AM8019 ARP2600P VCA


AM8019 Module

Overview This is a replica of the ARP 2600 Voltage Controlled Amplifier, which is a transistor VCA dating back to the ARP2500 and 1970.  This Euro Rack module makes use of matched transistor arrays and a high quality buffer Op Amp at the output stage. The VCA is designed to be used with the Athena VCO and VCF’s, enabling a replica of the 2600P or Odyssey in a rack format to be achieved.

I built my first 8019 in 2009 when replicating a complete ARP 2600 in FracRac. The AM8019 is the commercially available EuroRack version using slide potentiometers like the original, with 2x audio signal inputs and both linear and exponential control voltage inputs.

EuroRack Module:   16HP wide
User Manual:            Download PDF

Detailed Description This 16HP wide module has have enhanced from the original 1970 ARP design with high quality components and additional control inputs, the circuit has been adjusted to provide a better HF response than the original design. The VCA is based on a Wilson Current mirror, and the AMSynths version uses matched transistor arrays to replace the discrete transistors. There are two signal inputs with level controls, one inverted and both pass through a 470nF capacitor which acts as a high pass filter at 10 Hz, thereby blocking any DC offsets.

AM8019 Prototype

This is important as the  ARP 2600 VCO’s have a DC offset which needs to be removed to eliminate ADSR thumps. This means the AM8019 is not designed to be used as a ring modulator – see the AM1005 for this application. There are 2x linear control inputs and 2x exponential control inputs, all adjustable by front panel slider potentiometers.

There is also a GAIN slider pot on the upper right hand panel, with an amber LED output signal level indicator. The slide potentiometers have been especially manufactured for AMSynths and we have used coloured plastic caps to give the VCA that vintage look and feel.

The discrete transistor VCA is a product of the 1960’s before integrated circuits were affordable and the use of the CA3080 OTA chip. This modern and updated version takes the design into the modern era and provides a versatile and clean VCA. The Wilson current mirror and discrete VCA is used in a number of other AMSynths modules such as the AM8047 Multi-Mode Filter.

Outcome & Availability There are a couple of errors in the original schematics that needed correcting; the expo trimmer should be connected to -15V not GND and the HF trimmer circuit can be totally removed as it does not work. The buffer Op Amp is best upgraded to a TL071 or better and the bypass capacitor reduced in value to 22pF. Small electrolytic capacitors are also added to the current mirror supply rails.

The AM8019 modules was released in late 2013 and manufactured in 2014 and 2017. A triple VCA was created for the 2500 Rack project and further 8019,s will be made in the future.

 

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