# amp modiification



## spmpdr

Ive been seeing "modded" amps for sale on this site and would like to know what kinds of mods you can do to an amp? Can any amp be modded? How does it change the amp? Is there a mod to make an amp cleaner sounding? more power?


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## Boostedrex

http://www.diymobileaudio.com/forum/diy-mobile-audio-sq-forum/78570-amplifier-mods-upgrades.html

Start reading through that. Aside from the bickering, there is some good info.


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## spmpdr

Boostedrex said:


> http://www.diymobileaudio.com/forum/diy-mobile-audio-sq-forum/78570-amplifier-mods-upgrades.html
> 
> Start reading through that. Aside from the bickering, there is some good info.



Thanks for the link,lots of good info.


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## Ankit69

x2. thanks for the info.


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## audioaddict

Ankit69 said:


> x2. thanks for the info.


wow...you'll be at '50' posts in no time at this rate!!


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## ChrisB

I have a tiny little pet peeve that needs to be mentioned... Electronics are NOT cars and I really think it is a bad analogy to refer to an electronics modification like modifying a vehicle without mentioning more. 

If one is going to make the vehicle go faster, what did they do to make it handle better or stop faster? Did they beef up the internals on the engine to keep it from blowing up? How are they going to get this additional power to the ground while minimizing wheel spin?

Sorry, but it takes more than a few capacitors and Operational Amplifier swaps to actually gain something out of a modification, unless there was a problem with the originals to begin with. If one is doing it to have a "different product" or something "unique" then more power to them. Just do not think that your amplifier will have this miracle doubling of RMS power or Sound Quality bliss like some who modify amplifiers will tell you, because it will NOT. 

Although one can modify the hell out of something, they are still limited by the constraints of the initial design. They always tend to leave that little tidbit of information out when they are selling you on a modification. Because I was burned by believing lies perpetrated by another individual, I've come up with a couple of questions that one needs to ask themselves prior to sending an electronic device off for modification.

1. What do you expect to gain from the mod?

2. Is there a better or more cost effective way to achieve this gain?


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## kyheng

^Well, this is DIY anyway..... We DIY to push an equipment to its limit..... Modifying it to be more stable, sounded more good is the some of the goals.....


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## lycan

ChrisB said:


> I have a tiny little pet peeve that needs to be mentioned... Electronics are NOT cars and I really think it is a bad analogy to refer to an electronics modification like modifying a vehicle without mentioning more.
> 
> If one is going to make the vehicle go faster, what did they do to make it handle better or stop faster? Did they beef up the internals on the engine to keep it from blowing up? How are they going to get this additional power to the ground while minimizing wheel spin?
> 
> Sorry, but it takes more than a few capacitors and Operational Amplifier swaps to actually gain something out of a modification, unless there was a problem with the originals to begin with. If one is doing it to have a "different product" or something "unique" then more power to them. Just do not think that your amplifier will have this miracle doubling of RMS power or Sound Quality bliss like some who modify amplifiers will tell you, because it will NOT.
> 
> Although one can modify the hell out of something, they are still limited by the constraints of the initial design. They always tend to leave that little tidbit of information out when they are selling you on a modification. Because I was burned by believing lies perpetrated by another individual, I've come up with a couple of questions that one needs to ask themselves prior to sending an electronic device off for modification.
> 
> 1. What do you expect to gain from the mod?
> 
> 2. Is there a better or more cost effective way to achieve this gain?


I'd even go a little bit farther, with how bad the car analogy is. If you make an improvement to a car's power, you will expect to QUANTIFY the results, by measuring zero-to-sixty, or quarter-mile times. If you make an improvement to the car's brakes, you will expect to QUANTIFY the results, by measuring stopping distance. If you make an improvement to a car's suspension, you will expect to QUANTIFY the results, by measuring lap times. Of course, these measurements do not detract from the _enjoyment of driving_.

The audio game could, and definitely _should_, be quite similar. Sadly, it's not  

But the reason isn't because of an absence of well-documented tests, that can compliment the _enjoyment of listening_  The reason is, more often than not, that the measurements will indicate that no audio-band improvement has been realized 

How many car enthusiasts would tolerate that? 

So, if I may, i'd like to add a third question :

3. When the modification is done, how will i be able to QUANTIFY that an improvement has, indeed, been realized?


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## lycan

cajunner said:


> you will know, when the person doing the modification hands you a test sheet with before and after results. The work will undoubtedly show an improvement in S/N, slew rate, rise time, distortion, damping factor, impedance matching, phase angle, dc offset.... this list is just too long...


problem is, people don't understand the limits of audibility.

If the "spec sheet" shows a slew rate that "improved" from 40V/usec to 100V/usec (for example) ... when it may be straightforward to demonstrate that anything above 20V/usec (for example) is inaudible ... how much is that improvement "worth"? Same thing with damping factor : if a modification improves it from 100 to 500, when anything over about 20 becomes indistinguishable ... how much is that worth? Impedance matching ... where?

Sow the results in terms of : power, frequency response, noise, or distortion over 20kHz ... or go home.

The audio landscape is littered with terminology few understand (and almost nobody can apply), leading to conclusions ... founded mostly in ignorance ... that "more" must always be "better".


> when you take what you know about how an amp performs in your own particular application, and then hand that amp over to a tech who "improves" it, the period of time for your memory to be an accurate benchmark has since passed and you must simply accept that what the tech says, and the test sheet proves, is that what you gained was worth the money spent.
> 
> Myself, if an amp upgrade costs 125 bucks, and I can't tell that it's better because I can hardly tell the difference between clean gain blocks from different manufacturers, it's not a game I should be playing, anyway.


My point is this : the mods must be correlated to known & understood measurement parameters, that are actually impactive in the audio band, to give any support to the "value" of the modifications.

Improving a pre-amp's rise time from 10 nanoseconds to 7 nanoseconds ain't gonna matter at all. How can i write this, with such confidence?


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## cbrei1023

audioaddict said:


> wow...you'll be at '50' posts in no time at this rate!!


you too!


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## audioaddict

cbrei1023 said:


> you too!


Yeah, but I'm not trying to do it in one evening...smart ass.


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## lycan

cajunner said:


> because, it goes back to the limits of audible improvement?
> 
> I can't help but believe, after decades of reading the popular science of car audio, (and home, of course) that somehow the effects are cumulative.


Indeed, some effects _are_ cumulative. Additive, uncorrelated noise sources _are_ cumulative (as power). But some effects are _not_ cumulative. A rise time that's 100x raster than the human ear can possibly detect, will _not_ conspire with a damping factor that's 10x better than can possibly be heard, to magically _create_ something that's audible.


> that's a constraint, there are certainly some benefits to be had in that synergy of effect, one wants to believe that the correction by using a better, and certainly more costly parts count, will eventually accumulate and in the end result in an outcome that's orders of magnitude better than before...
> 
> is it simply a marketing ploy, then?


"Synergy" is pure marketing ploy. It's always used by those who don't understand the science of audio. Degradation that _may_ exist by using "inferior" parts, either in isolation or combination, is something that is _analyze-able and calculate-able_. The result can then be compared to well-known thresholds of human hearing. There's just no room left for marketing nonsense.


> I like to think that cost constraints are the primary reason why most amp builds differ in their eventual sonic signature. One cannot point at a single idiosyncratic gesture on the amp designer's part, that will lead to a suggestion that one might identify that amp from another in blind testing.


What EXACTLY is a "sonic signature" that does NOT show up in the amplifier's : gain, power, frequency response, noise or distortion?


> Maybe, the VST tube sound?
> 
> 
> or perhaps, the T-03 thing?
> 
> one might conclude a hot biased Class (quasi) A circuit is somehow giddy-inducing?
> 
> where is it laid, then. Damping factor is a noticeable function of amp sonics, I would have to agree there, but if it's loose, is it worse?


Agree ... with who? Certainly not me ..


> I have to argue that, as tube amps are warm, and loose, and so sloppy but yet they make the sound of an average digital device somehow more suitable to the analog wave that moves my tympani?


These descriptors have no value, and therefore no meaning. Tube amps may have higher even-order _distortion_, a higher _noise_ floor, and higher output impedance that results in in-accurate _frequency response_ when driving complex loads, but there's nothing about a tube amp's "sound" that is NOT accounted for by : gain, power, frequency response, noise & distortion.


> ha!
> 
> somebody stop me, I'm drunk on Saturday.


There's nothing about the "sound" of an amplifier that is NOT accounted for by : gain, power, frequency response, noise & distortion.

_"What about the type of solder used, and it's "synergy" with the dielectric of the printed-circuit board?"_ How does it impact : gain, power, frequency response noise & distortion? If the answer it "it doesn't", then you won't hear this "magical synergy".

_"But i've got this 100 watt amp that was built to a cost-point, and not a performance-point. Surely, it sounds worse as a result!"_ How does it measure, in terms of : gain, power, frequency response, noise & distortion? How do those measurements compare to the 100 watt amp that was built for performance, instead of price?


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## MarkZ

I don't know if it's been mentioned yet or not, but I think for our purposes the most useful mod would be to mod the amp to deliver more power into high impedance loads, since many of us use 8 ohm drivers. This requires stepping up the rail voltage, which is pretty easy in itself, but it also requires making sure that the rest of the circuit can handle that increased voltage. This means, on the primary side of the transformer, making sure that the switching FETs can handle a greater duty cycle, and on the secondary side it means possibly replacing caps with higher voltage ones. And it's only feasible if the SOA of your output transistors jives with the increased voltage.

It can be a tricky mod, but it depends on the amp. I can imagine some designs where all you would have to do is change out the feedback resistors to the switcher, but this would have to be an "overbuilt" amp.


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## Therum

MarkZ said:


> I don't know if it's been mentioned yet or not, but I think for our purposes the most useful mod would be to mod the amp to deliver more power into high impedance loads, since many of us use 8 ohm drivers. This requires stepping up the rail voltage, which is pretty easy in itself, but it also requires making sure that the rest of the circuit can handle that increased voltage. This means, on the primary side of the transformer, making sure that the switching FETs can handle a greater duty cycle, and on the secondary side it means possibly replacing caps with higher voltage ones. And it's only feasible if the SOA of your output transistors jives with the increased voltage.
> 
> It can be a tricky mod, but it depends on the amp. I can imagine some designs where all you would have to do is change out the feedback resistors to the switcher, but this would have to be an "overbuilt" amp.


Dont forget possibly upgrading the rectifier (to support increased voltage) and 15v regs (Has to drop the extra voltage to = +/-15v.


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## MarkZ

Yep. Depends on the regulator circuit for the accessory supply though. Sometimes you don't have to touch them at all.


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## ChrisB

cajunner said:


> I have to wonder if damping factor, and the control of back emf, would be a specification that would make the cut?


IMHO, damping factor is USELESS in the way it is currently marketed because the amplifier manufacturers fail to mention impedance or frequency. Going back to my car analogy gripe, that would be like stating horsepower without torque or RPM.

Going further, do you know your subwoofer's impedance at any given frequency? I always found damping factor more useful when I was involved with pro audio and my drivers were anywhere from 20 to 100 feet away from me.

Lastly, if one truly wants cone control, use a servo!


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## db-r

Meh, sorry I don't have the "Ear" for SQ.

As far as power upgrades, mosfets and bipolar output transistors (or mosfets in some cases) can be upgraded for more power (just a little more) but mostly will help with reliability and robustness under heavy loads. Fragile little 34 amp mosfets will bust when 100-200 amp mosfets will just be loafing.

Limitations in increasing POWER performance of amplifiers is mainly going to be limited by the size of the power supply transformers, the amount of copper in the board, the overall capacitance (B+ and rail capacitance), and in Class D amplifiers the size of the output filtering (LC) circuit. These are things that you CANNOT change without redesigning/making the amp physically larger so, basically I usually tell people to just "hang it up" when they start talking about or asking about mods to their amp to make it "go lower (impedance)" or put out "mo powa" etc.... Best to not try all that stuff, if you need more power, get a more powerful amp to start with. If you are interested in making an amp more robust, changes can be made, but will not make it sound better, and could cause other issues. Changing of power supply mosfets is limited greatly by the drive/pulldown circuit. High power mosfets have a high input capacitance and will not be driven with tiny average drive circuits. In many cases just changing the drive transistors to larger types will be all that is necessary to drive higher input capacitance mosfets, but again, remember, you can NEVER USE all that extra power potential because your amp is limited by it's transformer size and capacitance.


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## Therum

Well said.


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## MarkZ

db-r said:


> Meh, sorry I don't have the "Ear" for SQ.
> 
> As far as power upgrades, mosfets and bipolar output transistors (or mosfets in some cases) can be upgraded for more power (just a little more) but mostly will help with reliability and robustness under heavy loads. Fragile little 34 amp mosfets will bust when 100-200 amp mosfets will just be loafing.
> 
> Limitations in increasing POWER performance of amplifiers is mainly going to be limited by the size of the power supply transformers, the amount of copper in the board, the overall capacitance (B+ and rail capacitance), and in Class D amplifiers the size of the output filtering (LC) circuit. These are things that you CANNOT change without redesigning/making the amp physically larger so, basically I usually tell people to just "hang it up" when they start talking about or asking about mods to their amp to make it "go lower (impedance)" or put out "mo powa" etc.... Best to not try all that stuff, if you need more power, get a more powerful amp to start with. If you are interested in making an amp more robust, changes can be made, but will not make it sound better, and could cause other issues. Changing of power supply mosfets is limited greatly by the drive/pulldown circuit. High power mosfets have a high input capacitance and will not be driven with tiny average drive circuits. In many cases just changing the drive transistors to larger types will be all that is necessary to drive higher input capacitance mosfets, but again, remember, you can NEVER USE all that extra power potential because your amp is limited by it's transformer size and capacitance.


Most of those things are not considerations when you increase the rail voltage to run higher impedances. The POWER isn't being changed -- instead, you're basically going from a "high current" amplifier to a "high voltage" one.


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## Luke352

MarkZ said:


> - instead, you're basically going from a "high current" amplifier to a "high voltage" one.


Ok I see these terms all the time on some older SS stuff and some of the Audison stuff have either or selections, what I've never understood is what is one meant to achieve over the other. Is there any benefit to using high current over high voltage or vice versa.


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## MarkZ

Luke352 said:


> Ok I see these terms all the time on some older SS stuff and some of the Audison stuff have either or selections, what I've never understood is what is one meant to achieve over the other. Is there any benefit to using high current over high voltage or vice versa.


"High current" is shorthand for "able to drive low impedance loads". The amp would then be designed to dissipate X number of watts into a low minimum impedance. Amps that have a "high voltage" switch bump up the maximum output voltage, but usually warn you that you can't drive those low impedances anymore.

What I was talking about was modding an amp that's, say, 2 ohm stable in a way that would make it only 4 ohm stable but would deliver more power into 4 or 8 ohm loads. The way you do this is by increasing the rail voltage, which is the maximum voltage swing that the amplifier can produce. But when you increase the rail voltage, you have to make sure that all the circuitry in the amplifier can handle the higher voltage. Especially circuit elements that are positioned directly between the rail voltage and ground.


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## lycan

Luke352 said:


> Ok I see these terms all the time on some older SS stuff and some of the Audison stuff have either or selections, what I've never understood is what is one meant to achieve over the other. Is there any benefit to using high current over high voltage or vice versa.


You don't have a "choice" between "high voltage" and "high current". The speaker impedance decides that for you.

You have a given speaker impedance, *Z*. Once you decide how much power, *P*, to deliver to that impedance, then the voltage, *V*, and the current, *I*, are _completely determined_. It turns out that a _lower_ impedance will require _lower_ voltage and HIGHER current, while a _higher_ impedance will require a HIGHER voltage and _lower_ current. Study Ohm's law, and all will be revealed 

In other words ... you can't "choose" to deliver 100 watts to a 4 ohm load with "either" a high voltage, or a high current. The impedance & power level determine the voltage & current required.


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## Luke352

Thanks guys it all makes sense now and in reality is quite simple. Just never seen those terms really explained before.


Would it be possible to have amp that you can physically switch to either drive low loads or drive high impedence. Sort of along the lines of what Mark is saying by swapping out parts to mod an amp to run full power at higher impedence, could you physically create a circuit which you could decide how you wish to run the amp.


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## Luke352

I found the amp I was thinking off, the Audison HV Venti, has an option whereby you can run High Current 200w per channel @ 4 ohm and you can drive it down to 1 Ohm pr channel, or by inserting 4 four mini blade fuses it goes into a High Voltage setup whereby it will produce 400w per channel @ 4 ohms, but you can't drive low impedence loads. Apparently it uses two sets of Power supplies, go here Audison - Music Expression if you want to have a readt of the manual. 

Either way I'm happy with my Zed Leviathan, despite some initial issues it seems to be a well thought out amp which sounds like it has way more power then it's rated for, but I know it only makes about 10-20% more then rated so all I can put it down to is that it handles dynamic loads very well.


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## MarkZ

There are lots of amps that have high current/voltage switches. I'm looking at two sitting next to me as we speak.  [ESX Quantums]


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## MarkZ

And then there are always case mods. Today I stuck a DEI 600d in an old a/d/s/ heatsink I had. That way it matches the P840 that I'm using for my mains.  

I put two pieces of aluminum bar down, the board sits in between them and so the transistors mount to each bar. They're clamped down with aluminum u-channel (werewolf is going to have my head on a platter...). 

Here's a topless pic.


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## lycan

MarkZ said:


> And then there are always case mods. Today I stuck a DEI 600d in an old a/d/s/ heatsink I had. That way it matches the P840 that I'm using for my mains.
> 
> I put two pieces of aluminum bar down, the board sits in between them and so the transistors mount to each bar. They're clamped down with aluminum u-channel (werewolf is going to have my head on a platter...).
> 
> Here's a topless pic.


dude at least the aluminum channel is _bolted_ (or screwed) down


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## MarkZ

Haha yup. Each side has two banks of transistors, so they're screwed down at the edges of each bank for a total of 4 screws per side. I was prepared to split the u-channels to cover each bank if even the slightest hint of bowing was evident, but it wasn't. Everything is straight and tight.

I hate drilling and tapping holes and hoping that everything lines up. There were over two dozen transistors. This was a much easier solution.

Besides, I don't have any more of those plastic screw inserts.


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## Robin W.

I don't buy upgrades/mods that state the components or upgraded parts have a better "synergy" with existing internals of a given amp. HOWEVER I do believe that the "synergy" between different components that make up the TOTAL system are important. Amp A may honestly sound better in system A then Amp B in system A or vise versa. But like many have stated in this thread already it comes down to some of the measurable specs. A source and amp that have poor high frequency response may sound better on a tweeter that is abnormally bright compared to a tweeter that is also somewhat rolled off because the differences compliment each other. The same tweeter might sound harsh on a system that is made of components with good or excessive high frequency response.

When "upgrading" an amp the whole system should be considered and not just the amp. A perfect example is a PXA H700 that I'm working on right now, there are 5 electrolytic caps in the signal path of each channel, along with 2or3 op-amps plus the volume control IC, dac, muting transistors etc. While testing how the processor behaves without the muting transistors I bypassed 1 of 5 caps, 1 of 3 op-amps along with the muting transistors. No other changes were made, because this "upgrade" doesn't do much in the overall scheme of things I really found it hard hearing a difference. I would fail a blind test and I know it. However when I am done the entire analog stage will be modified, not just a tiny part of it. And to go along with this I will be bypassing the preamp stage of the amps. Now with ALL of these changes there is a good chance there will be a noticeable improvement.

So big warning to everyone out there, a small modification regardless of price without consideration of the whole system will have less chance of making an impact on the system as a whole. Changing one op-amp in a system with a combined total of 20 per channel will not be detectable, changing all 20 defiantly could, but that depends on how the op-amps are used, what type you are replacing and what you are replacing them with. And changing things at random may give a result that is worse than the starting point. 

From an op-amp perspective something that looks "better" on paper just may not work in the circuit you are trying to plug it into. TL07x's are common in a huge amount of electronics on the planet, but throwing that low distortion super fast, high bandwidth op-amp in it's place may cause dc offset or oscillation because these "high end" op-amps are often much pickier than those TL07x's or 4580's etc. 

That doesn't mean there isn't room for improvement in many pieces, but the best bang for the buck is to do it yourself or have a buddy do it for little to no cost in labor. Even good quality parts LME49720 op-amps, Elna Silmic II capacitors aren't crazy expensive, but paying someone $100 to install $10 worth of parts really cuts in to the "value" of the upgrade. 

This is a DIY site, and I think it would be great to see a series of simple upgrades, even if it's just electrolytic capacitor updates for 20 year old amplifiers. I plan to document my upgrades of the H700 it would be nice if it helped others take the plunge and try the modifications. The same goes for the optical output modification I performed on an Alpine CDA-9813, if there was a "how to" started for different brands and models that would cover this often cheap/simple mod but can have a huge impact on performance.


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## Luke352

Robin W. said:


> I
> 
> A perfect example is a PXA H700 that I'm working on right now, there are 5 electrolytic caps in the signal path of each channel, along with 2or3 op-amps plus the volume control IC, dac, muting transistors etc. While testing how the processor behaves without the muting transistors I bypassed 1 of 5 caps, 1 of 3 op-amps along with the muting transistors. No other changes were made, because this "upgrade" doesn't do much in the overall scheme of things I really found it hard hearing a difference. I would fail a blind test and I know it. However when I am done the entire analog stage will be modified, not just a tiny part of it. And to go along with this I will be bypassing the preamp stage of the amps. Now with ALL of these changes there is a good chance there will be a noticeable improvement.
> 
> .


Have you seen Simon's thread over at MEA PXA H701 Modifications - Mobile Electronics Australia

Replaced:
JRC4560 opamps with OPA2134.
All electrolytics in signal path with Blackgate Hi-Q NX capacitors
Decoupling electrolytics (3.3uF) with Rubicon XYF, higher values (47uF) to match the manufacturer's specs for the volume control I.C's
Board-mounted RCA sockets with insulated panel mount units.

Added:
100nF polypropylene across the electros
10uF electros + 100nF poly caps on each opamp for improved supply decoupling/stabilising

Removed:
Navi Mix circuit (including 1 opamp stage on front1/front2 outputs)


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## Robin W.

Luke352 said:


> Have you seen Simon's thread over at MEA PXA H701 Modifications - Mobile Electronics Australia
> 
> Replaced:
> JRC4560 opamps with OPA2134.
> All electrolytics in signal path with Blackgate Hi-Q NX capacitors
> Decoupling electrolytics (3.3uF) with Rubicon XYF, higher values (47uF) to match the manufacturer's specs for the volume control I.C's
> Board-mounted RCA sockets with insulated panel mount units.
> 
> Added:
> 100nF polypropylene across the electros
> 10uF electros + 100nF poly caps on each opamp for improved supply decoupling/stabilising
> 
> Removed:
> Navi Mix circuit (including 1 opamp stage on front1/front2 outputs)



Hi Luke, I have seen that thread it was part of the motivation for me to buy the service manual for this piece and start the modification plans. Even though my unit was brand new and has never seen a vehicle it's already been ripped appart. My first test mod was to remove the Navi Mix circuit which was the op-amp/cap/muting transistors. 

I will be following a similar upgrade process on my unit, however since analog signal processing is my field I will look at simplifying the signal chain after the dac. I will be replacing parts that are required, and removing anything that isn't necessary. My H700 will be followed by a line driver within a few inches of it's outputs so I may even remove the op-amp stage after the volume control ic's.

Depending on the final performance of the unit, I think the volume control IC's would be one of the best things to remove and replace with a different solution. This would leave the H700 with only dac/IV stages remaining and send that raw analog signal to another processor for volume/line driver duties. That is if the control signal for the existing volume IC's can be used/or atleast translated using another microcontroller to use something like the TI PGA2310 or even a relay network for volume control.

But I won't side track this thread anymore, it's about amplifier mods.
And the only mods I think that are worthwhile are:
-Modify your favorite amp to work at a different impedence (adjust voltage rails within the amps capabilities) but maintain similar power.
-Bypass features/processing that is not required.

That's it, if your trying to turn your 500w amp into a 1000w powerhouse, sell the 500w and go buy a 1000w amp. If you are trying to turn your Arc KS into an Arc SE, bypassing the processing might get you one step closer but an Arc KS will NEVER be an Arc SE. The same goes for virtually all brands/models etc, there is probably room for improvement but improvement only goes so far.

The final and most important tip: If you want to get the most value out of any modification or improvement try and do it yourself! Learn/read/ask, ask again, there is a ton of info out there, and many brilliant people willing to help along the way.


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## MarkZ

I have no idea what you just said.


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## MarkZ

cajunner said:


> okay..
> 
> how about this:
> 
> can an op amp swap be considered an audible improvement in A/B blind testing?
> 
> keep in mind, that we're taking out an op amp that by all measures, does it's job well enough to meet specifications but is no world-beater
> 
> and we are replacing it with a discrete op amp made by Burson, in which there are no integrated circuits involved in it's design.
> 
> 
> not going between TL07X and the OPA627's on bulldog adapters, going from low quality chinese copy TL07X clones to an actual discrete op amp.


If the FR/noise/distortion characteristics of one op amp are better than the other to such a significant degree, then quite possibly. You'd have to be using a really crap op amp though for it to yield audible differences though. Even the el cheapos offer flat FRs, <0.1% THD, and noise characteristics that far surpass inductive noise, etc. So, I'll generalize here and say, no, you won't hear a difference. Can you point out some commonly used op amps that are so bad that you'd hear a difference if you upgraded? The cool thing about op amps is that they all have datasheets, so we can see what factors could contribute to any possible differences.


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## MarkZ

Good post. Seems like you've thought a lot of these issues through.

My first comment about the 'op amp problem' is always the same -- which op amp are we talking about? A typical system will have three or more op amps in the chain. 1) Source unit's output; 2) Amp input buffer/xover; 3) Input stage differential amplifier. Let's ignore the first one because it's not in an amp. The third one is often discrete bipolars, not an op amp. So, people usually talk about the second one. My proposed mod would be to rip the ****er out and replace it with a wire which will be "cleaner" than even the most expensive op amp on the market.  This is one reason why I like the idea of getting rid of all the friggin op amps in the chain and running the DAC directly into the differential input. Usually you need an anti-aliasing filter and the appropriate shunt resistance in between, but that's simple enough. Amplifiers with digital inputs FTW.

And if I thought it would yield an audible difference, I'd have done it a long time ago. 

Anyway, like I said in my last post, we have extensive datasheets for almost every op amp out there, so we can do a really good job at predicting what the outcome would be with an op amp swap. Even your concern about the crap on the 12v line can be described completely by PSRR values in the datasheet. Also, if we're talking about input buffer op amps, they're relatively immune to the rest of the circuitry -- unlike the other stuff, there's really no dependence on other factors. So we can pretty much do a simple addition/subtraction here. Op amp #1 has THD of .01%, op amp #2 has THD of .05%, and that will translate directly into a .04% difference on the output. Noise calcs need to be multiplied by the gain of the amplifier, but I don't worry about that so much because the noise of an amplifier especially in a car is almost always dominated by ground loops and inductive noise.


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## MarkZ

BTW, I don't think I've brought this up in this thread yet. But, in most car amps, the mod that would have the biggest impact on distortion performance would be to mod the thermal tracking circuit. That generally means doing a better job of measuring the temperature (eg. measuring the output device case temps instead of heatsink temps) and recalibrating the bias and feedback networks to ensure class B operation.


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## Robin W.

cajunner said:


> this is almost a carbon copy of lycan's response.
> 
> from what I gather, noting the headfi crowd's penchant for subjective responses regarding headphone driven circuits where the actual working parameters have a lot of signal variation, it seems that here in 12V world, indeed, in DIY 12V world, op amps are considered to have zero consequence if they aren't working out of spec. As one of the only "safe" swappable parts that could have upgraded a signal in the chain, it's slightly irritating (imho) that this little piece of the puzzle isn't promoted with any verve, and simply declassed to non-significance.
> 
> what I have been led to believe, as most of the reading I've been doing of late regarding professional recording equipment, sound engineers would easily jump at the chance to promote a discrete op amp topology over the chips.
> 
> also, in 110V world, the sonics do seem contained in a somewhat stable power supply via the electric grid. 12V is more erratic, and it would seem to me that the op amp is more important here than home audio, in controlling what comes out ultimately through the output stages.
> 
> one might even say that it doesn't matter, because you are starting out with a 65db noise floor as a result of the mobile listening space, and why concern myself with something that has such infinitesimal amounts of difference.... and that is where I have to respond "What is wrong with trial and error, with taking a chance with a soldering iron?" Are people afraid that somebody is going to screw up their equipment?
> 
> If that's the concern, over what could be something fun to do over an afternoon, who here hasn't bit off a little more than they can chew, in the quest for a little individuality? Or is it that modifying amplifiers will mean they end up on the auction block tainted, I'm just not getting the downside yet...


I referenced the headphone system as well, but it is a much simpler signal path with less components that both cost less because of the power levels involved and the fact that we don't need eq/crossover/ta. When the whole signal chain after the dac consists of 1 or 2 op-amps driving headphones, changing those op-amps has a drastic affect on the sound of the amplifier.
I would probably get laughed at here, but I spent 3 months of critical listening to dozens of op-amps before choosing the stock and upgrade op-amp for a headphone amp I designed. The fact that even more wouldn't believe, is the stock and upgrade op-amp are the same electrical die, in a different package (one plastic, one metal) and they sound drastically different even though they have exactly the same specs. If anyone wants a demo of these two op-amps that are so the same but different, come on over and have a listen, if you can't hear the difference you would be the first person ever who couldn't pick the upgrade in MY HEADPHONE amp (I won't claim this will change your $200 car amp the same amount).
http://www.national.com/ds/LM/LME49720.pdf The "NA" is the plastic version, and the "HA" is the metal version. There is also a small price difference which will also probably stir the pot! The "NA" is 3.71 each (in quantities of 100) the "HA" is 16.15 each (in quantities of 100) That's only a small premium for electrically the same op-amp in a different package. Is it worth it? Hell ya, there isn't a single change in the amp or my system that has that HUGE an impact on sound quality, (please remember this is a headphone amp and not a car stereo)
If you were to attack all of the op-amps in a given car stereo system I do think there would be a very noticable difference. The system I'm putting in my truck will have some extensively modified equipment (mostly simplified, I'm bypassing anything that isn't required) The signal chain is like this:
cd player - optical to PXA-H700 (leave only the IV op-amp after the dac and the volume control chip) - Custom line driver will swapable op-amps - Modified Arc KS amps (the entire pre-amp stage will be removed, level will be adjusted by the line driver)
This process should remove about half a dozen op-amps per channel, leaving only TWO! It will also remove 5 or 6 electrolytic capacitors from the signal chain, I should be able to get by with 1 or 2 nice poly caps.

I encourage everyone here to have a listen to some GOOD headphones off a good dac & headphone amp system, you would be amazed what can be had for so little money.


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## MarkZ

Very interesting observations. You should make some measurements to determine which op amp is not working according to spec. If you're not equipped to do it, I can do some of it for you. If you don't want to send me the op amps, you can drive them with white noise and tones and capture the output on a high end sound card if you have one, and then send me the resulting files. If you're interested, shoot me a PM. I could probably put together some stimuli for you too.


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## Robin W.

MarkZ said:


> Very interesting observations. You should make some measurements to determine which op amp is not working according to spec. If you're not equipped to do it, I can do some of it for you. If you don't want to send me the op amps, you can drive them with white noise and tones and capture the output on a high end sound card if you have one, and then send me the resulting files. If you're interested, shoot me a PM. I could probably put together some stimuli for you too.


I would be happy to perform any tests that you suggest. I'm done RMAA testing using an EMU 0404 USB and there are no differences between the two setups in repeated tests. Unfortunatially the 0404 USB probably isn't clean enough itself to measure what's going on in the two amplifiers.

If you would like to read someone elses comments regarding the stock/upgarde differences (it was LME49860NA vs LME49720HA, but check the data sheets the only difference you will find is the rail voltage range of the *860NA can be higher than the *720HA, however the amp did not change)

6moons audio reviews: Wyred4Sound STI 1000


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## MarkZ

Robin W. said:


> I would be happy to perform any tests that you suggest. I'm done RMAA testing using an EMU 0404 USB and there are no differences between the two setups in repeated tests. Unfortunatially the 0404 USB probably isn't clean enough itself to measure what's going on in the two amplifiers.
> 
> If you would like to read someone elses comments regarding the stock/upgarde differences (it was LME49860NA vs LME49720HA, but check the data sheets the only difference you will find is the rail voltage range of the *860NA can be higher than the *720HA, however the amp did not change)
> 
> 6moons audio reviews: Wyred4Sound STI 1000


I'll check that link out. And I'll look at the datasheets later to see if there's something that strikes me as worth testing, other than basic FR/noise/THD measurements. It's also worth testing the voltage swing and the PSRR of both op amps to make sure something isn't wrong with one of them. What's their position in the circuit?


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## marshallb

How hard would it be to remove the xover secton from a class D amp?


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## MarkZ

Probably not terribly difficult, but class D amps that aren't full-range often have a low-pass filter on the input by necessity.


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## marshallb

I just would rather use the xover in my HU.


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## MarkZ

It depends on the circuit. Usually the crossover network consists of a few resistors and capacitors and an op amp. The op amp sometimes doubles as a buffer, sometimes not. You need the buffer. If there's a separate buffer AFTER the crossover section, then you can basically bypass the crossover circuit with a wire. Otherwise, it becomes a little more difficult, by opening and/or shorting some of the caps and resistors. You need to know how the circuit works before doing any of it.


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## Robin W.

marshallb said:


> How hard would it be to remove the xover secton from a class D amp?


Depending on the design of the Class D, the crossover section might not be the "weakest link" and it might not be worth the trouble. I have a pair of old MTX Thunder6500d's and I've only opened them to check the condition of the electrolytic caps. They will be used as is because I don't feel the difference would be worthwhile. The Arc KS300.4 I'm working on might improve because it appears to be a resonably well designed amp but it does use lots of cheap parts in the crossover/preamp section. This could be a worthwhile (and reversable) modification because once I figure out where to inject the raw signal and cut the trace to everything before it, there isn't much work involved.


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## waylouderthanyou

Boostedrex said:


> http://www.diymobileaudio.com/forum/diy-mobile-audio-sq-forum/78570-amplifier-mods-upgrades.html
> 
> Start reading through that. Aside from the bickering, there is some good info.


damn great link.


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## lust4sound

cajunner said:


> because, it goes back to the limits of audible improvement?
> 
> I can't help but believe, after decades of reading the popular science of car audio, (and home, of course) that somehow the effects are cumulative.
> 
> that's a constraint, there are certainly some benefits to be had in that synergy of effect, one wants to believe that the correction by using a better, and certainly more costly parts count, will eventually accumulate and in the end result in an outcome that's orders of magnitude better than before...
> 
> is it simply a marketing ploy, then?
> 
> I like to think that cost constraints are the primary reason why most amp builds differ in their eventual sonic signature. One cannot point at a single idiosyncratic gesture on the amp designer's part, that will lead to a suggestion that one might identify that amp from another in blind testing.
> 
> Maybe, the VST tube sound?
> 
> 
> or perhaps, the T-03 thing?
> 
> one might conclude a hot biased Class (quasi) A circuit is somehow giddy-inducing?
> 
> where is it laid, then. Damping factor is a noticeable function of amp sonics, I would have to agree there, but if it's loose, is it worse?
> 
> I have to argue that, as tube amps are warm, and loose, and so sloppy but yet they make the sound of an average digital device somehow more suitable to the analog wave that moves my tympani?
> 
> ha!
> 
> somebody stop me, I'm drunk on Saturday.


Question, when you ponder this topic, think words such as "idiosyncratic" how do you hear them in your head? Curious, are they accompanied by the Cajun Twang?


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## lust4sound

cajunner said:


> I have no twang, sir.
> 
> I am devoid of such rudimentary impediments, and exist in the autonomous zone prescribed by my forebears...
> 
> lol...
> 
> I just enjoy the verbiage for what it offers, some professional people diagnose the peculiar bent with derogatory classifications, such as defense mechanisms, or worse, use the very thing they themselves love, to cast dispersions on those who find curricular use of vocabulary pleasurable.
> 
> Nowhere else do you find such extensive derivative word processions as in the medical field, and yet they claim that those who find comfort in it, are actually compensating for low intellect and attempting to gain notoriety based on their perceptual underachiever status.
> 
> I have a strong accent when intoxicated, though. Certainly authentic and when combined with the multi-syllabic word use, an enunciation of iconoclastic intent...



"I am devoid of such rudimentary impediments, and exist in the autonomous zone prescribed by my forebears..."

Are you saying your great great great grandpappy was not a ******* therefore you've no regional diction? 

"Nowhere else do you find such extensive derivative word processions as in the medical field, and yet they claim that those who find comfort in it, are actually compensating for low intellect and attempting to gain notoriety based on their perceptual underachiever status."

The reference to bombastic medical practitioners and their "Linguistic grandiloquence" brings some bitter tidings, it's at its finest when you are being told you will die and yet your queries still fall on deaf ears, as if you're regarded as sharing kinship with a baboon family. Spurious is often the sincerity with which such tidings are offered..

Notoriety? Malaise in the order of healthcare, a general lack of urgency and disregard for the simple duty as prescribed by the neurologist or plain bastardization of the order of relevance, led to the loss of the family Patriarch. I am not referring to the time Pops went in for a urethral infection and paid for it with his prostate (yes he had a cold in his willy and they took his prostate instead.. All because someone botched the charts. True story) I am referring to the time he complained of severe pain in his leg, all indications pointed to high risk of stroke thus tests were ordered by the neurologist which were not performed resulting in a stroke some 14 hours after the fact which ultimately ended his life..(for 6 long agonizing months after the fact, he slowly drowned in his own fluids..)

Hardly the time and place for this, my apologies.. You're not a doctor are you?


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