Pars

I did the mods per simmconn/mwl168 prescribed for 400V supplies, using a pair of 150K resistors replacing the pair of 174K. Offset seems quite stable (no servo), better than many dynamic amps I've built in terms of not bouncing around. I didn't recheck the bias. Channel 1: PZTA42 Vce: 13.5/13.6 Drop across 20K: 24.7 C2M Vgs: 3.37/3.25 Channel 2: PZTA42 Vce: 7.4/7.5 Drop across 20K: 24.7 C2M Vgs: 3.36/3.03 Amp was not warmed up, offset at ~10V per side and dropping. The channel 2 PZTA42 Vce was a little concerning. Let me know what you guys think.

I know Amb recommended that for the SE out, the - goes back to the PSU ground, not the amp board grounds. That is the way I always do it, and never had problems. They are of course at the same potential as the amp board ground is, but gets any noise further away from the amp boards, at least that was his rationale for doing it that way.

OK. After 2 sets of board runs (pretty much into the trash; fortunately another larger board I need paid for the shipping), I discovered that the Neutrik jacks (as alluded to in willsw's helpful posts) sit too damn high from the board. Even if I had done slots to allow me to push the XLR all the way down, they are still too high, at least for the 4DPDT switch. So, I've decided to do daughter boards. For the mechanically switched board, the switch and Vampire (or ELECAUDIO ER-107) are on the daughter board. For the relay switched version, only the Vampire jacks are on the daughter board, and the main board allows for std. RCA jacks to be wired in. The daughter boards are wired in using standard 2.54mm headers, so distance is adjustable. If I put the Vampire footprint on that board, I'm still not sure that the jacks would reach even with the pins tack soldered on. It would be close, but since I have the boards designed, no point in fucking around. Switch board, and relay board sets.

Happy Birthday Fitz!

Is the Dynahi setup with 14 pin DIP sockets for the input devices (ie, THAT340)? If so, you can just plug the JFETs into the DIP sockets (assuming you use good machine pin DIP sockets). No adapter required.

Those all would appear to be hideously priced, and I for one am not digging the vibe. It seems that companies are just charging whatever the fuck they think they can. Good luck to them. I'll stick with my Von Schweikerts. Might have a look at the new Schitt power amps however...

Nice job Michael. I didn't do any of these changes as I know of to the Carbon I am building for another member. It will be off to another member to do the casework and finish it up. I hadn't posted pics of the whole thing as it exists, so here is one:

If you are using THAT340s for the input devices (BJT), impedance issues may be causing a problem. The Pass SuperSymmetry results in a low input impedance, which can cause problems for certain devices. One way around this is to use JFETs on the input instead, as these greatly raise the input impedance. Something like the Toshiba 2SK170/2SJ79 or the equivalent Linear Technologies singles or duals. I'm not sure what device package these boards are set up for. If it is surface mount, that would make this more difficult.

Happy Birthday Nate!

Happy Birthday Craig!

Put it back together and that was the problem. Offset and balance adjusted fine. I was a bit concerned when I first turned it on as it started to come up but blew the fuse (3.15A Slow blow). Replaced the fuse and it came up fine. No soft start or anything. Lights didn't dim or anything. Not sure if this is a problem or not. I'll see how it starts up in further starts to adjust and implement the opto servo. Bias is ~17mA; heatsinks don't seem to be warming much, but I didn't run it much (5 minutes). Might turn it up to 20mA bias, need to read the thread more (again) to see user comments on that. Can't believe I hadn't noticed that solder bridge before, but glad I don't need to try to source any unobtainium parts right now

No, the inputs need to be shorted (i.e., pot all the way down). If it like an SS Dynalo, there will be two trimpots controlling offset (one per channel). You want the offset as close to 0V as you can get. <10mV for sure. Nothing to get anal about, 1mV or less is very good. Spritzer might weigh in if he wants to.

I see an Andy Regan listed as president. Might be "Bluto". I think Dan is still CEO, but don't know for sure.

Spotted a solder bridge on 2 pins of the TO-71 socket. It was definitely shorted, now removed. I'll try to test it later. If that is it, that was easy

You measure DC offset at the outputs (signal to ground) with the volume pot turned all the way down. DC V or mV on your meter. Ideally you would disable the DC servos when doing this, but I doubt this is possible on this amp.

Posting some board pics, hopefully of good enough quality. #1 is the bad board, #2 is the good one.

Boy, the hf peeps are sure waxxing on and on about that Viva amp in the CJ meet thread (or amps, the stat one too). Hadn't heard of them (or remembered), but then ran across a thread here with Kevin and Birgir dissing it for the usual types or reasons (ala Rudistor or Mikhail). Nice Alps pot. All of this for $17K? SIgn me up!

I started troubleshooting this today (I'm working, so limited time). After disconnecting from heatsink/wiring, I decided to rerun Soren's CCS test using a bench supply. Both CCS's adjust fine on the bench, so I guess that tells me the 10M90s and DN2540 are fine? I guess the SIC and the PZTA42 are next up. I'll look the board over for solder joints, etc, and run diode tests on those devices. I do have some SICs and I should have extra PZTAs. I did have the opamp and the opto in on this board (no jumpers in). Hope this didn't destroy either of those. I don't think these (if dead) could be causing this issue, but will remove them for the time being.

Yeah, ASR pimps topping hard. I think Amir has a relationship with them. I won't bother reading... I wonder if he measured it correctly given past estat amp history?

Update: fired up the other channel and it works fine. Bias was right where I set it at 17mA. Offset and balance look good. Initial offset was around 32V, adjusted easily down to 0. Let it run a few minutes, it had drifted around 10V, adjusted back down (no servos yet). The heatsink (Modu 2U 300mm) was starting to get warm on that side. The one on the bad channel not getting warm. I did attempt to adjust the bias on the bad channel right side, but the pot had no effect, so guessing a bad device somewhere. I'll probably start with the DN2540 as I have a couple of those. I do not have any more 10M90s. I of course have some C2M1000170D but they are back in stock at Mouser now, and probably not one of those which is bad. I'll attempt to use the good channel to troubleshoot the bad one.

Happy Birthday Naaman! Hope you have a great one!

Went down and started working on this again. The offset pot measured 54.5 ohms in circuit. No adjustment I made to this made any difference and stayed pegged on 404Vdc on the O+->GND. The only thing I've noticed is the right side current adjust TPs show 0.11V. The left side is 0.85V, which is the 17mA i had adjusted to using Soren's procedure. Ohming out the larger devices shows no differences. When you say do a diode check on them, you mean use the diode function on the DMM? I also assume to check them both ways (flip the leads)? From the schematic, the DN2540 or 10M90s could be the culprit on that side. I didn't try adjusting the trimpot, but know they were both set to 17mA. I have a couple of DN2540s, but don't think I have any more 10M90s. I'm going to hook the other channel up and see how it behaves. I verified that the tail resistor for the offset is 120R and not 182R.

That is what I did with a 2CP I bought from PartsConnexion. I measured and plotted the response at several points, and sent it to Chris Johnson of PcX. He replaced it, and the replacement is fine.

Oh, those? They are just bog standard round pads, 1.1mm drill. I used a 1.9304 size on them instead of the Auto in Eagle. I used a square pad for pin 1. EDIT: Here's the datasheet as it is helpful tkd cp600as-e.pdf

Thanks Kevin. I'll check it out tomorrow (having a beer, not conducive to HV stuff). On your production schematic (kgsshvcarbonproductionv5.pdf), the offset pot is RV4 and the balance pot is RV2 I take it? I'm pretty sure I have either a 120R or 100R ohm resistor in instead of the 182R. And yes, my cheapie Harbor Freight expendable meter didn't like the HV (read 400V for the bias when testing the PSUs; Fluke disagreed at 580), so decided I needed another good meter.