Reply To: How to test universal preamp

[Dinx]

Short update: When I increase volume on R8 the hum appears, getting more and more loud as I increase volume with R8 dial. Very quiet when R8 at lower volume dial level and volume controlled with universal pre-amp. My understanding is that on PRE-IN the R8 is full power with volume controlled by universal pre-amp. Just to clarify: I purchased the PCB’s and R-Core transformer from you. In hind sight I should have chosen the one with 6.3 volt aux output (blue wires). I got the 15 volt model so I cannot at least try with AC for the heaters. Tried 4 x AA batteries. A good part of hum disappears, but still very audible. (Tried all of your suggestions) Next I will try star ground further away from power supply PCB’s. Might try 2 resistor voltage splitter on 12VDC SMPS. Eventually I will git’r done… Thanks