The pcb is designed for transistors: Toshiba 2SK389/2SJ109 and Hitachi 2SK214/2SJ77. I have completed all these transistors yet. So footprints are adequate for above transistors only. I know that purchase such old transistors is very difficult but not impossible. The pcb was designed for my project of preamplifier exclusively, not as an universal kit. Dimensions of pcb and placement of sockets and heat-sinks are suited to project of my preamplifier's housing.
I made some improvements of previous design: all power and output signal traces are wider (3-5mm), ground plane is on top layer (power plane) only, under (bottom layer) the PSU section and Power Section have ground plane but not connected to ground plane on top layer (AGND1-L, AGND1-R). Both bottom ground planes are connected to GND-Case's vias to connect them directly with housing star ground point) - it will be working as a shield under PSU section and Power Section. I hope it is suitable idea.
First I thought to use teflon as the board material but I gave the teflon pcb up (to costly and low mechanical durability). So finally the pcb will have features as follow:
1. material of the pcb: 2mm thick FR-4
2. double copper layers 70um each
3. both layers are gold plated
4. lack of solder-mask on top and bottom layers (gold plated layer are resistant to any oxidation and need not solder-mask)
5. the pcb will be screwed to 5mm thick teflon plate under the pcb
5. the pcb has 19 holes to fit with teflon plate + 6 holes to fit with both heat-sinks + 2 holes to fit shield of Power Section, so finally the pcb will be very rigid and resistant to any vibrations.
The pcb is finished but during few next days I will be looking at the pcb to find any errors or to make some improvements else.
I made some improvements of previous design: all power and output signal traces are wider (3-5mm), ground plane is on top layer (power plane) only, under (bottom layer) the PSU section and Power Section have ground plane but not connected to ground plane on top layer (AGND1-L, AGND1-R). Both bottom ground planes are connected to GND-Case's vias to connect them directly with housing star ground point) - it will be working as a shield under PSU section and Power Section. I hope it is suitable idea.
First I thought to use teflon as the board material but I gave the teflon pcb up (to costly and low mechanical durability). So finally the pcb will have features as follow:
1. material of the pcb: 2mm thick FR-4
2. double copper layers 70um each
3. both layers are gold plated
4. lack of solder-mask on top and bottom layers (gold plated layer are resistant to any oxidation and need not solder-mask)
5. the pcb will be screwed to 5mm thick teflon plate under the pcb
5. the pcb has 19 holes to fit with teflon plate + 6 holes to fit with both heat-sinks + 2 holes to fit shield of Power Section, so finally the pcb will be very rigid and resistant to any vibrations.
The pcb is finished but during few next days I will be looking at the pcb to find any errors or to make some improvements else.
Just finished reading the entire thread. I've been using and been very pleased with the original JC-2 kit from eBay. There is a new "modular" kit available that looks appealing, but this project is intriguing.
Just want to add my support for a possible group buy in the near future. I'm in if/when it happens.
BTW: Spent most of the last two days comparing my JC-2 with a Carver C-1 pushing the BA-3 liquid cooled build. The BA-3 (as configured now) is just short of what I like for "realistic" sound levels - with the speakers I'm using. I don't need a lot of gain, but something based on JC's preamp concepts would be the perfect addition.
Really looking forward to new developments here.
Hi Bob,
The new JC-2 that is modular is way better than the first version, you should test it, I personally love it!
The JC-80 is even better but is a balanced preamp. I have built mine about two years ago using AMB's a10 backplane, Delta 1, Delta 2, Sigma22 and LCDuino-1. Actually the whole AMB a10 x2 due to the balanced nature of the JC-80 modules except the a20 modules which I still have to eventually compare.
JKoch has done an outstanding job with his build and I do hope he can make it possible to retro fit some of the more commonly available Mosfets.
Ciao!
Do
Building and auditioning an end to end balanced system is near the top of my bucket list. It's one of those things that has to be experienced live to make any valid judgement - IMHO. I've read conflicting opinions of the comparative advantages.
Dominic - with due respect, it sounds like you have a lot of "gizmos" in that balanced signal path. I'm a fan of the KISS approach, and was attracted to the JC-2 after hearing it described as a "straight wire with gain". Are all those components necessary to get the best sound from the JC-80 you built - and will something similar be needed for the JKoch boards. Did you post a build thread or photos on that preamp?
JC - Did a quick search for the HCA-2000 but not much showed up. If you or anyone can point to a source I'd be happy to investigate that path.
BTW: A little off-topic, but I decided the C-1 still sounds pretty good for something that old. Compared to the JC-2 there is some "barking" at high loud passages and it has a bit of that "Solid State" edege from the mids up. The JC-2 is less forward with more space, warmer sound and a very comfortable stage. There are some upgrade kits/BOM for the C-1, but I think I'll hold on to my cash for the new design developing here.
Dominic - with due respect, it sounds like you have a lot of "gizmos" in that balanced signal path. I'm a fan of the KISS approach, and was attracted to the JC-2 after hearing it described as a "straight wire with gain". Are all those components necessary to get the best sound from the JC-80 you built - and will something similar be needed for the JKoch boards. Did you post a build thread or photos on that preamp?
JC - Did a quick search for the HCA-2000 but not much showed up. If you or anyone can point to a source I'd be happy to investigate that path.
BTW: A little off-topic, but I decided the C-1 still sounds pretty good for something that old. Compared to the JC-2 there is some "barking" at high loud passages and it has a bit of that "Solid State" edege from the mids up. The JC-2 is less forward with more space, warmer sound and a very comfortable stage. There are some upgrade kits/BOM for the C-1, but I think I'll hold on to my cash for the new design developing here.
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Hi Bob,
The LCDuino-1 is just a controller with LCD and does not affect anything in the signal path. The Delta 1 i a source selector and Delta 2 a R2R shunt ladder volume control that is far superior to a DACT or the likes and Alps pot, also, the relays on the Delta 1 and 2 are latching relays which means that the coil does not stay magnetized once its state has changed thus not impacting the signal that traverse them and since they are high end comunication relays with silver contact they will have little to no effect on SQ. The signal path is really short as well.
I can tell you that it is extremely good preamp and so is the newer JC-2 which I also been using for more than 3 months.
JKoch is using a different approach for volume control, it is a chip ladder if I'm not mistaking and he will also be using a controller on a different PCB.
If you have not tried the new JC-2 then I would consider it very much. It is I believe identical to the original circuit or extremely close. The older design has nothing to do with the original design and the jfet were starved in current due to the design.
Balanced desn't necesseraly sound better than SE, it is just a means of getting rid of additional noise floor and hum through the use of differential pairs but with all the tests I've done, the best of SE and Balanced are very much equal. Maybe another advantage is most DAC are by nature balanced and designers uses opamps for converting to SE. This where you could have a loss os SQ or coloration but nothing to go crazy about IMHO.
Ciao!
Do
The LCDuino-1 is just a controller with LCD and does not affect anything in the signal path. The Delta 1 i a source selector and Delta 2 a R2R shunt ladder volume control that is far superior to a DACT or the likes and Alps pot, also, the relays on the Delta 1 and 2 are latching relays which means that the coil does not stay magnetized once its state has changed thus not impacting the signal that traverse them and since they are high end comunication relays with silver contact they will have little to no effect on SQ. The signal path is really short as well.
I can tell you that it is extremely good preamp and so is the newer JC-2 which I also been using for more than 3 months.
JKoch is using a different approach for volume control, it is a chip ladder if I'm not mistaking and he will also be using a controller on a different PCB.
If you have not tried the new JC-2 then I would consider it very much. It is I believe identical to the original circuit or extremely close. The older design has nothing to do with the original design and the jfet were starved in current due to the design.
Balanced desn't necesseraly sound better than SE, it is just a means of getting rid of additional noise floor and hum through the use of differential pairs but with all the tests I've done, the best of SE and Balanced are very much equal. Maybe another advantage is most DAC are by nature balanced and designers uses opamps for converting to SE. This where you could have a loss os SQ or coloration but nothing to go crazy about IMHO.
Ciao!
Do
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Great info - thanks. Unfortunately it's starting to look like I'll end up with as many pres as I have power amps. The eventual clearance sale will be a humdinger! I'm planning/hoping to resurrect my phono source this winter so some (many) things have to go.
Guess that's just the cost of seeking the best match for my system and my ears - within my budget
The eventual clearance sale will be a humdinger! I'm planning/hoping to resurrect my phono source this winter so some (many) things have to go. Guess that's just the cost of seeking the best match for my system and my ears - within my budget
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Bcmbob, you make me smile. What I 'hate to do' today, you relish. I guess that more than 54 years of building Heathkits, Eico, Dyna, etc, and THEN building circuit boards, studio boards, etc, has got me happy with just the computer screen. Good soldering, I do remember when it was more fun for me.
Hey JC,
How have you been doing lately? Good to hear from you!
Good idea about the PLD-2000
Ciao!
Do
Very Nice JKoch,
Have you tried designing a regulator based on the TI TPS7A4700? Supposed to be real quiet supply.
Ciao!
Do
The TI TPS7A4700 is quiet (4,17uV output voltage noise) but it is housing in VQFN package only. I need not such quiet regulator in this place and the TI TPS76750QD has fixed 5V, so is simpler to use (one resistor only). The regulator will be supplied 2 x PIC uControllers and 2 x LED displays.
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