Pars

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.

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I struggle with this myself. Even with accurate center punches the bit seems to want to walk. Interesting concept to let the part float. I'll have to try that as I think that could help.

Congrats! Pics or it didn't happen

I've always like using the Neotech UPOCC teflon/copper solid for signal, and it is rated for 600V. Kinda stupid expensive though. Probably some snake-oil factor to it as well. http://www.soniccraft.com/index.php/neotech-wire-teflon-solid-cu-c-296_175_183_221

Ideal T-strippers work well on teflon, and any other wire.

Remember that the 47uf cap will effect what you are seeing when you ohm out the 100k and 500k resistors. Add the fact that these are in parallel with the 11k/1k/11k string and you will see some things that initially will look strange when ohming them out. I doubt there is anything unfixable with your current board, but do as you wish. The problem you are seeing relates to your very low reference voltages of 5mV, which is what the comparators are basing their decisions on DC offset, so if these aren't right, the circuit will not work. Also, the + and - 12V from the regulators needs to be pretty balanced. I had a bad + regulator (11.05V, with around -11.95V on the other rail) and was seeing +0.005V and -1.05V references, which of course didn't work.

Make sure the 11K resistors and the 1K are correct, and measure the voltage drops across them. Something isn't right with your reference voltages of 5mV was it? Those should both be around 0.5V, one + and the other -.

Do you have +12V (top of the 100K resistor, pin3 on U1/U2)?

Check the voltage + and - references at the 1K resistor in the voltage divider comprised of 11K / 1K / 11K. You should have +0.5V for the + reference and -0.5V for the - reference. You can check these on pin 7 on U1 (+) and pin 8 of U2 (-). Also check the +/- 12V. If the comparator trips for a fault, you will see around -12V (-11.x) at the junction of the 100K / 500K resistor (relay off). If all is fine, this will be ~ +7.x Vdc (relay on). All measurements to ground.

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For single-ended, because of the fully differential input stage, L- and R- need to be grounded when using the SE input, and wired normally when using balanced input. You would need some kind of switch to do this. It had been suggested that a 4PDT switch be used, to switch all 4 signals between the RCA/XLR, and to ground the - signals when the RCAs are being used. I'm not sure if you could get away with just using a DPDT to switch the - either to amp ground when using the RCA or to the XLRs in balanced mode. This would leave the + inputs connected to both the RCA and the XLR at all times.

Snagged. Thanks Marshall!

^ It is wired to the analog ground of either the amp board or to the ground on the PSU (single ended dynahi).

^ Don't think that would work. The combo jacks are 3-pin XLR and a TRS. You need 4-pin (minimum) XLR for balanced output (L+ / L- / R+ / R-). L- and R- cannot be tied together.

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I just have it breadboarded to test it and the mute switch/LED additions. I'll do an actual PCB up (mostly done) when I verify a couple of things there. And will use 12V regs on the board. I do have some of the TO92 regs (78L12/79L12) but assumed these might not be the best thermally with the relay being driven off the + one.