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Old 1st November 2003, 02:00 AM   #61
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Quote:
Originally posted by GRollins
Being two stages, it probably doesn't count as a true Zen amplifier any more, but speakers don't care.
As I recall from the original article, the Zen effort is an exploration
in simplicity, and I don't see why this wouldn't qualify.
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Old 1st November 2003, 02:01 AM   #62
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Look at this, it's 1 pcb. You may stack, for example, 5 units, on 1 heat sink. Parallel everything except for the speaker outs. Then, calibrate the 4 pots so that all the units match. Finally, bridge the speaker outputs & voila...

Non-VGS matched mosfets now matched.
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Old 1st November 2003, 02:29 AM   #63
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Quote:
Originally posted by Nelson Pass

As I recall from the original article, the Zen effort is an exploration
in simplicity, and I don't see why this wouldn't qualify.

And if we compare Grey's output stage+bosoz with a zen+bosoz, we still have the same "keep it simple" idea
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Old 1st November 2003, 01:46 PM   #64
audioPT is offline audioPT  Portugal
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Quote:
Originally posted by Brian Guralnick



Instead of trying to steal this thread, just post the question as a new topic, & if Mr Nelson feels up to it, I'm sure he'll add photos.

No one here is stealing threads
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Old 1st November 2003, 05:00 PM   #65
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Quote:
Originally posted by Brian Guralnick
Non-VGS matched mosfets now matched.
How much matching do you want? It's pretty easy to get
10 mV. we do it all day long. My standard max for output
DC is 100 mV, although some might say that's too much, only
rarely is it a real issue.
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Old 1st November 2003, 06:17 PM   #66
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Quote:
Originally posted by Brian Guralnick
Look at this, it's 1 pcb. You may stack, for example, 5 units, on 1 heat sink. Parallel everything except for the speaker outs. Then, calibrate the 4 pots so that all the units match. Finally, bridge the speaker outputs & voila...

Non-VGS matched mosfets now matched.
Brian,

I can follow your reasoning, but this is a very dangerous course of action. Even for a single, having 3 or 4 pots in an amp with all the drifting and aging is asking for problems. And parallelling 4 or 5 means that as soon as you close the lid after adjusting, they will start to drift apart, and one or the other will load down the rest, and it'll be a real mess.

Generally, it is considered a sign of competent design when no adjustments are needed, while still using unselected standard components. YMMV.

Jan Didden
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Old 1st November 2003, 06:20 PM   #67
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Quote:
Originally posted by Nelson Pass

How much matching do you want? It's pretty easy to get
10 mV. we do it all day long. My standard max for output
DC is 100 mV, although some might say that's too much, only
rarely is it a real issue.

100mv with many designs is not an issue. It's also easy to achieve when dealing with more than 10 mosfets. My illustrated circuit with the 20 turn precision pots allows you to adjust many modules, say 4 for example, down to 10mv, of less. Now, paralleling these modules without output series resistors for the speaker drive should allow for a balanced load across all the 8-10 mosfets a DIYer may have purchased.

Example PCB... (Another VIA-LESS design)
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Old 1st November 2003, 06:26 PM   #68
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When stacking this PCB vertically, you just need to feed 12aug solid core wires through CN1 & CN3, 18aug for CN5. On the top PCB, put in standard terminals for CN2 & CN4 & CN6.

RP3 & RP4 calibrates the CCS for Q3&4, TP1 & TP2 is there to measure the emitter resistor voltage.
RP1 & RP2 calibrates the output offset of mosfet Q1 & Q2.
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Old 2nd November 2003, 04:06 AM   #69
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Quote:
Originally posted by janneman


Brian,

I can follow your reasoning, but this is a very dangerous course of action. Even for a single, having 3 or 4 pots in an amp with all the drifting and aging is asking for problems. And parallelling 4 or 5 means that as soon as you close the lid after adjusting, they will start to drift apart, and one or the other will load down the rest, and it'll be a real mess.

Generally, it is considered a sign of competent design when no adjustments are needed, while still using unselected standard components. YMMV.

Jan Didden
That's why I built this device:
http://www.diyaudio.com/forums/showt...957#post257957
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Old 3rd November 2003, 04:07 PM   #70
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Quote:
Originally posted by janneman


Brian,

I can follow your reasoning, but this is a very dangerous course of action. Even for a single, having 3 or 4 pots in an amp with all the drifting and aging is asking for problems.

Jan Didden

Ok, got rid of the pots.

For the mosfet offset voltage, I'll just match the mosfets.

For the CCS side, I added an NPN transistor across (1 side example) Q3's emitter, base & V-15. Now, when the voltage across R9 is large enough, the base of Q3 will be pulled down creating a further regulated CCS.
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