KORG MS-20 Vintage - Furry Cap Syndrome!!

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KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby HideawayStudio » Sun Mar 16, 2014 8:29 pm

Thought I might share a recent workshop experience which may interest some vintage MS-20 owners...

I'm a synth engineer for a well known pop duo here in the UK and get to see/work on a lot of old and very cherished studio gear these days. What is starting to concern me is that an increasing amount of gear we used to take for granted as being bomb proof and ultra reliable is starting to become more troublesome.

It is easy to forget how old some of this "reliable" gear is now...

By this I mean the early to mid 80's Yamaha's and Korgs of this world...

This week I was confronted with an MS-20 straight off tour which was reported to have an LPF resonance control that went nuts from time to time. After pulling the beasty almost entirely to pieces (the MS-20 is perhaps not one of the nicest synths to work on in this respect as everything is bolted to the front panel!) I found a very unsubtle dry joint on one of the op amps on the filter board....

Actually it turns out that the soldering in the MS-20 is not great... far too many dry joints for my liking.

Anyway.. an easy fix other than the plethora of screws to undo..

Much more worryingly though was that I then caught sight of some curious blue furry corrosion on the legs of one of the 10uf 16 volt electrolytic caps. After poking around a bit I found that all of these parts were showing the same problem and on removing one of them found a blue powdery deposit oozing out of the legs and much more obvious on the underside of the devices. These caps are dotted around the entire synth and are used to decouple the analog supply rails. Needless to say that I very much doubt these components would have survived much longer before they failed and this is often as a short circuit in electrolytics.

Image

This is not a bad example in general so I'm a little concerned that maybe many more MS-20's could suffer from this issue. Although I am not an advocate of recapping - this is most definitely an instance where it is essential.

Certainly something to check if you are fond of your MS-20... and with those brilliantly crazy filters - who wouldn't be!
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Re: KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby Sir Ruff » Sun Mar 16, 2014 11:25 pm

Why aren't you a fan of recapping? Is it a case of "if it ain't broke, don't fix it"?
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Re: KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby yorgatron » Sun Mar 16, 2014 11:50 pm

Sir Ruff wrote:Why aren't you a fan of recapping? Is it a case of "if it ain't broke, don't fix it"?


I just got an Arp Omni and everyone, and I mean everyone, says recapping is mandatory.
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Re: KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby HideawayStudio » Mon Mar 17, 2014 12:35 am

Sir Ruff wrote:Why aren't you a fan of recapping? Is it a case of "if it ain't broke, don't fix it"?


There are many forms of cap that are inherently reliable - ie. ceramic, polyester, polythene and mica. To mindlessly replace these parts in so many designs is quite simply putting the instrument at more risk than its worth.

However...

Many Electrolytics and some Tantalum caps are notorious for failures and so many are in low impedance paths with supply rails so at the very least selective recapping makes a lot of sense as their failure modes often pose risks to the life of the circuitry around them.

The wider picture is that there is little doubt that caps in audio paths do impart character - whether this is due to the specification of the day or the effects of time. Although the basic specification of a vintage cap and its modern counterpart might be the same their impedance, ESR, leakiness and temperature stability may be considerably different and especially in high impedance circuits their effects may well be tangible.

For all the above reasons I strongly promote selective recapping over total recapping.
Last edited by HideawayStudio on Mon Mar 17, 2014 12:42 am, edited 1 time in total.
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Re: KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby HideawayStudio » Mon Mar 17, 2014 12:38 am

yorgatron wrote:
Sir Ruff wrote:Why aren't you a fan of recapping? Is it a case of "if it ain't broke, don't fix it"?


I just got an Arp Omni and everyone, and I mean everyone, says recapping is mandatory.


Yes, and I'm one of them - sadly some ARP designs from this era made use of abnormally poor quality tantalum capacitors. I had to replace 80 or so tantalum caps in my Omni-2 - not the nicest of things to undertake.
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Re: KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby Stab Frenzy » Mon Mar 17, 2014 5:18 am

I always though recapping just referred to elecs and tants, I personally never thought anyone would bother pulling out ceramics etc. That might just be me though.
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Re: KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby Steve Jones » Mon Mar 17, 2014 9:35 am

Every MS and PS series Korg synth that have come through my shop in recent years has leaking electrolytics.
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Re: KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby pflosi » Mon Mar 17, 2014 10:08 am

:shock: I might need to take my MS20+10 to my tech then :cry:
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Re: KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby Sir Ruff » Mon Mar 17, 2014 5:40 pm

Stab Frenzy wrote:I always though recapping just referred to elecs and tants, I personally never thought anyone would bother pulling out ceramics etc. That might just be me though.


To electronic inchoates (such as myself), I just took "re-capping" to be all encompassing. But this thread is reminding me why you might not want to bother recapping certain things in the audio path.

Hideaway: I understand the logic of not replacing older caps in the audio pathway for "character" (and also to minimize possible repair-related damage), but is it fair to say this will only apply to older synths? I was having another convo with a board member where he pointed out that replacing audio-related caps on mid-80s gear and beyond probably won't make much of a difference either way to sound quality (presumably because of either integrated circuit design or improvements in caps?) For example, I've heard mixed opinions as to whether having something like an Obie Xpander's audio caps replaced would actually be an improvement or not... but I haven't heard anyone say you will lose anything if you do. Is it also logical to assume that the more ICs are used for things like VCO/VCF/VCA (e.g., an xpander), the less difference changing caps would make?
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Re: KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby yorgatron » Mon Mar 17, 2014 7:16 pm

HideawayStudio wrote:
The wider picture is that there is little doubt that caps in audio paths do impart character - whether this is due to the specification of the day or the effects of time. Although the basic specification of a vintage cap and its modern counterpart might be the same their impedance, ESR, leakiness and temperature stability may be considerably different and especially in high impedance circuits their effects may well be tangible.

For all the above reasons I strongly promote selective recapping over total recapping.


personally, I think the variance in manufacturing tolerances is wide enough that you could have 2 synths built by the same company, on the same day, that would sound different from each other. how many times have you heard someone talk about a particular synth that sounded great, and they were never able to find another just like it?

also, since I also play clavinet/organ/electric piano/guitar through vintage tube amps, I know that it rarely changes the sound when they're recapped.

Image

true story; I was at a friend's house years ago and spotted a blond '63 Fender Bassman amp and asked about it.
he said he didn't play it anymore because it needed to be recapped.
I told him it wasn't an expensive procedure, and well worth doing, considering the classic status of that particular amp.
he said he hadn't done it because "it wouldn't be original anymore." :facepalm:
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Re: KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby sam » Mon Mar 17, 2014 8:06 pm

I have also seen this problem with ms20's.....And also Rolands from 76 to 79 have this green leaky thing going on.

I always replace the power supply caps and others where possible.

The other types of caps don't go bad but sometimes the legs break off....I saw this with ARP synths.
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Re: KORG MS-20 Vintage - Furry Cap Syndrome!!

Postby HideawayStudio » Tue Mar 18, 2014 12:17 pm

Sir Ruff wrote:
Stab Frenzy wrote:I always though recapping just referred to elecs and tants, I personally never thought anyone would bother pulling out ceramics etc. That might just be me though.


To electronic inchoates (such as myself), I just took "re-capping" to be all encompassing. But this thread is reminding me why you might not want to bother recapping certain things in the audio path.

Hideaway: I understand the logic of not replacing older caps in the audio pathway for "character" (and also to minimize possible repair-related damage), but is it fair to say this will only apply to older synths? I was having another convo with a board member where he pointed out that replacing audio-related caps on mid-80s gear and beyond probably won't make much of a difference either way to sound quality (presumably because of either integrated circuit design or improvements in caps?) For example, I've heard mixed opinions as to whether having something like an Obie Xpander's audio caps replaced would actually be an improvement or not... but I haven't heard anyone say you will lose anything if you do. Is it also logical to assume that the more ICs are used for things like VCO/VCF/VCA (e.g., an xpander), the less difference changing caps would make?

I may have overstated this... in high impedance tube gear I have experienced distinct changes in character depending on the types of cap fitted. What I was really trying to say is that generally I regard selective recapping as an exercise to prevent nasty failures in low impedance supply paths and PSUs as often their failures can bring on more complex secondary failures. In tube gear this must be extended to inter stage grid decoupling caps - in fact probably more so than HT PSU caps as, rather surprisingly, I've had surprisingly little trouble with 1950's/60's PSU caps which always amazes me. Again, I'm not advocating that we all ignore those metal canned multi-caps you find in so many old HT PSUs in tube gear but it is quite surprising how many are working well after so many years. If anything it's the low voltage uber high capacitance electrolytics in large old PSUs that frighten me!
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