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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!

Happy Birthday!

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.

Did you have the inputs grounded for this? Mine was < +/- 5mV, normally +/- 2mV without the servos in place.

Happy Birthday Ryan!

Damaged in what way? One of my cats chewed through the cord on mine, and the rep sent me a new one free of charge. Since you are in Canada, that might not be an option though...

Capacitance between the ground planes?

I finished up my breadboard testing for adding a manual mute switch and status LEDs to this circuit. I wound up going back to the 2N7000 with a PNP as used on amb's epsilon12 circuit. I could not get the LEDs to work properly on everything else that I tried, as below: Original circuit, with mute switch between relay coil and 2N7000 drain. Muted fine, but not enough voltage to drive the LED circuit. Moved the 2N7000 to above the relay, in between +12V and relay coil. This would not energize the relay. Here is the schematic of what I am planning on using. And here is the resulting board layout, extensively cribbed from Dr. Gilmore's layout (though I did try some others first) Still working on label clean-up, etc. Also, the BC 5xx transistors I used could probably be replaced with 2N3904 / 2N3906; just flip them around. I noted the transistor pin-outs on the layout, though they become slightly misaligned using Seeed Studio's CAM processor job. I also put in both the Phoenix terminal blocks and Molex KK connectors. The mute switch and LEDs only have the Molex connectors currently, with a shared ground on the LED connector. I think I will switch to a pair of 2-pin or a single 4-pin connector and might add the Phoenix terminal blocks for those if anyone is interested. Board size would probably go up a bit with those as well.

Happy Birthday!