# Class A Suggestions



## Fatbloke (Jul 23, 2008)

I've just got brand new tweeters (L1 Pro SE) and a new ride to put them in. I'm also thinking that now would be a great time to give them a new amp. I thought that having tried a fair few amps it might just be time to give the tweeters a touch of Class A.

Here's the question: A fair few poeple I know have Genesis DMA or the DLS Class As, I'd like the Soundstream but I need the amp to be reliable for competition and I can't trust something that old to be 100% when I need it. What other options do I have? Class A, Reliable and fairly new and if someone can suggest something that is fairly rare with it I'd love it.imp:

At the moment let's not worry about the trivia of budgets


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## basher8621 (Feb 21, 2009)

Does it HAVE to be class A. Will A/B work. If so ARC SE amps or the Ultra 4200AM are nice amps. I just put 3 Ultra 4200's in my car last night and they are AWESOME amps. They have TONS of power and it is extremely clean.


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## Exit9 (May 12, 2009)

A lot of the subwoofer (mono) amps seem to be class D. I would look into 2 and 4 channel amps for a class A. My Cadence TX3004 4 channel is a class A/B and I am bridging the rear channels for 150W RMS for a subwoofer. You probably are looking for something better, but I didn't shop in the higher price categories.


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## schuey_1 (Nov 11, 2007)

New Zapco class A


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## Mooble (Oct 21, 2007)

You do realize how precious few REAL class A amps there are, right? There were a couple of Monolithics and an HSS Fidelity. 

Now if you are talking high biased class A amps you have Genesis, Steg, and Audison (with the class A module). What DLS amp are you thinking about? I didn't know DLS had any high biased amps.

The Soundstreams Reference As are reliable, but not very heavily class A biased. If you're only pushing tweeters, it's not going to tax any amp anyway.


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## Mooble (Oct 21, 2007)

schuey_1 said:


> New Zapco class A


Oh yeah, forgot about this one. I still want more info. What's the current draw? How heavily weighted is the A mode? I'm interested for sure.


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## rmenergy (Feb 15, 2009)

I think thehatedguy will be selling his Monolithic Class A 501's shortly, make him an offer. If not, I know Greg @ Monolithic & can have somthing made for you (you just have to be patient w/him).


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## Oliver (Jun 25, 2007)

Pure Class A Output Topology for the utmost in musicality and definitive
power output. Soundstream's unique design allows the Class A amplifiers to
deliver incomparable sonics or, when operated at lower impedances, to...

http://www.soundstream.com/manuals/AMP/REFERENCE/rca5_10/rca5_10.pdf

http://www.soundstream.com/manuals/AMP/REFERENCE/r405/r405.pdf


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## 89grand (Nov 23, 2006)

True class A amps draw the same amount of power at idle as they do balls out. If an amp does not do that, it's not class A.

So like was already mentioned, there are only a few real class A amps on the market because they aren't even a good idea for use in the car. 99% of all amps that say "Class A" on them, are not class A.


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## dbiegel (Oct 15, 2006)

The MBQuart QAA4250 is also a very highly biased class A/B amp. If I remember correctly, it's class A up to the first 15 watts or so per channel. I'm using it on my horns so it's pure class A for me  I'm also using high sensitivity midbass so it's largely class A for them as well.

The problem is that these sort of amps are a HUGE power hog. In fact, I had a bit of a scare the other day. I was doing some testing and ran my system with the engine off for about 8 minutes at low-medium volume. I started the testing with a fully charged battery but I could BARELY start my car afterwards... I had a hard time believing my amps were that inefficient, so I took my car to Autozone to have the battery, alt, and starter tested. Everything checked out great, but I'm tempted to switch to a more efficient amp now. :blush:


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## thehatedguy (May 4, 2007)

You shoud buy my HSS Fidelity HT230. It's a pure class A tube amp.


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## subwoofery (Nov 9, 2008)

"Fairly new"? I'd say Sinfoni Prestigio 

Have one on my horns... LOVE IT 

Kelvin


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## Patrick Bateman (Sep 11, 2006)

Fatbloke said:


> I've just got brand new tweeters (L1 Pro SE) and a new ride to put them in. I'm also thinking that now would be a great time to give them a new amp. I thought that having tried a fair few amps it might just be time to give the tweeters a touch of Class A.
> 
> Here's the question: A fair few poeple I know have Genesis DMA or the DLS Class As, I'd like the Soundstream but I need the amp to be reliable for competition and I can't trust something that old to be 100% when I need it. What other options do I have? Class A, Reliable and fairly new and if someone can suggest something that is fairly rare with it I'd love it.imp:
> 
> At the moment let's not worry about the trivia of budgets


I've never seen a car audio amp that was actually class A. If you really want Class A, build one of the Nelson Pass amps. The schematics are on diyaudio. You can run one using a pair of laptop computer power supplies. Total investment is well under $150.

The Class D icePower amps are attractive. If I wasn't running Tripath, I'd run icePower.


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## MarkZ (Dec 5, 2005)

dbiegel said:


> The MBQuart QAA4250 is also a very highly biased class A/B amp. If I remember correctly, it's class A up to the first 15 watts or so per channel.


And then what? Distortion. 

Class A/B is not a very good design topology for audio amplifiers. I mean, you can do it and it will probably lead to inaudible distortion, but it's a bad implementation compared to class B or pure class A. When you switch from A to B, which is the case in an A/B design, you're turning off a transistor. When you do that, the current that the output stage draws gets cut in half, which ultimately leads to something called gm-doubling distortion. This (along with crossover distortion -- which is basically the same thing in the reverse direction) is maybe the most dominant form of distortion in most amplifiers.

So, if you're gonna run something with that amp at less than 15 watts, that's a great solution. But if you're going to run a conventional set of large-ish tweeters or something that's going to require a little more, I'd choose class B before I'd choose a high biased A/B amp.

But it's all moot because (all amps sound the same anyway).


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## t3sn4f2 (Jan 3, 2007)

Hmmm, will this be the popcorn thread of the night?


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## rmenergy (Feb 15, 2009)

Even the Monolithic's are high biased A/B. My latest 4 channel I had biased more towards B w/2 amps going across the input stage @ idle. When Greg sets up VERY high biased amps, they are not recomended for daily driven vehicles because of the amount of heat generated & the idle current draw.


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## rawdawg (Apr 27, 2007)

Really interested in this thread since I run horns. I was going to post "What's the prettiest thing I can power my horns with?". Right now they get 50w with the gains nearly at 0 so big wattage not a concern.

Keeping my ears open...


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## zwc0442 (Oct 24, 2008)

What are the odr amps considered? I have an RS-A2 and it says class A and for only a 100 watt amp it sure is plenty big.


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## thehatedguy (May 4, 2007)

The A1s were high biased a/b. In the manual for the A1 it cautioned against running more than one of them in a car without charging system upgrades.

My HSS is pretty much the shizzle on high efficiency speakers. Class A, all tube, and no negative feedback...she draws 23 amps of current at idle.


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## ACRucrazy (Mar 13, 2007)

zwc0442 said:


> What are the odr amps considered? I have an RS-A2 and it says class A and for only a 100 watt amp it sure is plenty big.


 Want anymore? I believe you can daisy chain up to 8 in a system. 














































I also have these.


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## ACRucrazy (Mar 13, 2007)

thehatedguy said:


> The A1s were high biased a/b. In the manual for the A1 it cautioned against running more than one of them in a car without charging system upgrades.


Correct. The RS-A1 and RS-A2 looked almost identical.


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## smithee419 (Aug 27, 2008)

What about poweramper? Are they true class A ar A/B.


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## freemind (Sep 11, 2008)

I miss my old Soundstream Class A 50 II...................................


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## thehatedguy (May 4, 2007)

There are only a handfull of real class A amps for cars. If you see something marketed as a class A amp and the idle current does not equal the max current draw, then it is not a real class A amp. Most of the amps marketed as class A are high biased a/b amps that would run class A for the first couple of watts (anything more and the heatsinks would not be able to dissipate the heat) and then switches to a/b or one of it's variants....which is great if your speakers are 105+ dB efficient.


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## thehatedguy (May 4, 2007)

I had 3 of those and 4 A2s at one point in time. I still have the ODR 10s, dome mids, and tweeters somewhere.



ACRucrazy said:


> Correct. The RS-A1 and RS-A2 looked almost identical.


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## dbiegel (Oct 15, 2006)

MarkZ said:


> Class A/B is not a very good design topology for audio amplifiers. I mean, you can do it and it will probably lead to inaudible distortion, but it's a bad implementation compared to class B or pure class A. When you switch from A to B, which is the case in an A/B design, you're turning off a transistor. When you do that, the current that the output stage draws gets cut in half, which ultimately leads to something called gm-doubling distortion. This (along with crossover distortion -- which is basically the same thing in the reverse direction) is maybe the most dominant form of distortion in most amplifiers.
> 
> So, if you're gonna run something with that amp at less than 15 watts, that's a great solution. But if you're going to run a conventional set of large-ish tweeters or something that's going to require a little more, I'd choose class B before I'd choose a high biased A/B amp.


When I'm running more than 15 watts to my horns, I don't think I'll have to worry much about switching distortion, since I'd be permanently deaf 

Anyway, not to be a dick, but I disagree with what you're saying. Don't take my word for it; two of the most historically trusted sources in car audio say that basically class B is horrible distortion, class A is the best but too inefficient to be practical, so a highly biased class AB (like the QAA) is the best we can do in a car:

Basic Car Audio Electronics (click the link to see distortion graphs, etc.)


"A class 'A' amplifier is very inefficient. This is not good for a car audio amplifier. We also said that a class 'B' amplifier will cause a signal to be distorted, which is not good in any audio amplifier. A class 'AB' amplifier is the best compromise."

"A class 'AB' amplifier is a class 'B' amplifier which has a small amount of "bias" current flowing through the output transistors at all times. This eliminates virtually all of the crossover distortion."

"A class 'AB' amplifier is much more efficient than the class 'A' but without the distortion of the class 'B'."

rec.car.audio FAQ:


"The biggest advantage of Class A is that it is most linear, ie: has the lowest distortion."

"The biggest disadvantage of Class A is that it is inefficient, ie: it takes a very large Class A amplifier to deliver 50 watts, and that amplifier uses lots of electricity and gets very hot."

"Class B amplifiers have a major disadvantage: very audible distortion with small signals. This distortion can be so bad that it is objectionable even with large signals. This distortion is called crossover distortion, because it occurs at the point when the output stage crosses between sourcing and sinking current. There are almost no Class B amplifiers on the	market today."


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## Patrick Bateman (Sep 11, 2006)

rawdawg said:


> Really interested in this thread since I run horns. I was going to post "What's the prettiest thing I can power my horns with?". Right now they get 50w with the gains nearly at 0 so big wattage not a concern.
> 
> Keeping my ears open...


There are some things you can do to improve the sound of horns that's cheaper than replacing your amps:


Put a roundover on the mouth. When a horn isn't properly terminated, sound is reflected back down the throat. Because the reflections are delayed in time, it screws up the polar response, reduces intelligibility, and introduces peaks and dips in the response of the horn. The reflections at the mouth also create phantom imaging cues, since the reflections can be every bit as loud as the compression driver itself. Google "homster" on diyaudio for more info.
Fill the horn with reticulated foam and then EQ it. The foam absorbs the reflections mentioned in point #1
Replace the compression driver with something better. BMS makes compression drivers that don't suffer from a big peak in the upper treble. Check out the spec sheets on any popular compression driver - you'll see a big fat resonance between 8 and 16khz, similar to what you see in an aluminum-coned woofer.

If you're up for it, there are a lot of modern waveguides which deliver better results than the "old school" horns in car audio, which are mostly based on 1960s diffraction horns.

If anyone's curious about that last point, I have a pile of compression drivers and waveguides in the garage. I could mount a set and measure them in the car, if anyone's curious how the new designs behave in-car.


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## rawdawg (Apr 27, 2007)

Oh, but I drink the Kool-Aid from the House of Bateman.

All those things you've bulleted I have on my "To Do" list for the 2010 season. But I am curious if a Class A amp would improve the sound of a horn vs. an AB. My gut instinct says, "It depends...".

I would love to see comparisons of old school vs. new school WG's. I think a lot of people on these boards would appreciate your findings.

Sometimes I wonder, if the Holdaways were to do a system based on their GN but stuffed full with all the things they've learned since then, how would the new system perform vs. the OG one? Has car audio come that far?

Your most devoted minion,
rawdawg


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## PaulD (Nov 16, 2006)

I was under the impression that class A was biased so that it draws 50% of it's max current at idle, not 100%


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## subwoofery (Nov 9, 2008)

You could try to ask Image Dynamics to modify their 700.2 to a High-Biased class A. 
Heard somewhere that the ID Q series amp had the best SQ in a blind test with a Brax and a Sinfoni. 

Kelvin


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## Patrick Bateman (Sep 11, 2006)

rawdawg said:


> Oh, but I drink the Kool-Aid from the House of Bateman.
> 
> All those things you've bulleted I have on my "To Do" list for the 2010 season. But I am curious if a Class A amp would improve the sound of a horn vs. an AB. My gut instinct says, "It depends...".
> 
> ...


Distortion in an amplifier is practically a non-issue, so I focus on the speakers.

Basically there's three easy ways to reduce distortion in a loudspeaker:


Reduce excursion - distortion goes up dramatically as excursion rises.
Use shorting rings
Use an underhung motor

When I first tried to copy the Grand National, I thought it was all about the horns. But once I really studied it, I started to realize the subs and the midbass played a big part too.

There are three things working in our favor now:


There are tons of affordable woofers with shorting rings and/or underhung motors. If you thumb through a speaker catalog from the 80s, you'll notice that underhung motors were basically non-existent, and shorting rings were only found in prosound gear. (Like the stuff in the GN.)
Amplifiers are cheap and ubiquitous
Clark owned a TEF system to measure the car, and the skills to build delays and noise gates. Nowadays, these features are available to anyone.

In a nutshell, the GN was way ahead of it's time, but the technology to do something similar is freely available and inexpensive nowadays.

If I was competing with my car, I'd probably invest a lot of time perfecting the Unity horns. The difference between a conventional horn and a Unity horn is one of those things you notice immediately. The improvement from roundovers and the reticulated foam is audible, but a lot more subtle. That's not to say that it's not worthwhile - it's just that it takes a few minutes to really appreciate the difference. But the Unity thing "grabs you" right away.


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## benny (Apr 7, 2008)

PaulD said:


> I was under the impression that class A was biased so that it draws 50% of it's max current at idle, not 100%


I was under the impression that Class A pulls full current, all the time


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## Mooble (Oct 21, 2007)

smithee419 said:


> What about poweramper? Are they true class A ar A/B.


Not hardly. They are probably even less A biased than the Soundstream and Genesis amps they copied.


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## 89grand (Nov 23, 2006)

PaulD said:


> I was under the impression that class A was biased so that it draws 50% of it's max current at idle, not 100%


True class A draws max current even at idle.


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## thehatedguy (May 4, 2007)

The crossover distortion is already pretty low in the amps.

We (few of us team members) are trying to get Eric to make a limited run of high biased or full class A amps. 

That is correct about the listening test. And that was with a stock IDQ amp...they get better when you bypass the whole front stage and change opamps. The real suprise is the 1200 watt monoblock with the frontend removed...flat to 60k hertz (I believe that is what Eric told me.



subwoofery said:


> You could try to ask Image Dynamics to modify their 700.2 to a High-Biased class A.
> Heard somewhere that the ID Q series amp had the best SQ in a blind test with a Brax and a Sinfoni.
> 
> Kelvin


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## thehatedguy (May 4, 2007)

But when you are using speakers in the mid-upper 100 dB sensitivity range, crossover distortion can be a very real issue...it's going to cause harshness. You can have a class a/b with low crossover distortion or use class A where there is no crossing over.

Atleast that's what Dr. Geddes said.




Patrick Bateman said:


> Distortion in an amplifier is practically a non-issue, so I focus on the speakers.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> But when you are using speakers in the mid-upper 100 dB sensitivity range, crossover distortion can be a very real issue...it's going to cause harshness. You can have a class a/b with low crossover distortion or use class A where there is no crossing over.
> 
> Atleast that's what Dr. Geddes said.


You're correct, I should have clarified that I'm not concerned about _harmonic_ distortion in an amplifier. (not crossover distortion.)

I am not aware of a car audio amplifier that publishes anything more useful than RMS ratings and THD ratings.

The Geddes thread on diyaudio left me with the impression that modern chip amps have a number of advantages over amplifiers with discrete devices.


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## thehatedguy (May 4, 2007)

Yeah, THD is pretty over rated.

I would like to measure XO distortion in amps, and I need to go re-read those thread where he mentions how to measure it.

I got that impression too. I wonder what that is the case? A chip amp would be plenty of power for a set of horns/high efficiency speakers.

So would the Mini-A on DIYAudio. That is a GOOD sounding amp.


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## MarkZ (Dec 5, 2005)

dbiegel said:


> When I'm running more than 15 watts to my horns, I don't think I'll have to worry much about switching distortion, since I'd be permanently deaf
> 
> Anyway, not to be a dick, but I disagree with what you're saying. Don't take my word for it; two of the most historically trusted sources in car audio say that basically class B is horrible distortion, class A is the best but too inefficient to be practical, so a highly biased class AB (like the QAA) is the best we can do in a car:
> 
> ...


See, this is precisely why I *hate* that the audio industry has bastardized the definitions of class A/B and class B. Realistically, what they're calling class A/B is really class B, and what they're calling class B is really class C. As a result, people get confused reading my posts.  This is why I wrote this tutorial a few months back:

http://www.diymobileaudio.com/forum/diyma-tutorials/61156-class-b-class-b.html

IOW, technically speaking, BCAE and the RAC FAQ (which I actually contributed to...) are wrong. 

Anyway, it's good that I wrote that tutorial (that nobody read...), because of this kind of thread! How do you distinguish between a bias scheme where only one transistor is conducting at a time, vs. a bias scheme where you've got overlap? In car audio, both would be called class A/B (even though the first scheme is, by definition, class B).

My point is that class B is better than class A/B because (in a perfect world) there's no gm-doubling distortion and there's no crossover distortion. If designed well, it mimics class A in that regard. Class A/B, on the other hand, ensures that there's no crossover distortion, but the side-effect is that there's gm-doubling distortion. That's why class B outperforms it. 

The problem is that, in order for class B to behave perfectly, it needs to change the bias as the temperature of the transistors change. Most manufacturers don't do a very good job of that -- and so you'll probably get a little crossover distortion or a little gm-doubling distortion. But, unless the design is completely off the wall, you should still get less distortion than an A/B amp (referred to as a "high bias A/B" amp in this thread). That's one reason why I don't like an A/B amp unless you're absolutely certain that you're not going to exceed the bias cutoff very often -- 15w in your case. 

But that makes me wonder why they don't just create a class G implementation of class A instead of the high bias A/B thing.


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## Mic10is (Aug 20, 2007)

subwoofery said:


> _You could try to ask Image Dynamics to modify their 700.2 to a High-Biased class A. _
> Heard somewhere that the ID Q series amp had the best SQ in a blind test with a Brax and a Sinfoni.
> 
> Kelvin


already been done to some extent. I have an amp w/ a high bias more toward class A with a ton of upgraded parts--very similar to what Matt Roberts did to the Zapco's in Kevin K's car


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## freemind (Sep 11, 2008)

"But that makes me wonder why they don't just create a class G implementation of class A instead of the high bias A/B thing. [/QUOTE]



That is the smartest thing I have read all day


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## MarkZ (Dec 5, 2005)

Patrick Bateman said:


> You're correct, I should have clarified that I'm not concerned about _harmonic_ distortion in an amplifier. (not crossover distortion.)
> 
> I am not aware of a car audio amplifier that publishes anything more useful than RMS ratings and THD ratings.
> 
> The Geddes thread on diyaudio left me with the impression that modern chip amps have a number of advantages over amplifiers with discrete devices.


The dominant source of harmonic distortion in most designs IS crossover distortion.



thehatedguy said:


> But when you are using speakers in the mid-upper 100 dB sensitivity range, crossover distortion can be a very real issue...it's going to cause harshness. You can have a class a/b with low crossover distortion or use class A where there is no crossing over.


There are class B designs where crossover distortion is pretty much eliminated. This is one of the many benefits of high negative feedback that you took a shot at earlier in the thread.  It also requires an excellent thermal tracking circuit, preferably with a sensor on the die or at least on the transistor case. I don't know who in the car audio world is doing it though. It's been very popular among the DIY crowd though.


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## thehatedguy (May 4, 2007)

I didn't take a shot at NFB...just stated my HSS didn't use any. I don't like negative feedback in the midrange/treble though.


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## tmieczkowski (Jan 5, 2009)

the a1 ODR amps are heavily A biased, 15x2 and a 30 amp fuse shoved in her lol! 
we had 3 of them back in the day and they got violently hot, melted plexi.
also, milbert tube amps are heavily a biased to the A side too


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## thehatedguy (May 4, 2007)

The Milberts are not anywhere close to class A. They are pretty heavily biased to class B.


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## subwoofery (Nov 9, 2008)

thehatedguy said:


> The Milberts are not anywhere close to class A. They are pretty heavily biased to class B.


Can you please explain? I know that you had one and since I have one too I'd like to know a bit more about it. 

Thanks, 
Kelvin


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## SQram (Aug 17, 2007)

rawdawg said:


> Oh, but I drink the Kool-Aid from the House of Bateman.
> 
> All those things you've bulleted I have on my "To Do" list for the 2010 season. But I am curious if a Class A amp would improve the sound of a horn vs. an AB. My gut instinct says, "It depends...".
> 
> ...


I also thought an old school/new school WG/horn comparison would be neat to see. In fact, I PM'ed Patrick about a month ago and offered to loan some Illusion and Veritas horns for measurement. Never got a response though, Patrick may be too busy? Offer still stands...


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## thehatedguy (May 4, 2007)

The Milbert is idling at 5 amps with a max draw of 20 amps. Not class A by any stretch of the imagination. My HSS idles at about 23 amps. Both are rated for the same about of power- 30 watts a channel. I will have to dig up some old posts by werewolf where he looked at the Milbert...but the amp is is based on, the Berning EA-230 has been talked about a lot in the home world.

I'll try to find more info on it.


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## 89grand (Nov 23, 2006)

It seems the Milbert amps operate in class A on the input side, but not the output.

"As always, the signal path is 100% all tube, and the tube input stages and drivers operate in Class-A mode. In fact, there are ten tubes in the BaM-235ab and zero transistors in its dual audio signal paths."

Most Musical Tube Amplifiers by Milbert Amplifiers


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## thehatedguy (May 4, 2007)

But that's not teh side of things that really matter in terms of this discussion.


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## chad (Jun 30, 2005)

89grand said:


> True class A draws max current even at idle.


Reduces my dimming when my tweeters "hit"


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## 89grand (Nov 23, 2006)

thehatedguy said:


> But that's not teh side of things that really matter in terms of this discussion.


I know. That's why I mentioned that is was only on the input and not on the output.


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## subwoofery (Nov 9, 2008)

thehatedguy said:


> The Milbert is idling at 5 amps with a max draw of 20 amps. Not class A by any stretch of the imagination. My HSS idles at about 23 amps. Both are rated for the same about of power- 30 watts a channel. I will have to dig up some old posts by werewolf where he looked at the Milbert...but the amp is is based on, the Berning EA-230 has been talked about a lot in the home world.
> 
> I'll try to find more info on it.


I know the Milbert is not a true Class A (and only Class A for the input stage)... 
but to say that the Milbert are pretty heavily biased to class B ; I'd like to know what makes you say that... 

Kelvin


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## thehatedguy (May 4, 2007)

The amp can not be high in Class A bias because it is the harder it is to keep the absolute dc flux balance within the one to two milliamps range where saturation occurs in most push-pull output transformers.


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## thehatedguy (May 4, 2007)

How do I design minimum current for 35W PP AMP - diyAudio


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## Fatbloke (Jul 23, 2008)

Guys this is interesting reading, absolutely fascinating in many ways.

However, I was hoping more for suggestions for all the names I've not heard of regularly over here (think US manufacturers) that do have true Class A.

My reasoning, simple really - I've heard what the best of Class B (with some minor Class A) can offer and I've heard some class A and there is a difference. I believe the Class A is an improvement over the alternatives and I'd love to combine that with, what I believe to be, the best tweeters I've ever heard.:heart::heart:

My budget isn't quite limitless so, while it's nice to look at, please don't just be suggesting $4,000 amps.:earmuffs::deal2:


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## Oliver (Jun 25, 2007)

Zapco Introduces Class A Amplifier

Here ya go 



From a reputable guy !



> this topic.
> *[email protected]*
> MECA Member
> 
> ...


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## Fatbloke (Jul 23, 2008)

Thanks for that, will look into that one further.

Anymore?


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## Mooble (Oct 21, 2007)

I think what we're trying to tell you is that most of those amps aren't class A in the first place, therefore there is little advantage to using them. 

The Genesis should be good for up to 26 watts pure class A before it switches to class G (depending on impedance). This would work well with most tweeters. This is the highest of the high biased class A amps that I know. I think the class A module for Audisons is considerably lower than this. Contact Steg and see what their class A amp is good for before switching. 

Your best bet if you are truly set on a real class A amp would be to contact Monolithic and see if they will build you one. It would take many months though.

FYI, I just emailed Steg about idle current and bias on the Masterstroke Classe A. I'm curious myself.


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## thehatedguy (May 4, 2007)

I thought your first post said not to worry about the budget?

Real class A (which there isn't much of) is going to cost you...cost you a lot.

The Monolithics aren't real class A either. They are an extremely high based a/b...really high biased. I will have a pair of A501Ms coming up for sale in the next couple of weeks.


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## Mooble (Oct 21, 2007)

Just got the word from Steg. They say that the Classe A is good for up to 50w pure class A. It's a variable bias 1-50w, but balls-out it will do 2 x 50w in class A before switching to B which is good up to 100w. I wanted to get idle current draw numbers, but no luck so I can't say if those figures are accurate or not. I think Tristan has one. He might know.


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## thehatedguy (May 4, 2007)

I know where a pallet of Steg are at in Austin...but he doesn't come around much any more. Yes, a pallet.


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## n_olympios (Oct 23, 2008)

50 watts pure class A? Forgive me for being sceptic, but wouldn't you need a powerplant to run an amp like that?


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## chad (Jun 30, 2005)

n_olympios said:


> 50 watts pure class A? Forgive me for being sceptic, but wouldn't you need a powerplant to run an amp like that?


kinda, but marketing is always right, right? I mean we should always trust marketing right?


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## Mooble (Oct 21, 2007)

n_olympios said:


> 50 watts pure class A? Forgive me for being sceptic, but wouldn't you need a powerplant to run an amp like that?


Well look at the size of the Classe A. I'm a tiny bit skeptical, but I wouldn't think it would have any problem matching the Genesis. I'm guessing it would draw at least 45a just at idle unless it has some radical power supply with dilithium crystals.


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## n_olympios (Oct 23, 2008)

n_olympios said:


> sceptic


Of course I meant to write skeptical. Writing greek words in english is difficult sometimes, even if you're greek.


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## thehatedguy (May 4, 2007)

You would need some SERIOUS heatsinking for that kind of power in class A. Maybe an A/C unit for the amp too.


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## MarkZ (Dec 5, 2005)

It's like we're going back in time. Pretty soon we'll be paying $3000 for a 8086 equipped PC...


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## t3sn4f2 (Jan 3, 2007)

MarkZ said:


> It's like we're going back in time. Pretty soon we'll be paying $3000 for a 8086 equipped PC...


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## thehatedguy (May 4, 2007)

The home guys are paying that for non-oversampling DACs that use 20 year old chips...



MarkZ said:


> It's like we're going back in time. Pretty soon we'll be paying $3000 for a 8086 equipped PC...


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## Matt R (Aug 29, 2007)

It seems like there is some misunderstanding about how an amplifier switches from class A to A/B. It's a misconception that an amp is not "real class A" unless it draws full current at idle. 

If an amplifier draws 10amps at idle and has a maximum current draw of 30 amps then that amp is in class A operation all the time. 1/3 of it's output power potential is being produced in class A operation all the time. Only when the current draw exceeds 10 amps is the amp considered to be operating in class A/B operation and only for one amp of that current draw. If the amplifier is drawing 11 amps of current 10 of those are still being produced in class A operation.

Really the only time you would get the switching distortion of the class A/B amp would be once the amplifier is already getting pretty loud. IMO the benefits of class A operation are best realized at lower listening level high detail situations. When your really getting on the system I think it gets much harder to realize the benefits.

Here is how Nelson Pass explains it. http://www.passdiy.com/pdf/leaving_class_a.pdf

The Zapco 2.0A that I am involved with Draws 8 amps of current at idle. The way I like to explain it is, with a typical 90db efficient speaker at average listening levels we are probobly only listening to 8-10-12 watts per channel. Only the dynamic peaks are being played with the amplifier switching into A/B operation.


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## bobduch (Jul 22, 2005)

You could get a really big dc to ac converter and run a 
Mark Levison 20.6 (+-110lb) 100 watt mono amp. (okay, maybe a little under rated)
Those things heat my den in winter. 

I'm afraid we're saying that unless your power requirements are very low this just won't work.


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## 89grand (Nov 23, 2006)

Matt R said:


> It seems like there is some misunderstanding about how an amplifier switches from class A to A/B. It's a misconception that an amp is not "real class A" unless it draws full current at idle.
> 
> If an amplifier draws 10amps at idle and has a maximum current draw of 30 amps then that amp is in class A operation all the time. 1/3 of it's output power potential is being produced in class A operation all the time. Only when the current draw exceeds 10 amps is the amp considered to be operating in class A/B operation and only for one amp of that current draw. If the amplifier is drawing 11 amps of current 10 of those are still being produced in class A operation.
> 
> ...


I'm tired and getting ready to go to bed, so maybe I'm off track here, but I think you are misunderstanding us. I think many of us are well aware of high class A biased A/B amps which seems to be what you are describing as full class A.

What I, and a few others were saying is that high class A biased amps are not actually true class A, and I still maintain that because non-switching class A amps do draw as much current at idle as they do at maximum output.

To me, any amp that switches at any point to class B, is not a real class A.


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## Matt R (Aug 29, 2007)

Ok, so there is still a misunderstanding of the classifications. There are three classes of operation we are talking about here, there is Class A, class B and class A/B. When a class A/B amp leaves class A it enteres class A/B. 

A class B amplifier has the opposing transistor turned off while the other one is working and vice versa. 

In class A and A/B amps the transistors don't turn off at all.

Saying the class A is "not real" is very misleading. 

This amp in my description is a pure class A amp up to about 17 watts of power. That is REAL!!!! Once it goes into it's 18th watt of power it is switching into class a/b operation. Not class B operation where the transistors turn off. 

I'm not here to argue with anyone about these topics. It just seems the misunderstanding of how it works could be misleading to other readers.


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## 89grand (Nov 23, 2006)

In my opinion there are 4 types.

*Class A* - Very few in existence. Draws max current even at idle because the output transistors are always on.
*Class B* - None in car audio that I'm aware of. Output transistors are off at idle.
*Class A/B* - What 95% of all amplifiers are. Small amount of current through the output transistors at all times. Low idle current draw.
*High biased A/B* - What 99.9% of all "Class A" car amps actually are. These amps run at class A up to some level then switch to class B. Higher current craw at idle than normal class A/B, but not max current like class A.


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## Matt R (Aug 29, 2007)

There is a bit of a marketing game going on in the audio world. It seems to me alot of it is based around the bias circuit and the misunderstanding of exactly how it works. 

A high bias class A/B amp has the sonic benefits of a class A at lower power and the power output capabilities of a powerfull class A/B amplifier. You really end up getting the best of both worlds.

Most manufacturers don't publish specs about how much of the power output is in class A operation. If you look at the link I attached Nelson actually tells the exact amount of class A power output and the total rated power (class a/b) of his amplifiers. 

One thing to remember about this kind of amplifier is all of the sound produced that is below the class A bias level is being produced in class A operation and has all the benefits of that. When you are listening to real music that means all the subtle details, finger plucking on strings, the ambient nuances of the room in the recording, the breath behind the vocalist are all being produced in pure class A operation.

Maybe the question that is being raised here is, should manufacturers disclose exactly how much of their amplifiers power is being produced in class A. I think most manufacturers don't want the consumers to know the answer to this question, mainly because most consumers don't understand what I explained above and what Nelson Pass explains on his site.

Matt


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## Matt R (Aug 29, 2007)

[QUOTE
*High biased A/B* - What 99.9% of all "Class A" car amps actually are. These amps run at class A up to some level then switch to class B. Higher current craw at idle than normal class A/B, but not max current like class A.[/QUOTE]

This is the misconception that I am trying to clear up. The post I made above tells exactly what characturistics the three different classifications have. If you want to call a "high bias class A/B amp" it's own classification, thats fine but, IT WILL NOT SWITCH TO A CLASS B AMPLIFIER. It will switch into class A/B operation. In a class A/B amp (wheather it has high class A bias or low class A bias) the transistors DO NOT, turn off.


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## Matt R (Aug 29, 2007)

Fatbloke said:


> Guys this is interesting reading, absolutely fascinating in many ways.
> 
> However, I was hoping more for suggestions for all the names I've not heard of regularly over here (think US manufacturers) that do have true Class A.
> 
> ...



Hey man, sorry to contribute to the hijacking of your thread. I have been highly involved in the engineering of the new Zapco C2K2.0 A and I would rather the people reading this thread and yourself to have a better understanding of how the amplifier topology actually works. I'm not an EE myself but I am the understudy to a great audio EE. His name is Mike Granger, he has worked on and hand built studio gear that was used in productions by David Parsons and Rick Wakeman from the band Yes, ust to name a few. 

Anyways the new Zapco amp is going to be on display at CES in a few weeks. There are a few of the prototypes out there right now and they are doing very well.


Matt


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## benny (Apr 7, 2008)

Matt, sorry to stay OT, but Im running an HCCA 225G5 on my tweeters currently, I know HCCA stands for High Current Class A, but its not really. Any idea on mods to bias this thing a little hotter?


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## thehatedguy (May 4, 2007)

No, HCCA is high current competition amplifier.




benny said:


> Matt, sorry to stay OT, but Im running an HCCA 225G5 on my tweeters currently, I know HCCA stands for High Current Class A, but its not really. Any idea on mods to bias this thing a little hotter?


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## benny (Apr 7, 2008)

oops, and all these years I thought it stood for High current class A. :blush:

Ignore me, carry on.


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## thehatedguy (May 4, 2007)

Nice amps though. I had some back in 93-94...you would think they were class A with as hot as they got- the red would be pink in a month or so from the heat.


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## MarkZ (Dec 5, 2005)

89grand said:


> In my opinion there are 4 types.
> 
> *Class A* - Very few in existence. Draws max current even at idle because the output transistors are always on.
> *Class B* - None in car audio that I'm aware of. Output transistors are off at idle.
> *Class A/B* - What 95% of all amplifiers are. Small amount of current through the output transistors at all times. Low idle current draw.


No, no, NO. 

Many car audio amplifiers aim to have only one transistor conducting at a time. That's their goal. They run a little bias to overcome the Vbe drop of a bipolar output transistor (and driver). But this is still class B. Class A/B is still common to car audio, but it's inferior to class B and I would wager it's just a way for a cheap manufacturer to get around bias tracking issues (which might be worse in a car because of the major swing in ambient temperature).

High biased class A/B is better than "pure" class A. It's an improvement. Why? Because rather than clipping, you switch to class B-like operation. Both cause distortion (clipping or switching), but switching causes less distortion...

This, by the way, assumes that the design is correct. But I think we're all making that assumption when we debate amplifier classes.


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## Matt R (Aug 29, 2007)

Yeah, I have 4 of em in my "retirement community" They all used to be in my truck my first season of competition. Two of them I've owned since the early to mid 90's

I have not tried to mod any of them. Alot of r&d goes into it.


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## 89grand (Nov 23, 2006)

MarkZ said:


> No, no, NO.
> 
> Many car audio amplifiers aim to have only one transistor conducting at a time. That's their goal. They run a little bias to overcome the Vbe drop of a bipolar output transistor (and driver). But this is still class B. Class A/B is still common to car audio, but it's inferior to class B and I would wager it's just a way for a cheap manufacturer to get around bias tracking issues (which might be worse in a car because of the major swing in ambient temperature).
> 
> ...


I've never heard of any car amplifier described as Class B.


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## MarkZ (Dec 5, 2005)

89grand said:


> I've never heard of any car amplifier described as Class B.


Lots of companies describe their class B amplifiers as "Class A/B". Read my tutorial.


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## thehatedguy (May 4, 2007)

I dunno, calling high biased a/b or b for MarkZ  class A is like calling hybrid amps with tube inputs "tube amps."

IMO


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