This is a Jim Williams Modified Aphex 320A Compressor and limiter. This unit can be very loud without seemingly affecting the signal very much. You can choose and blend between compression and leveling with them both being very transparent. It is a very pro unit and can easily be used for mastering or buss duties with channel linking. There is also a switchable limiter and stereo enhancement switch. It is set for 120v though you can change it with the right fuse. It doesn’t suit my needs anymore but I can highly recommend it for analog compression punch and presence duties! An easy and powerful way to get loud tracks without changing the signal very much.
What exactly does the Jim Williams Mod entail?
Jim Williams is known in the audio world for his "hi-fi" approach: he does not color the sound, but makes the signal path as pure as possible. For the Aphex 320A, the modification consists of the following steps: Op-amp Upgrade: The standard built-in operational amplifiers (op-amps) are replaced with high-end, modern variants featuring extremely low distortion and a very high slew rate. Capacitor Replacement (Recap): All standard electrolytic capacitors in the audio path are replaced with premium audio components (such as Panasonic or Elna Silmic). This ensures tighter, deeper bass reproduction and a more open high.
Power Supply Upgrade: The internal power supply is made more stable and equipped with better filtering to minimize hum, induction noise, and heat generation.
Retention of the VCA: The original Aphex VCA architecture (the heart of the compression) remains intact, preserving the unique, intelligent operation.
What do you notice about this in practice?
Extreme Transparency: You can make the signal extremely loud (high RMS value) without hearing the compressor 'pump' or breathe.
No Tone Coloration: No 'warmth' or 'mojo' is added; the input signal remains sonically exactly the same, only dynamically controlled.
Lower Noise Floor: The unit is many times quieter than the original from the '90s, making it perfect for critical stereo bus or mastering applications.

Overall in very good condition and working completely.