Ground loops (?) - creating feedback at high volume

[7enderbender]

Hi there,

I'm pretty much finished with my rack rebuilt and overall quite happy.

Here's what I have in my 8u SKB case right now (wired in this order)

Shure QLXD wireless or cable -> Dunlop Wah, TC tuner, [any pedal I feel like using if any] ->
Triaxis->
DBX 166XL (used as gate, one channel after the Triaxis with less sensitive settings, one in the loop for high gain stuff) ->
TC G-Force->
2:Fifty->
Mesa 2x12 (stereo) cab | Marshall 4x12 (as needed)

So, relatively straight forward, except maybe for the gate setup.

Problem is that I do experience a bit of buzzing on higher gain presets (only noticeable really, when the gates are either manually bypassed or open up). It gets a bit worse with the wireless receiver connected to the Triaxis (especially when running pedals to the front of the stage first and then back). Again, I'm running nothing fancy there.

I could live with a bit of buzz that is than killed by the various gates just fine.

PROBLEM now is that at higher volume, sometimes the high gain channels pick up a ground loop or something and create a feedback that is INDEPENDENT of guitar volume. In other words, it can even kick in when the guitar's volume (not just with one specific one, all of them) is completely rolled off.

Testing this under controlled circumstances at home shows that cranking up the volume on the poweramp can result in high pitched feedback even when no guitar is plugged in or with the wireless transmitter off. Anyone ever experienced this or something like this? Could a ground loop feed back on itself? I checked and swapped the preamp tubes already and carefully tapped all tubes (preamp and 6L6) for being microphonic (negative).

I have a Ebtech hum eliminator on order to see if breaking ground loops where they exist helps. And also some new plastic washers to better isolate devices.

Again, it's manageable with volume not cranked that high (I usually don't play that loud and rather mike my cabs for better control). But I'm afraid that in a place with bad PA, bad power and a need to take it up a notch I may loose control in my higher gain presets at times.

Plus, I'm really not clear why the power amp volume would trigger this, but it wouldn't do it at lower volumes. I have not checked or swapped the preamp tubes in the 2:50 yet. Could those be the culprit at all?

 

[soundguruman]

Hi there,

I'm pretty much finished with my rack rebuilt and overall quite happy.

Here's what I have in my 8u SKB case right now (wired in this order)

Shure QLXD wireless or cable -> Dunlop Wah, TC tuner, [any pedal I feel like using if any] ->
Triaxis->
DBX 166XL (used as gate, one channel after the Triaxis with less sensitive settings, one in the loop for high gain stuff) ->
TC G-Force->
2:Fifty->
Mesa 2x12 (stereo) cab | Marshall 4x12 (as needed)

So, relatively straight forward, except maybe for the gate setup.

Problem is that I do experience a bit of buzzing on higher gain presets (only noticeable really, when the gates are either manually bypassed or open up). It gets a bit worse with the wireless receiver connected to the Triaxis (especially when running pedals to the front of the stage first and then back). Again, I'm running nothing fancy there.

I could live with a bit of buzz that is than killed by the various gates just fine.

PROBLEM now is that at higher volume, sometimes the high gain channels pick up a ground loop or something and create a feedback that is INDEPENDENT of guitar volume. In other words, it can even kick in when the guitar's volume (not just with one specific one, all of them) is completely rolled off.

Testing this under controlled circumstances at home shows that cranking up the volume on the poweramp can result in high pitched feedback even when no guitar is plugged in or with the wireless transmitter off. Anyone ever experienced this or something like this? Could a ground loop feed back on itself? I checked and swapped the preamp tubes already and carefully tapped all tubes (preamp and 6L6) for being microphonic (negative).

I have a Ebtech hum eliminator on order to see if breaking ground loops where they exist helps. And also some new plastic washers to better isolate devices.

Again, it's manageable with volume not cranked that high (I usually don't play that loud and rather mike my cabs for better control). But I'm afraid that in a place with bad PA, bad power and a need to take it up a notch I may loose control in my higher gain presets at times.

Plus, I'm really not clear why the power amp volume would trigger this, but it wouldn't do it at lower volumes. I have not checked or swapped the preamp tubes in the 2:50 yet. Could those be the culprit at all?

You MUST use a professional isolated effects power supply.
Yes, it's probably a ground loop.

Ground loop:
also caused by three prong power cables.
Only ONE of the power cables should be grounded. (at the amp usually)
The rest of the grounds should be lifted (with this)
http://www.amazon.com/45086-3-Prong-2-Prong-Electrical-Adapter/dp/B00166TT3G/ref=sr_1_1/175-5481509-1527406?ie=UTF8&qid=1431363312&sr=8-1&keywords=adapter+2+prong+to+3+prong

Please
DO NOT cut the ground prong off of the power cable, use the adapter instead.