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Old 24th August 2011, 01:42 AM   #381
stoc005 is online now stoc005  United States
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Yes, I've simulated it and the only amp of interest to me is the single lateral fet output version. All the different output configurations keeps this thread kind of a moving target. It's sure is interesting to see the variants but the simple version should be "fun". To me this is still very much an experimental circuit(s) since there hasn't been a whole lot of them built and I don't think anybody has run these many variations for hours and did some difficult/shorted load tests to see how it survives.
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Old 24th August 2011, 01:46 AM   #382
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Lazy Cat View Post
So you think I did not check?

The input pair BJT's must have the same hFE and zero ΔT, in that case offset cancellation after I/V conversion is in direct proportion to ΔIcn-ΔIcp, which is automatically zero regardless T value.

The unique SSA's current feedback loop (bridge) has some specially good features still not really understandable to all ...
There s nothing specialy good since the global perfs seems average,
but it s true that the features are not well understood since the input
transistors Hfe has almost no importance as the bias circuit has low
impedance, hence the thermal stability is in proportion of the transistors
base/emitter voltages...
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Old 24th August 2011, 02:02 AM   #383
Bigun is offline Bigun  Canada
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Actually, I realized that it's not post 183, 196 or 336 I'm looking for but a CFP driver and single EF output. Not sure if this will work but attached is what I have in mind. Yet another variation
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Old 24th August 2011, 02:25 AM   #384
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Quote:
Originally Posted by wahab View Post
There s nothing specialy good since the global perfs seems average,
but it s true that the features are not well understood since the input
transistors Hfe has almost no importance as the bias circuit has low
impedance, hence the thermal stability is in proportion of the transistors
base/emitter voltages...
When DC offset is adjusted to zero V at the output, it actually means we compensated Vbe difference of the NPN/PNP input devices with the emitter currents correlation (Vben+Vren=Vbep+Vrep), after that ΔVoffset is only related to β/T dependence.

Global performance is even more average at LTP plus only one gain stage.

Last edited by Lazy Cat; 24th August 2011 at 02:30 AM.
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Old 24th August 2011, 02:38 AM   #385
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Quote:
Originally Posted by Bigun View Post
Actually, I realized that it's not post 183, 196 or 336 I'm looking for but a CFP driver and single EF output. Not sure if this will work but attached is what I have in mind. Yet another variation
It will work.

The second stage BJT is actually formed of a high current gain compound Darlington (Sziklai pair), which is in correlation of the max total gain we want to get in a simple SSA version like this.

Bigun I don't see anything stoppin' you at testing this version.

Last edited by Lazy Cat; 24th August 2011 at 02:40 AM.
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Old 24th August 2011, 02:48 AM   #386
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Quote:
Originally Posted by stoc005 View Post
Yes, I've simulated it and the only amp of interest to me is the single lateral fet output version. All the different output configurations keeps this thread kind of a moving target. It's sure is interesting to see the variants but the simple version should be "fun". To me this is still very much an experimental circuit(s) since there hasn't been a whole lot of them built and I don't think anybody has run these many variations for hours and did some difficult/shorted load tests to see how it survives.
I tested BIGBT version extensively, high temp, many hours, signal generator, music, different loads, no compensation caps, no oscillations, clear clipping, ultra fast slew rate, no DC-offset variations ...

Please make a short circuit on any of your's amp without overcurrent protection ... I can imagine that too.

Last edited by Lazy Cat; 24th August 2011 at 03:00 AM.
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Old 24th August 2011, 04:53 AM   #387
AKSA is offline AKSA  Australia
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I like your approach, Bigun. Very elegant, and the emitter driver output will have low impedance and drive the output stage very well.

Let's see, base to rail resistor for predriver would be 1K, we could run the driver quiescent at around 30mA, and this means, assuming cascode current is 2mA, the predriver emitter to rail resistor would be 47R. With a Zout at each driver emitter of around 1R, you'd have enough drive to propel the USS Nimitz, and of course nice local feedback around the driver circuit. One change, however; I'd put a 1K resistor from emitter to base on each driver to ensure residual current at all times through the predriver.

Cheers,

Hugh

PS I'm not dead sure of the cascode current, but 2mA seems about right to me.

Hugh
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Last edited by AKSA; 24th August 2011 at 05:00 AM.
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Old 24th August 2011, 06:05 AM   #388
MiiB is offline MiiB  Denmark
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I think the concept is very strong.. It scales easily.. can be fitted with a number of different output-stages....I am currently contemplating a version with a sort of current dumping configuration with laterals driving a number of BJT's

oh by the way the OLG...its about 70dB ant the OLB is app 50 KHz (-3 dB)

One thing i have trouble seeing through is how to adjust the current through the input pair/cascodes

Last edited by MiiB; 24th August 2011 at 06:25 AM.
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Old 24th August 2011, 07:18 AM   #389
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Quote:
Originally Posted by stoc005 View Post
All the different output configurations keeps this thread kind of a moving target.
Please believe me that I have time and energy barely to handle this SSA thread, not even imagining to start another. New threads can be started as a specific type of SSA performed by successful builders, with their own explanations.

This thread is more educational one if you didn't notice by now but where can you learn more than at moving targets.
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Old 24th August 2011, 09:33 AM   #390
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Quote:
Originally Posted by AKSA View Post
I like your approach, Bigun. Very elegant, and the emitter driver output will have low impedance and drive the output stage very well.

Let's see, base to rail resistor for predriver would be 1K, we could run the driver quiescent at around 30mA, and this means, assuming cascode current is 2mA, the predriver emitter to rail resistor would be 47R. With a Zout at each driver emitter of around 1R, you'd have enough drive to propel the USS Nimitz, and of course nice local feedback around the driver circuit. One change, however; I'd put a 1K resistor from emitter to base on each driver to ensure residual current at all times through the predriver.

Cheers,

Hugh

PS I'm not dead sure of the cascode current, but 2mA seems about right to me.

Hugh
Thanks Hugh for all your support.

Hopefully you will also find your favourite SSA someday to built.
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