Pres went through test and setup some time ago. They are Rev1.3, circa 2013. Pres were working fine with a dynamic mic and also the Hi-z input. This is the first time I tried phantom power with them with microphones actually hooked up. I wonder if the problem could be with my patch bays...…..
There is normally no connection between R21 and the 48V. But R21 is close to the 48V switch so I would check there is no unwanted connection like a solder bridge or a component lead touching the chassis plate around R21, C6, SW1.
I erroneously identified R21 as the burnt resistor. The burnt resistor is actually R1, which is right beside R21 on the PCB and is indeed in line with the 48volt switch, if I read the schematic correctly. I disassembled the preamp and checked for any obvious build errors and solder bridges, etc. , but everything looks OK. The other four of my MP573 pass 48volts throughout my system without any problem. I checked all wiring to/from mic panels to patch bays, as well as the microphone cables I was using at the time. Any other thoughts where to look?
I built two of these kits and did the setup/calibration. Everything went well and I installed them in my rack. Ran signal to them in-line from a balanced stereo source ( output of a Tascam CD recorder ) and they work fantastically, as expected. I then used them on un-balanced inserts from a stereo bus on my analog desk ( tip=send, ring=return ) and the output is almost non-existent, even turned up full. Tried all eight bus inserts to rule out a bad bus/cabling. Same result on all eight. Will this device not work on an unbalanced insert? Does it need a balanced input and output to work correctly? If so, is there a work-around?
The input and output of the TS500 are transformer balanced.
It does work on unbalanced in/outs but you must make sure both in and out XLR pin 3's are connected to the ground (to TRS shield).
I believe that this is probably not the case in your insert cables. The shield is probably only connected to XLR pin 1.
Your SK99 Op Amps are great! I have tried probably more than 10 different DOAs and hybrid op amps in my console mix bus (CAPI 2-ACA) and yours are the only ones that don't mess with the signal in any way I find objectionable. Thanks!