Attenuator Line Out Squealing

[JamesCardoza]

Hey everyone, here is an issue that I’ve been having recently.

I have my rig set up to run in W/D/W using a THD Hotplate as the line out from my amp (Mesa Mark IV). PBC Inputs 1-6 are run in the front of the amp, and 7-10 are routed to be fed from the Hotplate, and then run direct to FOH from the GFI systems cabzeus.

This system works great with a homemade Speaker/Line out converter box I made, which has a ground lift and level control. But when I use the Hotplate, I get this ungodly squealing sound. The sound is present even when the Hotplate is on the dummy load setting.

I’ve tried this set up with other amps, single Channel amps mainly, and don’t have any of these issues when I’m running mono with my wet effects in the amps FX loop.

Is this as simple as an exaggerated ground loop between the board, amp, and Attenuator? Would it be worthwhile to have a ground loft added to the Hotplate (once I determine if it’s at the speaker in, line out, or speaker out section)?

Any help is appreciated.

Here is a picture for reference.

 

[eljodon]

This is a common issue when using a dummy load especially if you get close to the amp. I ended up buying a GigRig Humdinger which is actually a box for running 2 amps and it has an isolated transformer plus a phase switch and it worked for me quite well. The more gain you use the more "squeal" you'll get.
I recommend getting a Suhr Reactive Load which will sound much better than anything out there. I've used several dummy loads for 30 years since I've always liked running my amps through a tube power amp live (using many different types of dummy loads that where built for me) because it gives me the flexibility to turn my amps to their "sweet spot" or using a NMV Plexi cranked up to 10. It also gives me more flexibility when using effects. I've rarely used a W/D/W system since I like to eq the signal after the dummy load. Also, sometimes a bad or cheap cable can cause this problem. I hope you can solve this problem because it can be very annoying!