TSSA - The Simplest Symmetrical Amplifier - Page 6 - diyAudio
 TSSA - The Simplest Symmetrical Amplifier
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 10th April 2012, 10:48 PM #51 diyAudio Member   Join Date: May 2005 Location: Denmark nope they are hard to find...sj74 could be an option.. but low idds makes them not so Suitable for CCS.. You need a longer channel higher IDSS part... a depletion p channel mosfet would be nice.
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Quote:
 Originally Posted by buzzforb Who wants to minimize even order distortion Question. If paralleling a resistor with pot, you want the power resistor to be smaller than pot so that it takes the heat, correct
Exactly - the power resistor should be higher in value than what you would calculate for the current you want to achieve, then use a pot that is even higher value so that it draws less current than the power resistor and shunts the power resistor to increase the overall current - adjustably.

If you want to idiot proof it (just in case you're building it for somebody else ) instead of a putting a pot in parallel with the power resistor, put an extra resistor in series with the pot, then put the Pot + series resistor combination in parallel with the power resistor. This extra resistor protects you in the case that the pot is turned down to zero

Quote:
 Originally Posted by Lazy Cat I could easily do TSSA BIGBT HP since it is much simpler than SSA and potentially even better performer.
yeah ! (I just like the elegance of 'simplest')

Quote:
 Originally Posted by Lazy Cat hehe almost Problem is to find and get some good p-jfet, any suggestions
don't do it, CCS's are evil, just say 'no'.... just kidding, although I've never used one (CCS or JFET for that matter)
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Last edited by Bigun; 11th April 2012 at 01:46 AM.

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Quote:
 Originally Posted by Bigun don't do it, CCS's are evil, just say 'no'.... just kidding, although I've never used one (CCS or JFET for that matter)
Hi Bigun

Over the weekend I measured few of them, not for the first time, I did it before also and was never realy satisfied. BJT as cascode in CCS had ten times higher Z100 kHz, noise and much more nonlinear impedance curve over audio band. But the one I posted with jfet cascode impressed me deeply. For rock solid DC current there's precision zener, for perfect AC performance there's jfet.

Jfet itself to form simple CCS is way too much temperature dependent (DC stability is bad) but here in cascode position it feels just perfect, made for this.
Attached Images
 CCS REF.jpg (182.8 KB, 1684 views)

 11th April 2012, 08:39 AM #54 diyAudio Member   Join Date: May 2005 Location: Denmark I think You saw that Jfet cascode trick in some other thread....
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Quote:
 Originally Posted by MiiB I think You saw that Jfet cascode trick in some other thread....
Yes here. Thank you MiiB

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Hi guys

TSSA all BJT version needs to be thermally compensated, for that reason 1N4148 were replaced by BD139/140 mounted on the heatsink together with outputs, also input BJT pair flats are glued together. In that way amp should be thermally stable even at high output bias current.
Attached Images
 TSSA BJT.jpg (291.2 KB, 1652 views)

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Or even less parts solution with thermal track output transistors, where tracking diodes have double function: bias input pair and compensates thermal drift.
Attached Images
 TSSA TT.jpg (284.8 KB, 1601 views)

 11th April 2012, 06:30 PM #58 diyAudio Member   Join Date: May 2005 Location: Denmark think that it would work better with lateral Fets as they are much easier to drive..
 11th April 2012, 06:37 PM #59 diyAudio Member     Join Date: Sep 2007 Agree, for 1 A load current BC's would have to provide extra 10 mA into bases of the outputs. Small power amp only.
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Quote:
 Originally Posted by Lazy Cat Or even less parts solution with thermal track output transistors, where tracking diodes have double function: bias input pair and compensates thermal drift.
LC is it worth to work on a pcb for this, i think i have all parts in stock

Marc
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