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Old 24th October 2012, 08:22 PM   #1281
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Originally Posted by Idefixes View Post
I am on wrinting a new topic on TSSA BIGBT HP building we will continue further step overthere if you are aware for more clarity.

Marc
Where did you vanished Marc?
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Old 24th October 2012, 08:46 PM   #1282
mikelm is offline mikelm  England
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You can always do it like this
That's a very BIG BT !
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Old 24th October 2012, 08:55 PM   #1283
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That's a very BIG BT !


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Old 24th October 2012, 09:06 PM   #1284
mikelm is offline mikelm  England
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Story about subjective & objective measurement in Audio - all comments welcome

When I first built TSSA 1.6 one thing in particular struck me - even though my fetzilla has same gain & a Jfet input device TSSA 1.6 with BJT has less audible hiss !

This is a disturbing issue - in theory my amp should have less noise because of super low noise Jfet i/p device.

I already new the design needed some "housekeeping" because it sounded better without bypass caps - even with snubbers so I went to work to eliminate the spurious noise.

Day 1 added the snubberized bypass caps - sounded dreadful

Day 2 spent time searches out potential sources of noise and at the end of the day on the scope the noise was measurable less but when listening to audible hiss on the speakers it sounded just the same as before but now the music now sounded very very nice - conclusion: even if we can't hear difference in noise with our ears the scope tells us an accurate story

Day 3 Continue with search for sources of noise - try several things on right channel and compare to unmodified left channel on the scope. However at the end of the day I can see absolutely no difference of noise levels on the scope - over different frequencies ranges both channels look the same - BUT when I listen at end of day for audible hiss now the modified right hand channel is almost silent and the left channel is hissing away as usual. Conclusion: The scope does not tell an accurate story, we have to trust our ears !

Tomorrow I will modify left channel same as right and listen to music . . . . .

Last edited by mikelm; 24th October 2012 at 09:10 PM.
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Old 24th October 2012, 11:09 PM   #1285
Harry3 is offline Harry3  Australia
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Hi LC,
Awesome output circuit you have posted - amazing!
I am not sure how to accurately connect it to the TSSA circuit you posted on page 16. Any hints for us novices?
Thanks.
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Old 25th October 2012, 01:35 AM   #1286
Jay is offline Jay  Indonesia
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Originally Posted by mikelm View Post
This is a disturbing issue - in theory my amp should have less noise because of super low noise Jfet i/p device.
I think it is the circuit, not the type of device used.

What is your JFET? JFET likes high current for low distortion, but high current with unsuitable JFET (Idss) will give high noise. Some favor 2SK170 because of its premium trans-conductance. I think there is some kind of dilemma in choosing the right JFET.
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Old 25th October 2012, 01:47 AM   #1287
Salas is offline Salas  Greece
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Minimal nvrtHz active part in amp level signals is not a primary issue. The feedback arrangement in SSA style is low impedance we must not forget and goes to emitters, so no contribution to a gate or a base of a classic long tailed pair. Random noise is uncorrelated so CMRR would not give as much a cancellation as in PSRR for 100Hz ripple.
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Old 25th October 2012, 01:53 AM   #1288
Salas is offline Salas  Greece
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P.S. In fetzilla case should be the 2K total resistance to gate and the 47R to source pin. Plus the bias arrangement to gate with the leds, trimmer, divider. Has a 22uF filtering only.
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Old 25th October 2012, 07:56 AM   #1289
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Quote:
Originally Posted by Harry3 View Post
Hi LC,
Awesome output circuit you have posted - amazing!
I am not sure how to accurately connect it to the TSSA circuit you posted on page 16. Any hints for us novices?
Thanks.
See the analogy now? Just parallel bipolar devices as many as you need same way as on the picture. Now all bipolars around one mosfet driver have to have the same current gain hFE (+/-5%)

P.S. IRF610/9610 mosfet drivers from your TSSA sch stays on positions as they are, so please ignore reversed mosfet positions on this pic because in Maximus it was completely different configuration of an output stage.
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File Type: jpg Maximus Output Stage BIGBT.jpg (252.4 KB, 295 views)

Last edited by Lazy Cat; 25th October 2012 at 08:03 AM.
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Old 25th October 2012, 08:09 AM   #1290
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Quote:
Originally Posted by mikelm View Post
When I first built TSSA 1.6 one thing in particular struck me - even though my fetzilla has same gain & a Jfet input device TSSA 1.6 with BJT has less audible hiss !
I was telling all the time how low noise level in this amp is. Low Z in every position is making the difference, probably lowering input Z would have similar noise result in Fetzila too.
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