Crunchy horrible sound Mod Duo X except when bypassed

Hi Guys,

Again, I am having trouble with my Mod Duo X.
It is much like the problem I had before: Mod Duo X problem no sound only when bypass

I am using loop 1 in the send/return loop of my amplifier.

  • When not connecting the Mod Duo X in that send/return loop → perfect sound
  • When connecting the MDX loop 1 in that send/return loop, and bypassing loop 1 → perfect sound
  • When connecting MDX in loop 1, and pulling just one purple cable from input 1 to output 1 → horrible crunchy sound.

Changing the master volume does not help (changes the volume, but still the sound is horribly distorted).
Input gain is set to 0%.
It gets weirder:
Changing the output volume of loop 1 → has no effect!
Changing the output volume of loop 2 → changes the volume! (but still crunchy output). How is that possible. I really have only loop 1 connected. The loops are not configured in stereo mode.

Changing cables (several ones) did not help. Also when bypassing the loop 1 everything works fine.

Also it happened suddenly. I was recording for a while, and then all of a sudden this happened.

Can anyone help please.

I was about to record the biggest hit ever written, but meanwhile I forgot how it goes…

PS: I made a video of the situation.

Hi @jk_sigtermans,

Sorry to hear you are having this issue.

There is a possibility you are facing a Ground Loop situation. Its a tricky thing to identify so we have put some information here:

If the problem persists, please open a support ticket sending an email to and share the video you made so our staff can help you.



Thank you @Leo_Germani , the ground loop situation might very well be the case. I will follow-up a.s.a.p.

KR Kjeld

@Leo_Germani It was at least the ground loop situation, my audio amplifier was ground lifted. I customized it with a grounded cable and it took away part of the problem.
Still the combination of the Mod Duo X and amplifier, BlueGuitar Amp1, seems not to be stable.
I have send the support team of BluGuitar a message, see if they recognize the problem.
Thank you for (partly) pointing me in the right direction.

Hello @jk_sigtermans,

a friend of mine uses the BluGuitar Amp1 and I have the ModX as well as the Mod. Maybe I can ask him to find the solution. Would you mind to post a picture of your cabling setup and settings as well as the mod pedalboard you use in your setup via pedalboard sharing if it is a special one? What kind of guitar do you play?

If you use the ModX as an effect insert, what is the FX Gain switch position? Manual says as follows:
FX Send-Output and FX-Return Input levels dependent on switching
LOW: -10dBU +/-1dB or 0.7V P2P
HI: +4dBU +/-1dB or 3.46V P2P
FX Send-Output impedance: < 1.3kΩ
FX Return-Input impedance: > 18kΩ

You find the FX Loop level switch on the underside of your BluGuitar amp as shown on page 34/86 in the pdf.

Greetings and God bless, Marius


@mj_prod Thank you Marius. Let me take a little time to replay the problem (if it will occur again) and then I’ll get back here.
About the Amp1: I also have had an answer from the boys at BluGuitar to fiddle with the serial/parallel setting when having the send connected to the return directly (shortcut). They say if in that case, the volume is NOT a little louder in parallel mode, something might be wrong with the Amp1. Will follow up asap.

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@Leo_Germani @mj_prod

The Mod Duo X’s loop 1 is in the send/return loop of the BluGuitar Amp1.
Just for test purposes, I have a pedalboard with only two purple audio cables, one connected from in1 to out1, the other from in2 to out2. Stereo link is off. Output levels are set to 80%, input gain (both) set to 0%. Master vol is 80%.

Changing the effect level loop switch from +4 / -10 dB on the Amp1 changes the volume a bit, but the problem is still there. I use several guitars, it is not the guitar. It is not the cables. The guitar is connected directly to the Amp1 input. Noise gate is off. The rec out/headphone connector of the Amp1 is connected to a USB sound card (stereo cable), which in turn is connected to my laptop (USB) and a audio amplifier (audio). The amp’s footswitch connector is connected to the MDX’s midi out, via the official BluGuitar midi adapter.

Furthermore on the MDX I have a MOD footswitch connected, a USB Bluetooth dongle (not in use), USB cable connected to the laptop. The MIDI in is connected to the sound card directly. So far, all the connections.

Although there was a ground loop situation (which I solved by making sure every device in the loop is connected to ground) and although the parallel/serial test seems to fail at the amp (waiting for a follow up by BluGuitar), I am still thinking the problem could be with the Mod Duo X.

Mostly because the problem is gone when clicking bypass1. So when the MDX loop is in full bypass, in the setup described here above, I get a very clean bypassed guitar sound. When not bypassed, just having a purple cable from in1 to out1 on the virtual pedalboard, the problem is back. Crunchy sound, like with a bad cable, or a bad transistor/amp…
Tested the above with in2/out2, same result.

Another thing is that the signal bypassed is way louder and clearer, then when not bypassed (Why is that?)

Interesting part: the effects are not/hardly noticeable when the amp is in parallel mode. This either gives me the idea there should be some sort of dry/wet mix option on the Amp1 (which I have not found), or the boys at BluGuitar are right and something is wrong with the Amp’s effects loop.
But why, then, do I have a normal sound when the Mod Duo X’s loop is bypassed?

UPDATE: last but not least: the problem seems to occur after having used the Amp1’s overdrive channel, and then changing back to clean (then there’s the crunchy sound). Then after a while (about 15 minutes), the problem is gone. I play a bit, use the overdrive channel, switch back to clean, then the problem is back. So that argument would point to the amp, HOWEVER when I disconnect the MDX from the Amp’s eff loop, the problem is gone immediately.

So, it has something to do with returning from distorted to clean channel, but only when the MDX is connected? Also, the problem disappears when the MDX loop is in bypass mode.
I think something is wrong with the Amp1’s serial/parallel section and effects loop.


@Leo_Germani @mj_prod

BlueGuitar thinks it is definitely NOT the amp.
Also all equipment has the same ground.
Could any of this be caused by my Mod Duo X?
I am going slightly mad here :slight_smile:

Guys, I have now tried it with another amp, a Marshall 80V combo, same problem.
No sound card, just the combo amp with the Mod Duo X in the eff loop, loop level set to 0dB, MDX master vol 80%, both ouput vol at 80%, not stereo linked, both input gain 0%, pedalboard has just a line from in to out (both). Sounds like …s$#@…
Going to find a official Mod support channel now.