Volume Box for HRDX hum

[Zouto]

What happens if you insert a jack-jack cable into the send/return? It could be a problem of the loop itself that goes unnoticed when you don't use it.

Patching send and return jacks with a standard guitar cable works fine without any hum/noise. Moving the aluminum box to different positions on top of the amp induces more or less hum, depending on it‘s position in relation to the PT. It obviously picks up hum from PT, no ground loop at all. So I got to find the best position.

[Helmholtz]

obviously picks up hum from PT, no ground loop at all.

Hum induction from the PTs magnetic field into the ground wiring would be the classic hum loop effect. Meanwhile I rather think that you have a shielding problem. Are you sure that all parts of your housing are well grounded? Sometimes lacquer coating prevents good contact.

[Zouto]

Hum induction from the PTs magnetic field into the ground wiring would be the classic hum loop effect. Meanwhile I rather think that you have a shielding problem. Are you sure that all parts of your housing are well grounded? Sometimes lacquer coating prevents good contact.

Thanks. I checked all the boxesˋ ground connections with my trusty Fluke 87 V DMM:
input jackˋs to output jackˋs ground 0,7 Ohms, both to boxesˋ surface 0,7 Ohms, 100K A potˋs grounding lug to in/output jacksˋ ground and boxes surface 0,7 Ohms, potˋs housing to box 0,8 Ohms. So I got no idea whatˋs causing that hum.

[Helmholtz]

Thanks. I checked all the boxesˋ ground connections with my trusty Fluke 87 V DMM

Does this include both parts (cover and bottom) of your housing?
You might have as well some shield problem with one of the cables.

[Zouto]

Does this include both parts (cover and bottom) of your housing?
You might have as well some shield problem with one of the cables.

Yes, the complete housing is connected to the jacksˋ ground, 0,7 Ohms. I tried four or five different high end cables like Vovox, George L, SommerCable etc., I got that hum with all of ˋem.

[Helmholtz]

Are we still speaking about hum with no instrument connected to the amp's input?

[Zouto]

Are we still speaking about hum with no instrument connected to the amp's input?

Yes, nothing plugged in and all controls at 0. Turning on volume and tone pots just add a little hiss etc. without any change in overall hum from volume box near PT.

[nosaj]

Yes, nothing plugged in and all controls at 0. Turning on volume and tone pots just add a little hiss etc. without any change in overall hum from volume box near PT.

How about for something completely different. Do you have another amp with a send /recieve or even a mixer board?

nosaj

[Zouto]

No, I have no other amp with an FX loop, but I‘ll check the box on a friendˋs HRDX tomorrow. I‘m eager to hear what will happen....

[Zouto]

Checking the box on two different HRDXs I got the same olˋ hum on both of ˋem. Moving it to different positions on top of the amps I could find a hum-free spot. Obviously the hum is induced by the PT, occuring in the same way on three different HRDXs.

[Helmholtz]

Could you post a picture of the innards of your box?

[Zouto]

Could you post a picture of the innards of your box?

Yes, here we are:

[Helmholtz]

Actually I am at a loss. Just for completeness you might try to directly connect the ground lugs of the jacks by a wire and maybe even ground the pot housing.

[The Dude]

It maybe says in the thread, but I couldn't find it skim reading. What value potentiometer are you using?

[Zouto]

It maybe says in the thread, but I couldn't find it skim reading. What value potentiometer are you using?

Itˋs an Alpha 100K A pot, the box hums even with the pot turned off completely.