Audio source is a via a shielded cable from a 1000:1 current amplifier transformer similar to the one shown below.
If I feed this into a PC sound card line-in, a hi-fi line-in or cheap audio pre-amp modules it works great with very low hum and good signal to noise.
If, however, I connect it to cheap Hi-Z guitar amps of several allegedly different manufacturers (may really be the same) the hum is HUGE and swamps the signal.
Here is the weird part: If I put the transformer into a closed earthed steel biscuit tin (Faraday Cage) even with no primary IT STILL HUMS like a beehive. the hum can be seen on a scope at the input. I suspect that the very high inductance is somehow upsetting a positive feedback impedance raiser in the input stage of the amp.
I have tried with a coupling cap and without and various values of 'damping resistor' with no effect.
My product does need to be connected and work with guitar amps.
Any input welcomed. I do not get why the Faraday Cage does not work. When used with a hi-fi amp the cage does quieten the already low hum.
If I feed this into a PC sound card line-in, a hi-fi line-in or cheap audio pre-amp modules it works great with very low hum and good signal to noise.
If, however, I connect it to cheap Hi-Z guitar amps of several allegedly different manufacturers (may really be the same) the hum is HUGE and swamps the signal.
Here is the weird part: If I put the transformer into a closed earthed steel biscuit tin (Faraday Cage) even with no primary IT STILL HUMS like a beehive. the hum can be seen on a scope at the input. I suspect that the very high inductance is somehow upsetting a positive feedback impedance raiser in the input stage of the amp.
I have tried with a coupling cap and without and various values of 'damping resistor' with no effect.
My product does need to be connected and work with guitar amps.
Any input welcomed. I do not get why the Faraday Cage does not work. When used with a hi-fi amp the cage does quieten the already low hum.