The JC-2 preamp schematic on the website is wrong...Mr.John C? - Page 3 - diyAudio
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Old 17th February 2004, 05:31 PM   #21
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Folks, I don't want to 'belabor' the point, but why confuse things? The schematic was drawn wrong when it was first published, in 3/77. It was changed in an update LTE in 2/78 of 'The Audio Amateur'. Only the drain leads are switched. This changes the feedback to negative. The basic circuit behaves identically, in either case, only the input terminal polarities are switched.
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Old 17th February 2004, 05:41 PM   #22
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Thumbs up The final word

Concise,straight forward, and the answer to everyone's guestion. Thanks John and thanks for a circuit that has become a classic.

"The idea is to swap the B and E connections TO THE INPUT PAIR."

There is no input pair base and emitters........ THEY ARE JFETS! If you mean gate and source, that isn't going to work either. As Mr. Curl said: swap the drains, for both pairs which is equivalent to swaping the gates for both input pairs. I think you will find swapping base and emitter leads in the second stage is much less transconductance. The second stage is where most of the transconductance is in the correct origional circuit. Build it, measure it and even model it, and report on your results.

Like they say......... No good deed goes unpunished. Sorry for trying to help. I won't do it again.
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Old 18th February 2004, 12:28 AM   #23
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Now I understand your concern, Fred. Actually, when I referred to base and emitter inputs, I meant the second stage only, because that is the only place where bases and emitters are used, BUT I can understand that confusing a base for a gate, and and an emitter for a source, could happen. It was not entirely clear that we were referring only to the 2'nd stage, when addressing B-E swapping. Of course, the switching of the drains does the same thing.
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Old 18th February 2004, 12:34 AM   #24
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Curl,

How much distorsion does the amp exhibit under typical output, let's say 2 volts RMS at 1k cps?

Regards\Morello
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Old 18th February 2004, 05:53 AM   #25
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I can't remember. It has been 30 years. With class A output bias of about 50 ma, it can be pretty good, however.
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Old 18th February 2004, 06:16 AM   #26
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Quote:
Originally posted by john curl
Now I understand your concern, Fred. Actually, when I referred to base and emitter inputs, I meant the second stage only, because that is the only place where bases and emitters are used, BUT I can understand that confusing a base for a gate, and and an emitter for a source, could happen. It was not entirely clear that we were referring only to the 2'nd stage, when addressing B-E swapping. Of course, the switching of the drains does the same thing.
I think Fred knows EXACTLY what we mean. Stop fooling around Fred, youve grown up, remember?

Jan Didden
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Old 18th February 2004, 06:50 AM   #27
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"Fred,

Don't want to upset you, but you either don't get it or you are to stubborn. The idea is to swap the B and E connections TO THE INPUT PAIR. It seems that everyone including JC agrees that that fixes it, except you. I know, if the majority selects a wrong it is still wrong, but in this case I think you are out in left field.

I think Fred knows EXACTLY what we mean.

Jan Didden"

No, I don't ........ are you talking about swapping the base for the emitter connection or switching inputs (bases or actually gates in the case of this circuit)? I had no intention of turning this into a soap opera. Swapping base and emitter connections for the output stage is not an equivalent circuit to swapping the gate inputs or drains for the input diff pairs. Are we on the same page now? It is unfortunate that a few people want vent their frustration about not knowing how the circuit works into a personal attack. I wonder if you are not annoying Mr. Curl more than me. I don't mind if you guys jump up and down when I to tell you something, but not everybody feels that dealing with psycho dramas when trying to be helpful is a good use of their time. Someone will eventually model and build the proposed circuit and find out what I am talking about.
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Old 18th February 2004, 06:57 AM   #28
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Lightbulb Distortion?

Quote:
Originally posted by Morello
Curl,

How much distorsion does the amp exhibit under typical output, let's say 2 volts RMS at 1k cps?

Regards\Morello

Quote:
Originally posted by john curl
I can't remember. It has been 30 years. With class A output bias of about 50 ma, it can be pretty good, however.
Morello and John,
Found back this post from my memory (0.005% harmonic distortion):
http://db.audioasylum.com/cgi/m.mpl?...rl&r=&session=

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Old 18th February 2004, 10:18 AM   #29
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Quote:
Originally posted by Fred Dieckmann
[Bare you talking about swapping the base for the emitter connection or switching inputs (bases or actually gates in the case of this circuit)? [/B]
if you had spent the time following through on XG's schematic, you would have realized how wrong you are, Fred.

Arguing for arguing's sake is bad, especially when you are wrong, and claimed to have worked on this circuitry for many years with many variations. it sounds like you simply do NOT understand XG's revised schematic.
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Old 18th February 2004, 04:58 PM   #30
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Let's beat this dead horse a little bit longer, or maybe it beer time.
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