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Please help with the preamp on the fritz (Art Powerplant)

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Please help with the preamp on the fritz (Art Powerplant)

Postby DC-Choppah » Fri Nov 22, 2019 1:46 am

I have an older guitar preamp in my rack that is an essential part of my sound (recording).

The preamp will get into a mode where it is broken-up, choppy, transistor about-to-die sound, very low amplitude, all broken up,really sad.

Then if I turn it off for a day, next day, maybe next week it is great!

The preamp is described here: https://www.soundonsound.com/forum/view ... 86#p505108

I have taken it to professional audio place and they 'fixed it'.

But the problem remains. But comes and goes on a weekly basis.

Any help is greatly appreciated!!
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby DC-Choppah » Fri Nov 22, 2019 3:59 am

Here is what it sounds like now:

https://drive.google.com/open?id=1uHNnc ... AO7Nzwzm0U

This is a Strat, into the Art Preamp and into a good working Fender amp.

Recorded with My TASCAM DR-07mkII handheld digital recorder about 6" away from the Fender speakers.


Hear how it breaks up and is very sad!.!!>!!.

If I bypass the preamp and go directly to the amp it sounds great.
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby Tim Gillett » Fri Nov 22, 2019 8:00 am

If in both cases it sounds fine out of the cab, it has to be distorting somewhere in the Tascam. Maybe the mics or their pre's are overloading?
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby Wonks » Fri Nov 22, 2019 8:32 am

It's got an effects loop. Probably serial, which means if those bypass contacts corrode, then you'll get some dodgy signals. So I'd first try some contact cleaner spray in those with multiple jack insertions for each socket to help clean them. I'd also clean the input and output sockets.

After that, try each pot to see if there's any change in the quality of sound when moved.

A dry joint is my next choice, so you could take the unit apart and check the PCB. Being 80s, it's more likely to have discrete rather than surface mount components, which makes visual checking for cracked or discoloured joints easier. Anything that looks dodgy, heat up the joint, suck or wick off the old solder and redo the joint with new leaded solder. (It will be leaded solder used on the board, and lead-free and leaded don't mix well).

After that, you're down to a failing component, which really involves a lot of checking whilst soak testing. If you are asking these questions, then this isn't something you'd be able to do yourself. Intermittent faults can take ages to track down so, as time is money, it could cost a lot to fix. Then again, with a circuit diagram available, someone experienced could look at it and identify the components most likely to give the problems you describe.
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby DC-Choppah » Sat Nov 23, 2019 12:11 am

Tim Gillett wrote:If in both cases it sounds fine out of the cab, it has to be distorting somewhere in the Tascam. Maybe the mics or their pre's are overloading?

No it sounds bad out of the amp. The TASCAM recording is what I hear listening out of the amp.
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby DC-Choppah » Sat Nov 23, 2019 12:16 am

One clue perhaps. When the preamp is doing this, and I remove it from my rack, and move it to my table and plug it in to look inside, it fixes itself and is working.

So the act of jiggling it to get it out an opened up fixes it. That is very frustrating indeed. :madas:

But then when I put it back in the rack, and some time goes by (a week +) it goes bad again.
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby DC-Choppah » Sun Nov 24, 2019 4:39 am

Some pics of the inside from today.

I De-Oxed the pots and switches and sprayed all of the socket contacts.
I removed the 2 white multipin connectors and sprayed De-Ox on those.

https://drive.google.com/open?id=1t1eCB ... b4skCGE0Xk
https://drive.google.com/open?id=19ffp2 ... SjFLpb1Ewz
https://drive.google.com/open?id=1hwrSo ... y977RsiocE
https://drive.google.com/open?id=1t1eCB ... b4skCGE0Xk

Installed it back in the rack and it sounds fine.

But I don't if this is just because it has been jiggled, or if I really cleaned something important. :problem:

One other possible clue.
When it was on the fritz, both the clean channel and the dirty channel were bad and broken up. When it comes back, both channels work fine.

It never has only one channel working. They always go together.
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby DC-Choppah » Sun Nov 24, 2019 5:40 am

Spoke too soon. I had only tested the dirty channel.

Since I reinstalled in the rack, now the clean channel only plays if the gain knob is all the way down to 0. Then if you turn the knob up the sound fades and by 9:00 it is silent. Also there is hiss when the knob is down at 0 that also goes away as you turn it up.

Also, the green light for the clean channel no longer lights up.

BUT when switched to the dirty channel, everything works and sounds right.

This is new. I did something to it this time.

:crazy: :sick:
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby ef37a » Sun Nov 24, 2019 9:02 am

These sort of intermittant faults can be the very devil to track down.

Even if Art were prepared to take it back for servicing (and they should IMO) there is no guarantee they would be 100% certain to find the fault. Indeed the fault might never occur for them!

What you really need DC is a tame (very tame) service tech' who is prepared to put the pre amp on a soak test rig, (and such a rig would have to be a bespoke creation) wait for the fault to show then pounce! He would then bill you on results, not total time spent as that could run to £100s.

I would have said the problem is with a loss of DC power but now the fault has 'differntiated' not so sure. Could be a dual op amp? TL07 which WAS failing totally but now just one section? But tis very rare.
Maybe just buckle down and do a complete re-cap? I don't normally suggest it but,
1: it can do no harm and all new caps eliminates them.
2) you might stumble upon a dodgy joint e.g.

You need to search long to find a schematic. Badger the A off Art!!

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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby John Egan » Sun Nov 24, 2019 11:13 am

I know you don't want to hear this, but it is probably time to find a replacement whose sound you can live with. It would be easy to spend the equivalent of a new(er?) replacement and still not have fixed the problem.
I had the same situation a few years ago with a much loved reverb unit and as fast as my tech found a fault and repaired it, something else blew shortly afterwards. This happened three times before I finally called time on the unit.
There are some very good preamps around. Maybe not exactly the same sound, but probably close enough for the audience. And who knows, you might like it !
Sorry to be so negative.
Regards, John
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby Wonks » Sun Nov 24, 2019 11:29 am

'Nothing' could indicate the channel select button, or might be a connector issue from the clean channel pot board. I know you've cleaned the push-in connectors, but it might be the soldering to the connectors that's faulty.

You really need to get round to removing all the knobs and taking out the rear of the circuit boards to have a look.

There's a discrete capacitor that runs from the circuit board to a screw holding the mains transformer down (ground connection), and the non-ground leg looks like it's very near the aluminum heatsink, which is itself grounded to the chassis. Remote chance that the signal side of this could be grounding on the heatsink when the top gets put on, so I'd wrap some insulating tape round it, just in case. It won't harm it.

There could be lots of component issues causing the fault, but it's relatively easy to rule out any more obvious issues first.
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby cyrano.mac » Sun Nov 24, 2019 12:46 pm

I've had a look at the pics.

The first thing I'd suspect, are the three ribbon cables in picture number two. These are known to develop cracks that induce the kind of intermittent connection problems you're experiencing.
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby Wonks » Sun Nov 24, 2019 1:06 pm

cyrano.mac wrote:I've had a look at the pics.

The first thing I'd suspect, are the three ribbon cables in picture number two. These are known to develop cracks that induce the kind of intermittent connection problems you're experiencing.

I'd certainly have a close look at them, but as those ribbons connect the drive channel controls to the main PCB, and it's the clean channel that's currently stopped working, that makes them far less likely to be the culprit here. There's no need to take the clean signal circuit output onto the drive circuit board.
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby DC-Choppah » Sun Nov 24, 2019 6:09 pm

ef37a wrote:These sort of intermittant faults can be the very devil to track down.

The preamp is now in the same state all the time.

The green light for the clean channel never comes on.

Clean channel has output only with gain knob at zero and then as you bring the gain up it gets quieter, hiss enters, and then sound goes to zero as you get to 9:00 and the unit is silent.

Dirty channel red light comes on, sound is OK, but is more broken up than normal.

All I did was clean stuff ?!?

I broke it permanently this time!
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby Sam Spoons » Sun Nov 24, 2019 6:11 pm

On the upside it does make the fault easier to trace....... :headbang:
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby cyrano.mac » Tue Nov 26, 2019 2:42 am

Wonks wrote:
cyrano.mac wrote:I've had a look at the pics.

The first thing I'd suspect, are the three ribbon cables in picture number two. These are known to develop cracks that induce the kind of intermittent connection problems you're experiencing.

I'd certainly have a close look at them, but as those ribbons connect the drive channel controls to the main PCB, and it's the clean channel that's currently stopped working, that makes them far less likely to be the culprit here. There's no need to take the clean signal circuit output onto the drive circuit board.

I haven't seen the schematics, just the pics...
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby DC-Choppah » Tue Nov 26, 2019 3:17 am

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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby Wonks » Tue Nov 26, 2019 8:06 am

cyrano.mac wrote:
Wonks wrote:
cyrano.mac wrote:I've had a look at the pics.

The first thing I'd suspect, are the three ribbon cables in picture number two. These are known to develop cracks that induce the kind of intermittent connection problems you're experiencing.

I'd certainly have a close look at them, but as those ribbons connect the drive channel controls to the main PCB, and it's the clean channel that's currently stopped working, that makes them far less likely to be the culprit here. There's no need to take the clean signal circuit output onto the drive circuit board.

I haven't seen the schematics, just the pics...

Neither had I, but I had read the thread fully, so had seen photos of the front of the unit, so knew where the clean channel controls were situated.
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby Wonks » Tue Nov 26, 2019 8:16 am


Well done for getting those. Not quite sure exactly how accurate those are, as the input socket wiring would never work as shown! The socket contacts have to be reversed per socket, otherwise the input signal gets sent to ground when a jack is inserted and no signal is sent to the rest of the preamp.

In fact, almost all the sockets are drawn incorrectly with the switched connection shown going to the circuit and the signal connection unconnected or led to ground. You normally have to mirror flip the diagonal arm with the arrow attached in each case to make it work.

The draughtsperson used the same template all the way through, when they needed to flip it over most of the time.

Undoubtedly the PCB has been created correctly, but this can't be the wiring diagram used, there must be a later version that's the corrected production version, despite this being a 1995 drawing and so of the mk 2 version of the unit
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Re: Please help with the preamp on the fritz (Art Powerplant)

Postby Wonks » Tue Nov 26, 2019 9:04 am

The schematics also fail to show the ribbon/plug connectors to and from the separate front panel circuit boards. Strange.
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