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Old 8th April 2012, 09:50 AM   #31
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Quote:
Originally Posted by Jay View Post
I'm curious why DC servo is not discussed with SSA circuits. It is hard to get a low THD without compensating other factors such as the DC offset (at least from simulation).
DC servo circuit cannot influence the distortion profile since it has the bandwith of influence of a few Hz or even less. Why we didn't put any effort on DC servo yet? Simply because there's no need, since the output DC fluctuations are within +/-50mV, of course if the input pair is thermally coupled. This DC offset at power amplifier's output terminals is none of practical importance, it is more cosmetic to have 0,5 mV here. For musical sources and preamps I agree, this value has to be below 1 mv.
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Old 8th April 2012, 09:53 PM   #32
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Originally Posted by buzzforb View Post
Might have to try this one. See how the bjt compares to jfet.
Hi buzzforb

TSSA schematic from post #1, built by sonnya, all together four transistors only and as you can see from the pics very promising results.
Attached Images
File Type: jpg TSSA by Sonnya.jpg (57.5 KB, 2114 views)
File Type: jpg TSSA 1kHz6W8R.JPG (125.6 KB, 1846 views)
File Type: jpg TSSA 10kHz6W8R.JPG (126.2 KB, 1681 views)
File Type: jpg TSSA 20kHz6W8R.JPG (125.1 KB, 1578 views)
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Old 8th April 2012, 10:32 PM   #33
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That looks a great deal like one of my amps, although I think his is neater. I have one laterals and BC5XX, sp might as well
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Old 8th April 2012, 10:37 PM   #34
Bigun is offline Bigun  Canada
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Originally Posted by Lazy Cat View Post
Logical evolution: TSSA with VAS.
no additional VAS please - the idea is simplest possible. To heck with THD, if it sounds good it is good
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Old 8th April 2012, 11:28 PM   #35
Boscoe is offline Boscoe  United Kingdom
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Just my small contribution...

You prob already have a schematic but I enjoy it and it's late so it may be incorrect !

Lazy cat mentioned that cap maybe beneficial so I assumed I could omit it for the neatness of my board please tell me if I'm wrong!

Click the image to open in full size.

Click the image to open in full size.
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Old 9th April 2012, 01:23 AM   #36
Bigun is offline Bigun  Canada
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I love it, such a simple pcb. Some thoughts...

a) make the pcb longer and cover the power devices, then screw through the pcb, through the power device into the heatsink. You can eliminate the separate pcb mounting holes.
b) are you sure you can get 2W rated trimmers of that size ? you may need a power resistor in parallel with a lower wattage trimmer
c) leave a little space between the caps
d) move the resistors a bit further away from the power device leads which will tend to want a fair bit of solder around them

IF I understand correctly, the extra cap helps ensure balance between the two feedback loops, which will minimize even order distortion. I don't think it's a big issue to leave it out.
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Last edited by Bigun; 9th April 2012 at 01:26 AM.
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Old 9th April 2012, 12:20 PM   #37
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Quote:
Originally Posted by Bigun View Post
I love it, such a simple pcb. Some thoughts...

a) make the pcb longer and cover the power devices, then screw through the pcb, through the power device into the heatsink. You can eliminate the separate pcb mounting holes.
b) are you sure you can get 2W rated trimmers of that size ? you may need a power resistor in parallel with a lower wattage trimmer
c) leave a little space between the caps
d) move the resistors a bit further away from the power device leads which will tend to want a fair bit of solder around them

IF I understand correctly, the extra cap helps ensure balance between the two feedback loops, which will minimize even order distortion. I don't think it's a big issue to leave it out.
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
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Old 9th April 2012, 09:02 PM   #38
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Originally Posted by Bigun View Post
no additional VAS please - the idea is simplest possible. To heck with THD, if it sounds good it is good
Why not?

I could easily do TSSA BIGBT HP since it is much simpler than SSA and potentially even better performer.
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Old 9th April 2012, 09:05 PM   #39
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Originally Posted by Lazy Cat View Post
Why not?

I could easily do TSSA BIGBT HP since it is much simpler than SSA and potentially even better performer.
do it, doit, do it....

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Old 9th April 2012, 09:45 PM   #40
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Why not?

I could easily do TSSA BIGBT HP since it is much simpler than SSA and potentially even better performer.
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