[sdiy] compressor response time in BBD devices (NE57X)

[anthony]

After I figured out that distortion in my R-870 was the result of a bad 
capacitor on the rectifier of the compressor - the very worst place for a 
capacitor to go bad from a performance standpoint, savr the timing cap on 
the BBD clock (but really when have you ever heard of a ceramic or 
polystyrene cap failing at low voltage?)
Where was I? Oh yeah after I fixed the cap I go to thinking: this affects 
the time constant for the rectifier - it sets how fast the compressor 
follows the input signal. Well 0.47uF seemed like a reasonable value anf 
that's what the Ibanez AD100 analog delay uses. But the Bel BF-20 uses a 1uF 
cap so this seems as reasonable as the aforementioned one. What are the big 
tradeoffs when changing compressor response time? I mean when you're not 
going too radical. I want to make the compandor portion of this unit as 
transparent as possible and I'm going to be hitting it with the output of my 
Hotfoot. I too a couple of diodes out of the Hotfoot (so it's cooler now 
ha-HA!), because the good distortion range was too small compared to the 
mild settings.

What I am tempted to do is bypass the NE571 altogether and put one of the 
little LM1894 Dynamic Noise Reduction boards I have in to use instead. It 
works just like the NE57X except it's not a VCA it's a VCF. It's 
single-ended, doesn't need a lot of parts and causes very little distortion 
even at radical settings (which just sounds like a 6dB or 12dB low-pass 
filter set kind of low.) Hardly anyone seems to have used them except 
Radio-Shack in the 80's in Video Sound Processors - fun pieces of gear to 
play with - 1 or 2 BBD's (depending on the model 1 RD5106 or an MN3006 & a 
MN3007) that you can voltage control (with some homemade vactrols and an 
analog joystick like I did), some cool Mino-Moog-style aluminium shaft Alps 
switches and a handful of JRC4558DD's (or LM1458's or RC4136's in the older 
ones). I've found through a lot of trial and error that the less you try to 
make them something they're not the more satisfied you'll be because keeping 
the original control format is comfortable and fun. The stereo synthesizer 
is fun too. I played around with this in combination with BBD-based stereo 
expansion long before I read about the Instant Flanger and I imagine the 
sound is well maybe a tiny bit similar. The stereo expander is a dual notch 
filter. But from my calculations their notch points are 153Hz and 5132Hz - 
moving them closer together would sound more like a fixed phaser I think.


Hey are my posts too long? Honestly I try to make them short & sweet but 
this is just what comes out. I'm like this in real life too.

aa