tiger, this is the way we roll around here, sometimes going a bit off tangent lays everything out, I could see this thread going on for a while.  

Chad


----------



## Ge0 (Jul 23, 2007)

Horton Hears The Who said:


> The guy genuinely wants to learn something and this is how you teach him?
> 
> He asked a question about a piece of test equipment that will teach him more about electronics than reading the preceding crap.
> 
> ...


Take it easy there stosh. Not trying to discourage him a bit. I would never discourage someone from expanding their knowledge base. I simply recommended he have his lab technician teach him how to use the scope first vs. us trying to do it through many reams of text here. I think that would be much more efficient. He could litterally learn the basics of using one in minutes if set right in front of him. It would take days to describe in messages here.

When he is ready we'll get into some meat and potatoes.

Now, are Chad and I guitly of filling this thread with useless fodder in an attempt to see who's dick is bigger. Of course  ... However, at least it remains somewhat on topic. This is stuff people could theoretically use. Besides, I have my doubts that Chad truely does have the biggest dick.

ge0


----------



## ErinH (Feb 14, 2007)

I ****ING HATE ALL OF YOU!!!


 


I know you guys are just messing with me, so it's all good.

I asked another tech and he said we have some 4 ohms resistors capable of handling 200+w. I'll get him to help me out with it, but he'll be learning on the fly, too. And, Chad...expect a call then, lol.


I'll post back when I have something with substance.


----------



## chad (Jun 30, 2005)

bikinpunk said:


> I ****ING HATE ALL OF YOU!!!
> 
> 
> 
> ...



You are SET on loads then. you can hit a 200W dale with more than 200W but watch how long you do it for. Anytime you are doing testing like this that is not classified as "torture testing" then keep your test periods short and let things cool down a bit. PWM amps don't like to run nuts out for very long anyways if you are using those. Testing with tones is NOTHING like testing with music the duty cycle is WAY higher. Just take your time and plan ahead so you are not "thinking" while a poor amp is sitting there sweating waiting on you to make up your mind on something


----------



## Ge0 (Jul 23, 2007)

bikinpunk said:


> I ****ING HATE ALL OF YOU!!!
> 
> 
> 
> ...


If you have specific questions, by all means ask. This is your thread and we feel inclined to visit it and help you out. Its just teaching someone totally GREEN in the use of a piece of lab equipment is difficult to do through these damn messages.

Ge0


----------



## ErinH (Feb 14, 2007)

chad said:


> You are SET on loads then. you can hit a 200W dale with more than 200W but watch how long you do it for. Anytime you are doing testing like this that is not classified as "torture testing" then keep your test periods short and let things cool down a bit. PWM amps don't like to run nuts out for very long anyways if you are using those. Testing with tones is NOTHING like testing with music the duty cycle is WAY higher. Just take your time and plan ahead so you are not "thinking" while a poor amp is sitting there sweating waiting on you to make up your mind on something


Good to know. 

May be a couple weeks before I get to it because I don't want him to be helping me while he's supposed to be doing other work.


On another note...I still haven't received an e-mail back from the acoustic levitation guy.


----------



## Ge0 (Jul 23, 2007)

chad said:


> You are SET on loads then. you can hit a 200W dale with more than 200W but watch how long you do it for. Anytime you are doing testing like this that is not classified as "torture testing" then keep your test periods short and let things cool down a bit. PWM amps don't like to run nuts out for very long anyways if you are using those. Testing with tones is NOTHING like testing with music the duty cycle is WAY higher. Just take your time and plan ahead so you are not "thinking" while a poor amp is sitting there sweating waiting on you to make up your mind on something


Oh, and don't set the load resistor on something that can melt. Also don't put your tongue on a hot load, err, resistor I mean...

Ge0


----------



## Ge0 (Jul 23, 2007)

bikinpunk said:


> May be a couple weeks before I get to it because I don't want him to be helping me while he's supposed to be doing other work.


Him? Aren't you the one wasting company time exchanging messages on this forum like the rest of us?

Ge0


----------



## ErinH (Feb 14, 2007)

Ge0 said:


> Him? Aren't you the one wasting company time exchanging messages on this forum like the rest of us?
> 
> Ge0


I'm not at work.


----------



## Ge0 (Jul 23, 2007)

bikinpunk said:


> I'm not at work.


DOOOHHHH!!! I am. I need to lay off this forum during the day. It's like a crack addiction.

Ge0


----------



## Horton Hears The Who (Nov 7, 2007)

OK, I'm easing down.

You're honest too. You admit filling it with useless fodder. 

I'm criticizing the fodder for the exact reason you stated teaching someone in person is better.

Efficiency. 

I understand it's easier to add useless fodder than actually write how to operate a piece of equipment. 

It might take pages back and forth. The fodder is also pages back and forth and it's not useful. 

I think the majority of forum members prefer less fodder.

There are countless forums filled with exactly the same. This one seemed... more efficient.

I agree with you that live and in person is more efficient. The question was asked here though, and instead of answering efficiently, it went the opposite.

You're allowed to fodderize, I'm allowed to criticize.

How about getting back on topic?

Is the cost of resistors to test an amplifier's output proportional to it's rated output? 

Are you saying it costs too much to scope a high powered amp?

This is a DIY forum, there must be an inexpensive way.

SCOPES ARE FUN!


----------



## chad (Jun 30, 2005)

Horton Hears The Who said:


> Are you saying it costs too much to scope a high powered amp?
> 
> This is a DIY forum, there must be an inexpensive way.
> 
> SCOPES ARE FUN!


Lower power resistors soaking in ATF 

I wish the Tektronix TDS-340 would come down in price more now that they are getting some age on them. Wonderful scopes for this type of stuff, especially for newbs, hit the "autoset" button and BAM a waveform. It also is a freq counter and P-P/RMS voltmeter, all kinds of measurements to do, even waveform math! I loved that scope and if you can get one for the right price I totally recommend it!

Chad


----------



## dogstar (Jan 31, 2007)

I'm no pro... in fact I couldn't carry a pro's tool bag, but I am studying this thread intently.

As it stands, this is pretty average how-do-i-do-it thread for diyma.
Eventually bikin will get his hands on the concept, then hopefully someone can sum all this up into a true how-to.
Point form with pics would be good.


----------



## Horton Hears The Who (Nov 7, 2007)

How long has the Tektronix TDS-340 been on the market?

What is considered a good used price?

I used Tektronix OTDR's from around 1981 to 2004. A good company with good equipment.

You get what you pay for, they were more expensive than competitors but were far more accurate and durable.

Can those custom made load resistors be used for anything else?

What did they cost?


----------



## chad (Jun 30, 2005)

dogstar said:


> I'm no pro... in fact I couldn't carry a pro's tool bag, but I am studying this thread intently.
> 
> As it stands, this is pretty average how-do-i-do-it thread for diyma.
> Eventually bikin will get his hands on the concept, then hopefully someone can sum all this up into a true how-to.
> Point form with pics would be good.


The thing is that there's one way to do it but so many different versions, for example, you will see on the pic of my loads on the pegboard there are BNC connections, those are tied right off the amp input and head off to the scope via a BNC-> BNC connector, it's all built in. But I will add this that was mentioned in the BSG Saga.......



> Me Sez:
> Yep,
> 
> Here's how it works......
> ...


----------



## chad (Jun 30, 2005)

Horton Hears The Who said:


> How long has the Tektronix TDS-340 been on the market?
> 
> What is considered a good used price?
> 
> ...


I'd say 8-10 years or close to that on the 340, even if you are a pro, it's great! So time saving! Don't like the digi resolution for doing tube biasing work though.

Sure you can use a custom load for other things. They have a great way to tell when they aren't put away, because you will trip over them  I have used them for dis-charging batteries before, that's about it.


----------



## crammit442 (Oct 9, 2007)

Here's a link to a tutorial on scope gain setting I found. He says he's an EE and this is what he does. No resistor mentioned. Does this make sense? 

http://www.thesuicidaleggroll.com/gain.htm


----------



## chad (Jun 30, 2005)

crammit442 said:


> Here's a link to a tutorial on scope gain setting I found. He says he's an EE and this is what he does. No resistor mentioned. Does this make sense?
> 
> http://www.thesuicidaleggroll.com/gain.htm


Yep it will totally work... as long as you never connect the speakers.

The amplifier will clip later with the amplifier un-loaded.


----------



## Oliver (Jun 25, 2007)

chad said:


> The thing is that there's one way to do it but so many different versions, for example, you will see on the pic of my loads on the pegboard there are BNC connections, those are tied right off the amp input and head off to the scope via a BNC-> BNC connector, it's all built in. But I will add this that was mentioned in the BSG Saga.......


Very informative


----------



## crammit442 (Oct 9, 2007)

chad said:


> Yep it will totally work... as long as you never connect the speakers.
> 
> The amplifier will clip later with the amplifier un-loaded.


Does that imply that the setting will be inherently flawed?


----------



## chad (Jun 30, 2005)

Yes, because when connected to a load the amplifier will clip at a lower voltage.


----------



## Ge0 (Jul 23, 2007)

crammit442 said:


> Does that imply that the setting will be inherently flawed?


Yes. The amount of flaw is dependent on how much the amps output is loaded. Error becomes worse as impedance drops. When impedance drops, so does the amount of clean voltage swing available to the output. However, in my experience, this is rarely a grose error. But, an error nevertheless.

A good rule of thumb I use if setting the clipping level of an amp with lightly loaded/unloaded outputs. Increase gain until the point to where the output just starts to clip. Then back off about 20%. This should cover you in all instances beyond loading the thing to insanely low levels outside its rating. But then again, you should not be doing this to an amp anyway.

Ge0


----------



## MarkZ (Dec 5, 2005)

Horton Hears The Who said:


> OK, I'm easing down.
> 
> You're honest too. You admit filling it with useless fodder.
> 
> ...


Don't get confused, now. I'm actually the dickhead in this thread telling him not to waste his time setting gains the WRONG way in order to learn how to use a scope. If learning how to use a scope is his primary goal, then he could come up with a much more useful application for it.

Don't hate the other guys, bikin. Hate ME.

Wait, chad's the one who called you bikinIpunk, I think, so go back to hating him.


----------



## Diru (May 23, 2006)

chad said:


> Big ****ing Resistors...... Soak power.... Make Heat..... no Blow Speakers... Speakers No Hooked Up.....




I just hook up my Chads, then turn it up until the eyes blink........


----------



## ErinH (Feb 14, 2007)

MarkZ said:


> Don't get confused, now. I'm actually the dickhead in this thread telling him not to waste his time setting gains the WRONG way in order to learn how to use a scope. If learning how to use a scope is his primary goal, then he could come up with a much more useful application for it.
> 
> Don't hate the other guys, bikin. Hate ME.
> 
> Wait, chad's the one who called you bikinIpunk, I think, so go back to hating him.


He did what!?!?  


Really, I was thinking about doing this so I can learn my amp's true capability. It kind of crossed my mind the other day when I saw a thread about the PDX's birthsheets. I wondered how they test them, then I remembered seeing someone using an o-scope to check clipping. I figured that maybe you could do this by using an o-scope, see clipping, get voltage at clipping, back that out of ohm's law and get power at a specified load. 

My amp came with a birthsheet, and in addition to that my speakers can't take more than the normal rated power anyway. So, I was mainly wanting to do this to play, more or less. 

*shrugs*


----------



## Ge0 (Jul 23, 2007)

This thread kind of died Bikinipunk. I don't want to leave you hanging. Did you ever learn the basics of using a scope and do what you wanted to with it?

Ge0


----------



## ErinH (Feb 14, 2007)

Nah. It was my last week of work and things gor alot more busy than I thought it would. Plus, with my recent back surgery I haven't left the house in a week. Can't drive for another week.


----------



## KnightWhoSaysNI (Jul 23, 2007)

Would this be a good deal? It should be good for 50hz and 1000hz for setting gains I assume. What do you guys think?

http://www.partsexpress.com/pe/show...290&vReviewShow=1&vReviewRand=5242838#reviews


----------



## chad (Jun 30, 2005)

KnightWhoSaysNI said:


> Would this be a good deal? It should be good for 50hz and 1000hz for setting gains I assume. What do you guys think?
> 
> http://www.partsexpress.com/pe/show...290&vReviewShow=1&vReviewRand=5242838#reviews


Either MCM or PE had a CRT one with a function genny built in for pretty cheap too not to long ago. two birds, one stone. it was like a 20-30 meg, more than enough for linear amps.

If, IF, he ever gets into building an inexpensive CRT will WAX an inexpensive Handheld. Especailly in tube work IF he does it and needs the resolution to see a bias dog-leg.

Chad


----------



## cpio311 (Aug 22, 2007)

http://cgi.ebay.com/ws/eBayISAPI.dl...item=350024256042&_trksid=p3984.cWAT.m240.lVI
how about this one? junk? my dmm died so i might as well for 250


----------



## Ge0 (Jul 23, 2007)

cpio311 said:


> http://cgi.ebay.com/ws/eBayISAPI.dl...item=350024256042&_trksid=p3984.cWAT.m240.lVI
> how about this one? junk? my dmm died so i might as well for 250


Looks like a cheap knock off of a similar device manufactured by Fluke. It may be OK for what you need it for. Do a Google search on the company and that particular model. See if what others have to say about the devices quality, features, and dependability. Does the manufacture stand by their product or abandon its customers when stuff does wrong? Does this line up with what you need or the risk you are willing to take to save a few bucks? If you come up with nothing in your search (i.e. no info available whatsoever) then I'd say stay away. 

Ge0


----------



## chad (Jun 30, 2005)

Flame shield up!

Handheld scopes suck, they have bad resolution, may be acceptable for checking for clipping but IMHO if you are gonna get a scope you may as well get one that can do more and you won't have to guess with.

Flame shield resume.

Chad


----------



## Whiterabbit (May 26, 2006)

chad said:


> I have another load I run wet bathed in Automatic Transmission Fluid, that gets me by for home purposes.


Uh, jesus man, we dont use liquid cooled dummy loads for 20kW generators.


----------



## chad (Jun 30, 2005)

Whiterabbit said:


> Uh, jesus man, we dont use liquid cooled dummy loads for 20kW generators.


They can be smaller when liquid bathed  Space is becoming a premium in my shop  The oil filled one is used for RF and is 50 ohms, it will need to dissapate 1500W for torture testing. It is housed in a 1Gal paint can. Fo audio I just use the big dales now.

Chad


----------



## ErinH (Feb 14, 2007)

Well, well… this has had some time to settle.

Alright, so back to the beginning here. I finally bought an oscope and some x1 & x10 probes. While I understand the basics of using one, it’s been a long time since I have and even then it was just following directions in the lab. I did have the computer setup which worked fine, but I wanted to buy actual hardware for bench testing. Dragging the laptop out everytime I want to test isn’t something I’m up for.
Here’s a link to the oscope I have:
http://i18.photobucket.com/albums/b138/bikinpunk/IMG_5193.jpg?t=1235072632

Here are the probes:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=300272471253


So, let’s start off simply. Flipping switches and all that doesn’t do much for me. What further confuses me is the center portion “channel 3”. Alright, so do I need to pay attention to this section at all? I assumed it was only the channel which I feed an input to, or is that wrong? 




To make sure I understand how to set this thing up…

First, RCA preouts:
Now, let’s say I have a headunit I want to test preouts of. let’s figure I expect 3v out of the headunit… I’d set the divisions up to 1, use a 1x probe, and expect the sin wave to remain unclipped up to the 3rd bar vertically?
Now, I’ve spoken to Chad about this and he said it would work; using a bnc-to-rca phone adapter to run a single rca out to the headunit.
That or use the probe with the end stuck in the center where the male goes, and the clip on the shield. Either of these seem right? If you look at the picture above you can see the rca/bnc connection on the scope. 

Secondly, testing amplifier terminal outputs: 
So, now I want to test amplifier voltage out and I expect 150w @ 4ohms. That works out to ~24.5VAC. So, using this info, let’s say I decide a 10x probe would be the best choice of probes. Alright, so 24.5/10=2.45v. Alright, so now keeping the division still set to 1div, I should expect the clipping point to fall between the 2nd & 3rd bar?
The x10 I’m not too sure about. 
I feel like a mo-Ron for having to ask, but do you simply need to connect the probe to the + terminal of the channel being tested? 
I’m just trying to make sure I understand the procedure. I know throwing the alligator clip on is a huge no-no in this case.

Also, FWIW, I’ve found these:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=019-025

Thought about picking one up. Figured it’d be all I ever need (except for subwoofer testing). Clipping on a subwoofer via no dummy load isn’t much conern to me, truly. That much power would be too much for my IB setup anyway, so that would be done by ear. 

Thanks, fellas.


Edit: This should probably be moved to the tutorial section?


----------



## chad (Jun 30, 2005)

I found my damn card reader last night so I'll try to get you some pics tonight... but oyu need to read this before you go putting that alligator clips on the negative speaker terminals 

http://www.diymobileaudio.com/forum/80724-post27.html


----------



## ErinH (Feb 14, 2007)

^ thanks. I recall reading that somewhere. In other words, if you connector the gator clip you're running two positives? 


If you don't mind, could you take pics of the various scenarios (rca, bridged/unbridged terminals)? Thanks again.


----------



## chad (Jun 30, 2005)

that post explains it all, one negative ain't negative don't put a grounded gator clip on it.


----------



## ErinH (Feb 14, 2007)

wtf do you do with that sucker then! It's a reference ground right? It's not part of a circuit when measuring, correct? So, the reference ground in that case is??? (nothing)?

So, just the probe itself goes into the + terminal for a straight shot unbridged. ?

Now, bridged is where I get confused. 

*waits for pics and quits posting about it*


----------



## chad (Jun 30, 2005)

One channel the pos is actually neg and the neg is positive due to the reasons in the link. The crude but effective way to check this is to probe all the terminals, 2 will have a noisy signal on them (because you have not hooked up the ground clip) those are the driven terminals, you can then clip ground onto the other. One channel will be clipped to negative, the other, likely positive.

Bridged gets tricky because you are driving the load with 2 positive that are flipped 180 degrees in phase to develop 2X voltage. YOU CANNOT CLIP THE GROUND LEAD TO EITHER OF THESE, ONE CHANNEL WILL TRY TO DRIVE THE CHASSIS OF THE SCOPE AND YOUR HOME'S SAFETY GROUND!

What I normally do is if I'm runing 4 ohms bridged I load each channel to 2 ohms to assume a 4 ohm bridged load and check each channel's output.


----------



## keep_hope_alive (Jan 4, 2009)

i just use standard 50ohm impedance probes to measure bridged signals. then you can clip on both positive and negative. 
like i did here http://forum.sounddomain.com/ubbthreads.php?ubb=showflat&Number=1076928


----------



## chad (Jun 30, 2005)

Do the probes have continuity from the gator clip to the knurl of the BNC? If they do.. no you can't


----------



## keep_hope_alive (Jan 4, 2009)

like these
CABLE LA06002 Oscilloscope Test Lead Kits,Test Lead Kits


----------



## keep_hope_alive (Jan 4, 2009)

i am aware you can't use the side gator clip to signal ground. he bought the wrong scope plugs - and paid more than he needed to.


----------



## chad (Jun 30, 2005)

No, you are driving the chassis of the scope with one channel of the amp, not a good thing at all. the 50 ohm reference is just the type of cable used.


----------



## ErinH (Feb 14, 2007)

FWIW, I hooked things up on my 'bench' (aka: washer/dryer). Put a pdx 4.150 to the power supply. 
took the oscope probe, put it to x10, and put it in the positive end. left the gator clip free from connection.
I get some kind of movement but not a waveform. It's at a horiztontal and it moves (changes oval width and length... in other words, it just expands) but goes at a perfect x/y slope. I recall reading something about DC measures slopes so I made sure everything was set to AC. 

I don't know if I've got a button pushed wrong or what. As far as the div settings, that's just toying around until you get the right image size as far as I can tell. That shouldn't effect the wave form itself, right?

Any idea? Do I need to take a picture?



Edit: put the gator clip on the amp's ground and nothing changes.


----------



## ErinH (Feb 14, 2007)

keep_hope_alive said:


> i am aware you can't use the side gator clip to signal ground. he bought the wrong scope plugs - and paid more than he needed to.


actually, when I was looking around on ebay, that was probably the cheapest shipped price I found for a pair. Could've saved maybe $1 or $2 if I had ordered 2 singles, but for the pair, that was the best price I found for that particular kind of probe. 

But, point taken. So, I need to buy the probes you linked for bridging, but not for non-bridging, correct?


----------



## chad (Jun 30, 2005)

bikinpunk said:


> FWIW, I hooked things up on my 'bench' (aka: washer/dryer). Put a pdx 4.150 to the power supply.
> took the oscope probe, put it to x10, and put it in the positive end. left the gator clip free from connection.
> I get some kind of movement but not a waveform. It's at a horiztontal and it moves (changes oval width) but goes at a perfect x/y slope. I recall reading something about DC measures slopes so I made sure everything was set to AC.
> 
> ...


What do you get when you touch the neg to the red. 2 of them will give you a nasty signal, the other two will likely give you a 60 cycle compoenet of ass. the one that'sthe 60 cycle component of ass or nothing is ground. as for your Div yeah just get a good resolution. AC or DC is fine I like DC to see offset, AC just basically puts a cap in line to ignore DC/DC offset, nice for doing tube amps where you have the signal riding on 450V of DC plate voltage.


----------



## keep_hope_alive (Jan 4, 2009)

http://i38.photobucket.com/albums/e128/phat_funky_beats/audio testing/headunitbridgingimages003.jpg

these are the alligator probes i use - and i can connect both to active outputs to read a bridged signal. that image is 400Hz with bridged output.


----------



## chad (Jun 30, 2005)

You are playing with fire, when you try that with a pro amp with a grounded plug you will do damage, stop doing that, bad practice, really bad practice. Some car amps STILL share input ground with speaker ground, you can nuke one of those doing that too. Sit back and think about it for a minute, that black is hooked to the scope chassis, to the 3rd pin, you are riding audio on your home's safety ground in that pic, most certainly, it takes one more connection that DOES occur in pro amps and sometimes in car amps to make them release their magic smoke.

Remember one thing, a scopes input is NEVER differential, you are giving it a differential input.


----------



## keep_hope_alive (Jan 4, 2009)

you misunderstand the difference between those probes. the ground clip on a 10x probe behaves differently than the alligator clips in conjunction with AC coupling.

it is not a dangerous situation and provides no additional danger to the amplifier. 

a pro amp like an Xtant? 
http://memimage.cardomain.net/member_images/1/web/337000-337999/337617_137_full.jpg

i have both types and use whatever suits the measurement.


----------



## keep_hope_alive (Jan 4, 2009)

i follow what you're saying, but don't know why my posts keep getting doubled. so i just edit the second one. and no, i'm not double clicking 

my scope and probes pictured provided were able to accurately and safely measure across a load that was powered from a bridged amplifier. i could measure each output separately then together.

FYI - if i switched to a 10x probe the ground clip instantly sent the HU into protection. i only did that once, just out of mere curiosity. 

both outputs measured separately to show they are out of phase (as expected)
http://memimage.cardomain.net/member_images/1/web/337000-337999/337617_129_full.jpg

measured across the load (ch B not connected)
http://memimage.cardomain.net/member_images/1/web/337000-337999/337617_131_full.jpg


----------



## chad (Jun 30, 2005)

AC coupling only decouples the red gator via a glorified cap, the black is still chassis ground... test it, take the plug out of the wall and check for continuity, AC coupling does NOTHING to the shield at all, defeats the purpose of the probe actually if it WERE decoupled 

No a pro amp as ones people make their living with:


----------



## chad (Jun 30, 2005)

auto dupe feature


----------



## chad (Jun 30, 2005)

keep_hope_alive said:


> you misunderstand the difference between those probes. the ground clip on a 10x probe behaves differently than the alligator clips in conjunction with AC coupling.


you are wrong about this, test it. Pull the AC plug and test it


----------



## chad (Jun 30, 2005)

keep_hope_alive said:


> i follow what you're saying, but don't know why my posts keep getting doubled. so i just edit the second one. and no, i'm not double clicking
> 
> my scope and probes pictured provided were able to accurately and safely measure across a load that was powered from a bridged amplifier. i could measure each output separately then together.
> 
> ...


the double post thing happens, hence my "auto dupe feature" responses 

Did you pull that AC plug yet and check the shield of the probe or gator rig to safety ground yet? No sense in replying till you do. I can assure you that AC coupling and DC coupling will make NO difference on the shell of the BNC.

Your world will change when you test an amplifier that does not have an isolated supply and indeed uses ground as the speaker common, it will change big time.

It's bad practice, this ain't my first dog and pony show when it comes to amps of all flavors on the bench


----------



## keep_hope_alive (Jan 4, 2009)

ok, so it turns out i'm technically mentally retarded. now i have to call my ex girlfriends and tell them to get themselves checked. you can call me Peter Griffin.

i cannot explain it, other than an increased resistance and an open circuit. the difference between my 10x probe and the alligator clips was a pin at the BNC connector. the 10x probe had a pin that tied the metal face of the scope to the shield. this shouldn't have made a difference, but it did. there was almost 4 ohms resistance between the alligator clip and the ground at my power strip. 

but i powered my system through a stand-alone battery and battery distribution. since there was no circuit to complete, the amplifier did not see a short. but yes, i'm retarded, and also extremely lucky. had i powered my system from a power supply it would have went into protect instantly. 

regardless, it worked, and worked quite well. i will never do that stupid sh1t again and i will not recommend that for anyone. 

a 10x probe attenuates the signal, so you will need to increase your V/div by a factor of ten.


----------



## keep_hope_alive (Jan 4, 2009)

thanks for questioning me. you probably saved me some future damage. i owe you one! 

you are also correct that AC or DC or GND coupling made zero difference in the resistance from either the alligator clip or 10x probe clip resistance to the ground pin.

maybe i should quit drinking while testing gear! 

of note: i have always been able to measure across a resistor in a circuit with alligator clips, never with a 10x probe. and not only at home, but in the EE lab as well. i've never had a problem before. that's right, i'm an EE with thousands of hours in labs building and testing circuits of all types. i am utterly confuzzeled. i need to figure out why that hasn't been an issue soon or i'll lose sleep. 

i don't mind being wrong, i just don't find being an idiot acceptable.


----------



## drtool (Nov 26, 2007)

Thread jack alert ... If one wanted to build a tube amp or maybe a lot of them, is the TDS-340 a must have or are there better options out there to do both. Build said amp, check for clipping.
Wayne


----------



## sqshoestring (Jun 19, 2007)

I bumped something and hit power, I forget exactly how was checking a PS IC in an amp, and near melted the probe ground wire. Yes had the scope grounded to the battery I was using, so watch that clip. I did have a 10A fuse on the amp and it did not blow, but that clip wire is small. I was told to use 10x on near everything. IIRC the clip is ground all the time no matter.

Reversed channel: I usually test or look in the amp as some you can see, the commons will be connected together and not used when bridged. Common, the RCA shields, and 12v ground may be connected somehow but some do it in different ways so don't trust them. The commons will go to center tap of the power supply transformer and the positives to the outputs of each channel. I tend to ignore the + and - markings. So if you are not sure just ohm test speaker terminals to the output transistors or transformer, with the amp unhooked of course.

I got the big ceramic wound type resistors but have to set up a fan on them yet, should be fun if I can ever get to it. But only have a 30A supply right now anyway.


----------



## chad (Jun 30, 2005)

keep_hope_alive said:


> thanks for questioning me. you probably saved me some future damage. i owe you one!


LOL lets just say that some learn by experience... and I was one of those people  and it was a BIG amp :blush: I melted an IEC cable.



keep_hope_alive said:


> you are also correct that AC or DC or GND coupling made zero difference in the resistance from either the alligator clip or 10x probe clip resistance to the ground pin.


It's always safety ground, HOWEVER I have seen some nuts clip it (safety ground) and run in ISO transformer, and float the chassis of the scope in wood. HOWEVER if you are testing a large amp bridged keep one hand in the pocket if you HAVE to touch the scope or don't touch the scope at all. that can be a bit disconcerting, 60 cycles will thump you, 1K flat out hurts!



keep_hope_alive said:


> maybe i should quit drinking while testing gear!


ABSOLUTELY NOT! you will ruin the (our) reputation!



keep_hope_alive said:


> of note: i have always been able to measure across a resistor in a circuit with alligator clips, never with a 10x probe. and not only at home, but in the EE lab as well. i've never had a problem before. that's right, i'm an EE with thousands of hours in labs building and testing circuits of all types. i am utterly confuzzeled. i need to figure out why that hasn't been an issue soon or i'll lose sleep.


the 10X probe has some capacitance built into it also, some even have a trimmer cap on them! Chances are that the probe was setting up some oscillation in the circuit in combination with the grounding.



keep_hope_alive said:


> i don't mind being wrong, i just don't find being an idiot acceptable.


again, it's all right man, totally cool, we all learn something every day.


Here's another place it will REALLY bite you in the ass and it happens so fast it's not even funny!

Say you have a scope and a signal generator, (properly grounded) Signal generator is single ended and the common is most certainly ground. That is tied to the shield of the amp's input, you hook it up as you were, one side is driving ground. Now lets throw a monkey wrench in this, the amp has differential inputs like a JL, audison, etc where the shield is actually an inverting input. Now you are driving an inverting input of the amp with the amp's output via the safety ground. First hint of input and POOF! Oscillation city, may as well order finals and drivers before you hook it up  I almopst always have the output of my signal generated 1:1 isolated it solves some headaches and keeps you from having to rebuild the output of the generator when you have accidents, even ones that happen from developing the "dropsies" when working.

My OLD bench had a cool patch panel too you may like this and it's SOOO easy.

Bench amp, old crown D75
Bench speakers
Dummy loads
Scope
BNC to bare end cables

Take 3 neutrik NL4MPR's and install them on the bench (female 4 pin speaker connectors) One is the amp's output, the other is the dummy load input, the other is the speaker input. on the one with the dumy load output install the bare ends of the BNC, the other goes to the scope. Now build a short whip of 4 conductor cable that's NL4FC to NL4FC (male 4 pin connector) and another long with with Nl4FC to bare (I used Pomona MDP banana plugs because I was doing professional stuff)

Now here's what you can do with that:

Drive the bench speakers with the bench amp while working for music

Drive a test speaker with the bench amp

Drive the bench speakers with a test amp

Drive the dummy loads and scope with a test amp while listening to music, 

And hell if you wanted to drive the dummy loads with the bench amp for grins and pic taking. 

Every possible configuration is handled on 3 plugs, fully 2 channel, and no more time-vampire swapping, everything is 2 twists away from being set up!

next thing, nice rig you have going there, those B&K scopes are rock solid and VERY intuitive to use. since you showed me yours, here's mine at home......



















Since then I've added a big honkin' Lambda supply and moved all but the HV supply under the bench in a rack I built, that brings the gear down a bit on the benchand makes it a bit easier for me, I'm one of those short guys :blush: The rack:










Nice to meet you, stick around, it's a fun place!

Chad


----------



## chad (Jun 30, 2005)

drtool said:


> Thread jack alert ... If one wanted to build a tube amp or maybe a lot of them, is the TDS-340 a must have or are there better options out there to do both. Build said amp, check for clipping.
> Wayne


I prefer a NON TDS to be honest, I found the analog scopes do better at showing the bias "dog leg" in fact I had a 340 and the only time I fired up the analog was to work on the tube stuff :blush:


----------



## chad (Jun 30, 2005)

sqshoestring said:


> Reversed channel: I usually test or look in the amp as some you can see, the commons will be connected together and not used when bridged. Common, the RCA shields, and 12v ground may be connected somehow but some do it in different ways so don't trust them. The commons will go to center tap of the power supply transformer and the positives to the outputs of each channel. I tend to ignore the + and - markings. So if you are not sure just ohm test speaker terminals to the output transistors or transformer, with the amp unhooked of course.


As bikini found out last night.......

you often times don't even need the ground clip. I just lose the clip and go across to see which ones have signal present, if there's no noise on the trace I rock it that way, if there I I clip to common.


----------



## tspence73 (Oct 14, 2008)

bikinpunk said:


> I have at least 10 of these things at my work but I have no idea how to use them to test my amplifier's clipping point. It'd be nice to know so that when I adjust gains when I do my next install I have an idea of what I cannot go past.


You are going to be shocked at just how low the output sounds on most amplifiers while unclipped. Especially in the bass region. That's what prompted me to buy the most powerful amplifiers I could across the board. I'm still wanting to upgrade my sub amp from 1200-watts to 2400-watts but I have my doubts I'll hear a difference.


----------



## Brian Steele (Jun 1, 2007)

chad said:


>


So what's with the JBL pro audio driver just hanging on the wall in the background, LOL. No good use for it?  Or is that one of the old GTi series?


----------



## chad (Jun 30, 2005)

Brian Steele said:


> So what's with the JBL pro audio driver just hanging on the wall in the background, LOL. No good use for it?  Or is that one of the old GTi series?


Old GTi, same basket as the 2226, it's cashed. If you ever find a 1500GTi recone kit will you please remember me?  Can't think of a project off the top of my head for a single 2226, BUT if I had another 2226, some 2426's and 2370's I'd be a happy camper  Because I'd have a new set of bitchin shop speakers!


----------



## chad (Jun 30, 2005)

tspence73 said:


> You are going to be shocked at just how low the output sounds on most amplifiers while unclipped. Especially in the bass region. That's what prompted me to buy the most powerful amplifiers I could across the board. I'm still wanting to upgrade my sub amp from 1200-watts to 2400-watts but I have my doubts I'll hear a difference.


If this is truly how you feel then I think you will be shocked at how inefficient your subwoofer system really is, I think you will also be shocked to find out that by going to 2400 watts you will gain less than 3dB after power compression and electrical system loading.


----------



## tspence73 (Oct 14, 2008)

chad said:


> If this is truly how you feel then I think you will be shocked at how inefficient your subwoofer system really is, I think you will also be shocked to find out that by going to 2400 watts you will gain less than 3dB after power compression and electrical system loading.


Yeah. I figured as much. I'm running with the recommended sealed enclosure with dual 12" subs. Should I upgrade the subs or is it the enclosure?


----------



## chad (Jun 30, 2005)

upgrade the enclosure. Try this if you have 2 subs at 1 ohm that means you can probably go to 4 ohms, try it at 4 ohms and see low LITTLE output you lose, in fact, you may find it to be better sounding with the more controlled dynamics 

and to keep it on topic I have to mentions *Oscilloscope! *


----------



## sqshoestring (Jun 19, 2007)

I tested an insignia ns a1000 amp on my hack setup, on 13v I showed 26v sweep and 37vac rms into a sony sub, so not much good anyway. But setup seemed to work after getting some kinks out. I did check it bridged with the clip on the 12v NEG, after checking if it had any current there. Scope not grounded to the PS, PS are grounded to AC power (12v NEG is to green wire not floating). It shows a little change in voltage without the 10x probe ground but not much. Had 32v sweep and 46vac with no load. This was all just under clipping, and I tested the HU playing the tone CD (at 45Hz) first to make sure it was playing clean. It came out to 335rms but may have been higher because I waited to check sub, but yeah need to get my load bolted together for real numbers. Also need to wire up so I can run my amp meter on the 12v wire. Either way I figure the new channel I put in it must be good, lol, it was a little warm after an hour of messing with it but not hot and I had a little fan near it.


----------



## ErinH (Feb 14, 2007)

Another thread brought up bench testing an amplifier. I gave my input and the OP did some searching and found this.
Measuring Amplifier Output Power

MOST IMPORTANT THING IN THE BCAE LINK:


BCAE said:


> Test Data:
> The following data was taken in a test to show how *calculating power when using the voltage across a speaker's terminals instead of the voltage across a non-reactive dummy load will result in false output data.* The frequency is the test frequency. The voltage is the voltage that was measured across the terminals of the load (either speaker or dummy load). The power is the calculated power using the speaker's nominal impedance (4 ohms) and the voltage across the speaker's terminals at the various frequencies. The voltage across the dummy load will be virtually the same across the range of frequencies so only one voltage reading was necessary. The amplifier is capable of producing only 205 true watts (RMS power). When using a speaker, it appears to be able to produce as much as 376 watts (which it clearly is not capable of doing).


Check the table:


----------



## chad (Jun 30, 2005)

Well yes and no, sometimes you don't have a choice because you need to use a tone and these tones can easily damage a speaker if you are not careful with a big amp. so for the sake of the driver you need to use a load. 

What you are seeing is the driver's impedance curve, for example my Dayton NEVER HITS 4 ohms in the passband I use it in, it's more like 6 ohms from 20 to 80. The post you quoted totally drives the point I try to make over and over home though. an amplifier WILL INDEED have different clip points when loaded differently so NEVER assume that if it clips at X voltage at 4 ohms that it will clip at that voltage at 1 ohm, it will clip much earlier


----------



## ErinH (Feb 14, 2007)

I totally understand your point. I was just wanting to throw out the results from his tests with and without a dummy load since there was so much argument here (or was it somewhere else?) about it.

Either way, I don't care what anyone does. I just think the data he provides is useful to see the benefit of a dummy load.


----------



## chad (Jun 30, 2005)

When i was telling people to load the amp I was basically providing that for 2 reasons, 

1 regardless, if it's a speaker or a resistor you CAN'T assume the unloaded voltage as even being close to accurate (proven in your post) It does not HAVE to be a resistor but see below.

2 some nimwit is going to test the clip point of their tweeter amp with a tweet hooked up and roach the tweets and then I would be an *******. Therefore I NEVER mention testing with drivers hooked up, only loads  If the results above hold true (in relation) to other amplifiers, setting with a load will certainly assure you will be safe with a speaker.

3 I allow my amps to enter clipping, because if the sucker hit clip with the headunit wide open at 0dBFS it would never be able to play the music source loud enough


----------



## chad (Jun 30, 2005)

dupe


----------



## ErinH (Feb 14, 2007)

chad said:


> When i was telling people to load the amp I was basically providing that for 2 reasons,
> 
> 1 regardless, if it's a speaker or a resistor you CAN'T assume the unloaded voltage as even being close to accurate (proven in your post) It does not HAVE to be a resistor but see below.
> 
> ...


I gotcha. I agree that a dummy load should be used. Ever since Ian posted the picture of the 8ohm vs. 4ohm results at the same gain point on the amp; showing the 4ohm was well clipped while the 8ohm wasn’t. That made a believer out of me. 

I think Autofile said that most mfg’s use a -3dB tone for testing. Is that right? I’ve never herd one way or the other. Regardless, to the end user, it’s up to them. I’d use -3dB myself. Andy Weyhmer suggested even -5 & -10dB tones could be used since the ear couldn’t detect that level of distortion anyway, and you would get better dynamics.


All interesting. I still need to get my butt in gear and order some dummy loads.


----------



## chad (Jun 30, 2005)

I leave 6-9dB of "overlap" as a general rule of thumb.


----------



## sqshoestring (Jun 19, 2007)

A load is the only way to make any comparison in amps, unless everyone had the same exact sub to test on. That is what I meant by saying "I tested an insignia ns a1000 amp on my hack setup, on 13v I showed 26v sweep and 37vac rms into a sony sub, so not much good anyway." Not much good because it was into a sub, but I should have said 26v +/- rails not sweep that would have been 52v.

Nearly done with my load, just have to finish the fan spacer/stand. I have the BCAE DVD right here, takes a long time to read it all. Fantastic material for me, a relative noob to amp electronics. I blew the shields out of my test HU and had to mod that...think I have a tail light socket here someplace.

I agree 100% with Chad I never bother with level setting, I just do it by ear. Since I don't have grossly oversized amps I need the room to get max on them with a lower level recording. Most of the time like this HU, the volume is too slow for me and I only run it past half way anyhow. Even that is more than I can take. I have no idea how they can manufacture such a retarded encoder into a HU volume control.

Yeah, I would be very wary of power testing an amp on your car speakers...not going to show you much anyway. The 4/8 ohms- remember the speaker is dynamic but still a resistor of sorts. Less resistance means more current flows through the amp and speaker. 

At one point I figured people set amp gains via AC voltage because they could not hear the distortion with the ear plugs they had in. I still don't know why else you would do that, but each to his own.


----------



## keep_hope_alive (Jan 4, 2009)

a good thread still kicking! 

the test tones i use to test for clipping are always stronger than any recording i'll have. if i start to clip at full output (or my determined max output from the HU) i'll call it good. 

anyone know the best/easiest way to determine THD from the output of a head unit?


----------



## sqshoestring (Jun 19, 2007)

Still no time to finish my load, was thinking of putting an LED on it though so I don't forget and leave the fan on. I blew the RCA shields out of my HU and had to mod it to external, have to find a light bulb to put in it.


----------

