ART Pro MPA II...one channel dead?

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straight8413

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I have had a ART Pro MPA II for about a year now that I got off of eBay used...I semi-retired the unit for a month or two while playing with a different preamp, then when I eventually fired it up again the 2nd channel doesn't function. If the gain and output level on that channel are cranked I get a tiny bit of signal but nothing more than that. I've swapped in and out known working tubes and swapped the tube from channel one, with no change in performance. Channel one works as it always has.

I have a ART Pro Channel with this same issue as well, with the Gain, Preamp and Master controls cranked it will pass a very VERY faint signal but nothing more.

Anybody have this same problem with these units, and was it ever resolved?
 
I had an MPA several years ago...never had any problems.
I currently have two VLA units...never had any problems, but TBH, I haven't fired them up lately, so I'll keep my fingers crossed.

If it's not the tubes...I can't see what else would cause them to just die off like that.
Do you live in a very humid area...? Might be contact issues both internal and external...oxidation will do that, cause loss of signals and noises.
If it's been sitting around awhile unused...maybe that's the problem. Clean everything, re-seat all connections, internal and external.
 
Interesting. I have both the MPA II and VLA II units, both in constant use for the past two years. No problems. If you find out more, please post.
 
Agree with the contacts being a possible cause. A little contact cleaner in addition to reseating them might help.

Also, with the unit off, work all the controls for that channel through their full ranges. Push all the button switches in and out a few times, including the operating level button on the back.
 
Not a humid area at all. I worked all the controls and cleaned the contacts, put all new JJ tubes in both units and left them on for a few hours for the new tubes to burn in. No change in operation. Channel 2 of the Pro MPA II is still pretty much inoperable, only the very faintest of signals with it cranked...tried to override Channel 2's controls by using the stereo function...still no change. Same with the Pro Channel, barely discernible signal with it cranked. Channel 1 of the Pro MPA II works perfectly as always though.

I have another Pro MPA II that has an annoying hum on Channel 1 as well...so not having much luck with ART products I guess.

Does anybody know if ART repair products outside of their warranty (and purchased secondhand)? I couldn't find any information on their website about repairs outside of warranty.
 
I'm tracking some vocals tonight with my Pro MPA II and channel one started acting up by fading in and out and finally went dead. This has been an ongoing problem which I believed to be the interconnecting cables connecting PCB's, but after switching over to channel two it started doing drop outs as well. I hit the 4dB/-10dB switch on the back a couple times and it seems to have brought back channel one which I now back to using. Tomorrow all the switches get a dose DeOxit contact cleaner and see if that helps maintain some longevity in working. Have not had an issue with any hum.
Also have an ART Pro Channel which has had zero problems.
 
well a new one is $269, so shipping it out for repairs probably isnt worth it. I shipped a MPA2 out this week and it was about $40!! and a small Neve preamp was $35 ...I also spent $10 on shipping tape and crap...so the whole shipping costs kind of killed the buzz.
I lost money on the ART MPA2.

at this level of gear pretty much disposable, get a new one.

I had a VLA used in a cart today and then realized with shipping and taxes I could get a brand new for $58 more.
 
CoolCat I agree...I do have an electronics repair shop within driving distance and as a last resort I'm going to that these units there. If they can do something, then great. If not, pull the tubes and sell as parts on eBay.

Just messing around today with the ART Pro Channel...I hooked it up to a Tascam 2488 MKII and plugged a guitar into the Hi-Z unbalanced 1/4" input just for giggles and played around with it. With the 2488's channel preamp up to about 3, and the gain/preamp/master volume on the Pro Channel cranked all the way I got a audible signal...obviously with a ton of hiss...with the compressor and EQ bypassed. Interestingly, when I un-bypassed the EQ (all setting at 12 o'clock) I got a noticeable fainter signal. When I bypassed the EQ and un-bypassed the compressor I got ZERO. Nothing. Also tried it with both the compressor and EQ engaged...nothing. No signal at all. So it seems that with the compressor in the signal path there is nothing coming out. By even with the EQ/compressor off it is WAY too faint a signal. Also noticed that by just tapping the face of the Master Volume knob did result in some noticeable volume changes so I'm going to clean the pots and see what happens after that.
 
straight8413 said:
Also noticed that by just tapping the face of the Master Volume knob did result in some noticeable volume changes...
Click to expand...

If tapping causes a change but turning the knob doesn't cause crackling or crunching noises it makes me suspect a solder joint or a faulty pot.
 
I agree, tapping can mean a bad solder point.
spraying the dust out is the first easy step, spray electronic lube...

tapping for bad solder joints..
I repaired an amp once and all from inputs on the internet. Tapping around with a wooden stick(drum stick) protects you from shock and has some reach to tap capacitors etc see if the suspect shows up.

potentiometers and jacks are also a common suspect because of the mechanical use.
 
Picked up a can a couple of cans of DeOxit today and set to work. The results were:

ART Pro Channel: Pulled the entire top PCB board and cleaned all the pots. Unit works perfectly.

First ART Pro MPA II: Cleaned out the pots and some connections plus used the non-lubricated stuff in the tube sockets. Still negligible output on Channel 2 although I can hear a very very faint signal through it with the gain maxed...output volume doesn't do it alone although it controls the amount of hiss. The Gain or +20dB button really have zero effect on the hiss though. Channel 1 works like a champ.

Second ART Pro MPA II: Repeated the same procedure for this unit. Still plenty of hum on Channel 1, doesn't matter if there is a mic XLR plugged in or not (cables have been checked and double-checked right off the bat). The -10dB pad or output volume bring it down but not the gain. Channel 2 works like a champ.

So a win on the Pro Channel anyways...going to bring both of the Pro MPA II's in next week and see if a local guy can make it work. In the meantime, anybody reading any symptoms throwing up red flags?

Other than using low-end equipment, that is.
 
forward progress, alright. did you try tapping the capactiors etc for a possible cold solder?
 
Yeah, I have a dedicated chopstick for such jobs. I restore classic cars for a living so I do work on old tube radios sometimes...but I have my limitations. Especially with modern gear like this.
 
Opened up my Pro MPA II down this afternoon after more signal drop outs on channel one.
- The board that has the channel one pots mounted on it if moved a bit would intermittently pass signal.
- Pulled the board out and set about reflowing the solder on all the joints that looked questionable, particularly those on the GAIN pot as when that one was pushed bit it seemed to create the problem. Didn't help.
- Hooked an ohm meter up to the PCB connections on the GAIN pot and when the pot was physically pushed the resistance would change randomly.
- Removed the pot from the PCB and checked the pot by itself and it appeared OK.
- The PCB holes for the pot are through plated to connect both sides of the board. Cleaned and fluxed the topside pads and applied some solder that flowed into the hole. Wicked off excess solder to open up the holes.
- Reinstalled the pot and soldered in.
- So far so good and the signal seems solid even when the board is given a push.

I think the problem was with the through plating not making a connection to the bottom to top of the board, possibly cracked. I believe that crappy lead free solder which appears to have been used in manufacture didn't flow well into the solder holes to bridge crack if there was one. Flowing new real lead/tin solder into the hole may have done the trick to bridge any gaps. Time will tell if this was the fix or not.

If anyone has a schematic/service manual for the Pro MPA II I'd appreciate a PDF copy. I have one for the MPA Gold, but not sure how close it is.
 
thats awesome, good info to pass along. :thumbs up:

you saved $260 so now you can go buy something else..lol
 
Good info man, glad it worked out for you.

If you ever find that schematic please post it!

I figured out on my "Channel 2 is dead" MPA II that these components are microphonic as hell on Channel 2...reflowed the solder underneath but no improvement

Photo Jan 13, 12 45 38 PM.webp
 
Have you called ART for any help? Maybe they could suggest a test or sending it in. Anyone got a repair quote?

Still for $260+ a new one is attractive. As they age capacitors can dry out, static electricity in the dry winter zapping gear.
$260 over 5yrs lifetime or longer is a great deal imo.

Would you buy another one or do something different?
I like used prices but more I think about it I worked on a 1990's preamp and it worked a short time and something fried out. So old components is a reality too.
 
I see B&H has the pair MPA and VLA w/cables for $499...free shipping, no tax.
$250 each, great deal. 3yr defect warranty.
 
that deals off now its $575 for the combo. not much of deal then, save $25.....ho hum.almost retail.
 
I know this was all a long while back but I had exactly the same problem and came across this thread. Mine turned out to be a dodgy 20db gain switch. Lots of contact cleaner and on/offing and it now works perfectly.
 
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