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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.

Happy Birthday!

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.

Happy Birthday!

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.

Got this working, think it was floating input causing the problem. I dug up a pair of 12V regulators and put them in, but no joy. Turns out the positive reg was an ST Micro (probably one of the pair that I had problems with) and only put out 11.05V (vs. -11.9+V on the neg regulator, not ST Micro), which had the effect of unbalancing the reference voltage divider. Ref voltages were +0.05V and -1.01V, which didn't work so well Went back to just the bench PSU and it started working. I'll have to grab some more 12V regulators... have all sorts of 15V etc. but no 12V other than LM317/337s.

I only had 2 of the outputs tied together, but the inputs were floating (just a single 100k resistor). I'll tie both of these to ground. I am running this from a +/- bench supply and noticed the 100k/500k combo only ohmed out at 8k or so in series with the bench supply connected. Removing it and the resistance went up to 22k or so, which makes sense since the reference voltage divider is in parallel and is 23k. I may dig up some 12V regulators and wire them up to isolate the circuit from the bench supply. I also threw a 10uf film cap in in place of the electrolytic to no avail.

Have a version of this breadboarded right now and something doesn't seem right. I was going to modify this to put in a manual mute switch and a pair of LEDs. I only have a pair of inputs wired up to the LM339 (single right now), and at the junction of the 1K/100K/500K resistors and the cap, I am seeing -9V or so, feeding the gate of the FET. Relay is off. Since the relay is connected to signal using the NO contacts, I should think with no signal in, it should be ON and conducting the input signals to the output? I am using a 47uf electrolytic cap currently, with the - on V- and the + at the resistor juncture. I do not have the protection diodes in on the 2 inputs I have wired. The outputs of the LM339 are sitting at ~ V- unless I overload using a 9V battery. I've never used the LM339 before, particularly on dual supplies.

Try posts 312, 315 and 319 and around that area. You do realize that a single balanced dynahi board is 1 channel (+ and -)? Hope you got two boards...

Jocko seems to know his shit with digital/RF. Enjoy it, and mod carefully. Shouldn't be a problem to add a power switch, though this might be best left on. Some of Pass' preamps don't have a power switch (Aleph P for instance). And you can contact Jocko on diyhifi.org, though he is,umm, cantankerous

Happy Birthday!

I was thinking RN60s also, but for some reason they weren't coming up in my search on Mouser. I should have directly looked for them. Also, I have a couple of RN65s and they aren't that huge that with creative lead bending they couldn't work. Though I suppose at these voltages, you don't want to give anything an excuse to arc

Last fall, both HBO and Showtime announced unbundled services would be offered in 2015. It looks like HBO is available (HBO Now). Not sure when Showtime will be. http://www.fool.com/investing/general/2014/11/16/hbo-cbs-and-showtime-are-helping-you-cut-the-cord.aspx I guess if your HBO Go is working, run with it

Yeah, probably a little big current wise as well. They do make 8A also IIRC, but if you need an insulated package, then I guess the parts you guys have identified are the ones to go with. As for > .25W resistors, Mouser does stock Dale RN65 in a 178K, .5W, 350V. I couldn't find the schematic for that particular PSU either, but I only looked briefly.

I've never used their diodes, but just avoid their regulators. This is one I might think about using, unless someone sees something that doesn't meet the parameters required here. 512-RHRP30120

I also avoid ST Micro parts like the plaque. Had some negative regulators from them that didn't work right. National and On Semi parts worked just fine. Diodes I like Fairchild personally, depends on the individual rectifier diode I am looking for.

Happy belated Birthday!

Happy Birthday!

That was pretty much my understanding as well; the cable shield is part of the chassis ground, which may or may not be the same as signal ground. I also recall ground loop interupters, such is what is used on my headamp Gilmore refererence board. Basically a low value resistor (4.7 ohms?) and a cap, tieing board ground to chassis. I don't see this done much anymore, unless I haven't been paying attention. GND LOOP CAPACITOR 1 DIGIKEY EF4104 GND LOOP RESISTOR 1 MOUSER 280-CR5-4.7 EDIT: probably shouldn't have made the topic so cryptic