What Compressor

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StephenGiles

Well-known member
Joined
Jun 4, 2004
Messages
792
Location
South Croydon, England
Just to let y'all know that I successfully built one channel of "What" compression while on holiday last week. The 200 year old cottage, fully modernised, had a table in the kitchen by the window which got sunlight until 9.30 each night, so great light conditions for soldering as the weather was fantastic. Having grabbed a load of components at the last minute, I was only stuck for the PNP transistor. Luckily I found a 2n5087 and guessed the pinout - well, there's only so many combinations! It worked first time - not bad for veroboard.
 
how much compression does this offer? I thought i read somewhere that it wasn't much, maybe 2:1 max.. is this correct or does my mind trick me?

would you recommend building a number of them and using them for general compression or stick with VCAs?
 
1.5:1 according to the designer. Also, some of the unprocessed signal is fed back to the output. It is unclear whether this is reflected in the measurements. Transparent indeed.
 
This is off David's website.

How About Specs?
We have an audio analyzer where I work, so I can oblige.

Compression modes: Stereo or Dual mono, true bypass
Dynamic Range: >120dB
THD @ 1KHz +4dBu: <0.05% for all knob settings
Maximum Gain Reduction: 14dB
Stereo Tracking Error: <1dB
Compression Ratio: Variable, Max. Approx. 1.5:1


I don't get it. He says the gain reduction is 14dB. Doesn't that correspond to a 5:1 ratio? Could the 1.5:1 be a typo? :?:
I think 1.5:1 would be a 3.5 dB gain reduction and that would hardly justify all the fancy footwork in the sidechain.

Tamas
 
Ah, but if you increase R5 to 47k you go from "some" compression to "a lot" of compression. So - why not put a 47k pot in series with the existing 10k R5 and have the best of both worlds. I also use NSL 32 optos here because I don't have any VTL5C9s, but you need a very small series resistor, something like 100 ohms. Perhaps this might generate some discussion.
 
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