Reply To: How to test universal preamp

[Dinx]

Hi Jim. As you predicted, I am experiencing a 60hz hum from both channels. I just cannot seem to find where the problem is. At first I thought it might be coming from the little transformer feeding the motorized pot, but when I took it completely out of the circuit, it did not make a difference. I am having difficulty in interpreting some of your instructions however: on the Power Supply drawing Note 9 you state ´NO Preamp or RCA Grounds. However, on your as built pictures the ground from RCÀs go to the star ground point, so that is what I did. Hum. On J4 I tried grounding negative straight to star chassis ground, then B- with same results. I feel it is so close, but yet everything I have tried results in a 60hz hum. My B+ voltages are 295.7 and 295.4. P2: 194 and 195. P6: 13.6 and 13.7. P3: 6.11 vdc. Would appreciate your thoughts and input. Warm regards, Gilbert Lessard