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AM 8020 Module - ARP 2600 ADSR and AR
Overview This is a
replica of the ARP 2600 Envelope Generators, both the ADSR and AR. The module is built into a single FracRac module.
Original Circuit
The original design first appeared in the ARP 2600 in 1970, but the circuit is a derivation of the ADSR in the earlier ARP 2500. It is a transistor based design with a Op Amp used as an output buffer. The schematic printed in the ARP 2600 Service Manual has at least one mistake, possibly three:
R22 is duplicated, the left hand R22 is actually 68K not 180K R8 is shown as 10K but should be 33K R4 is shown connected to -15V, it should be GND
The ADSR does not function unless the first error is corrected. A took me a few months to work out why my replica didn't work, as I didn't have access to
the original ARP blueprints.
AM8020 Module My FracRac module replicates the original design exactly except for the following changes:
The Op Amp has been upgraded to a TL072 This provides both positive and negative outputs The hard to locate TZ581 and 2N5367 are replaced with 2N3702 The 2N4392 can be replaced by a 2N5459 There is a front panel LED and GATE push button
The module has the following front panel controls:
There are five 3.5mm jack sockets mounted on the left hand side of the panel, these are:
GATE input TRIGGER input AR output ADSR Inverted Output ADSR Output
Front Panel The front panel is a 3" wide FracRac with Alpha potentiometers and push fit mixer style knobs.
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