Parasound JC3 Phono

[Bob Cordell]

Originally Posted by 6L6

Under the circumstances, I think Mr. Curl is being very polite, considering what he could say.

The tone of a statement is extremely hard to convey in a web forum. My guess is if he were speaking those words to you, you might not hear what you have read.

The real question concerning politeness is actually this - is it proper to pump a professional designer for info (on an open web forum, no less...) on a retail product that is brand-spankin-new??? And then taking offense when he declines?? Seriously??

Hi 6L6,

I was certainly not trying to "pump" John on his new design, and I thought I made that clear. I completely respect his right not to say anything. Indeed, I think his preamp is really nice, and showed interest because of that. I did take offense, but not because he refused to answer. Nobody likes to feel that they are just being blown off. You should read the posts more carefully. In any case, if John thinks I was pumping him and angry with him for not sharing details, then I owe him an apology.

John does beutiful work, and it is not unusual to be interested in learning more if he is comfortable sharing. That's all there is to it. BTW, I am really surprized that John did indeed forget what they actually used, and apologize for that.

Cheers,
Bob

[john curl]

Kamis, you are quite correct in your 'block diagram' description of the JC-3 phono preamp. It is essentially an IC based version of a Vendetta Research phono stage. My BIGGEST headaches are still: 'What IC to use, and where?' The tradeoffs are real and difficult to completely bridge, AND even I, at 69 years old, can hear differences in IC's that are basically the same, when evaluated as a 'black box'.
I wish also to point out that I really don't appreciate 'sniping' when it comes to my designs. This happens often when people put a value judgement on an effort, without even knowing anything about it. For example, if one should make a measurement, and presents it, the 'sniper' will reject it, out of hand, insisting that something is 'wrong' with the measurement. Another example, might be to insist that if a design in 'confidential' in some way, that it must be a fake, or a placebo, if it does well in the marketplace, or even that the designer must be 'ashamed' of the design compromises. This is really an effort for the 'sniper' to get an edge on the designer, not to encourage fair discussion. I have been subjected to it for the last 30+ years. I do grow tired of it, I'm afraid, like the old school teacher finally deciding not to put up with rowdy students in class, after years of it.

[Bob Cordell]

Originally Posted by john curl

Kamis, you are quite correct in your 'block diagram' description of the JC-3 phono preamp. It is essentially an IC based version of a Vendetta Research phono stage. My BIGGEST headaches are still: 'What IC to use, and where?' The tradeoffs are real and difficult to completely bridge, AND even I, at 69 years old, can hear differences in IC's that are basically the same, when evaluated as a 'black box'.
I wish also to point out that I really don't appreciate 'sniping' when it comes to my designs. This happens often when people put a value judgement on an effort, without even knowing anything about it. For example, if one should make a measurement, and presents it, the 'sniper' will reject it, out of hand, insisting that something is 'wrong' with the measurement. Another example, might be to insist that if a design in 'confidential' in some way, that it must be a fake, or a placebo, if it does well in the marketplace, or even that the designer must be 'ashamed' of the design compromises. This is really an effort for the 'sniper' to get an edge on the designer, not to encourage fair discussion. I have been subjected to it for the last 30+ years. I do grow tired of it, I'm afraid, like the old school teacher finally deciding not to put up with rowdy students in class, after years of it.

Hi John,

Thanks for this additional information. I understand what you are saying about sniping, and I assure you that was not my intent here. As one who has been designing phono preamps since the vaccuum tube days in the '60s, I'm really interested in the design challenges faced by phono preamps, and am always interested in the tradeoffs. BTW, I don't mean to imply that I was much of an expert on phono preamp design in the tube days when I was a teenager.

I'm also intensely interested in how phono preamps are measured and how they are reviewed. For example, in many cases the S/N for an MM preamp is stated with the input shorted, which to me seems a bit optimistic because it kills cartridge/termination voltage noise and kills input current noise if the preamp uses a BJT input. It would seem that a better measurement would be with a typical cartridge in place, but which to choose and how many vendors would buy into that when it yields a worse number?

When a phono preamp is reviewed, I wonder if it was reviewed in MM or MC or both modes. What cartridge and loading were used for the review? The list goes on, and many of these things can make a difference in the reviewer's perception of sound quality.

Cheers,
Bob

[john curl]

There is no ideal IC that will give best S/N with ALL phono cartridges. You know this, Bob. You can only do the best with what is available. IF I were allowed to use a low noise Jfet input, I could have had a more extended range of low S/N, however I was specifically asked not to use more low noise jfets in this design, because we were overextended in trying to procure them for all the other designs that we make, at the time. There is NOTHING SPECIAL about the S/N of this design. It would be the same as IF someone else used a single AD797 in a normal way. There is nothing to quibble about, or to seriously question.

[Bob Cordell]

Originally Posted by john curl

There is no ideal IC that will give best S/N with ALL phono cartridges. You know this, Bob. You can only do the best with what is available. IF I were allowed to use a low noise Jfet input, I could have had a more extended range of low S/N, however I was specifically asked not to use more low noise jfets in this design, because we were overextended in trying to procure them for all the other designs that we make, at the time. There is NOTHING SPECIAL about the S/N of this design. It would be the same as IF someone else used a single AD797 in a normal way. There is nothing to quibble about, or to seriously question.

Hi John,

I don't think we are quibbling about anything here. I don't think you told me enough about the circuit to quibble about anyway :-). I completely understand that you had constraints. As designers we all have to work with what we are allowed to have, and we have to pick our poison.

When you refer to being asked not to use more low noise jfets due to procurement limitations, are you referring to the complementary types? Its OK if you prefer not to answer.

Cheers,
Bob

[john curl]

No, even just n channel jfets looked to be difficult to obtain as well, at least a year ago or so. Just yesterday, I picked up 1000 Toshiba 2SK170 jfets from a group buy. They seem to be easily available, and if I knew that they would be as available, I might have designed them into the JC-3. However, it works OK without them.

[sakellogg]

john, first off thanks for your additions to our hobby. i enjoy your stuff very much
i do have question or 3 that i have always wanted to ask you or nelson or both.
when you design anything for a company, do they come to you? and if they do, do they say what they want? like a amp @ 5watt class d useing parts 123? and if so do you come up with two or three to show them and they pick one?
or....
do you go to them saying i got a 5watt class d amp it uses parts 123. do you want it.
and after the sale...if your name is on it how much control do you have ? can you say i only want parts 123 used?
purely wondering. and if im prying let me know.ive always wondered. i have no complaints at all.

[john curl]

It goes both ways, but normally someone with funding comes to me to design something specific. They usually leave it to me, as to how it needs to be done. Only severe parts shortages can get me to change my approach.

[sakellogg]

i want to be clear. the questions i asked is in no way a poke at your phoino stage,your coments on there request brought these questions to the front of my mind.
thanks again.

what has been your fav. production peice that you have been involved with?

if you hand them a few samples to chose from how do they chose? do they take it home and try it out? or is it based on random guys trying it out?
has any thing you have presented made it to the consumer ......just like you made it in the prototype?

[sakellogg]

please forgive the spelling my phone dose not use the spell check.

and thanks for your time.