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Post subject: Roc Pro 1000 - Turning off the power switch then *CLACK!*
Posted: Mon Nov 15, 2010 8:47 am
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I'm sure this isn't an isolated problem, a quick search on Harmony Central threw up a few posts mentioning the same thing, but I assumed this forum would be the best place to ask:

What is the solution to this ridiculously loud noise when the amp is switched off?

Can I add/subtract components to the circuit board? Set the volume/gain to a specific level? Close my eyes before I operate the switch?

Any help would be appreciated, thanks.


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Posted: Mon Nov 15, 2010 3:19 pm
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I have the immediate predecessor; the Performer 1000 (I think the Roc Pro is supposed to have a better distortion circuit or something, but I haven't A/B'd the two). The thing is that while these amps have a nice clean (and LOUD) sound, there seems to be a couple of design flaws that have proven to be detrimental. Mine has exhibited a number of strange behaviors including:

* the drive channel being intermittently activated while playing clean.
* loud, random popping noises.
* snap, crackle, and pop when trying to manipulate the controls.
* volume would drop off intermittently.

These issues have made the amp completely useless and unreliable. I had a discussion about this on the Solid State Amp Forum and someone suggested that the design of the circuit was poorly executed. I am thinking that it is not worth fixing and that I should harvest the Celestion speaker and drop everything else off the side of a building.


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Posted: Mon Nov 15, 2010 4:44 pm
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Try to spray contact cleaner in your switch, by the pusd button. It works sometimes


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Posted: Mon Nov 15, 2010 4:46 pm
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The switch off "pop" is due to transient differential supply voltage drop at off (at On ?) that activate amplifier driven an unexpected current within the loudspeaker; May be check supply capacitors (C71/72; C73/74) or // resistors (R172/173; R160/161 that may drift.

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Posted: Mon Nov 15, 2010 5:45 pm
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>stratele52
Thanks, I'll give it a try, I hope it's as simple as that!

>Tissan
The "pop" is when I switch off. I assume "//" means parallel? I know some basic electronics but I'm not sure what you mean by capacitors/resistors drifting. I have the schematics and would be capable of replacing them if that's what you mean. Thanks for the reply too.


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Posted: Mon Nov 15, 2010 6:05 pm
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Have you ever replaced the 12AX7 in the pre-amp?

It's possible that with aging, the tube has accumulated some micron-sized debris from the elements within the bottle itself that are arcing to the heater element upon shut-down.

HTH

Arjay

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Posted: Mon Nov 15, 2010 6:20 pm
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Arjay, In the same vein as your thoughts about bad 12AX7's, I remember a Pro Reverb that did the same thing. Loudest pop (loud enough to make one worry about the speakers), everytime you turn the darn amp off.

After tightening all sockets, cleaning them, putting in new tubes, checking the PS caps...etc. It ended up being a solder point on the 12AT7 socket (driving the reverb tank). Fender just folds the socket tang over between pins 2 & 7 and solders the tangs. Well, this point had become cold. But not cold enough to hamper the reverb's tone. But, cold enough to cause the LOUDEST pop ever, maybe from flyback or just the right (or wrong in this case) mechanical jarring (like hitting the off switch). Resoldering the tangs solved the problem.

Ever since then, I not only clean & tighten the sockets on these older amps... but also touch-up the solder points to all the tangs. See layout:

http://www.ampwares.com/schematics/pro_reverb_aa165.pdf


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Posted: Mon Nov 15, 2010 6:26 pm
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Great diagnosis and an excellent recommendation for what we called in the service "PMCS" (preventative maintenance, checks & service). Aging solder joints are always a source of concern but a quick "touch-up" with the Weller is one way of nipping those problems in the bud.

Arjay

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Posted: Tue Nov 16, 2010 12:55 am
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// effectivelly means parallel. Drift --> unexpected evolution: resistor increasing or caps that have current leakage ....

Have look on supply caps if you see liquid or ageing effect and all solder joint. But before, test a new 12AX7 as Retro propose even if the amp is mainly solid state.

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