I know the ICE is in the preamp. All three channels too. Tweed, Edge, and all voices of CH3. It sounds like breaking glass inside your ear drum. It could be GEQ related, which I believe to be the case. This is what the output looked like on the send jack with a 750Hz sinusoid signal on the front end at 700mV. The green trace is the output. Note the postive sharp peaks on the leading edge of the distorted wave form. the negative signal looks correct, not flat, has some harmonic content and no sharp edges. I had assumed it was V4B crapping out or not behaving properly but it could also be V5A since the phase changes when it passes through a gain stage. Not sure on the phase change of the GEQ circuit (it was turned off but the differential amp is still used to make the FX send signal on its final transistor stage). That is ice pick. What throws me off is the decay rate practically do zero after the first impulse. Look more like a cap discharge curve. The Boss pedal was used in its bypass mode. Also, it can handle the line level signals as I did the same thing with the TC50. IT was also one of the pedals that did not suck in the Mark V90. Figured it was ok to have that in the circuit as I did not want the cable unloaded.
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JP2C under the same conditions looks normal to me. It is an asymmetrical distortion. the positive transition has more of a square shape but the edges are rounded indicating a roll off of upper harmonics. There is some ripple in that as well which is related to the generated harmonics. The only difference, the Send signal does not pass through the GEQ circuit with the JP2C, it is a tube driven circuit. GEQ runs after the FX loop. I will have to look into things a bit deeper. Something must have crapped out in the GEQ or is not properly soldered in the Mark V90. It never sounded good from the start, first thought the ICE was from the power section, sure it was overheating and eating power tubes. I was sort of in a desperate time when I got that amp in the first place. Lets just say I was going through a major change in my life that was difficult to deal with.
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The clean channel has a much higher output level than the gain channels. No compression or distortion. Everything was at noon except for the channel masters, those were dialed out. Did much the same with the V, but had to run the volumes up as they are in front of the FX loop. the global volume was dialed out. Nothing worse than hearing a single frequency through a speaker. Not very appealing even when distorted.
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