Ground loop breaker and unbalanced connections

[abbey road d enfer]

So I tried it with a TL071, with a 680n cap between input and R11 to AC couple the input. only I changed R12 from to 100K to 1Meg, I not sure if it is subjective but I feel there was a bit more high-end (tested with a guitar).

That's correct; the electric guitar has been designed in conjunction with amp that had 1 Meg input impedance. It's still today the recommended impedance for passive guitars (even more so for humbucker-equipped guitars).

  It works very well and sounds good, it's even strange not to get hum when switching to single coils on a strat.

It's a coincidence. Hum on single-coils is due to the magnetic field; as I wrote earlier, grounding is no help against magnetic fields.

 

[CJ]

many amps are using that input cap nowadays,  may or may not negate bad effects of turning down the guitar vol pot which can load down input circuit,

here is a Marshall input circuit  for an acoustic git amp that might give you some ideas, has xlr+1/4">

 

[saint gillis]

It's a coincidence. Hum on single-coils is due to the magnetic field; as I wrote earlier, grounding is no help against magnetic fields.

Ok

many amps are using that input cap nowadays,  may or may not negate bad effects of turning down the guitar vol pot which can load down input circuit,

Ok, I will check what happens with the volume down on the guitar.

 

[abbey road d enfer]

many amps are using that input cap nowadays, 

Which one?

 

[saint gillis]

many amps are using that input cap nowadays,  may or may not negate bad effects of turning down the guitar vol pot which can load down input circuit.

I must say there was a tiny difference of sound with or without the input cap with the guitar volume very low, but it was at the limit of subjectivity, and the difference of timbre between high and low volume guitar pot is so bigger than the difference of timbre between with or without input cap... So I think it's very acceptable, maybe put 1µ instead of 680n..

 

[abbey road d enfer]

I must say there was a tiny difference of sound with or without the input cap with the guitar volume very low, but it was at the limit of subjectivity, and the difference of timbre between high and low volume guitar pot is so bigger than the difference of timbre between with or without input cap... So I think it's very acceptable, maybe put 1µ instead of 680n..

680nF with 1Megohm introduce a pole at 0.23 Hz. The response of your amp is probably more than 90dB down at this frequency, your ears too. I suspect autosuggestion...

 

[saint gillis]

680nF with 1Megohm introduce a pole at 0.23 Hz. The response of your amp is probably more than 90dB down at this frequency, your ears too. I suspect autosuggestion...

Obviously. I suspected some interaction with the resistance of the volume knob, but as the voltage divider is before the cap it is true that they can't form a filter..