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Drip Electronics Opto 4 Stereo Compressor

This project has been on my work bench for about two years now, the effect of putting one band to rest with a 34 track double-disc-finale and then birthing a whole new band and building a studio.  So this holiday season I set to work and wasn’t going to walk away until I completed it.

This basically two LA2A Compressors in one box with stereo link functionality.  The circuit board and design is from Drip Electronics and Ibuilt the case custom for my needs.  A couple additions are a control for the HPF Sidechain and two release modes (one nice thing about using this circuit is Drip Electronics offers two OPTO T4B Cells – one with a fast release and the other slow).

Update:  ah yes, i guess i could have been a little more descriptive.  Caleb is right.  It compresses audio (squishes it) and people go to great lengths to squish their audio just the “right” way (or the way that pleases the most).  A very transparent compressor would squish the dynamics down without affecting the tone, but some compressors color the sound in a way that is pleasing too.
Also, there are transformers both to the audio coming into the compressor and then also on the way out.  So even with the compression set to zero (just running the audio thru the box) some pleasing color still happens.
The LA2A compressor is somewhat famous for its sound and design and this circuit is based on that circuit.  It uses T4B Opto cells to compress.  The T4B has a light source (like say an LED) and then a sensor that reads that light.  As the audio lights up the LED, the sensor compresses the audio down as the audio/light get louder/brighter.  This creates a softer compression as the light and sensor have a bit of play to the way they work.  This is a very simple explanation – someone with a lot more knowledge could do a much better job.
Drip Electronics sells both the circuit board and his own custom T4B cells and you supply the rest of the parts.

Update:  ah yes, I guess I could have been a little more descriptive.  Caleb is right.  It compresses audio (squishes it) and people go to great lengths to squish their audio just the “right” way (or the way that pleases the most).  A very transparent compressor would squish the dynamics down without affecting the tone, but some compressors color the sound in a way that is pleasing too.

Also, there are transformers both to the audio coming into the compressor and then also on the way out.  So even with the compression set to zero (just running the audio thru the box) some pleasing color still happens.

The LA2A compressor is somewhat famous for its sound and design and this circuit is based on that circuit.  It uses T4B Opto cells to compress.  The T4B has a light source (like say an LED) and then a sensor that reads that light.  As the audio lights up the LED, the sensor compresses the audio down as the audio/light get louder/brighter.  This creates a softer compression as the light and sensor have a bit of play to the way they work.  This is a very simple explanation – someone with a lot more knowledge could do a much better job.

Drip Electronics sells both the circuit board and his own custom T4B cells and you supply the rest of the parts.  There is also a company “Collective Cases” that sells Cases that are Cut, Drilled, and Painted for these projects if you don’t want to build your own case.

Links:

Drip Electronics

Collective Cases