Strange Hum on Sustainor

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RockmanCentralBob
Posts: 309
Joined: Fri Feb 06, 2015 2:10 am

Re: Strange Hum on Sustainor

Post by RockmanCentralBob » Sun Jun 11, 2017 12:25 pm

Sorry, a little late, but hope some of this will help...

Don't replace the JFet... there are parts matched to it and changing it would throw out the calibration.

The casing of the Jfet goes to ground, if I'm not mistaken. So touching it would affect the audio. Not unusual for it to do that.

I noticed in the top picture there was the metal grounding tape, but not in the second.... did you remove it? If so, put it back... it's there to help with noise.

Depending on your case, it sounds like there could be a part that is shorting out on the case (most likely on the bottom). Some of those cases had metal paint added to the inside to act as an RF shield, but they are also conductive.

Check the polarity of all the caps you replaced, and their values. They are not all the same value!! Also, check that they aren't shorted out on other components.

Check for loose solder causing shorts. I boxes up a Sustainor I modded into a Rev 20 for 10+ years because I couldn't get it to work. When I decided to try again to fix it, I found a tiny solder ball stuck between 2 parts. I removed it and it started working again (still had other things to fix, but that was the main culprit).

Hope one of these leads you to the problen!

dreamevil
Posts: 27
Joined: Mon Nov 16, 2015 7:11 pm

Re: Strange Hum on Sustainor

Post by dreamevil » Sat Dec 23, 2017 7:24 pm

Hi again everyone.
After applied every advices given here(extra shielding), Recapping again, changing the transformer still the same issue.
I think the source of the problem was Smart Gate. It doesn't matter that the gate is on or off. When i touch (shown on the yellow arrow) part on the pcb it started to hum like hell.
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Last edited by dreamevil on Sun Dec 24, 2017 11:38 pm, edited 3 times in total.

RockmanCentralBob
Posts: 309
Joined: Fri Feb 06, 2015 2:10 am

Re: Strange Hum on Sustainor

Post by RockmanCentralBob » Sat Dec 23, 2017 10:38 pm

dreamevil wrote:When i touch (shown on the yellow arrow) part on the pcb it started to hum like hell.
Is this really an issue?
I mean, how often are you going to touch the PCB when you are using it?

dreamevil
Posts: 27
Joined: Mon Nov 16, 2015 7:11 pm

Re: Strange Hum on Sustainor

Post by dreamevil » Sat Dec 23, 2017 11:23 pm

Yes, this is already the main issue. I had uploaded a video on the first page of the topic. The hum can occur anytime.(by shaking or without)
But even the case of sustainor closed, it occurs when i touch upside of it.

https://streamable.com/1luer

Chuck Nuggets
Posts: 9
Joined: Mon Apr 08, 2019 8:31 pm

Re: Strange Hum on Sustainor

Post by Chuck Nuggets » Tue Apr 09, 2019 10:06 pm

dreamevil wrote:
Sat Dec 23, 2017 7:24 pm
Hi again everyone.
After applied every advices given here(extra shielding), Recapping again, changing the transformer still the same issue.
I think the source of the problem was Smart Gate. It doesn't matter that the gate is on or off. When i touch (shown on the yellow arrow) part on the pcb it started to hum like hell.
Holy smokes! Sustainor hum issues are [99% of the time] caused by failed shielding continuity. You can test for poor continuity, by tapping the front left and top of the Sustainor with your finger. If you hear intermittent hum loss and noise while tapping, which you more than likely will, it's a shielding issue. To address this, you will need to clean the surface of the shield bridge. This is the foil covered ribbon that runs from the front to the back if the Sustainor. Clean the surface of the ribbon with 9O% rubbing alcohol. Using 9O% alcohol, clean the shielding that is adhered to the underside of the Sustainor lid. Before securing the lid, pull the shielding bridge upward as far as it will go. Don't pull too hard! Just enough to where all the slack is gone. The idea here, is to achieve maximum contact between the shielding bridge, and the lid shielding. Secure the lid.

For the model 2OO Sustainor:
Remove the lid, and clean the top edge of the front and rear jack/control plates using 9O% rubbing alcohol. Next, clean the corresponding channels in the Sustainor lid. You don't need to do the base, only the lid. These are the channels that make continuity with the jack/control plates... See where this is going? To create a gasket, cut a piece of tin foil long enough to extend from one end of the jack plate to the other. Fold the foil over the top jack plate edge. Don't make it too wide, as you don't want it extending down into the circuitry. Form the foil over the plate, but don't push down too hard. You want the lid channel, foil, and jack plate to make as much contact as possible. Just did two this week... Hum-free!

In regards to replacing the electrolytic capacitors... The stock caps I've removed from Rockman units have lower ESR than brand new China made replacements. Those old caps are great, and can last for 7O years, possibly longer. Heat is what kills the electrolytic, and the Rockman boxes generate little to no heat. Unless a capacitor/s have failed, I'd leave them alone. Replace the PSU capacitors, but leave the signal caps alone. I just love me some stock Rock Modules! If you can find some NOS USA/Japan capacitors, keep them handy for when you actually need them. Keep caps fresh, by powering up your gear 1 x per week/month.

Also, leave the stock black screws and power button as-is. Some lunatic out in Texas has been pimping-out Rock Modules, by replacing the stock screws with stainless, and the power button with a chrome button. No telling how many modules this idiot has defaced. Those stainless nuts on the rear panel are not an "upgrade" either. Stainless steel is a poor conductor. Use the stock nuts, or find some proper non-stainless replacements.