The JC-2 preamp schematic on the website is wrong...Mr.John C?

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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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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.
 
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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john curl said:
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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"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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Fred Dieckmann said:
[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.
 
Now that we have resolved the schematic error, and the measured distortion (Thanks Elso, I had forgotten that I had gotten one out of storage to measure), we should address WHY I bothered to design this circuit in the first place.
First, OP AMPS had been around for almost 10 years. In 1966, I worked with the UA702 and UA709 op amps, and the UA741 op amp in 1969. These parts were a god-send for minaturization and for servo control, but fairly lousy audio devices. In 1970, Harris Semi (then Radiation Inc) came out with a dielectrically isolated op amp with low noise (9nv/rtHz) 50 ma peak current, +/- 24V/us operation, and a slew-rate of +5/-2.5 V/us slew rate. Selected units could measure fairly low distortion as well. This seemed to be the answer to an audio designers needs, BUT once we used them, we found them not to be sonically as good as tubes.
What to do? Well I decided to build a discrete circuit with a fet input that had a minimum circuit thru-path, high open loop bandwidth, and as linear as possible operation for each device.
For line amp operation, the circuit that we have previously discussed worked for me. Both Mark Levinson and the Grateful Dead used this circuit as line drivers for several years.
For higher closed loop gain needs, another circuit design was necessary. Then, the op amp configuration works better.
 
John,

That is understandable; much of the so-called sold state gear was crummy at that period. My first electronic project was a phono-amp that used a Fairchild u739 about 1976. It surprisingly sounded much better than the Mac C26- phono section, but that was not much of an accomplishment.

I guess the only real completion for the JC2 at time was SAE, GAS and Audio Research and some obscure brands like Audire.

Yep opamps have come a long ways, however to my amazement some folk still use 5534 and 5532.
:)
 
Now that we have resolved the schematic error, and the measured distortion (Thanks Elso, I had forgotten that I had gotten one out of storage to measure), we should address WHY I bothered to design this circuit in the first place.
First, OP AMPS had been around for almost 10 years. In 1966, I worked with the UA702 and UA709 op amps, and the UA741 op amp in 1969. These parts were a god-send for minaturization and for servo control, but fairly lousy audio devices. In 1970, Harris Semi (then Radiation Inc) came out with a dielectrically isolated op amp with low noise (9nv/rtHz) 50 ma peak current, +/- 24V/us operation, and a slew-rate of +5/-2.5 V/us slew rate. Selected units could measure fairly low distortion as well. This seemed to be the answer to an audio designers needs, BUT once we used them, we found them not to be sonically as good as tubes.
What to do? Well I decided to build a discrete circuit with a fet input that had a minimum circuit thru-path, high open loop bandwidth, and as linear as possible operation for each device.
For line amp operation, the circuit that we have previously discussed worked for me. Both Mark Levinson and the Grateful Dead used this circuit as line drivers for several years.
For higher closed loop gain needs, another circuit design was necessary. Then, the op amp configuration works better.
 
Pope?

Here is one for you Fred...............:D
 

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Sorry for the double posting. Let's go on, if we can, as to WHY we would want to build simple circuits, rather than use complicated thru-paths? Now, when I mean 'simple' I don't mean crude, or elementary. Push pull is OK, so is 4 quadrant operation so that you can have both balanced inputs and balanced outputs. This can be useful, even when using only one output, as a phase inverter for generating absolute polarity with different software.
Also, think about distortion and what the harmonics look like.
And finally, think about high open loop bandwidth, which is difficult, but not impossible with OP Amps. Why would we want high open loop bandwidth?
 
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