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Old 16th November 2011, 05:14 PM   #1421
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by Salas View Post
There are ~0.6V pinch off Jfets to use. My latfets ain't matching also, just picked out off the tube.
What I see in simulations tells me it's not just a bit of voltage drop, it changes the behaviour of the VAS. That's not to say it's bad or wrong, but for me with my limited way of thinking, it's no longer a symmetrical VAS.
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Old 16th November 2011, 05:24 PM   #1422
Salas is offline Salas  Greece
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Much better than a running away CFP. Irrelevant for your VAS and BJT output stage. Its another amp with same input stage topology. Did you simulate a Sziklai CFP BJT-LAT, or just dropped a JFET in your CCT and simmed? Mismatch the LATs as they really come and it blends nicely enough. If avoidable, then cool. If its a jumpy output CCT on bench, an appreciated band aid.
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Old 16th November 2011, 05:46 PM   #1423
Bigun is offline Bigun  Canada
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I just dropped a JFET in my CCT and simmed. I just happen to have a bunch of BJTs to use up, otherwise I would have bought Lat's just for the change.
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Old 16th November 2011, 09:10 PM   #1424
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Quote:
Originally Posted by sonnya View Post
If the SSA was driving mosfet like my CFB with EXICON it would also be assymetric by a few volt. because of difference in the N and P channel.

So the few volt accross the JFET does not matter if the total voltage swing is +/-35V...

It will only be noticed by clipping....
By mine BIGBT outputs you actually drive the mosfets and it is interesting how nicely IRF610/9610 Vgs matches not only at threshold level but also across entire Id range, so in my case, SSA is still perfectly symmetrical amp all over.

I use these BIGBT compound outputs (IRF+2SA/2SC) for more than a decade till these days and they never let me down, never noticed even a hint of a local oscillation or any kind of problems and still they can be easily expanded to provide enourmous output currents. The only thing one has to provide is NPN/PNP matching within +/-5% hFE. I guess the answer of its stability lies in BIGBT's symmetrical topology where all artefacts tends to be self canceled within positive-negative side in a balanced way, so it is natural that for a SSA topology BIGBT's are the first option of choice.

Last edited by Lazy Cat; 16th November 2011 at 09:18 PM.
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Old 16th November 2011, 09:24 PM   #1425
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Quote:
Originally Posted by Salas View Post
Its a very worthy bridge front end from the moment you get to know its traits. Such stuff usually lives on miniscule silicone area, trimmed and thermally homogenous current feedback op amp world. Was a refreshing idea you brought it back to DIY discrete world power amps Andrej. Hats off for that.
Thanks again Salas, bipolar transistors also deserves to be a leading actor in this topology, they need a little more care and understanding than fets, but they also give back a lot. As I already once said, LTP input is not on my menu anymore.
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Old 16th November 2011, 09:25 PM   #1426
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That's why God had created cascodes ;-)
Hehehe
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Old 16th November 2011, 09:27 PM   #1427
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Quote:
Originally Posted by Bigun View Post
I just dropped a JFET in my CCT and simmed. I just happen to have a bunch of BJTs to use up, otherwise I would have bought Lat's just for the change.
Hi Gareth, it's your turn now ... TGM5
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Old 17th November 2011, 01:45 AM   #1428
Bigun is offline Bigun  Canada
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Originally Posted by Lazy Cat View Post
Hi Gareth, it's your turn now ... TGM5
Indeed. I'm back from my latest business trip, should be the last this year. Just getting over jet lag. I hope this weekend to start making some progress again.
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Old 18th November 2011, 09:54 AM   #1429
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Exclamation SSA Headphones Amplifier

Quote:
Originally Posted by Dr.H View Post
Hi everyone,

Is there a variation of this amp that can be used to drive headphones?

Thanks
Ryan
Hi Dr.H

Here's your mission target.
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File Type: jpg SSA Headphones Amp.jpg (674.2 KB, 485 views)
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Old 18th November 2011, 10:46 AM   #1430
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Hi Lazy Cat,

I must say, you always know how to put a smile on my face with your circuits

Nice circuit you have there.

You need to change one thing though, your name ! Take away the lazy part and make it Busy or Active Cat

Cheers,

Audiofanatic
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