Sound Skulptor forums

Build help and troubleshooting => CP554 Diode bridge compressor => Topic started by: laurenz.zs on May 20, 2024, 03:56:13 PM

Title: Attack times
Post by: laurenz.zs on May 20, 2024, 03:56:13 PM

Dear People,

I hope you are doing well.

a few days ago i finished puting a pair of CP554s together.

I enjoyed a lot the process; Thanks JPK for making this possible.

I think both units are doing well and I calibrated as mentioned in the guide.

A little Burn in time I started testing.

I realised that even at 0.5ms Attack my CP554s fail to catch a lot of peaks.

Out of curiosity I did a test.

The test I did is not "super" precise!

I recorded a Sine Wave with 10dB of gain Reduction at different Attack/Release settings and then by reading the waveform i decided where Attack and Release starts and ends.


This is what came out:

Gain Reduction 10 dB/Ratio 3:1

Attack 0.5ms: 10ms - Release 400: 360ms
Attack 1ms: 25ms - Release 400: 300ms
Attack 2ms: 31ms - Release 400: 260ms
Attack 4ms: 97ms - Release 400: 230ms
Attack 8ms: 142ms - Release 400: 300ms
Attack 16ms: 175ms - Release 400: 360ms

Attack 1ms: 15ms - Release 100: 150ms
Attack 1ms: 13ms - Release 400: 270ms
Attack 1ms: 25ms - Release 800: 585ms
Attack 1ms: 22ms - Release 1500: 2200ms
Attack 1ms: 35ms - Release A1: 550ms
Attack 1ms: 10ms - Release A2: 2900ms

The Attack Values I recorded are off by factor of 10-20 compared to the Values on the Faceplate.

This seems to be a lot and maybe I messed something up?

If this behavior is (https://i.imgur.com/P434BJq.jpeg) normal; is there a way to speed up Attack times?


FYI: to spice things up and making the learning part a bit more fun i swaped out some components.

Resistors: Most replaced by Carbon Film Resistors (same Values but twice the wattage 0.5W instead of 0.25W/2W instead of 1W)
EL Caps: Most replaced by specs except for Voltage sometimes (example:1000u-35V replaced by 1000u-50V)
Tantulum: original
Ceramics: original
Film Caps: original
Opamps: Sparkos

Thanks a lot

Stay safe

Title: Re: Attack times
Post by: JPK on May 21, 2024, 04:10:20 PM

The front pannel attack times are more realistic in the 6 or 12 ratios.
In the lower ratios they are slower because they depend on the side chain signal level and this is by design.
The CP554 1ms position matches the originial Neve circuit which doesn't have an attack time switch. 
You can reduce all the attack times proportionnally by reducing the value of C37 but this will increase the distortion in the lower frequencies.