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Old 19th February 2013, 11:45 PM   #3981
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Paulo, it seems your doing it right. The snubber needs to be next to the input transistor.

I don't know about CDIL parts but I've heard they're okay.

Best test for the input snubber is to do your input-finger test and adjust the input snubber until it did not happen. Use a large capacitor for the 20pF and a trimmer for the 3.3k; adjust trimmer until no radio noises and then lower capacitor as much as you can.
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Old 20th February 2013, 06:53 AM   #3982
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My only two qualms with the Circuit would be the Class B nature and need for extra electrolytics used. Has anyone found the quality of cap used affecting the subjective sonics?, probably not as much since there us a dc bias on all three of .6 v min. My design uses two more bjts, but only one e cap along with an adaptive bias open loop current buffer, of course there are many ways together to the same or similar result, but as mentioned prior, where current feedback excels is the mids and highs, just have to be aware of the series feedback resistor value otherwise if too high it's as bad as overcompensating with too much miller comp.


Colin

Last edited by vynuhl.addict; 20th February 2013 at 07:13 AM.
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Old 20th February 2013, 01:55 PM   #3983
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Quote:
Originally Posted by vynuhl.addict View Post
My only two qualms with the Circuit would be the Class B nature and need for extra electrolytics used.
I believe your point one irrelevant for two reasons.
- The amp works in class A for normal listening levels.
- The problem of class B is distortion induced by the crossing. With current feedback amps, the speed is fast enough for the feedback suppress any issue. As thermal effects are more a concern, you will find an optimum bias, and notice that, ioncreasing-it will not improve the sound in anyway, but the contrary.

Point 2, you have other choices than electrolytic, in the signal or feedback path. On my side, i use film one for the input, and electrolytic in the feedback with no negative issue on the sound. Tried servo: no real change on the signature of the amp, and nothing witch destroy its transparent and fast aspect.
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Old 21st February 2013, 06:56 AM   #3984
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Esperado,


Fair enough, relying in feedback for correction, in any case it's a requirement. How would this amplifier do with electrostatics?, a difficult load and imagine it would change the flavour of sound with increasing phase shift and possibly stability issues. What kind of speaks are you driving with the ssa?.

Colin
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Old 21st February 2013, 08:31 AM   #3985
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Esperado,
How would this amplifier do with electrostatics?, a difficult load and imagine it would change the flavour of sound with increasing phase shift and possibly stability issues. What kind of speaks are you driving with the ssa?.

Colin
Remember that there are many versions of SSA!

Esperado's SSA-Crescendo is not as stable as other SSAs. My version (more or less VSSA) for example is the most stable among others. Incredible performance (phase behavior, Zout, etc) in LTSpice except for THD, which is about the average of SSA. Those with VAS cascode (BIGBT HP and SSA-Crescendo) have lower THD. SSA-Crescendo has very good sonic.
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Old 21st February 2013, 11:32 AM   #3986
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Jay,


How about on the ground, spice doesn't concern me as it all can go to hell in a hand basket once applied to a board, current feedback is very sensitive to layout and parasitics due to its speed. My concern is the sound with various loads, this is where a good current buffer comes into play, preferably out of the global loop.

Colin
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Old 21st February 2013, 05:38 PM   #3987
Jay is offline Jay  Indonesia
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Jay,
How about on the ground, spice doesn't concern me as it all can go to hell in a hand basket once applied to a board, current feedback is very sensitive to layout and parasitics due to its speed.
First, assuming that capacitive load modeling is relevant, some SSA is incredibly stable.

Second, some SSA is too simple to screw up. You can make a very short connection from output to input emitter and from stage to stage.

Third, I prefer to parallel the output mosfet, even tho one pair is enough to drive low impedance load. Fetzilla also has been reported to be able to drive low impedance load. I think it's of the same family.
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Old 21st February 2013, 08:24 PM   #3988
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First, assuming that capacitive load modeling is relevant, some SSA is incredibly stable.
If there is one point where usual sims are not relevant, this is it.
And the reason is, with so fast and high bandwidth amps, the slighest parasitic capacitive load, induced by real/physical implantation can turn phase significantly (those parative caps are not taken in consideration in sims).
Reason, i believe, why L.C design & built his amps in real world, taking care of stability issues.
About Crescendo, i don't understand why you talk about this, but, how can you say something about its stability ? Did-you had build one ?
In the last private message i received about it in this forum, i quote: "...Now very stable under all conditions.".
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Old 21st February 2013, 10:26 PM   #3989
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Originally Posted by Esperado View Post
If there is one point where usual sims are not relevant, this is it.
And the reason is, with so fast and high bandwidth amps, the slighest parasitic capacitive load, induced by real/physical implantation can turn phase significantly (those parative caps are not taken in consideration in sims).
Reason, i believe, why L.C design & built his amps in real world, taking care of stability issues.
About Crescendo, i don't understand why you talk about this, but, how can you say something about its stability ? Did-you had build one ?
In the last private message i received about it in this forum, i quote: "...Now very stable under all conditions.".
I don't have the need to measure stability of the real builds. Anyhow I pay attention to the simulated stability. And I still believe somehow that there is correlation.

I didn't say that SSA-Crescendo is not stable (no amp is 100% stable under all conditions anyway), I was comparing relative stability of SSA-Crescendo with other popular SSA and especially the VSSA. If you think this is wrong (that the simulated stability cannot be relied upon) then please give an expert analysis between any 2 SSA.

Quote:
Originally Posted by Esperado View Post
In the last private message i received about it in this forum, i quote: "...Now very stable under all conditions.".
I don't get it. Is there any change to the circuit or PCB?

Shaan knows how to make a good PCB layout. LC is even more with his very compact approach. The Crescendo PCB is terrible.
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Old 21st February 2013, 11:42 PM   #3990
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Jay, i would not like to be in a plane driven by a pilot only experienced as a flight simulator player.
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