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Ampeg Micro VR Cutting Out

B

ByrdyBass

May 23, 2024
32
34
#1
Hello all,

I've had an issue with my Micro VR head for a bit. Basically, it will all of a sudden get quieter and quieter, and then cut out completely. Sometimes when I turn it on it's silent already. I've found a temporary fix in diming the gain and hitting a big note on the bass. Then it comes back to life and works normally for quite a while and I can turn it to a reasonable volume. It'll work fine for 5-10 minutes and then do the same thing again.

A while back I noticed that the -15db pad switch (or maybe the limiter switch; it was a long time ago...) and a couple of the pots were scratchy. I opened it up and did my best to clean all of them out with some deoxit fader cleaner. That fixed the scratchiness and now the pots and switches don't seem to have any issues, but the problem above persists.

Does anyone have any ideas? If there's a component that you think might be bad, I do have enough experience to swap it out. I just don't have enough experience to know what would be causing this weird issue.

Dunno if this is helpful but here's a link to the schematic: http://bee.mif.pg.gda.pl/ciasteczko...g/Ampeg_Micro-VR_power_Amp,_PS_Schematics.pdf

Any help appreciated! Thanks!
 
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#2
ByrdyBass said:
Hello all,

I've had an issue with my Micro VR head for a bit. Basically, it will all of a sudden get quieter and quieter, and then cut out completely. Sometimes when I turn it on it's silent already. I've found a temporary fix in diming the gain and hitting a big note on the bass. Then it comes back to life and works normally for quite a while and I can turn it to a reasonable volume. It'll work fine for 5-10 minutes and then do the same thing again.

A while back I noticed that the -15db pad switch (or maybe the limiter switch; it was a long time ago...) and a couple of the pots were scratchy. I opened it up and did my best to clean all of them out with some deoxit fader cleaner. That fixed the scratchiness and now the pots and switches don't seem to have any issues, but the problem above persists.

Does anyone have any ideas? If there's a component that you think might be bad, I do have enough experience to swap it out. I just don't have enough experience to know what would be causing this weird issue.

Dunno if this is helpful but here's a link to the schematic: http://bee.mif.pg.gda.pl/ciasteczkowypotwor/#pro_audio/Ampeg/Ampeg_Micro-VR_power_Amp,_PS_Schematics.pdf

Any help appreciated! Thanks!
Click to expand...
Does it have ribbon connectors in it?
Those might need to be reset and maybe cleaned.

But I am always wary of using “contact cleaning” sprays inside of any electronic. Some of those are known to melt the plastics used in some pots.
 
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#3
DJ Bebop said:
Does it have ribbon connectors in it?
Those might need to be reset and maybe cleaned.

But I am always wary of using “contact cleaning” sprays inside of any electronic. Some of those are known to melt the plastics used in some pots.
Click to expand...

Howdy!

Yes, there are two main ribbon connectors. I'm attaching some pics of the inside here that shows pretty much everything. And yes I've read a lot of similar sentiment about contact cleaner since I did that originally. I did read that deoxit fader is "supposed" to be plastic-safe if I remember correctly, which is why I chose that one. But yea probably not the best choice.

Another update is I just tried to recreate the issue again and could not get it to go back to normal. There's definitely some bad connection somewhere. The only way I could get any sound was to dime the three eqs and the gain, and I could get a real crackly signal that sounds almost like a bad cable or jack. But I could not figure out where the bad connection was. I turned all the pots a lot and they all seem to be doing their normal job, as well as the pad switch and the limiter switch. The input jack and output/speaker jack also seemed quite secure.

It also seems to be post-gain/eq, pre master out. Because the peak indicator was acting normally and going crazy when I had everything dimed, so it seems that the signal going in and through the gain/eq stages was alright. The master volume switch also seemed to be functioning normally.

Should I just try reseating the ribbon connectors? That white ziptie in the pic also makes those two pretty dang tight; not sure if that could be causing a bad connection by pulling on them so much.

IMG_1070.JPG


IMG_1072.JPG

IMG_1073.JPG
 
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#4
ByrdyBass said:
Howdy!

Yes, there are two main ribbon connectors. I'm attaching some pics of the inside here that shows pretty much everything. And yes I've read a lot of similar sentiment about contact cleaner since I did that originally. I did read that deoxit fader is "supposed" to be plastic-safe if I remember correctly, which is why I chose that one. But yea probably not the best choice.

Another update is I just tried to recreate the issue again and could not get it to go back to normal. There's definitely some bad connection somewhere. The only way I could get any sound was to dime the three eqs and the gain, and I could get a real crackly signal that sounds almost like a bad cable or jack. But I could not figure out where the bad connection was. I turned all the pots a lot and they all seem to be doing their normal job, as well as the pad switch and the limiter switch. The input jack and output/speaker jack also seemed quite secure.

It also seems to be post-gain/eq, pre master out. Because the peak indicator was acting normally and going crazy when I had everything dimed, so it seems that the signal going in and through the gain/eq stages was alright. The master volume switch also seemed to be functioning normally.

Should I just try reseating the ribbon connectors? That white ziptie in the pic also makes those two pretty dang tight; not sure if that could be causing a bad connection by pulling on them so much.

View attachment 7263780

View attachment 7263781
View attachment 7263782
Click to expand...
Those are different and not the kind I was referring to. This type of thing…

1751310521077.jpeg


I have a Carvin BX1500 that had the type I posted. It does the same thing if I haven’t used it in a while. That is one thing I have done in the past, turn it up loud and hit a note. Now that I know what the problem is for me, I just open it up and reseat the cables and it works.

The cables on yours look more substantial but the problem is in the connection. You still might try just wiggling the connector to see if it makes a difference.
 
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#5
DJ Bebop said:
Those are different and not the kind I was referring to. This type of thing…

View attachment 7263787

I have a Carvin BX1500 that had the type I posted. It does the same thing if I haven’t used it in a while. That is one thing I have done in the past, turn it up loud and hit a note. Now that I know what the problem is for me, I just open it up and reseat the cables and it works.

The cables on yours look more substantial but the problem is in the connection. You still might try just wiggling the connector to see if it makes a difference.
Click to expand...
That makes sense. I will try messing with those connections and see if I can isolate the problem area. I had a similar thing with a keyboard where the PCB junction was not secure for a multi-wire connection and kept cutting out. Heated up the solder joints and worked like a charm. Hopefully something as simple as that for this problem. Thanks for your advice!
 
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#10
ByrdyBass said:
Ahh yea I see what y'all mean. TBH tinkering around with problems like this is how I've learned the most, and this amp was cheap and is my backup anyway so not an enormous risk to try a few things. If I figure out what the problem is I'll post the results!
Click to expand...
Well then, be safe and don't get hurt 😊
IMG_2011.gif
 
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#12
ByrdyBass said:
Ahh yea I see what y'all mean. TBH tinkering around with problems like this is how I've learned the most, and this amp was cheap and is my backup anyway so not an enormous risk to try a few things. If I figure out what the problem is I'll post the results!
Click to expand...
Yes, tinkering is how things generally get broken worse. It's something that techs don't care to work on because there is usually new and unexpected hidden damage...
 
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#13
I was going to say the same thing as @JimmyM did. It doesn’t require any finagling around inside, just take a patch cable and patch the effect send to the effect return and see if the problem stops. I had a similar problem with an SVT-III and it was dirty contacts in the effects loop. Granted that was an SLM-era Ampeg, but the issue seems not to be uncommon. I cleaned the jacks, but the most reliable solution, short of replacing the jacks (which I figured would just get dirty again), was simply to leave a short patch cable in place.
 
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#16
farace said:
I was going to say the same thing as @JimmyM did. It doesn’t require any finagling around inside, just take a patch cable and patch the effect send to the effect return and see if the problem stops. I had a similar problem with an SVT-III and it was dirty contacts in the effects loop. Granted that was an SLM-era Ampeg, but the issue seems not to be uncommon. I cleaned the jacks, but the most reliable solution, short of replacing the jacks (which I figured would just get dirty again), was simply to leave a short patch cable in place.
Click to expand...
I think that was 100% the problem! I'd never encountered that before and never would have thought of it on my own. Thanks all!
 
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#17
agedhorse said:
Yes, tinkering is how things generally get broken worse. It's something that techs don't care to work on because there is usually new and unexpected hidden damage...
Click to expand...
Yeah that makes sense and I understand. If it was a newer and more expensive amp I'd def follow that advice and just take it somewhere. However I have learned a lot through tinkering in conjunction with advice from forums, youtube, repair manuals etc., and usually worth it for me because most of the stuff I have is worth less than the cost to take to a shop (both of my amp heads were < $200 used). Thankfully this one turned out to be super easy thanks to y'all's suggestions! But I do appreciate and respect your advice; it makes a lot of sense.
 
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#19
JimmyM said:
Awesome! Ya, those jacks can get a little corroded over time, especially if you don’t use them as I don’t.
Click to expand...

They really do seem like a weak point in the amp design. I never use the effects loop, either; I’d rather it not be there at all causing problems. There has to be a more reliable way than trusting those tiny little contacts on a switching jack to stay clean and pass through all of the signal cleanly.
 
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#20
farace said:
They really do seem like a weak point in the amp design. I never use the effects loop, either; I’d rather it not be there at all causing problems. There has to be a more reliable way than trusting those tiny little contacts on a switching jack to stay clean and pass through all of the signal cleanly.
Click to expand...
It’s a holdover from the 80s when we were all told by one of the big pedalboard gurus (maybe Bradshaw) that we should be running effects after the preamp. The entire industry joined in on it and tried to convince us, and some people actually took the bait.

Blech!
 

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