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Korg MS-20 Serial Numbers and Characteristics

Posted under Early Korg Serials at . Last updated 2022-05-01 19:54.
Tags:Korg, MS-20, reference

Conventional wisdom has it that there were distinct versions of the MS-20 over time, the original having a pair of KORG35 chips on the KLM-127 board, but no supporting screw into the heatsink from the VCA panel [1]; the screw was apparently added after some time, and then for no very clear reason about a year later the filter was changed, with a daughterboard (KLM-307) being wired in in place of the KORG35s, using LM13600s. [α] While online comments sometimes say itʼs not so simple, this often seems to be interpreted like there were specific points of change from early no-screw KORG35, to screw KORG35, to late-model LM13600. If so, it should be possible to use serial numbers to construct a timeline for the changes?

Examples Found

s/n [2] screw filter circuit voltage [3]
140014yes?220
140090yes?100
140097yes?100
140163no?1002022-05 ebay
140218no?100Also appeared here (same original source).
140255yes?100
140277yes?100
140353yes?100
140360yes?100
140363yes?100
140367yes?100
140426noKORG35240 (mod)2021-08 ebay.au; seller writes It is an early model featuring the OG Korg 35 filter.”
140438yesKORG35??The seller wrote: The Mk1 [ . . . ] i have owned both and did the test. What test? No other evidence, but chances are it is a K35.
140451noKORG35?100the MS title for a1 calls this a Mini but itʼs not; reappeared (a2) with Early filter type, 2022-02 ebay.jp
140466no?100
140514no?117
140624yes?115 (mod)converted from 220/240
140645noKORG352402022-03 ebay; Vintage Korg MS20 mk1 with the sought after Korg 35 filter chips. 240v UK version
140650yes??
140665yes?240Reappeared here shortly after, same pics.
140893yesKORG35?240 (mod?)2021-02 ebay
140895noKORG35230 (mod)originally 100V; early MK 1 model with the original and very sought after Korg 35 filter
141002no?100
141014no?100
141056yes?220?
141066no100also appeared earlier with fewer pictures
141104no?1002022-02 ebay.jp
141118noKORG35100Mark 1 / Korg 35 chip
141151no?117
141177no?100?s/n not visible
141213yes?100
141219yes?100previously 2021-04 ebay.jp
141256yesKORG352022-01 ebay.jp; Early filter type + picture
141272yes?117the s/n is not wholly legible, missing the third digit, but it could only be a 1
141317yes?220
141447yes?100 (mod?)
141509yes?100
141532yes?100
141562yes??s/n not in pics
141567ano?100Two MS-20s with the same number — see Twynthesisers.
141567byes?100
141575no?100?
141576no?100Apparently also appeared earlier with the same ergonomic improvement, though at the time of writing in that post the serial number is not shown, though one of the pictures has a numberplate — but itʼs of a Roland Juno 106S. This may be a db glitch at Matrixsynth, as the picture also appears here.
141595yes?1002020-12 ebay.jp
141605yes?100
141720noKORG35220at reverb.com mkI Korg 35 filter; modded
141800no?100
141822yes?100
141832no?100?
141846noKORG35117? (mod)original 35 filter version; seems to be modded from 100V
141954no?100?
141968no?1002021-04 ebay.jp
142002no?100
142018no?100
142037no?100
142053no?1002021-04 ebay.jp
142064noKORG35117old filter; reappeared 2022-04 ebay.us
142090yes?240
142104no?117
142113no?117
142145no??s/n given in text
142146noKORG35240KORG35 filter version
142273no?117fake wood
142283yes?2202020-12 ebay.de
142292no?100
142319no?100?
142377no?100
142520noKORG35240Type 35 Filter; voltage may be a mod
142525yes?117
142542yes?117
142557no??s/n not legible
142560yes?117
142567no?1002021-06 ebay.us
142661yes?100?s/n not legible in pics
142659yes?100
142715no?117
142726no?117
142796yes?2402021-08 ebay
142810yes?240reappeared 2020 ebay
142811yes?240
142823yes??2021-02 ebay
142835yes??
142863yes?100
142874yes???s/n not in pic
142888yes?117
142899noKORG35220Première version avec filtres Korg 35; 2022-02 ebay.fr
142989yes?100
143015yesLM13600230 mod2021-02 ebay. MK2 Seller claims to have changed the voltage tap, so has probably seen the KLM-307 board.
143063yes?220
143175yes?220
143312noKORG35100Early filter type; 2022-01 ebay.jp
143314no?1002021-01 ebay.jp
143347yes?100Reappeared here.
143356??100
143371yes?100
143376no?100
143418no?100
143475noKORG35(mod from 100?)the earlier, grittier Korg-35 filter
143490no?1002021-01 ebay.jp
143502noKORG35120 modseems to be modded from 100V; This is the original vintage version, meaning it comes equipped with the legendary original Korg 35 filter. (Notice it doesnt have a screw in the center above the VCA graphic.) This indicates that it has the original filter which produces a much more aggressive tone than later models.” (This is marginally suspect and does not indicate that the seller has actually looked.)
143510no?100
143539???text-only reference
143555no?117
143566?noKORG35(117?)s/n might be 143565. Seller says (or quotes) that it has the KORG35 filter on the LPF . . . which implies that they havenʼt looked, as itʼs none or both, unless possibly modded. See also 144807 and 147963.
143741yes?100
143763no?100
143980yes?100
144008yes?100
144132no?240
144219yes??
144243noKORG35240Mk1
144340yes?240?
144419no?117
144468yes?220
144507noKORG35?220Mark I
144571no?220This appeared here with SQ-10 152096; they also appear in this post focusing on the SQ-10.
144668yes?100
144677yes?100
144758yes?100?s/n not legible; reappeared here, still not legible (same pics).
144764no?117
144796yes?1002021-05 ebay.jp
144807yesKORG35117This seller is probably the same as that of 143566 and 147963, and uses some of the same text regarding the filter.
144809no?117
144812no?117
144946no??s/n not in pics
145003no?100
145022yes?240
145045yesKORG35?2402021-01 ebay. Mk1
145103yes?240
145125noKORG35?117Notice there is no screw on the VCA section panel.. this is an original 35 filter version.. known to be much more aggressive in tone and much rarer than the latter filters : ) The first assumption here is likely, but remains to be demonstrated, and we seem to be finding that the LM13600 is rarer.
145147noKORG35117This MS-20 includes the earlier Korg35 filter
145162yes?100
145169?noKORG35(117?)This MS-20 includes the earlier Korg35 filter
145174no??s/n not in pics
145213no?240
145326yes?1002021-03 ebay.jp
145359no?1002021-01 ebay.jp
145372yes?100Reappeared here.
145374yes?1002022-03 ebay; was 100V at this point but about to be modded for destination voltage
145452no?100Reappeared here a few months later.
145497yes?117
145565yes?240
145616noKORG35100a beautiful MKI MS-20 with the original Korg 35 filter design
145639yes?1002022-04 ebay.jp
145663???s/n not in pic
145695no?220
145773yesLM13600100Filter section does not use KORG35 chip. It has a filter daughter board.”
145914noKORG35100Mk 1
145930no?100
145968no?100?s/n not legible
145976noKORG35100Appears at the main link here with an SQ-10 (no serial number shown); they had previously appeared with no serial numbers at all here; the MS-20 appeared later here, with a photograph showing the interior. (No daughterboard.)
146025no?(220)This is a Swedish import (Matrixsynth says German, but no) by Hagström. Like other Hagström imports it has their own number plate, though in this case it seems that the original number was used, only prefixed with 53. The voltage will be 220 but is not actually stated.
146311no?220
146323no?100
146421no?117
146502yes?100
146504no?100
146513no?100
146530no?100
146537yes???s/n not in pic
146656yes?1002021-10 ebay.jp
146739no?117
146799yesLM13600100MKII Filter
146815yes?100s/n not in pics
146845yes?100
146861yesLM13600?1002021-01 ebay.jp. late model
146971yes?1002021-01 ebay.jp
146984yes??100
146992no?2402021-01 ebay
146995yes?1002022-03 ebay.jp
Entertainingly, this MS-20 is on ebay.jp twice at 2022-03-12, or at least there are two listings using the same photographs and some of the same descriptive text, by different sellers with addresses several hundred miles apart, at significantly different prices. You may not gets what you pays for?
147040no?100
147054no?100
147082yes?100?s/n not visible in pics
147114no?117
147120no??
147141no?117?
147239yes??100
147262no?220
147324no?100
147325yes?240 (mod)2022-04 ebay
147345yes?100
147539yes??probably ebay 2020; vanished before I went back to check
147562no?117
147577no?117
147624?noKORG35117?Difficult to read s/n. Reappeared here with text. (This MS-20 has the original and legendary Korg-35 filter as opposed to the LM13600)
147677no?117
147777yes?240
147855no?220
147882no?117
147888no?117
147891noKORG35?These pictures show a KORG35-version board without a daughterboard; pic 4 incidentally shows the serial number.
147918no?100
147945no?117Reappeared repaired here.
147963noKORG35117This seller is probably the same as that of 143566 and 144807, and uses some of the same text regarding the filter.
147965no?117
147966yes?100
147969no?117
147985no?117wood!
148015yes?100
148029yes?100
148126noKORG352202021-05 ebay; Here a rare Korg MS-20 MK1 release that mount the first filter release (KORG 35)
148358yes?100
148421yes?100
148457yes?100
148514noKORG35117original MK1 version with the 35 filter Reappeared shortly afterwards here.
148721yesLM136002202022-01 ebay.be. Modded with added amplifier & speakers. Cannibalised, missing several keys, pots, most knobs. (personally examined)
148753yes?2202021-06 ebay; reappeared 2021-12 ebay
148855yes?117?
148878no?2402020-11 ebay
149126yes?2402021-05 ebay
149199yesKORG35?probably ebay 2020; vanished before I went back to check
149201yes?100
149206yes?1002021-03 ebay.jp
149245yes?1002022-01 ebay.jp
149286yes?240 (mod)2022-03 ebay
149363yes?220
149394yesLM13600240Rev 2; 2021-05 ebay
149400yes?220
149500yesKORG35220(personally examined)
149534no?100?s/n not legible
149542yes?100
149560yes?100
149615yes??
149668no?2202022-04 ebay.de
149762yes?220
149850yes?220
149947yes?1002021-03 ebay.jp
149968yes?100Seller wrote Has the more sought after "screw"filter version.” Itʼs not clear what this means.
149984yesKORG35?220?MARK 1 VERSION. WITH THE (IN)FAMOUS IC35 SCREAMING UNIQUE AND TERRIFYING FILTER.”
Synthesisers have had some sort of cultural impact over the last sixty years, would you say?
439010yes?100
439039yes?100
439093yes?100

(Total: 232. Last updated 2022-05-01.)

Interim Conclusions

Well, thatʼs a no. There seem to be some anomalies here, if we believe the story that the heatsink screw was added and then the filter was changed, simple as that.

Heatsink Screw

Clearly, the screw may be present at any point in the sequence. Why this would vary as much as it does is unclear. Something to do with the weight of the heatsink? And that would perhaps be determined by the heat dissipation requirements of the voltage regulators . . . ? Strength of the boards used at different stages? Or perhaps itʼs to do with the mechanical strength of the main attachment of the board to the panel, which is mostly via the potentiometersʼ soldered legs; if the pot type differed over time, perhaps some legs might have been thought weaker. But on the basis of pictures Iʼve seen (see Board Versions, below) of non-screwed KLM-127 boardsʼ component sides, there doesnʼt seem like that much difference.

Filter Type

The 43s are strange representatives of the block, all found so far being over 439000, and all 100V; perhaps it started at 439001. Which would make sense since the lower 43s are occupied by the EPS-1. Presumably Korg planned to retire the MS-20 before the thousand was up. With those exceptions none of the numbers found are outside the 140001–149999 range, so production probably stopped at around 10,000 (plus perhaps only a hundred 43s, and perhaps minus an unknown number of 14- GT-6s?[4]). So thereʼs nowhere else for a significant group of MkIIs to be hiding. As some of the last of the 14- block are certainly KORG35, it seems that only some of the later MS-20s had LM13600 filters? And the earliest LM13600s started in the 3000s? Perhaps it was simply an availability issue rather than a design preference. [5]

There may be a reporting bias in these results — as the KORG35 filter has acquired a superior reputation, perhaps people are inclined to say that they have it for sale when they think they do, but people who donʼt are inclined not to mention it. Probably several of the unknowns are in fact LM13600 but itʼs impossible to say which. Even so, it seems that the LM13600 filter may be substantially the rarer of the two. Currently 6:36, but take that with a large pinch of something. And it should be noted that only a very few of these results are clearly demonstrated; some of them may simply be writersʼ opinions, based on conventional wisdom about the relationship of screws and filters.

I think it is possible to say that the KORG35 filter is not old or MkI in production terms, though it is the early design; but while it is a later design, the LM13600 board was only used intermittently. And it seems several KORG35s come later in the sequence than the last LM13600. (However, in recent years Korg themselves have taken to referring to the Rev.1 and Rev.2 filters. Not, as far as I can tell, the whole synth, just the filters.)

Filter/Screw Correlation

So far — but this is a very limited sample size — all LM13600s identified have also had the screw; which might make sense in terms of the slight extra weight of the daughterboard, but itʼs only about 40g. And itʼs clearly not the determining factor in screw use.

Board Versions

At least versions C, D, E, F, & G of the KLM-127 board exist. I did think there was no significant distinction between them, but now with close examination — albeit with a small sample set of 1–3 each — it seems that:

  1. versions C through F have KORG35 chips and associated components on board, but version G has connection points for the KLM-307 board instead; and
  2. versions C, D, & E have no panel screw hole, but F & G do.

Unfortunately there are only three cases where I can directly associate board types and serial numbers — 147891 is version D, and the personally examined 148721 and 149500 are G and F respectively. It is unclear whether there may have been earlier boards with panel screw holes and/or KLM-307 connections, or whether these things may have been done differently. [6] But the first known serial numbers are associated with screws, and some LM13600s were used well before the only known KLM-127D. So these relationships remain tentative.

tentative summary of KLM-127 board revision features
CDEFG
filterKORG35LM13600
screwnoyes
known s/n 147891149500148721
sources [β],[γ],[δ] [ε] [ζ] PEX [η], PEX
Korg MS-20 Nº1 KLM-127F board, components side Korg MS-20 Nº1 KLM-127F solder side
KLM-127F, comps side (with front-panel spacer post) and solder side.
Korg MS-20 Nº2 KLM-127G board, comps side Korg MS-20 Nº2 KLM-127G solder side
KLM-127G, comps side (with front-panel spacer post) and solder side (with daughterboard connections and spacers).
(Here SW1, VR10, VR25, VR29 are awaiting replacement.)

The KLM-127 diagram in the (original) service manual does not give a revision number, but it appears to be earlier than rev.F at least. [7] (I would of course expect it to be the original production version rather than anything later, but who knows?) n.b. while the KLM-307 is sometimes described as a filter board, some examination of the service manual indicates that in rev.G, the VCA circuitry is also on the KLM-307 rather than the KLM-127.

(Update: Turns out VSE is now hosting a revised version of the MS-20 service manual with clearer diagrams and additional LM13600-version schematics and drawings. It distinguishes old production and new production KLM-127s but doesnʼt give revision codes.)

There were multiple versions of the KLM-128 (patchbay) board too, though Iʼve only seen rev.C, and Iʼm not clear what the differences were. The service manual for the MS-10 shows a revision of the noise generator circuit, with the revised version being the same as the circuit shown in the MS-20 manual. There is no indication that the circuit changed in the MS-20, but it may have?

An Unlikely Explanation

One possibility that should be acknowledged, though I donʼt think it likely, is that the serial numbers are not a chronological sequence, but may have been assigned either randomly or algorithmically from within the 14- block. That would explain the above results, but still . . . 

There are two specific points of evidence for Korg using incrementing rather than random or algorithmically distributed serial numbers in this period:

  1. The service manual for the MS-10 states that a change was made in the noise circuit, so that all MS-10s from 132828 had the new type — strongly implying a chronological sequence.
  2. The numberplate on Sigma 5663 appears to have been stamped twice with 5662 and then 5663.

And in general, some models with model-number type serial numbers seem to show (relatively) low production volumes with serial numbers concentrated at the low end of the number space, e.g. at the time of writing all BPX-3 serial numbers are between 400001–401500 rather than randomly distributed from 40001–499999. I donʼt think anything other than normal ascending incrementation is tenable for this time period.

(More recent manufacturing has been able to calculate and print quasi-random serial numbers with built-in validity-checks, but that would have been an atypical use of computing resources in 1978.)


Comment or Question about this page?write


Notes

  1. Or, it depends what you mean by conventional wisdom. While compiling this page I came across this classic seller misrepresentation at Matrixsynth (my emphasis):

    Originally, the filters used Korg's proprietary KORG-35 chip. Later, the filters were redesigned to use off-the-shelf LM13600 OTAs. MS-20 fitted with LM13600 filters have a small daughter board. This one here has the later filter (the small screw above the VCA graphic on the outside it's a newer filter, if it has no screw it's a korg35. That screw is what holds the daughter board for the newer filter. )

    (source)

    This is quite wrong, but it does seem to be a popular belief. In reality the screw is into a spacer post, the other end of which is screwed through the heatsink for the power regulators and the KLM-127 board. It may assist in supporting the slight extra weight of the daughterboard (which is affixed to the KLM-127 board with plastic spacer posts) where present, but the screw is clearly used sometimes whether or not thereʼs a daughterboard, for unclear reasons. Consequently the screw does not indicate LM13600s, and assertions of its presence on this basis are wholly unreliable. To check, all you have to do is unscrew the left end panel and look inside; if thereʼs a daughterboard connected to the back of the main (KLM-127) board under the heatsink, itʼs LM13600-based; if not, KORG35:

    Korg KLM307 board end-on  
  2. Serial numbers have links where the sources are quasi-permanent. Where there are no links the online appearances were ephemeral, but I usually have the original photographs saved. Sometimes the source gives a serial number in text but not in pictures.  
  3. Iʼve been collecting voltage information where possible on the basis that it might help to establish batch relationships or national-market differences. So far this does not seem to be telling us anything for the MS-20s, but who knows?  
  4. See Early Korg Serials §Model Numbers.  
  5. Tim Stinchcombe (2006) [θ] suggested that it was to do with CV bleed-through in the KORG35 chip, or the cost of matched transistors. Unless the former was intermittently fixable it seems unlikely, as there does not seem to have been a single replacement event. The latter may be true to some extent, as it would simply be a cost→availability issue, which might have varied over time.  
  6. It may be worth noting that the KLM-307 board uses three standoff posts rather than the usual one per corner, as if the designers were working with the constraint of the existing KLM-127 design rather than taking an opportunity to change it, although revision G does have several changes compared with C–F. If rev.G was the only board used with the KLM-307, we might expect that the redesign would have incorporated all changes on the board itself, but it seems possible that rev.G is a later redesign intended to streamline production with a prëexisting KLM-307? Use of the KLM-307 with an earlier revision KLM-127 (A or B?) might also explain why rev.D was in use so much later than the earliest LM13600s?

    (Update, 2022-04-17: Some further examination suggests that there may have been a revision of the KLM-307 board, as seen at Studio Repair, as compared to my board which is presumably the original design but has some added signal coupling capacitors which appear to have been incorporated into the revision. Perhaps even earlier MS-20s didnʼt have these? However, it should be noted that both these KLM-307s are used with KLM-127Gs.)

    (Update, 2022-04-20: Thereʼs an image at synthesizor.wordpress.com which shows a KLM-307 with the same components and screening as the SR one, which has a screened code KLM-307A.)  

  7. As far as I can see, the diagram has C6 and R126 which are absent on the rev.F board, and the board has a D40, D41, R201, R202, R203, R204, R205, R206, R207, C50, C51 and C52 not on the diagram. The rev.G board also has these changes, along with others relating to the shift to the KLM-307. Also, R123 is in a different position on the KLM-127F compared to the diagram but absent on the rev.G.  

References

  1. Nearest thing to horsesʼ mouths on this would be: Korg Inc., Interview with Mieda Fumio and Nishijima Hiroaki, MS-20 designers, 2013 (YouTube).  
  2. Pictures at Matrixsynth Flickr  
  3. Pictures at Matrixsynth Flickr  
  4. Pictures at Korg Kornukopia  
  5. Pictures by Synthfool  
  6. Pictures at Matrixsynth  
  7. Pictures at Studio Repair  
  8. Stinchcombe, Timothy E., A Study of the Korg MS10 & MS20 Filters, 2006 (updated 2009), available at timstinchcombe.co.uk.  

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