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Happy Birthday Raffy! Don't ride too much

Oh shit, I forgot to use the C37 lacquer... I'm truly fucked now

Pics (iphone) Input jacks with switch for RCA/XLR Amp boards and pot Sigma22 psu and transformer, set for +/- 16.2Vdc (gain resistors still socketed). L channel amp board. Still have the bias resistors (R38/39) socketed, 301R in there currently, resulting in 18-19mA current in the output stage. Also using 2SJ74/2SK170 JFET input. I also didn't populate the 4.7uf Wima caps as I'm not sure there is any point to them being there. Sounds very good, still evaluating compared to my other Dynalo. Dead quiet. I have only tried SE inputs so far, and don't notice any difference between the switch up (- inputs into the amp tied to ground), or down (- inputs wired to XLR but floating). Gain seems sufficient now that I have the input wiring issues sorted. It will be awhile before I case this, so I just mounted it to some scrap veneered plywood I grabbed from home depot for a buck, stained and polyed. EDIT: small pieces of clear tubing used as board standoffs, in case anyone was going to chastise me for mounting them directly to the wood

Happy Birthday!

Found that there is nothing wrong with the pot. When I saw that the measurements of each section at a particular rotation weren't really far off, it didn't jive with what I was hearing. I found some connection issues; 2 crushed pins on the L out from the pot, and 2 broken wires on the input cable from the L jacks (that were still making some connection). Once fixed, it sounds much better now. This is the first time working with the radio shack rainbow wire (a favorite of rickcr42 from HF, RIP), and I can't say so far that I am a fan, other than it being ribbon and solid core. The insulation absolutely sucks as it melts if a soldering iron looks cross-eyed at it. So, in the words of the immortal Emily Litella, "Nevermind, bitch".

It looks like this other than mine has the flatted shaft:

Alps RK27 10K motorized

Thanks GT and Kevin. I could always pull the opamps for what GT is saying. I could also just measure it on RMAA (I think my Audiophile 24/96 will do balanced?). Not only for L/R channel balance, but what effect do pot imbalances have regarding +/- channels? I would certainly think some as well, but not sure how that manifests itself. I wonder if Birgir has any of the 4CP-601 TKD pots he'd be willing to part with? Also, I recall the thing you can do to a 2 channel pot to use it for 4-channel, but it seems that only typically works on certain types of inputs? EDIT: No on my m-audio box doing balanced

Listened to my multiamp a bit yesterday and this morning. I seem to have a slight channel imbalance, using SE inputs with the L/R- inputs tied to ground. Swapping the input and output cabling around, it seems to be the pot that is causing the problem. The R channel is slightly louder than the left. Measuring the pot, this is what I get at the approximate rotation I was using for listening: L+ L- R+ R- pot total 9.884 9.707 9.721 9.811 3/4 rot 5.714 5.768 5.643 5.776 % 57.81% 59.42% 58.05% 58.87% This doesn't seem off that much (57.81% vs. 58.05%). All figures in K ohms. Output taken to ground. Any thoughts? It seems worse at lower volumes and gets a bit better at higher volumes, though going much beyond 3/4 rotation gets louder than I care to listen to. I've checked resistances some on the cabling from input through the pot, and I didn't find any bad solder joints or anything yet. Any thoughts?

Thanks all! Had a very nice birthday, low key, but nice.

Machine pin sockets like Mill-Max, Augat, etc. hold the IC pins much more securely than the type you are using. When I was a tech back in the '80s I spent a lot of time reseating chips in the kind of sockets you are using; once reseated, equipment back in business (for another day or so). Sockets are so cheap you might as well use good ones. Kevin commented on this in post 95, parts list using 571-1825093-3. vs.

You really should use better sockets for the opamps and I presume the THAT340 that one you have there (those are junk). Mill-Max or equivalent machine pin sockets 575-193308 for the 8 pin 575-193314 for the 14 pin are good ones.

RIP BB King

Happy Birthday!

Use their economy shipping (Mouser). I just placed a small order on Wednesday and got it today ($4.99 shipping). BTW, mounting my multiamp on a piece of veneered plywood for now. Any recs for a fuse? I have a 2A fast blow in right now, no issues, but seems a bit high?

Happy Birthday Ari! Hope you have a great one!

Happy Birthday Shelly!

Sure. Pick up some techflex and heatshrink (adhesive) of an appropriate size to dress up the bundle. Use teflon 600V wire as mentioned by others, and vary the color if you can to eliminate errors in wiring.

Kerry, Thanks for the comments. Actually, the Neutrik XLRs and the switch are on the back side of the board. The Molex connectors are on the front. The switch is intended to protrude through the back panel (slot). As I mentioned, I haven't checked the mounted heights of the XLRs vs. the switch to see how that would work out. And for support, it might need a standoff or two on the back side. EDIT: Actually you are right in that the XLRs were drawn from a front perspective. Corrected now (not in image above).

Wasn't sure where to put this, so here seemed fine, though applicable to a bunch of amps here. Balanced-SE input jack board with switch. I was playing around in Eagle (after having to manually wire one of these up). This is set up to use either a 4PDT switch (for isolating all 4 signals) or a 2PDT if you only want to switch the - signals to ground for SE, but leave the + signals connected to the RCA jacks. Pads are provided to connect RCAs. I haven't verified the heights of the Neutrik NC3FAV jacks versus the switch height. My goal would be to have the board mounted to the faceplate via the Neutrik jacks only, with the switch sitting behind the faceplate and the toggle only extending through a slot. Might need a standoff or two as well. Switches this is designed for are the NKK M2042 (633-M2042SS1G03) 4PDT or M2022 (633-M2022SS1G03) DPDT. Board outputs are set up for either Molex 0.100 KK connectors, or you could use the pads as wirepads and solder the wiring in. I know Birgir has a balanced input jack board, but his is for including a pass-through connection, and not for balanced and SE. Any comments welcome.

Beautiful work Kerry!

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The semiconductor manufacturer I used to work for used these on their laser systems (back in the '80s). No opinion on how well they work for audio. I did pull a floor tile once to find the hose running from the laser PSU/cooling unit to the laser was spewing water all over the 440V OneAC under the floor Fortunately it was DI water, and we got the breakers shut down

Happy Birthday!

The outputs should be fine (SE and balanced), no switch there. The differential input requires the - signal to be grounded in the case of SE, so that is why you need a switch or something there. On the Pass Aleph P preamp I had, which has both SE and balanced inputs, shorting plugs were provided which needed to be inserted into the XLRs on channels where you were running SE input on. The XLR->RCA adapters do the same thing.