Archive for compressor

Gates Sta-Level

Posted in Repaired, Restored with tags , , , , , , , , , on January 22, 2014 by AnalogAudioRepair

A client gave me a beautiful original Gates Sta-Level to bring back to life.  It had all original components but had not been turned on in over ten years.  After testing all the tubes, I brought it up on my Variac with just a solid state rectifier installed.  The power supply filter caps were good, but not great so they got replaced first.  With the new PSU caps and the tubes installed the unit was working ok, but had a very strange frequency response.  Above 1kHz it was fairly even, though not quite up to spec.  Below 1kHz it increased steadily to about +12dBm at 30Hz!  It turned out the feedback caps from the 6V6 output stage to the 12AU7 were leaky.  I replaced those and the coupling caps and things are now back to factory spec.

Vintage Gates Sta-Level

Original Gates Sta-Level

Gates Sta-Level original guts

The guts – dead stock!

Gates Sta-Level power supply re-cap

New Power Supply Caps

Gates Sta-Level capacitors

Replaced Film Caps


4 Channel Mic Pre & Limiter

Posted in Modded, Racked Modules with tags , , , , , , , , on December 31, 2013 by AnalogAudioRepair

Another fun project for engineer and lover of odd gear, Dan Physics.  He dubbed it the Mic RipPre 4.  These are funky little portable mic preamps with opto limiters that were designed to run on two 9v batteries.  They have Beyerdynamic input transformers and 600 ohm output transformers.  I gutted four of them, recycling the XLR connectors and circuit boards, and fit them in a 1U rack case with a +/-15v power supply and +48v phantom power.  The only other mod was a control for the amount of limiting.  It’s not exactly threshold, nor is it really ratio – just “amount”.

They are pretty clean sounding preamps, no surprise with such a simple circuit.  All new capacitors didn’t hurt either.  One board needed a new diode in the limiter, but otherwise they were in good shape.  Fitting all of the controls on the front panel was the hard part!  The original preamps had nice little collars around the toggle switches so I used those to prevent accidents with phantom power.

mic preamp/opto limiter

Stripped down boards

laying out 4 channel mic preamp/opto limiter

Making sure it will fit.

mic preamp/opto limiter control panel layout

Control layout

hand drilling panel for mic preamp/opto limiter

Why I need a Drill Press

wiring 4 channel mic preamp/opto limiter

All wired up

4 channel mic preamp/opto limiter

Completed unit

knobs and switches


CBS Volumax Limiter Mods

Posted in Modded with tags , , , , , , on December 29, 2012 by AnalogAudioRepair

This was a project for a client from Brazil – modding a CBS Stereo Volumax discrete transistor limiter.  The Volumax is a two band limiter with transformers in and out.  You can do fun stuff like turn off the high or low frequency limiting, vary the HF level, change the release times, and much more.  This was a pretty standard mod that also included XLR in and out.  Amazing units when you do a bit of work to them!

DuKane 2A81 Compressor Mods

Posted in Modded with tags , , , , , , , , on November 28, 2012 by AnalogAudioRepair

Here are a pair of vintage DuKane compressor/limiters.  They use an all discrete transistor circuit path with a FET for gain control.  They come stock with a (useless) noise gate, two inputs, and some controls on the rear panel.  These mods remove the noise gate, move the ratio and bypass to the front, and add release time settings.  Everything gets cleaned up and boards are re-capped if needed.  The results?  “A super smash box” according to one user!