While participating in the beta process for the new LM3886 based MyRef Fremen Edition power amp, I have tested several approaches to volume control. The Parasound JC-2 has been described as a “Straight Wire with Gain” solution. There are already a couple of threads dealing with this design; however the goal here is to focus on a specific offering by an established eBay supplier.
Symmetric Complementary J-FET preamplifier JC-2 kit ! | eBay
A similar product is available but I have not had any experience with the supplier.
JC-2 Preamplifier Class A Dual differential FET input PER-AMP Kit DIY | eBay
For some background on developments here at diyAudio:
http://www.diyaudio.com/forums/solid-state/10160-need-build-jc-2-preamp.html
http://www.diyaudio.com/forums/solid-state/120243-variation-jc-2-preamplifier.html#post1468164
The primary reason to focus on a kit is simply the availability of a common starting point. Some forum members may prefer a more open approach. A close integration between this preamp and the Fremen Edition power amps could produce a world class combination.
Some other interesting material:
Audio Advisor Insight - Parasound JC-1 and JC-2 Back Story - YouTube
Parasound Halo JC-2 Preamp Review - YouTube
NOTE: These two links are included as general public information only. I contacted Parasound in California and received notice that the kits above are not authorized JC-2 versions, nor do they in any way represent the products and/or designs of that company. Their representative has stated there is no desire to encumber the DIY community on their part, but appreciate a clear distinction between their circuits and those being developed without official sanction. The title of this thread was to be “JA JC-2 Optimization”, but has been changed to “JA Pre and MyRef Integration” accordingly.
In any event, I think it is a killer preamp package and hope it will attract much interest.
The Floor Is Open.
Symmetric Complementary J-FET preamplifier JC-2 kit ! | eBay
A similar product is available but I have not had any experience with the supplier.
JC-2 Preamplifier Class A Dual differential FET input PER-AMP Kit DIY | eBay
For some background on developments here at diyAudio:
http://www.diyaudio.com/forums/solid-state/10160-need-build-jc-2-preamp.html
http://www.diyaudio.com/forums/solid-state/120243-variation-jc-2-preamplifier.html#post1468164
The primary reason to focus on a kit is simply the availability of a common starting point. Some forum members may prefer a more open approach. A close integration between this preamp and the Fremen Edition power amps could produce a world class combination.
Some other interesting material:
Audio Advisor Insight - Parasound JC-1 and JC-2 Back Story - YouTube
Parasound Halo JC-2 Preamp Review - YouTube
NOTE: These two links are included as general public information only. I contacted Parasound in California and received notice that the kits above are not authorized JC-2 versions, nor do they in any way represent the products and/or designs of that company. Their representative has stated there is no desire to encumber the DIY community on their part, but appreciate a clear distinction between their circuits and those being developed without official sanction. The title of this thread was to be “JA JC-2 Optimization”, but has been changed to “JA Pre and MyRef Integration” accordingly.
In any event, I think it is a killer preamp package and hope it will attract much interest.
The Floor Is Open.
Great work so far Bob. I am very interested in this project, it may be a good alternate for me if the LN does not work out. Mating it to the MyRef FE project is a great idea too. I think having more FE RC users with a similar setup will help the group agree on the improvements of various component swaps. The price is hard to beat too. A savvy builder could probably build a finished stock unit for around $100.
Thanks Bob
Thanks Bob
One channel is showing 9.1 mV and the other is 5.4 mV. That indicates I need to adjust the on-board trimmers again. The process is clearly explained in the documentation.
Sounds worrying to me. Does it drift with heat, or time?
I would not want any DC going to my amp.
I would not want any DC going to my amp.
erin,
From my experience using two types of LDR attenuation, a Dynaco PAT-4A, dbx 234, Carver C-1, the pre on a Lexicon usb module - this unit and the bare pot have been the cleanest and least intrusive. If I had to describe "the sound" I could only suggest a bit of "sweetening" across the entire spectrum.
EDIT: The LDRs don't introduce artifacts to my ears, but there is a bit of horizontal stage drift at the extremes of the controlling volume pot. Both the LS and LN have a balance pot to address this.
Because my eBay pot is now on the pre, I ordered these to pieces to try/compare as both a bare pot and a component of this build. Never had the highly rated Alps (also used by Parasound) so it will be interesting - assuming they are not knock-offs
ALPS 100KA LOG Stereo Audio RK27 Potentiometer Pot 1pc | eBay
1pc PCB for ALPS RK27 RK16 Potentiometer Tin-Spraying | eBay
From my experience using two types of LDR attenuation, a Dynaco PAT-4A, dbx 234, Carver C-1, the pre on a Lexicon usb module - this unit and the bare pot have been the cleanest and least intrusive. If I had to describe "the sound" I could only suggest a bit of "sweetening" across the entire spectrum.
EDIT: The LDRs don't introduce artifacts to my ears, but there is a bit of horizontal stage drift at the extremes of the controlling volume pot. Both the LS and LN have a balance pot to address this.
Because my eBay pot is now on the pre, I ordered these to pieces to try/compare as both a bare pot and a component of this build. Never had the highly rated Alps (also used by Parasound) so it will be interesting - assuming they are not knock-offs
ALPS 100KA LOG Stereo Audio RK27 Potentiometer Pot 1pc | eBay
1pc PCB for ALPS RK27 RK16 Potentiometer Tin-Spraying | eBay
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Your DC concerns are certainly valid. I can only tell you that with several sessions of continued play ranging from four to six hours, the pre has been stable and caused no problems with several MyRefs and the Fremen Eddition betas.
Another option just discovered.
Symmetric Complementary J-FET preamplifier JC-2 PCB stereo !! | eBay
Symmetric Complementary J-FET preamplifier JC-2 PCB stereo !! | eBay
Out of curiousity, have you ever run a square wave through the pre amp?
I'm curious to know at what frequency the square wave starts to visibly start rounding off.
This is an arbitrary request, i know it would have little to do with the subjective sound.
I'm curious to know at what frequency the square wave starts to visibly start rounding off.
This is an arbitrary request, i know it would have little to do with the subjective sound.
I just started collecting tools to get into this area. Installed RMAA6 and Visual Analyzer, dug out my signal generator - but it will be a while till I understand what I am doing.
I did shoot off a message to Stanton requesting any publishable data he may have from the development process.
Attachments
I would expect to seeing "rounding" at 10kHz square wave. That would imply attenuation of frequencies around 100kHz.
I would NOT expect to see overshoot, if the circuit and it's necessary input filter are correctly designed.
I would NOT expect to see overshoot, if the circuit and it's necessary input filter are correctly designed.
I have a few questions
What transformer do you use for this preamp ?
How does the JC-2 compare to the DCB1 ?
Have you tried any parts substitutions to boutique parts ?
What transformer do you use for this preamp ?
How does the JC-2 compare to the DCB1 ?
Have you tried any parts substitutions to boutique parts ?
Hey squalor,
Antek AN-0518 right now and have no problems. I intend to try an R-Core at some point primarily because I've never had one and they are reported to be quieter. The toroid itself is silent and there is no hum from the JC-2. The only advantage I could imagine is just cleaner power to drive the circuit.
I've thought about building a DCB1 but the difference in cost would have to better this pre, a bare pot and the Lighter Note for me to make that jump. From what I have read - it doesn"t. Dario will be able to make a direct comparison in a few weeks. He is also working on a boutique BOM. Mine is still a stock unit/kit as shipped from Jim's Audio.
Antek AN-0518 right now and have no problems. I intend to try an R-Core at some point primarily because I've never had one and they are reported to be quieter. The toroid itself is silent and there is no hum from the JC-2. The only advantage I could imagine is just cleaner power to drive the circuit.
I've thought about building a DCB1 but the difference in cost would have to better this pre, a bare pot and the Lighter Note for me to make that jump. From what I have read - it doesn"t. Dario will be able to make a direct comparison in a few weeks. He is also working on a boutique BOM. Mine is still a stock unit/kit as shipped from Jim's Audio.
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FYI,
I did some testing this morning. The Lighter Note had been in a different build till last night when I reconfigured it as a stand-alone piece with new wires and RCAs. This was the first time I was able to try it with the FEs. The source was the Mini DAC fed with a computer. I set the volume on both the Ln and the JC-2 to peak ~ 88 db.
The Lighter Note still sounds as clean and pure as ever. There are element of sparkle, airiness and immediacy I have never found with any other device. Bass is full and controlled, mids are punchy and balanced and I get the impression there is nothing being left behind on the source. A pleasant surprise was a lot more available SPL when attached to the FEs. I could not max out the LN pot as was necessary with the V1.2 and V1.3 builds. I would assume that is much the result of the giant 300VA toroids as well as some of Dario’s approach.
The JC-2 held its own, was super close with a few cravats. More than ever I detected some horizontal drift as the volume pot was adjusted. It was serious enough that I wasn’t sure I was getting a truly centered image. I used some audio software to create a mono version of a song with a strong vocal (Paul M’s “Say Say Say”) and played it through the system while adjusting the LN balance pot. The musicality and range of both units was a very, very close match. The stage width was almost identical but the LN had a clear advantage in depth.
I still think the JC-2 is a top choice here for a few reasons.
1. The “Swap & Twist” dance (Dario’s Salsa shuffle) we did on the FE beta run convinces me that proper component choices and placement could recapture the superlative upper end of the Lighter Note. Same for the depth of stage.
2. The stage drift is not present with the JC-2.
3. Cost differences – The JC-2 may be a more likely choice for builders on a tight budget.
I do want to state clearly that I still believe Uriah’s LDR devices are IMO – top notch. He has openly stated a redesign of the Lighter Note is in the works with the goal of simplification and I suspect he will also address the drift. I'm sure some of what I have mentioned can be corrected by adjusting the many on-board trimmers while listening to live signals, as Uriah suggests. To date I've done all my calibrating on the bench with a VOM. Nothing needs to be changed in terms of sound quality and purity. I’m looking forward to his quick recovery and more of his magic tricks.
I’ve also taken the time to read through the other two JC-2 threads and am more convinced than before that this is a great point of departure. It appears Stanton has done his homework and several people are quite pleased with the results.
I did hear from John Curl and his response was similar to that from Parasound. Paraphrasing – “Have at it boys, just remember that the eBay offerings are not my circuits/implementations, nor those of M Levenson or Parasound."
So there we are. There's lots of schematic and components variations on the other posts for those so inclined.
I did some testing this morning. The Lighter Note had been in a different build till last night when I reconfigured it as a stand-alone piece with new wires and RCAs. This was the first time I was able to try it with the FEs. The source was the Mini DAC fed with a computer. I set the volume on both the Ln and the JC-2 to peak ~ 88 db.
The Lighter Note still sounds as clean and pure as ever. There are element of sparkle, airiness and immediacy I have never found with any other device. Bass is full and controlled, mids are punchy and balanced and I get the impression there is nothing being left behind on the source. A pleasant surprise was a lot more available SPL when attached to the FEs. I could not max out the LN pot as was necessary with the V1.2 and V1.3 builds. I would assume that is much the result of the giant 300VA toroids as well as some of Dario’s approach.
The JC-2 held its own, was super close with a few cravats. More than ever I detected some horizontal drift as the volume pot was adjusted. It was serious enough that I wasn’t sure I was getting a truly centered image. I used some audio software to create a mono version of a song with a strong vocal (Paul M’s “Say Say Say”) and played it through the system while adjusting the LN balance pot. The musicality and range of both units was a very, very close match. The stage width was almost identical but the LN had a clear advantage in depth.
I still think the JC-2 is a top choice here for a few reasons.
1. The “Swap & Twist” dance (Dario’s Salsa shuffle) we did on the FE beta run convinces me that proper component choices and placement could recapture the superlative upper end of the Lighter Note. Same for the depth of stage.
2. The stage drift is not present with the JC-2.
3. Cost differences – The JC-2 may be a more likely choice for builders on a tight budget.
I do want to state clearly that I still believe Uriah’s LDR devices are IMO – top notch. He has openly stated a redesign of the Lighter Note is in the works with the goal of simplification and I suspect he will also address the drift. I'm sure some of what I have mentioned can be corrected by adjusting the many on-board trimmers while listening to live signals, as Uriah suggests. To date I've done all my calibrating on the bench with a VOM. Nothing needs to be changed in terms of sound quality and purity. I’m looking forward to his quick recovery and more of his magic tricks.
I’ve also taken the time to read through the other two JC-2 threads and am more convinced than before that this is a great point of departure. It appears Stanton has done his homework and several people are quite pleased with the results.
I did hear from John Curl and his response was similar to that from Parasound. Paraphrasing – “Have at it boys, just remember that the eBay offerings are not my circuits/implementations, nor those of M Levenson or Parasound."
So there we are. There's lots of schematic and components variations on the other posts for those so inclined.
Attachments
Reason I ask, I own a 30VA 15+15 Avel from TP that is currently unused. I also have a Antek AS-1215 that I bought for a DCB1. I also have a DCB1 hypnotize PCB. I have not populated it yet because of my FE issues and I don't know who to buy matched sets of 2SK170-BL from.
For my situation, I probably don't need JC-2 or DCB1 . All sources will be within 2ft of the amp and speakers are very efficient. I'm catching flac from the wife again but did leverage a C-note limit after a lick and a promise. Isn't it interesting that wedlock rhymes with headlock.
I had a quick look at the other threads. The conflicts and reasoning of the others are beyond my understanding. Is it true that the original circuit can not be built unless NOS parts can be sourced; the kit Jim is selling is quite different than the Mark Levinson product ? due to adjustments in values to accommodate the newer jfet ?
If I understand right, the JC-2 has something the DCB1 does not; gain. Gain = Loud , loud is good.
For my situation, I probably don't need JC-2 or DCB1 . All sources will be within 2ft of the amp and speakers are very efficient. I'm catching flac from the wife again but did leverage a C-note limit after a lick and a promise. Isn't it interesting that wedlock rhymes with headlock.
I had a quick look at the other threads. The conflicts and reasoning of the others are beyond my understanding. Is it true that the original circuit can not be built unless NOS parts can be sourced; the kit Jim is selling is quite different than the Mark Levinson product ? due to adjustments in values to accommodate the newer jfet ?
If I understand right, the JC-2 has something the DCB1 does not; gain. Gain = Loud , loud is good.
Are you building a Lighter Note or a LDR ? Did you see my reply to your question on the FE thread ? (anything else should I order with my Mouser FE order) I suggested the regi-reg. It's a great way to power a LDR without buying a dedicated transformer for it.
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