EMS Synthi 100 First Aid Kit
List of components used in EMS Synthi 100. Some information useful in servicing VCS3 (and Synthi A(KS)) as well?
Synthi 100 is an analog / digital hybrid system. Digital chips (TTL/MDTL) are mostly used in Sequencer circuitry.
Most potentiometers are ERIE 10k LIN M0, 3/8″ bushing, 1/4″ (6.35mm) shaft. Exceptions are:
- 5K log:
- Reverb LEVEL
- All octave filter potentiometers
- All input amplifier potentiometers
- All external treatment potentiometers
- Joystick RANGE
- 5K lin:
- Joystick X/Y
Original potentiometers are not super high quality ones. You can potentially clean them, but opening will most likely break them. Spraying will be a temporary fix only.
Recommended replacement is TT Electronics P261 (solder lugs but super rare) or P260 (pins) series.
Most likely all potentiometers could be 10k, which are easier to get. 5k log potentiometers are used as they are used in VCS3. But on VCS3 the matrix is not buffered, and this is the reason to minimize impedance and use lower resistance pots. As a rule of thumb, don’t mix 5k and 10k pots on the same circuit.
Sliders on Synthi 100 are unusual Preh 10k 274 with ~70mm travel. Sourcing NOS ones starts to be difficult, and NOS ones can also be jerky after many years of no use and hardened rubber parts. As the travel is unusual, to my knowledge there is no contemporary substitutes. Slider held together by three 1.5mm copper rivets. Cleaning and lubricating is an option.
Especially the mute switches are extremely low quality and disintegrate over time. I find C&K 7000 series superior substitute of all good quality miniature switches (NKK or Mountain). The shaft is slightly smaller on these compared to original switches, but shoulder washer (from 0.625″ to 0.25″) will help.
Resistors are mostly from E12 series, more or less every value up to 10M.
On filter bank also:
- 1k3, 1k6, 4k3, 9k1, 13k, 16k, 43k, 91
Log modulator also:
- 3k and 20k
Todo, although nothing out of ordinary.
The main transistor pair in Synthi 100 and VCS3 is 2N5172 or BC169C as NPN and 2N4288 as PNP. These are all general purpose transistors with E-C-B pinout. MkII VCS3 switched using BC169C (npn) and BC258B (pnp) without any (?) changes to the circuits.
2N4288 is now ultra rare and I don’t think there was any real reason in using it in the first place. The complement pair of 2N5172 (still in production) is 2N6067, which has almost identical specs as 2N4288. So 2N4288 looks like a substitute in the first place. They maybe got a good deal of random general purpose transistors and used them until they run out of stock.
I don’t think it is necessary to source the original transistors unless you really want to. For NPN and PNP you can use contemporary general purpose transistors from the same family. Low noise ones would be BC549C/BC559B, but you have to cross legs as the pinout is different. The exact gain group is most likely not significant either. For pin to pin drop in you can do 2N5172/2N6067.
- 2N5172 (general purpose) E-C-B ( => BC549C legs crossed )
- BC169C (general purpose, NOS) E-C-B ( => BC549C legs crossed )
- 2N2916 matched NPN pair
- CA3018 DUAL NPN METAL CAN
- 2N4288 (general purpose) E-C-B ( => BC559 legs crossed )
- MM2614 (general purpose metal can) ( => BC557? or if needs more mA then 2N3906 )
- 2N4852, could be replaceable with another unijunction transistor
- HS1395 (silicon) => 1N4148 (according Hinton VCS3 schematics)
- HS2036 (3.6V Zener)
- HS2062 (6.2V Zener)
- DK10 or HG5009 (germanium) => use any small signal diode like OA47, 1N34A or 1N60 (although Hinton schematics uses 1N4148 here also)
- SFD83 (silicon, not sure what this is, not used on VCS3 version of the circuits)
- REC53 (power diode?)
- 2N4302 (N-FET)
- 2N5163 (N-FET)
- 2N5457 (N-FET)
- 2N5461 (P-FET)
- LM741 (opamp)
- CA3046 (NPN array)
- CA3080 (OTA)
- MC1303C (dual stereo preamp)
- PA324 (power driver opamp)
- TAB101 (Ring modulator) (ebay)
- MP1403 (MOS memory) = ML1403 / MM1403
All chips are standard TTL. Most likely can be replaced with at least LS-family chips.
- 7440 ( driver NO=30 version of 7420, 74LS20 should work)
- MC1812 (EOR Gate, looks like it would be pin to pin compatible with TTL EOR gate 7486)