Yamaha CS-20M

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Pics of the inside below. The YM-615 chip is the keyboard controller according to sounddoctorin.

This one does need work.

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Korg Poly 61M Vintage Analog Synth with MIDI SN 001636

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""Unlike many Poly 61s that are out there, this one is not all bashed up. The body is in great condition, with only a few minor nicks, and the synth is in very good working form. It has never had a battery leak, so all the functions work perfectly, and I did the following to it, to get it in top shape:

- I replaced the original battery with a CR2032, in a battery holder on a longer set of wires to make changing it easy.
- I totally refurbished the keyboard, cleaning all the keys, cleaning all the contacts, and adding carbon discs to the contacts, as per the solution by Sounddoctorin.com. That brings all the keys to perfect working condition.
- I removed all the tactile button switches and replaced them with brand new ones. That solves the annoying problem of having to keep hitting the program buttons many times until they work, or having them double count because of contact bounce. Now all the programming buttons work flawlessly. There is a photo showing the new switches(blue) on the two switch circuit boards.
- I cleaned all the pots to eliminate scratching noises and jumping values.
- I replaced any of the screws that were missing, and all the feet are there, too.

This is a really great sounding synth, with a pure analog voice signal, and very stable tuning thanks to the digital control of the oscillators. And with factory midi, it is just a dream to own. It is fully tested, and loaded with sounds from a file I downloaded onto my phone from the internet. There are lots of those out there, and it is easy to do. And of course, you can create and save your own sounds."

Crumar DS2 Vintage Analog /Digital Synthesizer SN 129

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"This is an amazing keyboard in many ways. It's one of the original series of Digital oscillator synths ( really analog controlled 74ls221 multivibrator chips. One for each mono osc and one for the poly organ which routes with noise and ext. input to analog mainboard. I documented mass info. on these. see my youtube tech vids). Only 150 or so of DS1 were made and it just lacks poly section and second LFO. They made I think a couple thousand DS2 maybe. MANY are badly rusted ( like my studio one I don't dare sell for fear of more troubles) This one however is pretty great. I fabbed a handle. I also spent many hours going over it on a few occasions and hopefully it's reliable now. The story is documented on my sounddoctorin site."

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DIY Synth Knobs & Slider Caps | Side Panels for Korg Polysix / Poly 61 & Siel DK600

New products unveiled. Synth knobs, Sides for PS6 + DK600! Rhodes pre-piano chimes

Published on Apr 11, 2019 sounddoctorin

"Bob Weigel of http://www.sounddoctorin.com Shows the newly created mold for precision knob replicas and Soon available Walnut sides for Korg Polysix/ 61 and Siel DK600/Opera 6/ Kiwi. And a teaser for the upcoming Rhodes Pre-piano video. I can make another mold when needed but set this one up for 6 crumar, 2 arp omni 1, 1 arp 2600, 1 arp pro-soloist, 2 polymoog, 2 roland juno 6/60, 2 juno 106, 2 Yamaha CS-20m / 40m, 1 Aelita, 2 korg mini/maxi D shape and 2 oval, 1 Chroma Polaris."

Yamaha CS5 repair tips/demo/feature review

Published on Jun 14, 2018 sounddoctorin

"Bob Weigel of http://www.sounddoctorin.com shows a peculiar manifestation of a bad IG00156 vcf chip in the Yamaha CS5 synthesizer from 1978. Pardon absence of highest frequencies that my camera and audio at 22khz doesn't register but I was hearing those shrill upper notes here and sounded reasonably in tune :-) . I added a description of this issue to my global synth resource pages for synths using this vcf in case others see this failure mode."

OBERHEIM OB8 ANALOG POLYPHONIC SYNTHESIZER

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A few issues with this one:

"1. The F# and A# keys in the top octave of the keyboard are intermittent (the ones with dimes on them in the pics). They work, but you have to sometimes depress them a few times before they come back to life. This is a fairly common problem with any keyboard that uses a Panasonic keyboard (Memorymoog, OB8, Polysix, Matrix-12 etc...). For me it hasn't been an issue because I use my OB8 like a sound module via MIDI, using a master keyboard controller. But if you want to use the keyboard, these keys need their contacts cleaned.

2. There are four buttons on the front panel called 'group' buttons: A, B, C, & D. These let you select which bank of programs you want to play. The C and D buttons also need cleaning. They do work, but like the keys mentioned above, you sometimes have to tap on them a few times to get them to light up and work. But they do light up and work. One of the pics shows all four lit so you can see for yourself.

3. The number 5 program button is also a little fussy, but it definitely works. It has the same personality disorder as the others mentioned above. It needs to be cleaned.

(And by the way, There is a guy on YouTube that goes by the name of "sounddoctorin" who sells replacement contact strips for the OB8 keys)."

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Layering Sounds on the KORG M500 & a Warning on Leaking Capacitors

Korg M500 demo/ GENERAL TECH NOTE for later 70's korgs/ oliver leslie preview

Published on Sep 23, 2015 sounddoctorin

"Bob Weigel of http://www.sounddoctorin.com shows some new features I wasn't aware of on the M500 micro preset (ie. the ability to mix settings... why didn't I try this before? Some fabulous sounds available that way I'd never explored) , but also shows a problem that surfaced in both the unit shown here and my own M500. Be sure to open yours and remove the 220uF 16 V capacitors. Note how there is probably acid eating the traces under them. Restore as noted in the video and also 33uF capacitors were having the same issue in mine. THose particular values seem to be fail prone at this age. I assume the same parts were being used in other synths of the ear including MS series, PS series... possibly my PE1000 I should also check. Tuning is varying some anyway.. Look for discolored traces. Not hard to see. I also show off my home made horn for the oliver orbital sound projector I'd just finished at the end. :-)"

Crumar Performer with octave slider plus sustain options!

Published on Aug 1, 2015 sounddoctorin

"Bob Weigel of http://www.sounddoctorin.com shows a tech brief and demo of his latest modification. The last Crumar Performer version I have used the SSM2040 vcf and a SSM2056 eg in place of the moog vcf and discrete eg. with it's quirky interactive behavior used in the original units. The last version also adds an octave switch.

As it turns out barely over an octave can be achieved at the summing node for pitch without causing oscillations to cease for whatever reason I discovered, as I installed a slider instead of a switch in this unit giving a lovely contiguous transition of pitch for 1 octave. Provided you don't retune it with the tuning pot on back :-). There is a requirement to readjust the trim pot I installed if you do that. But as long as you keep it on A440 it's a nice octave. SEE MY PREVIOUS video on the performer mod to see details of how to give yourself four modes of operation with regard to sustain and crescendos."

Korg Mono/Poly MP4 "Midipoly" upgrade- project teaser & prototype ARP2600 expander

Published on Jul 7, 2015 sounddoctorin

"Bob Weigel of http://www.sounddoctorin.com shows some installation tips re: the Midipoly upgrade which offers Midi, obviously, to the MP4 as well as several other features including use of velocity values to 15 which translate to codes that tell which VCO(s) to trigger! Also a hint of why I'm doing this. A brief look at the prototype for the ARP2600 expander that will add a fantastic capability to anything like the ARP2600 though I'm designing it specifically with that in mind. More to come! I'll put up a demo when I get it all working right!"

Crumar DS-2 glide mod, tech overview and WAVEFORMS.

Published on Feb 17, 2015 sounddoctorin

"Bob Weigel of http://www.sounddoctorin.com does a more recent review of the Crumar DS-2 synthesizer and shows the waveforms being generated by the DCO's and poly section before the VCF. If there is call I'll try to do the rigorous circuit run through video. I've just been too busy...look for upcoming products for modular users :-). Give me a month or so."

Siel DK600 + Expander Synthesizer Demo

Published on Apr 24, 2014 sounddoctorin·189 videos

"Bob Weigel of http://www.sounddoctorin.com demonstrates an assortment of layered sounds from the two 6 voice "DCO" analog units. (Actual 2 analog oscillators each that drive a divide down network to create digital waveforms that are assigned to 6 analog synth channels as needed. An op amp saw converter produces the sawtooth waveform and PWM with comparator as is common. These synths have 3 LFO's but two are for one DCO each and are tied to the same set of controls. Added warmth. Really great pad and clav sounds and some brass."

Follow-up to Siel DK600 tech talk; a tough nut to crack

Siel DK600 tech talk; a tough nut to crack

Published on Apr 24, 2014 sounddoctorin·188 videos

"Bob Weigel of http://www.sounddoctorin.com gives a tech overview of The Siel DK600 aka Opera 6 aka Kiwi. This synth has some fantastic attributes if you can get one working reliably. I've found some problems besides the common battery spill which just requires a lot of socket/chip changing, trace repair and cleanup usually. The voltage on 5V supply can drift too low and particularly hitting notes hard the s+h cells for key voltage will bleed back onto the power supply through the analog switch 4051's. This creates a phantom lfo strangeness when you hit keys hard. Anyway you may find yourself in a labor of love on these and hopefully this video helps some people. Always check the website for more tech tips, parts etc.

The architecture is somewhat similar to the polymoog except with only 6 voices instead of fully polyphonic in that it uses analog VCO's driving a divide down network. In the Polymoog the frequencies are hard wired of course like an organ but in the siel they are assigned to synth channels by the computer like any polysynth. Watch the demo video showing more of the sounds layered with the Expander module! (A Dk600 with only volume and tune knobs that are analog controls for the vco's)"

RARE CRUMAR COMPOSER SN 00442

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"It is an Italian analogue polyphonic synth. Less than 500 of these were produced! Serial number is U1/00442. It is very rare and unique synthesizer.

It sounds thick and combining all 4 instruments (solo synth, poly synth, organ and strings) gives a unique sound.

In solo synth section you have 5 waveforms to choose. You can mix it with poly synth to create thick 3 oscillator synthesizer! Leslie emulation sounds great and strings will take you to 80's :)

Interestingly Composer uses the same CEM chip to VCA, filters and envelope at such giants as Memorymoog, Oberheim OBX, OBXa/OB8, SCI Prophet 5!

This is a description made by sounddoctorin and a comparison and list of chips used in the Crumar.

Used chips:
- oscillators: (same used in: Crumar Stratus, Trilogy, Performer, Multiman)
- envelopes: Curtis CEM3310 (same used in: Crumar Stratus, Trilogy, Memorymoog, Oberheim OBX, OBXa/OB8, SCI Prophet 5)
- filter: Curtis CEM3320 (same used in: Crumar Stratus, Trilogy, Memorymoog, Oberheim OBXa/OB8, SCI Prophet 5)
- VCA: Curtis CEM3330 (same used in: Crumar Stratus, Trilogy).

Some great functions: keyboard split, mixer for all sections, ADSR, positive/negative envelope amount, cutoff, resonance, independent outputs for all parts, breath controller.

Check for more info here.

Some videos and demos of a Crumar Composer in action:" [posted here]

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EML 101 Electrocomp demo

Published on Nov 10, 2013 sounddoctorin·187 videos

"Bob Weigel of http://www.sounddoctorin.com demonstrates a bit of the EML101 before sending it over to England."

KORG PE-2000 Vintage Synthesizer

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This one is from the synth tech sounddoctorin.

"The PE2000 was created in 1976 as I recall and has the one of the most definitive phaser effects of the era I think working with preset sounds through EQ and A-R envelope. And three oscillator divide down with all it's analog glory. :-) This one has been reconditioned to perfect shape and I play it in 'a few of my favorite strings' video on the sounddoctorin youtube channel [see this post] for a sound demo. As you can see the cosmetics of the keyboard is marvelous. The case has it's wear and tear but nothing too bad. Probably could get some of the same type material and use a good adhesive to hold it in the little missing strip you see there. But I figured it's just part of the vibe on this one and at least the parts that matter usually are awesome. ALSO note that only the middle latch works. The outer ones could be replaced by common latches if someone thought that important for more secure xport but didn't seem a priority to me. I have too many string machines and need to bail out some of the expenses from repairing vehicles including an old '73 wagoneer we're using for prospecting that was sold to me 'ready to drive' with a cam that had flat lobes. lol. Doing some gold prospecting this summer. What fun! Hopefully on the trail of something good here but haven't been showing my face around youtube or ebay as much as a result. WATCH FOR MORE AUCTIONS though including some classic combo organs and synths! And sub my youtube channel as hopefully I'll have a lot more synth repair vids etc. up there soon along with our prospecting exploits :-).."

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trip1 WY CO Jorge's awesome synth collection

YouTube Uploaded by sounddoctorin on May 11, 2011

"Bob Weigel of http://www.sounddoctorin.com begins his month or so long journey to see former Bozeman residence the Wiest family in Sheriden, WY and former roommate Alfredo Pinto in Denver area. Also quick interview with Jorge about his awesome synth studio featuring a Jupiter 8, Teisco 110F, Prophet 5, Juno 60, Minimoog, Korg MS-20, (I said 10...) Roland SH-5, Octave Cat, etc."

New video above Uploaded by sounddoctorin on Jun 20, 2011
"Bob Weigel of http://www.sounddoctorin.com talks with Jorge in Denver area about his collection of classic analog synthesizers including the Roland Jupiter 8, Sequential Circuits Prophet 5, Teisco 110F, Roland SH-5, Minimoog, Korg MS-20, Roland SH-101, Roland Juno-60, Octave Cat etc."

A few of my favorite strings

Published on Oct 30, 2012 by sounddoctorin

"Bob Weigel of http://www.sounddoctorin.com assisted by Mr. Baxter who asks annoying questions to help confuse me, demonstrates basic 8'/4' mix on some of the classic string machines of the 70's. The Freeman String Symphonizer, Crumar Multiman, ARP Omni, Roland RS-202, Korg PE-2000, Hohner Stringer, and the late 70's and early 1980 ARP Quartet (Siel Orchestra) and the Moog Opus 3."

The George Jenny Ondioline synthesizer!

YouTube Published on May 17, 2012 by sounddoctorin

"Bob Weigel of http://www.sounddoctorin.com gets a glimpse of what is apparently one of the few remaining original high portability synthesizers; the George Jenny Ondioline. Parker is planning to sell this to a museum so don't ask about acquiring it at this point. This is just for historical reference and to give a little visual on an instrument that probably doesn't have any youtube coverage otherwise. This instrument obviously used vacuum tubes and no I have no diagram for it. The tilters on the left are for changing various typical parameters of this type of thing. Probably footage mixture and filter controls. As some know it's the instrument used in Del Shannon's 'Runaway'. I do a song by this title also. Mine doesn't use an ondioline :-). It does have great lyrics and a moving beat though. It's found on my myspace site as I recall. enjoy :-)"

Casio SK-200 demo/ Ava Aston's doggy day comedy

YouTube Uploaded by sounddoctorin on Nov 24, 2011

"Bob Weigel of http://www.sounddoctorin.com plays a silly song on the casio Sk200 for hoots and giggles and whatever else can be made of it. Check out sister Ava's studio project and donate if you feel led!"

RARE CRUMAR COMPOSER

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SN 00180

"Crumar Composer - italian analog paraphonic synth. Less than 500 of these were produced! Serial number is U1/00108. It is very rare and unique synthesizer. It sounds thick and combining all instruments (solo synth, poly synth, organ and strings) gives a unique sound.

In solo synth section you have 5 waveforms to chose!!! and you can mix it with poly synth to create thick 3 oscilator synthesizer! Leslie emulation souds great and strings will take you to 80's :)

Interestingly Composer uses the same CEM chip to VCA, filters and envelope at such giants as Memorymoog, Oberheim OBX, OBXa/OB8, SCI Prophet 5! This is no joke, check for yourself! This is a description made by sounddoctorin and a comparasion and list of chips used in the Crumar.

Used chips:
- oscilators: (same used in: Crumar Stratus, Trilogy, Performer, Multiman)
- envelopes: Curtis CEM3310 (same used in: Crumar Stratus, Trilogy, Memorymoog, Oberheim OBX, OBXa/OB8, SCI Prophet 5)
- filter: Curtis CEM3320 (same used in: Crumar Stratus, Trilogy, Memorymoog, Oberheim OBXa/OB8, SCI Prophet 5)
- VCA: Curtis CEM3330 (same used in: Crumar Stratus, Trilogy).

Here's a review of sounds/features per section:
There is a mixer for the 4 sections and bender for monosynth only ,mod for all other sections' vibrato (with speed knob right there by the wheel) and 'touch dynamics' knob for touch vibrato. Also it has a breath input (tubing goes directly in) which can be switched to give volume control for either poly or mono synth section.
1) Monosynth is one fat oscillator. But you have 5 waveform types - pulses and triangle added and also you can vary footage from 32' to 4'. PORTAMENTO amount is very useful for creating sounds where the lead lage the other parts. This thing can sound very phat.
2) Polysynth is at least as nice as the ARP omni's I think overall. I dunno that ARP filter is awful cool sounding I think. But the curtis CEM3320 is ok too in it's own way and there is one of them shared again with eg retrigger when all notes are lifted. CEM3310EG, and CEM3330vca. These same three chips are in the mono section also. But on the poly section there are three presets...a nice piano enveloped sound and a more brassy sound and a more tweaky synth sound... and then you can select 'free' which means you program it with the knobs for ADSR, amount (invertable like Korg Delta etc.) and cutoff/resonance. Anyway in the oscillator control section there are two oscillators and both can be dropped an octave with a switch and one can be detuned up or down a fifth or like that. Also second oscillator can be muted. You can select between square and saw for both independently.
3) 4 great preset organ tones plus percussion stops with master volume and decay knobs. Overall organ 'sustain', a release envelope. It's all paraphonic with retrig on all notes off but wow. Great BBD leslie emulator that speeds up and slows down like the real thing. And nice tone selection.
4) Performer sounding strings pretty much save the cool eq of the performer of course. But at least the same kind of quality for the tones it does have and a decent eq sweep and 8' 16' 'stops'.
Other funtions: keybord split, mixer for all sections, ADSR, positive/negative envelope amount, cutoff, resonance, independent outputs for all parts, breath controller.

Check more info:

link 1
link 2
link 3
link 4
link 5

Other demos of a Crumar Composer in action:" [videos posted here]

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