Ground Loop Whine in 4CM with VP-4 + Fryette PS-2A FX Loop (Drive Channels Only)

S

Shagrath

New Member
Hi all,

I'm running into a persistent high-pitched ground loop-type whine when using the Fractal VP-4 in a 4-cable method (4CM) setup. After a lot of testing, I’ve narrowed the issue down to how the Fryette Power Station PS-2A’s FX loop interacts with the VP-4. I’m hoping someone here has insight or has run into something similar.

Rig Overview​

  • Fractal VP-4
    – Powered via its original power brick or Voodoo Lab Pedal Power 3 Plus (same result)
  • Friedman BE-50 Deluxe (main amp)
  • Fryette Power Station PS-2A
    – Used as a reactive load and attenuator for the Friedman
    – FX loop engaged to route signal through the Fractal
  • Orange PPC212 closed-back cab
  • Bright Onion Shifter Switch Patchbox v2 (includes FX loop ground isolation)
  • Power: All devices on the same AC outlet
Cables:
  • Patchbox → amp connections: Cordial CSI 3 PP-Metal
  • Pedalboard → patchbox connections: Ernie Ball Flat Ribbon Patch Cables

Signal Chain (4CM Configuration)​

  1. Guitar → VP-4 Input (L/Mono)
  2. VP-4 Output (L/Mono) → Friedman amp input
  3. Friedman FX Send → Fryette FX Send → VP-4 Input (R)
  4. VP-4 Output (R) → Fryette FX Return → Friedman FX Return

Symptoms​

  • The high-pitched whine only appears when the FX loop is active
  • Only affects gain channels (BE/HBE) – clean is totally quiet
  • Removing the FX loop (running Fractal only in front) = no noise
  • Running 4CM into Friedman FX loop alone = totally clean
  • The issue did not occur with my old pedals (e.g., Strymon Flint, etc.) — only started with the VP-4
  • Fryette sounds better than the Friedman loop with the VP-4, so I’d prefer to use it if possible
  • Strongest noise occurs with VP-4 FX Send → Fryette FX Return
  • Lesser noise also present on Fryette FX Send → VP-4 Input
  • Fryette Ground Lift switch has no effect

Additional Testing​

  • Jumpering FX Send/Return inside the patchbox (removing Fractal from loop) = Fryette is silent
  • Bypassing the patchbox (connecting cables directly to VP-4) = same noise
  • FX Level on Fryette set to LO
  • Global 4CM Routing = Enabled, and presets properly show “4CM 2/2”
  • Bright Onion patchbox is confirmed v2 with FX ground isolation

Questions for the Community / Fractal Staff​

  1. Does the VP-4 internally share ground across the FX Send/Return and Output paths?
  2. Is this kind of ground loop expected behavior when using devices like the Fryette PS-2A in the FX loop?
  3. Would a line-level isolation transformer (e.g., Palmer PLI-05, Radial SB-6) be the appropriate fix?
  4. Are there any known best practices or routing workarounds for using the VP-4 with tube-based gear or reactive loads?

I love the VP-4 and am impressed with its sound and flexibility. The Fryette loop sounds noticeably better than the Friedman’s in this setup — I’d just like to resolve the loop noise so I can keep using it that way.

Thanks in advance for any help,
 
"High-pitched whine" and "ground loop" don't fit together well. Ground loops have lots of low-frequency content. If you're up for more testing...

- When you're hearing the whine, roll your guitar's volume knob all the way down to zero. Is the whine still there?


Nice, thorough description and testing, by the way.
 
I am running 1 VP4 in the front of a TK Tri tube and one in the loop. I observed a high pitched whine when using the drives or running high gain but this is only when the VP4 is hooked up via USB to my computer.
 
Thanks for the kind words and your input — really appreciated.

Regarding the question:

“High-pitched whine” and “ground loop” don’t fit together well... try rolling down your guitar volume knob to zero. Is the whine still there?
Click to expand...
Yes — I’ve now tested with:
  • Guitar volume at zero
  • Amp master volume at zero
And the high-pitched whine still persists. It also occurs even when nothing is plugged into the VP-4 input, which rules out the guitar or front-end pedals as the source.

This issue only occurs when the Fryette PS-2A FX loop is connected to the VP-4 in 4CM. If I bypass the FX loop (jumper the patchbox), or use the Friedman BE-50 Deluxe’s FX loop instead, the noise disappears completely — even with the same cables, gain structure, and routing.

Fryette support confirmed it’s a signal ground loop, not a power loop, and it can cause oscillation or high-frequency whine, not just hum. They recommend using a signal isolator (e.g. Radial SB-6 ) on the FX Send and/or Return lines to break the loop between the VP-4 and the PS-2A.

Everything in my rig is powered from the same AC outlet, and all pedals (including wireless) are running off a Voodoo Lab Pedal Power 3 Plus with isolated outputs. The Fryette’s ground lift switch doesn’t affect the issue, and there’s no USB connected to the VP-4.

Question to the group:
Has anyone found a clean solution for this type of loop without needing a physical isolator in the FX loop?

Would love to hear if anyone solved this through routing, grounding, or settings within Fractal gear — or if a transformer isolator is the only clean way forward.

I have attached the Fryette diagram as this type of thing can happen to multiple amps using the 4 CM.

Thanks again for the support and ideas — much appreciated.
 

Attachments

Shagrath said:
Thanks for the kind words and your input — really appreciated.

Regarding the question:


Yes — I’ve now tested with:
  • Guitar volume at zero
  • Amp master volume at zero
And the high-pitched whine still persists. It also occurs even when nothing is plugged into the VP-4 input, which rules out the guitar or front-end pedals as the source.

This issue only occurs when the Fryette PS-2A FX loop is connected to the VP-4 in 4CM. If I bypass the FX loop (jumper the patchbox), or use the Friedman BE-50 Deluxe’s FX loop instead, the noise disappears completely — even with the same cables, gain structure, and routing.

Fryette support confirmed it’s a signal ground loop, not a power loop, and it can cause oscillation or high-frequency whine, not just hum. They recommend using a signal isolator (e.g. Radial SB-6 ) on the FX Send and/or Return lines to break the loop between the VP-4 and the PS-2A.

Everything in my rig is powered from the same AC outlet, and all pedals (including wireless) are running off a Voodoo Lab Pedal Power 3 Plus with isolated outputs. The Fryette’s ground lift switch doesn’t affect the issue, and there’s no USB connected to the VP-4.

Question to the group:
Has anyone found a clean solution for this type of loop without needing a physical isolator in the FX loop?

Would love to hear if anyone solved this through routing, grounding, or settings within Fractal gear — or if a transformer isolator is the only clean way forward.

I have attached the Fryette diagram as this type of thing can happen to multiple amps using the 4 CM.

Thanks again for the support and ideas — much appreciated.
Click to expand...
The solution is simple.

I always have two LEHLE P-ISO in my accessory bag. And yes, there is no other solution.
The four-cable method is always prone to hum and noise. If you're lucky, it will work fine with your gear, but often you have to take additional measures. I can still remember the TC G-System well. A disaster in this regard.
 
Keybi said:
The solution is simple.

I always have two LEHLE P-ISO in my accessory bag. And yes, there is no other solution.
Click to expand...
In 4CM mode I also use this one between the VP4s OutR and the Return of the Amp. That is enough to get rid of ground loop noise.
I also have a Radial Engineering SB-6, which also works great but this one is more expensive. But it has two channels. Other similar devices will also work if they have galvanic isolation. Just a ground lift is often not enough.
 
Shagrath said:

Signal Chain (4CM Configuration)​

  1. Guitar → VP-4 Input (L/Mono)
  2. VP-4 Output (L/Mono) → Friedman amp input
  3. Friedman FX Send → Fryette FX Send → VP-4 Input (R)
  4. VP-4 Output (R) → Fryette FX Return → Friedman FX Return
Click to expand...
Is this correct? You shouldn't be sending a signal from one Send jack to another Send jack. Likewise with the return jacks.
 
The main issue was the Amp in. I used the Radial Engineering SB-6 for the amp in and the return loop. had to use the ground button on it for the amp in. issue went instantly away.
 
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