Trying to avoid ground loop hum

[dai h.]

from the accutronics site:

Untitled Document

2. As with all low level audio circuits, care should be exercised with the circuit design and grounding techniques. Accutronics offers all combinations of input and output insulated and non-insulated phono jack connectors, for any grounding scheme. The best system, and the most applicable, is to insulate both the input and output from the chassis, grounding the chassis separately.

Steve(or anyone), where do the currents flow as re: the tank?

http://www.accutronicsreverb.com/des..._05/drive1.pdf

The front and back just look like (the signal current) goes through the windings, but what about the springs? Has to go through the springs (signal experiences delay) but which way do they come back (since everything has to go and come back)?

[Steve Conner]

Dai: What travels through the springs is sound waves, not electric current. They're purely mechanical and not part of any electrical circuit.

The tank just needs to be grounded so that the metalwork can shield the receiving coil.

[dai h.]

wow that was quick thanks.

What travels through the springs is sound waves, not electric current. They're purely mechanical and not part of any electrical circuit.

so, would it be like the 'two paper cups and string' (ear to ear) experiment you do as a kid?

The tank just needs to be grounded so that the metalwork can shield the receiving coil.

I gather the same care as with a transformer needs to be taken (orientation, distance) to hum induction into the tank from noise sources (since there are coils). (Oh, and small weak signals needing the protection/shielding via the metal housing and shielded in/out cable. Wonder if there is such a thing as a hum bucking tank...)

[Chuck H]

so, would it be like the 'two paper cups and string' (ear to ear) experiment you do as a kid?

Yup. Think of the input like a speaker motor that has no cone to shake, but springs instead. At the other end you need to re-amplify the voltage produced in that coil by the vibrating springs.

I gather the same care as with a transformer needs to be taken (orientation, distance) to hum induction into the tank from noise sources (since there are coils). (Oh, and small weak signals needing the protection/shielding via the metal housing and shielded in/out cable. Wonder if there is such a thing as a hum bucking tank...)

Sounds like a good idea to me I grounded everything but the output coil - (and consequently it's shield) to the - of the isolated phone jaks. I grounded the output coil to the re-amp chassis. The tank # I indicate in the schem represents an isolated output jack. Though I isolated mine by refabricating it.

As for EMF, I once built a head style amp with reverb. Of course it hummed if I just jammed the tank into the head. But the EMF of a transformer isn't uniform so I was able to scootch the tank around and find a quiet spot. One inch in either direction and it hummed. But silent in the right spot. All kinds of things happen with EMF and it's possible I either found a void in the field or a spot that phase cancelled the hum or a combination of the two. The trick would be repeating this performance predictably.

Chuck

[Chuck H]

P.S.

A special nod and thank you to Jon Wilder. I realize now that the ground scheme I'm using was his original suggestion. Steve's post somehow got through and ultimately it was my own observations based on these two posts that got me to my solution.

Thank you

Chuck