[sdiy] [AH] FIXED: Arp Solina with excessive chorus noise

[random variate]

Good work fella!

Tim
________________________________
From: tprivitera at nc.rr.com<mailto:tprivitera at nc.rr.com>
Sent: ‎27/‎02/‎2016 00:45
To: analogue at hyperreal.org<mailto:analogue at hyperreal.org>
Cc: synth-diy at dropmix.xs4all.nl<mailto:synth-diy at dropmix.xs4all.nl>
Subject: [AH] FIXED: Arp Solina with excessive chorus noise

Hi Everyone,

I wanted to follow up with the list on the fix for this.  It was indeed a VERY noisy TCA350Y BBD chip and it took a while to get a NOS one shipped to me.  I just replaced it last night.  About $10 each from either musicpartsguru on eBay or Wutierson in Spain.

I first replaced the decoupling caps on each of the 3 modulation boards while I was waiting on the chip delivery (I had the 220uf caps handy and figured it wouldn't hurt).  The chorus got a little louder, relative to the bypassed sound, which was a good thing, but the loud, obnoxious swooshing sound remained.  The little pots on each of the 3 boards are volume pots for each chorus section.  I simply raised and lowered each one until I found the one that affected the volume of the swooshing noise.  Beware the pads and traces on these boards are very delicate, so be careful.  Just using my hand-held, spring-loaded solder sucker pulled up a couple of the pads.  Everything was pretty easy to work on "in place" as the boards are mounted on a hinged support tray, which is easy to access from both sides.

Disengaged, the unit is dead quiet and engaging the button for the chorus yields very little background hiss at all - no more than the chorus on my Juno 60, which is pretty quiet.

The Solina truly sounds amazing now and I hope this will help anyone trying to troubleshoot a similar issue.

BTW, I did end up re-capping the power supply after the BBD chip replacement, just for peace of mind, as everything has '76 date codes.  Please no religious wars on the preemptive capping issue (-:

Tim
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Hi all,

I recently picked up a 70's Arp Solina String Ensemble. It has the button on the right cheek block to turn the chorus on/off and it is not the later version with LEDs.

It's in pretty good condition, every function works and it sounds great, but there is, in my opinion, excessive noise and 'swooshing' when the chorus/modulation circuit is engaged.  It is dead silent with the chorus turned off.  Not a big deal when you are playing notes or chords, but enough to be annoying when it's idling.

I downloaded the service manual/schematics and it looks like there are adjustment pots on the modulation boards.  Anyone had one with a similar issue adjust these or can suggest some ideas to reduce the noise?  I will be re-capping the power supply later this week for preventative maintenance, as I do with all my synths, combo organs, etc.

Thanks in advance,
Tim

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