I need some assistance from this amazing body of knowledge. I will try to make this not longer than it needs to be.
I have a hum that occurs when the preamp is in the circuit. When I use the DAC output (W-4 S DAC – 2) and connect directly to my amplifiers, Manley NeoClassic 250 mono blocks, the system is dead silent.
If I take two sets of interconnect and connect them with a coupler from DAC to amps, it is still dead quiet.
When I replace the couplers with the preamp there is an audible hum, whether the preamp is turned on, turned off, or if the power cord is entirely disconnected. The hum is at the same volume level in all three conditions.
Suspecting some kind of a common problem within the preamp I use one coupler and then only one channel of the preamp. I still get the same result on the channel with the preamp.
The hum is not as loud as an open input, nor as loud as a faulty(open) ground .
The preamp is a simple line tube preamp, with dual modo construction, using tube regulation and to rectification, and two tubes per channel for gain. It has four relay switched inputs, and one volume pot.
Because the hum level is the same whether one channel or both channels are used, whether the preamp is on or off, or whether a power cord is connected or not, I suspect that there is some kind of a grounding problem with in the preamp that allows an induced hum from some sort of lack of shielding.
Thank you in advance for any responses. I am flummoxed.