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.