ADA Preamps > MP-1 Classic

Pops and clicks when switching from one program to another

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StarfishPhoenix:
Hi guys! when I switch between programs I get a pop and a massive difference in volume, I've tried several sets of valves but it makes no difference. I have reset it to factory presets for reference. starting from patch 01 (Quiet patch) switch to 02 with a loud pop (Much louder patch) switch to 03 with a quieter pop (quiet patch), you get the picture (I hope).

Any idea whats causing this?

StarfishPhoenix:
*UPDATE*

I have replaced resistor 151 and resistor 382 and I still have rumble, no top end on tube patches, severely reduced tube patch volume and loud popping between patches.

rnolan:
Hey StarfishPhoenix, sorry I missed you initial post  :facepalm: . So as we are in the MP1 Classic area I'm assuming that's what you have ?  I haven't used or had much to do with the MP1 Classic but as it came after the MP2 some features are similar/the same.  I get the same loud pop with my MP2 these days changing from clean voice to higher gain voice (I'm not sure if it's related but the Classic is a bit of a hybrid of the MP1 and MP2).  It sounds to me there is some issues with the tube biasing switching when changing voices (as in the tube voicings are created by changing parameters around the tubes (eg bias, eq, gain etc in the 4 tube triode gain stages, this is "partly" how ADA get so many different voices from 2 x 12AX7s (twin triode = 2 x triodes (gain stages) per tube, so 3 tube voices in your case and 10 in my MP2s).
Questions to try to narrow it down (BTW this is much more MJMP territory):
If you change between SS voice patches is there any issue ? (ie no tubes involved)
If you change between patches with the same tube voice (eg clean tube or Brown tube overdrive etc), do they work OK ?? is it ok when you go patch to patch with same voice ?
If you dial in say 3 patches, one for each voice (2, 3 & 4), do they work ok individually ??
Are you using the stage outputs or the cab sim outs (cab sim outs will reduce top end as they are designed to plug into desk/recording etc with full range speakers, not guitar cabs) ?

StarfishPhoenix:
Yes its a classic, I bought it not too long ago and it had a modified eq section to boost top end. the mod wasn't done by either the previous owner or myself but I did reverse the modification as it was horrendous to listen to and after testing it was working fine for well into a year before it was removed from the previous owners live rack and stored in a studio rack.

if I start with an SS patch it is clean, loud and bright with no problems altering eq to suit

when I switch to any tube voice there is a small pop, some minor rumble and static which increases with gain, noticeably quieter. if I switch between a patch that has the same voicing there is no pop but if I switch between voicing I get a pop.

Only the SS patch works correctly but when switching to SS from any tube patch I get a pop that clips the master and eq LED. the patches work individually in a way but anything tube related is lower in volume and noisy with rumble.

at first I was testing using the headphones output with and without cab sim but now I have it straight out of stage A output into half of my Peavey Classic 50/50.

I have spoken to MJMP though email and upon recommendation have replaced a few resistors that are usually suspect and re capped the power section.

I had a feeling my post got missed :) No problem though, I was going to use this MP-1 Classic in the studio next month but as a precaution I have dusted off my old Digitech 2101 and a few amps I had in storage so I have a selection of tones and effects.

rnolan:
Hey SP, so as SS works, all is good in the signal chain to the outputs (patch master vol works, eq works, chorus works ?, output works) and it's something to do with the tube section.  IIRC you ruled out tubes by trying a multitude of (known ?) good tubes. So this points to other things in the tube circuit (MJMP chime in anytime you like here).  I assume there are trim pots in the tube section (to adjust overall gain in each tube stage) as there are in MP1 and MP2.  It's worth trying cleaning the trim pots and giving them a few full up down tweaks to clean the tracks (it may be all that's wrong  :dunno: and probably something we all should do from time to time as they are exposed (probably as part of a tube change and/or when we are cleaning contacts jacks etc).  With some direction from MJMP, you should measure voltages around the tubes to ensure it's not power related.  You may be able to pin point it by trying different voice and OD 1 & 2 settings.  So the OD 1 & 2 settings in a patch change the gain in each tube (OD 1 for tube 1 and OD 2 for tube 2). So there is a thingy (MJMP will know) that accepts a number (via switching/digital input ?) that the patch is set to (eg 6.3), this controls another thingy which "actually" controls the signal gain in that tubes circuit (probably input gain ???).  If you pick a tube patch and scroll OD1 up and down, and then OD 2 up an down and they work/flow smoothly as expected (ie more/less gain/distortion) then I suspect an issue with the tube voicing "sub" circuits.
The voicing settings, again, use switching input from the patch to adjust various thingys in the tube circuit. From what I understand, they affect tube bias and eq (there is preset eq applied within the tube circuits to "flavour" the tone and create the "voice" (as do boogie and fender amps, but they locate their tone controls in the tube "stack", ADA voices are preset (partly to "mimic" them).
So I'm just trying to narrow in on the issue, partly by ruling various things out.

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