Author: sgeorge, Posted on: 9 October 2026 14:31
Been a long time since the last post in this category, but today lets take a look at another of my favourites, a Symetrix 501. I have about 4 distinct 501's and this one is my favourite that I use a lot.
The 501 saw a lot of revisions over its time. Face plate changes, toggle switches to push buttons, colour changes, logo changes and even... design changes!
Unlike the 525, this one is fully balanced input and output, but its a mono compressor and limiter without the downward expander.
What makes this one so special is that its my holy grail of 501's. It has a factory output transformer (in place of using two capacitors for balanced output) and the coveted Valley People VCA (in this case the EGC-101).
(the other oddball chip you see, the TRW 516-3-103G is a 10k 3% resistor network).
The EGC-101 marks this as an "early" release. Allison Research released the blue EGC-101 first, then later merged with Valley Audio to create Valley People Inc, and then later released the smaller green TA-101 VCA. Its rare to find a push button switch 501 with the early VCA in it.
Later releases went to the DBX 2150A VCA chip.
Later versions I have (you can see the two capacitors in place of where the output transformer sits.
This one has the DBX branded 2150A VCA
This version has the THAT branded 2150A VCA (this is the latest revision of the four I have)
All four of mine are gray faceplate revisions, not the last dark blue faceplate versions that they produced.
tags: Audio, Compressor, EGC-101, Symetrix, TA-101, VCA, Valley People
(dont include links in your comments.)