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Amplifiers - Transparency and Precision
Overview Whilst
the filter is designed to colour the sound, the voltage controlled amaplifier is at its best when it is transparent with no sonic signature and no noise either! The original VCA designs from the mid 60's relied on discrete transistors,
but the OTA chip soon took over by the early 70's until high quality custom VCA designs appeared from the late 70's and matured to very high quality in the 1980's.
AM Amplfifiers VCA's are important in an analog
synthesizer but not the most interesting to design - there is some logic in only designing with the very latest VCA chips to get the very best qualities. However I have recreated some designs from the past, so I have a broad range of
different designs. Here is the list:
AM2000 This is the CA3080 OTA based design from the E-mu Systems Analog Modular, it is very similar to a variety of CA3080 designs from the 1970's. This one has both expo and linear CV response.
AM2005 One of the first custom VCA chips ever manufactured,
designed by Ron Dow and Dave Rossum, this uses the SSM2010 chip which is ultra rare. AM2010 A dual
VCA from the E-mu Systems Modular with the SSM2020 VCA chip also used in the original SCI Prophet 5. A nice feature on this VCA is the LAG control which smooths out fast moving CV's from sequencer triggers.wn. AM3280 One of the best OTA chips ever made is the CA3280, but
unfortunately obsolete. I have a tube of these chips, so here's my first VCA based on one. It's not my best design...I was at the start of the learning curve. AM8018 Now here is a precision VCA and a really good design with the modern SSM2018 VCA chip. Very good performance, and an exponential response.
AM8164 Another modern SSM VCA chip is the quad SSM2164. This module takes the chip and creates a dual VCA with expeonential and linear responses.
AM8160 A single VCA that uses the widely available LM13700 OTA
chip. Not yet completed as a module.
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