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Let's Get Technical => All PREAMP Tech Tips & Support => Topic started by: Hanneman213 on January 12, 2020, 11:47:16 PM

Title: MP2 Instant Volume Increase
Post by: Hanneman213 on January 12, 2020, 11:47:16 PM
This problem repeated. I dont think that its a tube related problem. I changed both with 12ax7 Tung sol's in 04/2018 and I did not play too much since that date. I replaced them each other. But The problem continues.

When I am playing, the sound Instantly Increases like you turn up the volume or you press a tube screamer. Then it turns back normal levels and gain.

What the problem can be ?
Title: Re: MP2 Instant Volume Increase
Post by: vansinn on January 13, 2020, 01:21:52 AM
Uh oh..  a very careful guess is one the vactrols controlling how various levels gets defined has gone bad.
No doubt MJMP will chime in on this.
Title: Re: MP2 Instant Volume Increase
Post by: MarshallJMP on January 13, 2020, 05:13:13 AM
Does this happen on all voicings?
Title: Re: MP2 Instant Volume Increase
Post by: Hanneman213 on January 13, 2020, 05:42:24 AM
Good question. It did not come to my mind. I will check it at home. I use Warm Hi gain mostly. I will check it also in cleans.
Title: Re: MP2 Instant Volume Increase
Post by: Hanneman213 on January 13, 2020, 10:21:25 AM
I spent sometime to get problem again. Because it has an irregular timing. The problem is happening on crunch voicings. Sounds increases and decreases with a wavy motion.
And one more thing. The display screen can not be visible with a straight front angle. I can see it with like 45 degree angle from a side.
Title: Re: MP2 Instant Volume Increase
Post by: rnolan on January 14, 2020, 12:12:23 AM
The display screen is an easy fix, it uses the same one as Quadverb and a few other gadgets, even comes in various colours, just be careful around the ribbon cable.  There's some posts about it from a while ago.In recent discussions regarding using the loop returns for other preamps to pick up the cab sims (and I thought the tremolo as well as that's what the signal flow diagram in the manual indicates) MJMP said the volume vactrol was also used for/by the tremolo, maybe an/the issue ?  Just a guess based on it being a wavy motion.
Title: Re: MP2 Instant Volume Increase
Post by: Dante on January 14, 2020, 08:40:33 PM
I have been battling this for a while now. I keep thinking it's a bad jack or cord, or whatever. Now, I'm convinced it's not.

Honestly, it's one of the reasons I don't use my MP2 live anymore. That, and the fact that I've beaten the crap out of it so much that it's now delicate.

Let's see if this gets worked out...I'm much better with a soldering iron now.
Title: Re: MP2 Instant Volume Increase
Post by: vansinn on January 14, 2020, 09:28:25 PM
Generally, I'm thinking:
If signal goes up'n'down non-rhythmically, it's likely related to bad connections, soldering..
If signal does it rhythmically, it's likely caused by an oscillating circuitry, involving a capacitor.
If [dialed-in]distortion/gain remains constant, it likely isn't in the tube gain-staging section.

I have a problem seeing this problem located with the main volume vactrol; even though this one also does the tremolo effect, this is controlled by an algorithm in the software and I cannot see how such an code snippet can become unstable.

Over time, we've seen several issues with the compressor circuitry.
When this signal gain wobbling problems is present, is the compressor set active?

Another potential: When touching the various inst/line-level switches on the back panel, does gain stay constant, or does is result in flickering gain + scratching noises?
Title: Re: MP2 Instant Volume Increase
Post by: MarshallJMP on January 15, 2020, 07:47:12 AM
If it's the vactrol it should happen on all voicings. To be clear you hear volume changes not gain changes?

As for the lcd, try to connect disconnect the grey flat cable a few times on both ends.
Title: Re: MP2 Instant Volume Increase
Post by: Hanneman213 on January 16, 2020, 12:53:52 AM
Volume increases and my classic tight ''metallica sound''  becomes like a Marshall MG 10
Title: Re: MP2 Instant Volume Increase
Post by: Kim on January 16, 2020, 03:54:36 AM
I have what appears to be the same problem with both my MP-2s.
In my case, it seems that the Loop jacks are the culprit, as wiggling around/plugging/unplugging seems to "fix" the issue.  I may need to source new jacks if a good contact cleaning doesn't help.

Btw, it's exactly what you described; suddenly the volume jumps tremendously with a complete wash of ugly harsh fuzz and mess....
Title: Re: MP2 Instant Volume Increase
Post by: MarshallJMP on January 16, 2020, 12:02:39 PM
Kim, this could also be the loop gain switches.

Hanneman, so the sound also changes?
Title: Re: MP2 Instant Volume Increase
Post by: vansinn on January 16, 2020, 08:34:53 PM
One of my MP2's has known bad gain switches (the push-type ones on the backside).
While it doesn't sporadically change gains, it nevertheless doesn't have constant gain.
Massaging those switches cures the problem - for a while..

Corrosion in switches, jacks and potmeters can manifest in weird ways ,ile gain changes.
A corroded contact point can behave as both a resistance and a diode stretch, causing gain drops, noise and distortion.

Clean and/or replace - remember, we're dealing with fairly old electronics that does need maintenance.
Title: Re: MP2 Instant Volume Increase
Post by: rnolan on January 16, 2020, 10:53:42 PM
I've had issues in the past with my studio MP2 where I lost a channel (Cab sim outs), the culprit seemed to be one of the push switches, seems they need a clean from time to time.
Title: Re: MP2 Instant Volume Increase
Post by: Hanneman213 on January 23, 2020, 06:05:59 AM
I changed the patch cable ( which I bought new) with my another old one and as yet, I hear no problem. I think, I'm gonna wind around the seller with it.
Title: Re: MP2 Instant Volume Increase
Post by: Dante on January 25, 2020, 04:56:27 PM
I did that too, but it only worked temporarily. I cleaned the jacks with de-oxit (then inserting/pulling out a cord 1,000 times)
Title: Re: MP2 Instant Volume Increase
Post by: Kim on January 26, 2020, 07:58:40 AM
I changed the patch cable ( which I bought new) with my another old one and as yet, I hear no problem.....

I did that too, but it only worked temporarily. I cleaned the jacks with de-oxit (then inserting/pulling out a cord 1,000 times)

My #1 MP-2 started doing this about 2 months ago, seemingly at random.  I cleaned the jacks and switches as best I could and hoped for the best.  However, it still happened randomly so I bought another MP-2 for backup.  Wouldn't you know, the #2 unit did the same thing.    :(
Now, I'm experimenting by actually using BOTH MP-2s in my Live Rig.  #1 is used as a preamp/compressor for the EHX "9" pedal section of my rig, and #2 is my guitar preamp.  #1 has nothing in its Loops, and is currently working flawlessly there.  #2 continued to do the Volume Increase at random, and it is using the Loops.  The last time it happened, I reached back there and wiggled stuff around while it was acting up and appeared that one of the patch cables was causing it.  I pulled that particular pair of cables (shit Radio Shack ones) out and replaced them with new cables of a better quality.  Since then, it has only happened once so far and just a little wiggle of the cable inside the jack fixed it.   

I have concluded that the problem must be within the jack itself, and not the cables or switch.
Title: Re: MP2 Instant Volume Increase
Post by: Dante on February 01, 2020, 09:00:11 AM
I have concluded that the problem must be within the jack itself, and not the cables or switch.

I have to agree. I came to the same conclusion with mine, but I just stopped using it. It embarrassed me at a gig and that was it  :nono:
Title: Re: MP2 Instant Volume Increase
Post by: MarshallJMP on February 03, 2020, 03:21:26 PM
What happends if you set the loop to off?
Title: Re: MP2 Instant Volume Increase
Post by: Kim on February 06, 2020, 06:55:14 PM
What happends if you set the loop to off?

I haven't tried that, but I will remember to check that whenever the problem comes back again.   :wave:
Title: Re: MP2 Instant Volume Increase
Post by: Hanneman213 on February 06, 2020, 11:24:11 PM
Update; I was very happy to solve this one, yesterday I was having fun with my new Mooer Radar with various Impulse responses through headphone, but it repeated. Tried 3 different cables, all 4 outputs (including recording outputs). It was random. I was doing it though my TC Gmajor 2, ( when I play with headphones Tc began to be noisy  :facepalm:)
I activated noise gate of tc. Later I plugged MP2 Only. The Noise gone, gain turned back and first I thought the problem was on G Major2. But The problem repeated again  I was about to burn and throw it from the window. Left them simply, without gathering anything, went to bed.
Title: Re: MP2 Instant Volume Increase
Post by: Hanneman213 on February 07, 2020, 10:38:14 AM
I turned to out in stereo fx loop, I will try in this way.
Title: Re: MP2 Instant Volume Increase
Post by: Hanneman213 on February 10, 2020, 02:17:49 AM
Day Two: No problem yet. Besides, I dont use FX loop, I connect serial. So I shut down completely.