Fat-N-Pretty compressor for recording?

[Pablo]

i've been wanting to build a compressor to rack mount with an aphex107, EQ & effects
processor for recording purposes. i have built a flat line from john hollis site and realy
like the sound of it and thought about building a second one but would  like the added
controls that the Fat-n-Pretty has.

so, i'm thinking of building two of these in a rack unit and i've got a few questions.

http://www.moosapotamus.com/Fat-n-Pretty/Fat-n-PrettySCH.gif


1. is this suited for use as a clean/slightly colored
   vocal/instument compressor or is it more suited for
   guitar/bass applications?
   i would like to be able to use it for both.

2. what is the value of C1 on this schematic? from here it looks
   like 0.47p but i can't seem to find that value anywhere.

3. moose uses an VTL5C3 optoisolator. is this better than
   using LDR's or is this just what he had?

Any other suggetions for somewhat simple compressors out there?

Thanks guys

[stm]

3. moose uses an VTL5C3 optoisolator. is this better than using LDR's or is this just what he had?

Good question. I remember a long time ago someone (probably Mark Hammer or Puretube) gave a list of the Vactec's optocouplers and their suggested or intended use. Unfortunately I haven't been able to find that post using the SEARCH function, so it would be good if that person is "listening" then could "repeat" that.

I am assuming the fastest the LDR the better for AGC loops and compressors (fast turn-on), however sometimes I guess it is desirable that the turn-off time constant be within certain range for optimum results...

Also, looking at the datasheets of the different Vactec's I found the different models are intended for different resistance ranges, and different LED current ranges, apart from the turn-on and turn-off times.  In summary, selection is not trivial, and seems more that you need to fine tune YOUR circuit for the particular characteristics of the device you are using. I'm afraid there are only two valid methods here: by ear and trial and error.

[Garrett]

If you could add a gate circuit to this, I might give it a shot. It's hard to beat my dbx 266. 

How do you like the 107?  Is it fairly easy to get good levels?

Thanks, gArrock

[bwanasonic]

Not DIY, but a fantastic deal-

FMC Really Nice Compressor

Kerry M

[Garrett]

Not DIY, but a fantastic deal-

FMC Really Nice Compressor

Kerry M

cool Kerry,

Never seen this one. Looks quite affordable too.

thanks, Garrock

[Pablo]

stm,
thanks for the info,  i think i'm gonna just stick with LDR/LED as i have quit a few different ones around here.
also thanks for all the great designs on your web page.      you guys ROCK!

Garrett,
i haven't had a chance to put the 107 to work yet but have seen some mods for it that i may try if needed.
i'm in the process of switching from recording to 4-track cassette to a computer setup. santa's supposed
to bring me a delta 44 sound card and i'll know more about the 107 once i get that installed.

Kerry,
yea, from what i've read thats the best bang for the buck out there but i'm really wanting to build my own
seeing as how i've got a lot of the parts for it already. and this old dual rack chassis that is just begging for
me to build something in it.

so, can anyone answer my capacitor question?
the smallest value pf cap i can find is 2pf or does the "p" in (0.47p) stand for something else other than pf?

[stm]

I've had quite good results using a DIY LED+LDR pair.  The fastest LDR I could find within my reach was a VACTEC VT935G available from RS Components P/N 234-1044.

Quick specs are:

Peak spectral response: 550 nm -> use a standard or hi-eff lime-green LED to match it (not the newer ultra or hyper green ones!)
Trise: 35 ms -> you need to provide long decay in your circuit, since this is too fast for good decay
Tfall: 5 ms -> provides fast attack
Size: between 4 and 5 mm -> matches perfectly a T1-3/4 LED

Regards.