What Compressor
« on: June 18, 2004, 04:37:13 PM »
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.
The best place to find a helping hand is at the end of your arm!


What Compressor
« Reply #1 on: June 18, 2004, 04:45:58 PM »
What are your impressions soundwise?


« Reply #2 on: June 18, 2004, 04:57:05 PM »
Very transparent indeed from the previous channels I have built.
The best place to find a helping hand is at the end of your arm!


What Compressor
« Reply #3 on: June 18, 2004, 06:05:50 PM »
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?
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What Compressor
« Reply #4 on: June 18, 2004, 08:09:44 PM »
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.

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What Compressor
« Reply #5 on: June 19, 2004, 11:08:44 PM »
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.



What Compressor
« Reply #6 on: June 20, 2004, 01:13:30 AM »
compression ratio is 1.5:1 and the gain reduction ratio is 5:1. Those are two different things.

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What Compressor
« Reply #7 on: June 20, 2004, 12:14:57 PM »
Let's see if I am getting it right. So is the minimum allowed threshold -14dB then?


« Reply #8 on: June 20, 2004, 03:37:56 PM »
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.
The best place to find a helping hand is at the end of your arm!


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