[sdiy] Roland JX-3p vca - noise

[Tom Wiltshire]

If you're going to desolder the jack anyway, put a new one on. Don't mess around with the old one. It's 25 years old and it probably needs replacing.
Once that's done, you've got a reliable connection you can trust for the next 20 years and if crackles still show up, you know it isn't from there. If you put the old one back, you'll never be sure ("well, it sorta *looked* ok…").

I'm not one for recapping every electrolytic in the synth just cos, but I do reckon that most old gear needs a new filter cutoff pot and jack socket for starters. They get wrecked. It's the bare minimum. At least on the JX3P you don't have to worry about the cutoff pot!

2 cents,
T.


On 27 Feb 2013, at 19:16, Travis Thatcher <recompas at gmail.com> wrote:

> Thanks Tony - I'll look into the output mute transistors when I take
> the synth apart tonight to check everything else out.  Its been a bit
> of a mess of weird problems since I got it this summer (used to have
> one  years ago) but its close to fully functional now.  What exactly
> is the purpose of the muting transistors? Just to make sure the signal
> goes to ground if there's no actual synth signal coming through - kind
> of like a gate?
> 
> As for the outputs - the right output barely works at all. I'm going
> to desolder the jack and test the mechanics of it off board. Same with
> the headphones and looking at the schematic the two signals seem
> isolated.  The audio connector could very well be corroded so I'll
> definitely give that a good check.
> 
> Thanks!
> 
> On Wed, Feb 27, 2013 at 2:28 AM, Oakley Sound <oakleylist at btinternet.com> wrote:
>> It's probably a poor connection somewhere since it goes away when you change
>> the volume levels. But if not, one other place to look is the output mute
>> circuit. TR7 and TR8 being the mute transistors. These can go bad and
>> produce some odd distortion effects.
>> 
>> Virtually every JP-6, which has a similar circuit to the JX-3P, I have seen
>> has poorly output mute transistors. But that tends to manifest itself as an
>> overdriven sort of sound when you have the VCA level and volume up. I
>> sometimes see a comment about the JP-6 having some sort of deliberate
>> overdrive capability but it's usually just a bad output mute circuit. Take
>> the mute circuit out and it's as clean as a whistle.
>> 
>> Since the output of the JX-3P is stereo - does it crackle identically on
>> both sides? If so the problem is possibly before or in the chorus unit.
>> 
>> Tony
>> 
>> http://takla-makan.bandcamp.com/
>> http://www.oakleysound.com
>> 
>> 
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> 
> 
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