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 it’s 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] | |
---|---|---|---|---|
140014 | yes | ? | 220 | |
140090 | yes | ? | 100 | |
140097 | yes | ? | 100 | |
140163 | no | ? | 100 | 2022-05 ebay |
140218 | no | ? | 100 | Also appeared here (same original source). |
140255 | yes | ? | 100 | |
140277 | yes | ? | 100 | |
140353 | yes | ? | 100 | |
140360 | yes | ? | 100 | |
140363 | yes | ? | 100 | |
140367 | yes | ? | 100 | |
140419 | yes | KORG35 | ? | “A beautiful MK-1 original MS-20” |
140426 | no | KORG35 | 240 (mod) | 2021-08 ebay.au; seller writes “It is an early model featuring the OG Korg 35 filter.” |
140438 | yes | KORG35? | ? | 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. |
140451 | no | KORG35? | 100 | the MS title for a1 calls this a Mini but it’s not; reappeared (a2) with “Early filter type”, 2022-02 ebay.jp |
140466 | no | ? | 100 | |
140514 | no | ? | 117 | |
140591 | yes | ? | 100? | 2022-08 ebay; reappeared 2023-04 reverb.com |
140611 | no | ? | 100 | |
140624 | yes | ? | 115 (mod) | converted from 220/240 |
140645 | no | KORG35 | 240? | 2022-03 ebay; “Vintage Korg MS20 mk1 with the sought after Korg 35 filter chips. 240v UK version”; the pictures shown don’t actually show the voltage clearly — this may be a mod since it has the “Keio Giken” plate |
140650 | yes | ? | ? | |
140665 | yes | ? | 240 | Reappeared here shortly after, same pics. |
141747 | no | KORG35 | 100 | 2022-10 ebay.jp; “Early Filter Type” |
140893 | yes | KORG35? | 240 (mod?) | 2021-02 ebay |
140895 | no | KORG35 | 230 (mod) | originally 100V; “early MK 1 model with the original and very sought after Korg 35 filter” |
140934 | no | KORG35 | 100 | “Early MS-20 with the greyer faceplate and desirable Korg 35 filter type” |
141002 | no | ? | 100 | |
141014 | no | ? | 100 | |
141056 | yes | ? | 220? | |
141066 | no | 100 | also appeared earlier with fewer pictures | |
141104 | no | ? | 100 | 2022-02 ebay.jp |
141118 | no | KORG35 | 100 | “Mark 1 / Korg 35 chip” |
141151 | no | ? | 117 | |
141163 | no | ? | 100 | |
141177 | no | ? | 100? | s/n not visible |
141213 | yes | ? | 100 | |
141219 | yes | ? | 100 | previously 2021-04 ebay.jp |
141256 | yes | KORG35 | 2022-01 ebay.jp; “Early filter type” + picture | |
141272 | yes | ? | 117 | the s/n is not wholly legible, missing the third digit, but it could only be a 1 |
141317 | yes | ? | 220 | |
141445 | yes | ? | 100 | 2022-12 ebay.jp |
141447 | yes | ? | 100 (mod?) | |
141509 | yes | ? | 100 | |
141532 | yes | ? | 100 | |
141562 | yes | ? | ? | s/n not in pics |
141567a | no | ? | 100 | Two MS-20s with the same number — see Twynthesisers. |
141567b | yes | ? | 100 | |
141575 | no | ? | 100? | |
141576 | no | ? | 100 | Apparently 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 it’s of a Roland Juno 106S. This may be a db glitch at Matrixsynth, as the picture also appears here. Reappeared 2022-08 ebay.us (with s/n). |
141595 | yes | ? | 100 | 2020-12 ebay.jp |
141605 | yes | ? | 100 | |
141720 | no | KORG35 | 220 | at reverb.com “mkI Korg 35 filter”; modded |
141800 | no | ? | 100 | |
141822 | yes | ? | 100 | |
141832 | no | ? | 100? | |
141846 | no | KORG35 | 117? (mod) | “original 35 filter version”; seems to be modded from 100V |
141954 | no | ? | 100? | |
141968 | no | ? | 100 | 2021-04 ebay.jp |
142002 | no | ? | 100 | |
142018 | no | ? | 100 | |
142029 | no | KORG35 | 240 (mod) | 2022-06 ebay; “mk1 edition original Korg MS20 monosynth featuring the type 35 filter” |
142037 | no | ? | 100 | |
142053 | no | ? | 100 | 2021-04 ebay.jp |
142064 | no | KORG35 | 117 | “old filter”; reappeared 2022-04 ebay.us |
142090 | yes | ? | 240 | |
142104 | no | ? | 117 | |
142113 | no | ? | 117 | |
142145 | no | ? | ? | s/n given in text |
142146 | no | KORG35 | 240 | “‘KORG35’ filter version” |
142273 | no | ? | 117 | fake wood |
142283 | yes | ? | 220 | 2020-12 ebay.de |
142292 | no | ? | 100 | |
142319 | no | ? | 100? | |
142377 | no | ? | 100 | |
142520 | no | KORG35 | 240 (mod) | “Type 35 Filter” |
142525 | yes | ? | 117 | |
142542 | yes | ? | 117 | full set of images on flickr |
142557 | no | ? | ? | s/n not legible |
142560 | yes | ? | 117 | |
142567 | no | ? | 100 | 2021-06 ebay.us |
142661 | yes | ? | 100? | s/n not legible in pics |
142659 | yes | ? | 100 | |
142715 | no | ? | 117 | |
142726 | no | ? | 117 | |
142796 | yes | ? | 240 | 2021-08 ebay |
142810 | yes | ? | 240 | reappeared 2020 ebay |
142811 | yes | ? | 240 | |
142823 | yes | ? | ? | 2021-02 ebay |
142835 | yes | ? | ? | |
142863 | yes | ? | 100 | |
142874 | yes? | ? | ? | s/n not in pic |
142888 | yes | ? | 117 | |
142899 | no | KORG35 | 220 | “Première version avec filtres Korg 35”; 2022-02 ebay.fr |
142912 | yes | ? | 240 | 2023-05 ebay |
142939 | yes | ? | 240 | 2023-01 eb |
142989 | yes | ? | 100 | |
143005 | no | ? | 100 | 2022-12 ebay.jp |
143015 | yes | LM13600 | 230 mod | 2021-02 ebay. “MK2” Seller claims to have changed the voltage tap, so has probably seen the KLM-307 board. |
143063 | yes | ? | 220 | |
143175 | yes | ? | 220 | |
143281 | yes | ? | 100? | s/n given in text |
143312 | no | KORG35 | 100 | “Early filter type”; 2022-01 ebay.jp |
143314 | no | ? | 100 | 2021-01 ebay.jp |
143347 | yes | ? | 100 | Reappeared here. |
143356 | ? | ? | 100 | |
143371 | yes | ? | 100 | |
143376 | no | ? | 100 | |
143418 | no | ? | 100 | |
143475 | no | KORG35 | (mod from 100?) | “the earlier, grittier Korg-35 filter” |
143490 | no | ? | 100 | 2021-01 ebay.jp |
143502 | no | KORG35 | 120 mod | seems 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.) |
143510 | no | ? | 100 | |
143539 | ? | ? | ? | text-only reference |
143555 | no | ? | 117 | |
143566? | no | KORG35 | (117?) | s/n might be 143565. Seller says (or quotes) that it has the KORG35 filter on the LPF . . . which implies that they haven’t looked, as it’s none or both, unless possibly modded. See also 144807 and 147963. |
143657 | yes | ? | 100 | 2023-03 ebay.jp |
143657 | yes | ? | 100 | listed shortly afterwards with new photos on reverb.com |
143694 | yes | ? | 100 | 2022-09 ebay.jp |
143741 | yes | ? | 100 | |
143763 | no | ? | 100 | |
143980 | yes | ? | 100 | |
144008 | yes | ? | 100 | |
144132 | no | ? | 240 | |
144219 | yes | ? | ? | s/n not shown in pics |
144243 | no | KORG35 | 240 | “Mk1” |
144340 | yes | ? | 240? | |
144419 | no | ? | 117 | |
144468 | yes | ? | 220 | |
144507 | no | KORG35? | 220 | “Mark I” |
144571 | no | ? | 220 | This appeared here with SQ-10 152096; they also appear in this post focusing on the SQ-10. |
144668 | yes | ? | 100 | |
144677 | yes | ? | 100 | |
144758 | yes | ? | 100? | s/n not legible; reappeared here, still not legible (same pics). |
144764 | no | ? | 117 | |
144796 | yes | ? | 100 | 2021-05 ebay.jp |
144807 | yes | KORG35 | 117 | This seller is probably the same as that of 143566 and 147963, and uses some of the same text regarding the filter. |
144809 | no | ? | 117 | |
144812 | no | ? | 117 | |
144890 | no | KORG35 | 240 | 2023-01 ebay; seller included pic of the KORG35 chips; may have had voltage modded? |
144946 | no | ? | ? | s/n not in pics |
145003 | no | ? | 100 | |
145022 | yes | ? | 240 | |
145045 | yes | KORG35? | 240 | 2021-01 ebay. “Mk1” |
145063 | yes | ? | 240 | 2022-09 ebay |
145103 | yes | ? | 240 | |
145125 | no | KORG35? | 117 | “Notice 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. |
145147 | no | KORG35 | 117 | “This MS-20 includes the earlier Korg35 filter” |
145162 | yes | ? | 100 | |
145169? | no | KORG35 | (117?) | “This MS-20 includes the earlier Korg35 filter” |
145174 | no | ? | ? | s/n not in pics |
145213 | no | ? | 240 | |
145326 | yes | ? | 100 | 2021-03 ebay.jp |
145359 | no | ? | 100 | 2021-01 ebay.jp |
145372 | yes | ? | 100 | Reappeared here. |
145374 | yes | ? | 100 | 2022-03 ebay; was 100V at this point but about to be modded for destination voltage |
145452 | no | ? | 100 | Reappeared here a few months later. |
145497 | yes | ? | 117 | |
145565 | yes | ? | 240 | |
145616 | no | KORG35 | 100 | “a beautiful MKI MS-20 with the original Korg 35 filter design” |
145639 | yes | ? | 100 | 2022-04 ebay.jp |
145663 | ? | ? | ? | s/n not in pic |
145695 | no | ? | 220 | |
145773 | yes | LM13600 | 100 | “Filter section does not use KORG35 chip. It has a filter daughter board.” |
145914 | no | KORG35 | 100 | “Mk 1” |
145930 | no | ? | 100 | |
145968 | no | ? | 100? | s/n not legible |
145976 | no | KORG35 | 100 | Appears 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.) |
146025 | no | ? | (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. |
146311 | no | ? | 220 | |
146323 | no | ? | 100 | |
146421 | no | ? | 117 | |
146502 | yes | ? | 100 | |
146504 | no | ? | 100 | |
146513 | no | ? | 100 | |
146530 | no | ? | 100 | |
146537 | yes? | ? | ? | s/n not in pic |
146656 | yes | ? | 100 | 2021-10 ebay.jp |
146739 | no | ? | 117 | |
146799 | yes | LM13600 | 100 | “MKII Filter” |
146890 | yes | LM13600 | 100 | 2022-11 ebay; “this is the MK2 original”; replacement wood ends |
146815 | yes | ? | 100 | s/n not in pics |
146845 | yes | ? | 100 | |
146861 | yes | LM13600? | 100 | 2021-01 ebay.jp. “late model” |
146898 | yes | ? | ? | 2023-02 ebay.jp. Duplicate sales — see Korg Duplicate Sales, MS-20 146898. |
146971 | yes | ? | 100 | 2021-01 ebay.jp |
146984 | yes? | ? | 100 | |
146992 | no | ? | 240 | 2021-01 ebay |
146995 | yes | ? | 100 | 2022-03 ebay.jp. Duplicate sales — see Korg Duplicate Sales, MS-20 146995. |
147040 | no | ? | 100 | |
147054 | no | ? | 100 | |
147082 | yes | ? | 100? | s/n not visible in pics |
147114 | no | ? | 117 | |
147120 | no | ? | ? | |
147141 | no | ? | 117? | |
147239 | yes? | ? | 100 | |
147262 | no | ? | 220 | |
147301 | yes | ? | 100 | |
147324 | no | ? | 100 | modded |
147325 | yes | ? | 240 (mod) | 2022-04 ebay |
147345 | yes | ? | 100 | |
147539 | yes | ? | ? | probably ebay 2020; vanished before I went back to check |
147562 | no | ? | 117 | |
147577 | no | ? | 117 | |
147624? | no | KORG35 | 117? | 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”) |
147677 | no | ? | 117 | |
147765 | yes | ? | 240 | |
147777 | yes | ? | 240 | |
147855 | no | ? | 220 | |
147882 | no | ? | 117 | |
147888 | no | ? | 117 | |
147891 | no | KORG35 | ? | These pictures show a KORG35-version board without a daughterboard; pic 4 incidentally shows the serial number. |
147918 | no | ? | 100 | |
147945 | no | ? | 117 | Reappeared repaired here. |
147963 | no | KORG35 | 117 | This seller is probably the same as that of 143566 and 144807, and uses some of the same text regarding the filter. |
147965 | no | ? | 117 | full set of images on flickr |
147966 | yes | ? | 100 | |
147969 | no | ? | 117 | full set of images on flickr |
147985 | no | ? | 117 | wood! |
148015 | yes | ? | 100 | |
148029 | yes | ? | 100 | |
148101 | yes | ? | ? | 2022-12 ebay; the voltage seems to have been misstamped but is probably 240; being sold alongside SQ-10 152984 |
148126 | no | KORG35 | 220 | 2021-05 ebay; “Here a rare Korg MS-20 MK1 release that mount the first filter release (KORG 35)”; full set of images on flickr |
148358 | yes | ? | 100 | |
148364 | yes | ? | 100 | 2022-06 ebay.jp |
148421 | yes | ? | 100 | |
148457 | yes | ? | 100 | |
148514 | no | KORG35 | 117 | “original MK1 version with the 35 filter” Reappeared shortly afterwards here. |
148721 | yes | LM13600 | 220 | 2022-01 ebay.be. Modded with added amplifier & speakers. Cannibalised, missing several keys, pots, most knobs. (personally examined) |
148753 | yes | ? | 220 | 2021-06 ebay; reappeared 2021-12 ebay |
148855 | yes | ? | 117? | |
148878 | no | ? | 240 | 2020-11 ebay |
148890 | yes | ? | 240 | 2023-04 ebay |
149126 | yes | ? | 240 | 2021-05 ebay |
149199 | yes | KORG35 | ? | probably ebay 2020; vanished before I went back to check |
149201 | yes | ? | 100 | |
149206 | yes | ? | 100 | 2021-03 ebay.jp |
149245 | yes | ? | 100 | 2022-01 ebay.jp |
149286 | yes | ? | 240 (mod) | 2022-03 ebay |
149352 | yes | ? | 220 | |
149363 | yes | ? | 220 | |
149394 | yes | LM13600 | 240 | “Rev 2”; 2021-05 ebay |
149400 | yes | ? | 220 | |
149500 | yes | KORG35 | 220 | (personally examined) |
149534 | no | ? | 100? | s/n not legible |
149542 | yes | ? | 100 | knobs replaced |
149560 | yes | ? | 100 | |
149615 | yes | ? | ? | |
149668 | no | ? | 220 | 2022-04 ebay.de |
149744 | yes | ? | 240 | 2022-08 ebay.au |
149762 | yes | ? | 220 | |
149850 | yes | ? | 220 | |
149914 | yes | ? | 220 | 2023-01 ebay.it |
149947 | yes | ? | 100 | 2021-03 ebay.jp |
149968 | yes | ? | 100 | Seller wrote “Has the more sought after "screw"filter version.” It’s not clear what this means. |
149984 | yes | KORG35? | 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? |
439010 | yes | ? | 100 | |
439039 | yes | ? | 100 | |
439057 | yes | LM13600 | 100 | info. from Vincent Presley |
439078 | yes | ? | 100 | 2022-12 ebay.jp |
439093 | yes | ? | 100 |
(Total: 261. Last updated 2023-05-18.)
Interim Conclusions
Well, that’s 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. (Current totals: 139 with screws, 119 without.) 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 it’s to do with the mechanical strength of the main attachment of the board to the panel, which is mostly via the potentiometers’ soldered legs; if the pot type differed over time, perhaps some legs might have been thought weaker. But on the basis of pictures I’ve seen (see Board Versions, below) of non-screwed KLM-127 boards’ component sides, there doesn’t 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- tuners? [4]). So there’s nowhere else for a significant group of “MkII”s 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 don’t are inclined not to mention it. Probably several of the unknowns are in fact LM13600 but it’s impossible to say which. Even so, it seems that the LM13600 filter may be substantially the rarer of the two. Currently 8:41, 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 writers’ 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. (Update, 2023-04-07: We now have a confirmed LM13600 in the 439- block.) (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 it’s only about 40g. And it’s 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:
- 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
- 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.
C | D | E | F | G | |
---|---|---|---|---|---|
filter | KORG35 | LM13600 | |||
screw | no | yes | |||
known s/n | 147891 | 149500 | 148721 | ||
sources | [β], [γ], [δ] | [ε] | [ζ] | PEX | [η], PEX |




(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 doesn’t give revision codes.)
There were multiple versions of the KLM-128 (patchbay) board too, though I’ve only seen rev.C, and I’m 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 don’t think it likely, is that the serial numbers are not a chronological sequence, but may have been assigned either randomly or by some other algorithm from within the 14- block. That would explain the above results, but still . . .
There are two specific points of evidence for Korg using incrementing serial numbers in this period:
- 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.
- 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 found are between 400001–401500 rather than randomly distributed from 400001–499999. As a back-of-a-spreadsheet calculation, the average numberspace proportion of the low-end and high-end numbers found (where >1 numbers known) for each model are at 0·044 and 0·489, which would be a −0·234 bias compared with random or other even distribution. I don’t 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.)
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Notes
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. )”
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 there’s 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 there’s a daughterboard connected to the back of the main (KLM-127) board under the heatsink, it’s LM13600-based; if not, KORG35:
↖
- 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. ↖
- I’ve 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? ↖
- 14- numbers were used on some GT-6s, and on at least one (presumably more) Micro-Six. See Early Korg Serials §Model Numbers. ↖
- 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. ↖
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 didn’t have these? However, it should be noted that both these KLM-307s are used with KLM-127Gs.)
(Update, 2022-04-20: There’s 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.) ↖
- 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
- Nearest thing to horses’ mouths on this would be: Korg Inc., Interview with Mieda Fumio and Nishijima Hiroaki, MS-20 designers, 2013 (YouTube). ↖
- Pictures at Matrixsynth Flickr ↖
- Pictures at Matrixsynth Flickr ↖
- Pictures at Korg Kornukopia ↖
- Pictures by Synthfool ↖
- Pictures at Matrixsynth ↖
- Pictures at Studio Repair ↖
- Stinchcombe, Timothy E., A Study of the Korg MS10 & MS20 Filters, 2006 (updated 2009), available at timstinchcombe.co.uk. ↖
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Comments
Got an MS-20
by Vincent Presley on 2023-04-06 17:03
I just got an MS-20 and thought I would send you it's info since I found this article very useful.
Serial Number 439057
Has screw
100V from Japan
Confirmed it has the daughter board / LM filter by removing the side.
comment?