PBC Tone Suck from Parallel FX loop/line mixer? And grounding issues

Hey Ron,

So just had a custom pedalboard build with a PBC10, with loops 7-10 running in parallel to my Diezel VH4S amp’s Parallel FX loop and am experiencing some tone suck that my previous set up did not have. I’ve narrowed the tone suck to being something in the parallel FX loop, and not anything before the amps input. So either at the PBC10’s internal line mixer, or the custom passive pass thru box on my board my tech here made for me. Wanted to pick your brain on some possible causes/solutions as it’s a bit outside me and my techs experience level.

Worth noting, the first issue we ran into was lots of ground loop noise in the FX loop send/returns that my previous setup didn’t have at all. My previous setup used a passive analog signal splitter to split send from amp into my separate reverb/delay pedals, then the outs of each pedal went into a $100 6 channel Yamaha submixer. And then the left/right out of the Submixer went back into the amp. This set up, though a bit clunky, sounded phenomenal, with NO ground loop issues. So was a bit surprised when my thousand dollar PBC10 suddenly was having huge ground loop noise issues. After doing some research on these forums, my tech added some ground lift switches at every send/return to the amp in the custom pass thru box on my new pedal board as a fix. The best results being, ground not lifted for Amp input, and ground lifts lifted for the amp send, and the left/right efx returns.

This eliminated most of the ground loop noise, however it’s still noisier than my previous set up :(. Also getting a subtle ground loop noise that only happens as you sweep the volume pedal(plugged into insert 1 on pbc.) This sweeping ground noise is mostly noticeable on high gain channels, we tried different volume pedals and also experimented with removing the ground on a custom patch cable from volume pedal to PBC, with no change in result, so that’s a bit confusing as to what's causing that noise.

The other more frustrating issue in comparison to my previous setup is there’s subtle but noticeable tone suck, (slight volume drop, and the dimension of the tone is slightly smaller and not as wide, delay trails don’t feel as separated, rich, and clean, also sounds like there's some digital clipping happening somehow from the parallel fx, mostly noticeable from the delay/timeline.)

If I bypass the Custom Pass thru box and PBC10 parallel loops, and plug my amps parallel FX send directly into timeline, and then timeline back into amp FX returns, issue goes away, and tone is huuuge again. So it’s either something to do with the line mixer on the PBC10, or the custom passive pass thru box. Though everything on the Custom Passive pass thru box looks like its correct. Do you know if having to run multiple ground lifts would cause this tone suck? Would high headroom buffers at the FX send returns from pedal board be a fix for that? Or is it something inherent or defective on my PBC10? Any other ideas what would cause tone suck?

For cabling we're using Evidence Monorail with SPS7 TRS connectors. Now they are sharing a ground naturally, could that be a cause of some of the tone suck?

Rig:


Guitar
-> buffer
RJM PBC10
L1 - Cali76 compressor
L2 - PitchFork
L3 - Mobius(mono)
L4 - empty
Out 1-4 - Volume Pedal Send(Ernie Ball 6165)
IN 5-6 - Volume pedal Return(Getting ground loop hum)
L5 - empty
L6 - empty
OUT 5-6 Diezel VH4S Amp Input
In 7-10 - Diezel VH4S Amp FX Send to PBC
L7 - empty
L8 - Timeline (parallel)
L9 - Bigsky (parallel)
L10 - Mercury 7 (parallel)
OUT A/B - Diezel VH4S Stereo Parallel FX Return (Getting ground loop hum)

Thanks Ron!
 
It's pretty hard to say what's going on there without being there to debug it. You need to tackle things one issue at a time.

First thing - is the dry signal turned on in the PBC? If so, you should turn it off if you already have it in a parallel loop.

The volume pedal issue sounds like a ground is missing somewhere. Do you get more noise in certain pedal positions than others?

What happens to the sound if you turn off loops 8-10?
 
Hey Ron,

Thanks for getting back to me.

Yes dry signals are turned off for each parallel loop. And all the pedals in parallel loops are in kill dry mode. So shouldn't be any phasing issues from that. Also I did experiment with turning buffers on and off from the PBC, but buffers bypassed on PBC still sounded better to my ears.

The volume pedal issue, yes, it gets more noise when in the in between full and off positions. We tried two different Ernie ball pedals with same noise coming through both, we swapped cables, and even tried a custom patch cable with ground lifted, and same noise issue persisted. Its not really noticeable on my clean/lower gain channels, but becomes more obvious on high gain channels, naturally. However, in my previous set up this wasn't an issue, so the variable seems to be the PBC10 or cabling, but we tried different cable options to no avail, so that's what makes me lean toward something with PBC?

Turning off loops 8-10, the dimension and depth of tone stay the same, which would seem to hint at the cabling or the custom passive pass thru box? So maybe something to try is bypass the custom pass thru box, and go straight from the PBC to amp...however I won't have the ground lifts in signal chain anymore, so will have that blaring ground noise issue in the way.

Here's a link to some pics to pedalboard setup if this is of any help. Let me know what you think to try next from here, thanks so much Ron!

Nick

 
Does the pass thru box have isolation transformers in it, or does it just lift grounds?
 
When you say this, do you mean that it's the same as when loops 8-10 are turned on, or the same as when there's no PBC in the loop?
Its the same as when loops 8-10 are turned on, but NOT the same when PBC/Pass thru box are taken completely out of the signal chain.

The only way for me to do that without getting ground loop issue is to just plug my effects loop send from amp into a single pedal, which I use my Timeline for this A/B test, and just going straight into the timeline and then back to amp in the parallel FX loop is where I notice the difference in tone. Its wider, deeper, like bigger dimension, a little bit louder volume, and the delay trails sound richer, more full frequency response, clearer separation etc.
 
If the problem still occurs when all loops and buffers are off, then I'm at a loss. At that point, all of the PBC's active circuitry is out of the signal path. It's just relays at that point, and there isn't much effect they can have on your signal except to turn it off entirely.
 
If the problem still occurs when all loops and buffers are off, then I'm at a loss. At that point, all of the PBC's active circuitry is out of the signal path. It's just relays at that point, and there isn't much effect they can have on your signal except to turn it off entirely.
Interesting, ok.

Couple questions I have from here, how does the PBC split the signal in the Parallel loop section of PBC? Is it possible there's some signal loss/degredation there when loops 8-10 are on?

Do you think transformers at the passive pass thru box would be helpful?

Thanks for your time/help with this Ron.
 
If loops 7-10 are turned off, no splitting is going on at all. But, when one or more parallel loops is turned on, then the dry signal feed is split to feed any active parallel loops (and the mixer, if dry signal is enabled). This would only be a problem if the amp's effect loop is not great and you're not using any buffers.

I mentioned transformers because they can be the cause of problems of exactly the type you describe. Lifting grounds is a better approach, from a tone standpoint.
 
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