Interesting Astor compressor circuit
« on: July 02, 2019, 03:07:32 AM »
I'm in the process of acquiring and sorting through a bunch of old Astor Australian made broadcast gear, some of which I have schematics for very closely related modules, some of which I don't. One is an 'intercom' module with a mic input, speaker output and a built-in compressor. Still tracing it out, but it's very closely related to the schematic for the talkback section of an Astor mixer of the same era.
     This section has a little compressor, (schematic attached, compressor section down the bottom) which is using a transistor to drive a diode into conduction to pull the signal down. Although similar, it's not a diode bridge. I've seen some theoretical discussions on this type of compressor, but nothing comes to mind of actual products using this.

  Will be a while before I have time to get these modules functioning and actually listen to them.  Any thoughts, examples, explanations or other opinions on this kind of compression circuit?

abbey road d enfer

Re: Interesting Astor compressor circuit
« Reply #1 on: July 02, 2019, 03:41:59 AM »
Although similar, it's not a diode bridge.
A diode bridge has a self-cancelling effect on distortion; a single diode has not. The crude performance may be acceptable for TB, but not for any kind of "noble" audio application. Maybe for a telephone effect...
This crude and cheap approach is in contrast with the rest of the circuit, which is rather well designed (xfmr in/out, nice power amp...); they may have deemed it sufficient for the purpose... I guess German engineers would have had a different approach.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


Re: Interesting Astor compressor circuit
« Reply #2 on: July 02, 2019, 04:47:57 AM »
I don't really expect it to be 'hi-fi'. :) They certainly don't write manuals like they used to, see the attached circuit description.


Re: Interesting Astor compressor circuit
« Reply #3 on: July 02, 2019, 04:48:38 AM »
And tech specs.


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