Prague Analog Mono Synth


Overview The AMSynths Prague is an expanded version of the 1979 Moog Prodigy, with the same VCO’s, VCF, VCA and Contour Generators but with improvements. The Prague is built across two PCB’s; one holds the panels controls and the other contains the analog circuits. The PCB’s attached to a black anodised front panel which fits into a 60HP Eurorack case. The panel can be easily fitted into a Moog 60HP case and I have designed a small power supply PCB that slots into the rear holes.

Moog Design The Moog Prodigy was launched in 1979 and was hugely popular over the next 5 years with over 10,000 manufactured. Whilst it lacked some more advanced features it was a great bass and lead synth that maximized it use of the Moog 24dB ladder filter. A street price of £295 or less also contributed to the large number of sales!

The Prodigy used heated transistor pairs in the VCO exponential generators, just like in the Micro (1975) and Multi Moog. This improved the stability of the VCO’s from the Mini Moog. The usual transistor ladder filter uses CA3046 chips and their are plenty of 1458 Op Amps and 3080 OTA’s. It runs off a 12V power supply.

I bought one second hand in the 1990’s and had a lot of fun with it. I recording some filter FX sounds surprisingly enough, which I still use today. I refurbished the wood end cheeks and eventually sold it as part of my studio downsizing in 2003.

Panel Mockup

AMSynths Design I have followed the Moog for the core circuits but changed the LFO to the one in the Oberheim OB-1 which is very similar but uses a 1MA rather 2.5MA rate potentiometer and has a S&H waveform. The switches are all 3 way to provide extra features:

  • OSC1 LFO MOD has a half modulation option
  • OSC2 PW MOD has both LFO and ENV1 as modulation sources
  • OSC SYNC also has a fixed cross mod option
  • VCF KYBD has a half modulation option
  • VCF LFO MOD has a half modulation option
  • SUB oscillator has both 1 and 2 octave below options
  • Contour Release has an option for VCF envelope to be off and VCA envelope on

I have kept the panel layout simple and not added extra potentiometers. The Sub oscillator volume is controlled by OSC1 level. I could have added Noise into the mixer but felt this was not a useful option. I laid out the PCB’s over a weekend in March 2021 and ordered a prototype set of PCB’s in matt black. The front panel was laid out the next weekend.

Outcome & Availability As at Easter 2021 the synth is at prototype stage, with the intention of going into production in May, with completed modules and PCB/Panel kits. The Moog 60HP case (make sure it is the Mother 32 version which has the holes in the rear) is available second hand or new for £60 – £100.

 

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