Contest: Linear Power Amp in a mint tin (class Aa, class AB, or class B) - Page 12 - diyAudio
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Old 27th November 2012, 04:40 PM   #111
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So, who's going to do a class AaH or AaG amplifier with some fets? That's the state of the art in cellular transmitter amplifiers and if applied to audio, it could, perhaps make Class D look outdated.
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Old 27th November 2012, 04:51 PM   #112
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I've had another play with the circuit in real life - I tried both EF outputs and CFP. I think I prefer the performance of the CFP. One thing is the superior bias stability, which is likely needed when your heatsink is a tin of golden virginia

I'm getting some parasitic oscillations but the circuit is a mess of wires and jumpers on a breadboard. Next week I will have time to etch a PCB and see how the circuit really performs. I will test it with the TIPs and see what the actual measured performance is like. I will post harmonic spectra.

This is not to say I haven't taken aboard the recommendations for better output transistors, I just want to see how well the TIPs will actually work in real life. A 100W amplifier I repaired in real life seems to achieve rather good performance with "glacial" 1Mhz Ft output transistors.

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Old 27th November 2012, 04:51 PM   #113
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You are going to confuse people by referring to glitching as noise.

When you go totally without bias, you not only have transistor glitches to worry about, but the current spike induced by the error voltage. On miller compensated amps this will be monstrous. It will be near impossible to achieve low distortion this way. AC behavior will change dramatically with output.
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Old 27th November 2012, 04:53 PM   #114
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Quote:
Originally Posted by keantoken View Post
You are going to confuse people by referring to glitching as noise.

When you go totally without bias, you not only have transistor glitches to worry about, but the current spike induced by the error voltage. On miller compensated amps this will be monstrous. It will be near impossible to achieve low distortion this way. AC behavior will change dramatically with output.
I'm not going to be running the amp with no bias, I just turned it right down to see how the circuit coped with the glitch - apparently quite well.
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Old 27th November 2012, 05:01 PM   #115
bigwill is offline bigwill  United Kingdom
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Quote:
Originally Posted by danielwritesbac View Post
So, who's going to do a class AaH or AaG amplifier with some fets? That's the state of the art in cellular transmitter amplifiers and if applied to audio, it could, perhaps make Class D look outdated.
We mustn't get carried away This is an amplifier in a tin. I think the fact that I'm putting a mini-blameless in a tin is pushing it already
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Old 27th November 2012, 05:35 PM   #116
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Quote:
Originally Posted by danielwritesbac View Post
So, who's going to do a class AaH or AaG amplifier with some fets? That's the state of the art in cellular transmitter amplifiers and if applied to audio, it could, perhaps make Class D look outdated.
How out of date would it be to use a an IR4312 to feed power to a complimentary class A output stage? I wonder if the single channel version IR4311 could be used with asymmetrical power supplies, to save switching loss. That would require more chips though, which I guess are already breaking the rules.

Last edited by Andrew Eckhardt; 27th November 2012 at 06:04 PM.
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Old 27th November 2012, 06:07 PM   #117
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Assuming you could find some output transistors that were still linear with 5 volts across them, the minimum 1A bias current would still be burning over 20 watts for a pair of amplifiers. Getting rid of that much power in that small of a package would require a high speed fan that would make enough noise that you'd be a lot better off with the D amp chips by themselves.
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Old 27th November 2012, 06:26 PM   #118
bigwill is offline bigwill  United Kingdom
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I just popped my first ever electrolytic thanks to this thread!
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Old 27th November 2012, 06:33 PM   #119
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I was replying to post 110 Bigwill.
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Old 28th November 2012, 01:05 AM   #120
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Originally Posted by Andrew Eckhardt View Post
. . . It would require more chips though, which I guess are already breaking the rules. . .
Chips are okay to use, and observe that this is posted in a chip amp forum.

I'm aware that you can't safely run 9w bias (18 watts bias for stereo) in a mint tin . There's hugely generous leeway for Classes Aa, AaH, AaG and other dynamic Class A. Dynamic class A that also uses adaptive power source is an extremely efficient state of the art solution that may be a future for linear audio.

There's just 2 things to watch out for:
Please don't convert the analog input signal to digital inside of the mint tin (providing an "extra" digital input is fine if the amp also has a source selector to allow the possibility of an all analog path).
The Dynamic class A amplifier (Aa, AaH, AaG, etc. . .) must pass common tests at least as nicely as Class B for the first 9 watts per channel, stereo.

For AaH, that looks like, Class A tiny bias, class a 9w (adaptive bias), but class H for headroom management at points over 9w. Right?
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Last edited by danielwritesbac; 28th November 2012 at 01:13 AM.
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