I am building a 4 channel tube preamp based on the REDD-47
If any of the channels is left without input load termination, there is noise on all the channels outputs.
Without input transformer secondary load resistor the noise is 2KHz and upper harmonics. If I add a 130K resistor across transformer secondary, the noise is at 20KHz
The noise disappears if I connect a 150 ohm resistor across the input transformer primary. But obviously it is not ideal having to keep mics plugged in all channels at all time to obtain noise free operation.
Should I tweak the transformer secondary load resistor or perhaps add a zobel network ?
I assume the noise is coupled to the audio path via the chassis ground because I tried powering the non terminated channel from a completely separate power supply and the noise stayed the same, but the channels were still grounded on the same chassis.
If any of the channels is left without input load termination, there is noise on all the channels outputs.
Without input transformer secondary load resistor the noise is 2KHz and upper harmonics. If I add a 130K resistor across transformer secondary, the noise is at 20KHz
The noise disappears if I connect a 150 ohm resistor across the input transformer primary. But obviously it is not ideal having to keep mics plugged in all channels at all time to obtain noise free operation.
Should I tweak the transformer secondary load resistor or perhaps add a zobel network ?
I assume the noise is coupled to the audio path via the chassis ground because I tried powering the non terminated channel from a completely separate power supply and the noise stayed the same, but the channels were still grounded on the same chassis.
