Hi John,
Thanks for clearing that up. What op amp do you use?
Can you say a few words about the architecture without spilling too many beans?
In MC mode, how many op amps are in the signal path?
In MM mode, what does the cartridge look into? A BJT op amp? A FET op amp? A discrete FET buffer?
This is a beautiful-looking preamp.
Cheers,
Bob
C,mon, John, it does matter, and I doubt you forgot what op amp you used. If you'd rather not say, why don't you just say so?
Its a really nice preamp and we'd just like a peek under the hood.
Cheers,
Bob
I got a wrong information in a Internet JC3 review. But John Curl has already described topology of that phono preamp. It could be described as Vendetta with op-amps. First stage linear gain low noise IC , then passive HF eq. Second stage is feedback LF eq. First stage op-amp could be some of low noise J-fet input, like AD 745.
Only mistery for me in power supply is common mode choke value. I know it is horizontal Panasonic choke . Mr. Curl has right not to tell us design secrets of this brand new commercial preamp . It has probably his contract obligations.
Hi Kamis,
Thanks for this info.
You're absolutely right about John having a right not to tell us anything he considers proprietary, and he very well may have contractual obligations to keep quiet about certain things. However, I don't think it is right for John to BS us with statements like "it doesn't matter" or "I don't remember". That is simply rude. The courteous response is to tell it like it is, and tell the truth. Something like "I'd rather not say" or anything of the like. We also need to recognize that John is a gifted designer who was probably under a lot of cost pressure, and may not be that proud of this particular design, and may therefore not want to get into a conversation about it where a bunch of guys may second-guess him, not taking into account the business realities he has to design with.
Cheers,
Bob
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??
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Thank you, 6L6. You were very kind in your input. As I cannot remember which one we finally selected after listening tests (what a concept, sonic differences in similar IC designs) we selected one that was cheaper and sounded just as good as the AD797, which was our initial choice. It had other smaller advantages, as well.
Second, however, I did not want to get into a 'dogfight' over the choices that I made for THIS design which, in truth does not make it as UNIVERSAL in its application as it would be IF IC's were more ideal. However, they are what they are, and this design will work well with most phono cartridges available today in the cost range that they should be, such as around $1000 (the cost of the cartridge that I evaluated it with) or less, even though it will work just fine with some more expensive cartridges.
However, it is just too noisy to work with my newest cartridge (for me) the Lyra Helicon SL with its LOW output, or an old ADC like Soundminded likes to use, because the inductance is just too high, and bias current just might effect this cartridge. Who knows?
Second, however, I did not want to get into a 'dogfight' over the choices that I made for THIS design which, in truth does not make it as UNIVERSAL in its application as it would be IF IC's were more ideal. However, they are what they are, and this design will work well with most phono cartridges available today in the cost range that they should be, such as around $1000 (the cost of the cartridge that I evaluated it with) or less, even though it will work just fine with some more expensive cartridges.
However, it is just too noisy to work with my newest cartridge (for me) the Lyra Helicon SL with its LOW output, or an old ADC like Soundminded likes to use, because the inductance is just too high, and bias current just might effect this cartridge. Who knows?
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
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.
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
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
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.
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.
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.
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?
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?
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