no one asked, but here it is anyway...

[Johan]

cool..I dont spot any misstakes in the layout..but R6 should be 2k7 not 27k and I shoose 100uf only so I dont have to stock up on too many vauels, but I wouldnt go lower than 1uF on input/outputcaps. depending on where you use it, you might loose som bass...
the VTL5c2 is the best comersiall optocoupler I found, but I prefere to use two led's and LDR. that way I get attenuation on both positive and negative voltage swing and dont depend on the LDR to smoth things out..it will be much cleaner in the low freq's,( below 250Hz ) that way...I heard Manley used two opto's ( VTL5c2 ) connected antiparrallell for the same reason..but that is soo much more costly..

thank's for the layout work..
johan

[lowstar]

thanks, i updated it.
for now, i chose 1µF NP.
that sounds interesting with the antiparallel optos...like, if i would mount them standing up, and one just 180 degrees reversed ?
what value would you recommend for R9 for the VTL5C2 ?

cheers,
lowstar

[Johan]

thanks, i updated it.
for now, i chose 1µF NP.
that sounds interesting with the antiparallel optos...like, if i would mount them standing up, and one just 180 degrees reversed ?
what value would you recommend for R9 for the VTL5C2 ?

cheers,
lowstar

just put in a 1k to start with...it's much easier with separate LEDs and LDR, that way you can just lock at the LEDs when playing with the GR knob and see when they dim and get brighter, that way you know it's right
from what I understand, Manley just put two VTL5c2 in, parrallelled but with the LED reversed..I use two LEDs and one LDR...vactrol's are expensive, and using them would pretty much double the total cost of the whole project
johan

[lowstar]

i have some 5c2´s at home, i don´t mind...
so,they us it like this ?

oxxxxxxx      oxxxxxx
xxxxxxxx+    xxxxxxx-
xxxxxxxx-     xxxxxxx+
oxxxxxxx      oxxxxxx

cheers
lowstar

[Johan]

yes..that will be just what I'm talking about..
johan

[lowstar]

UPDATE:

the layout is verified 
i used a vtl5c2, at the moment rx is 1k as suggested.
with a passive bass, that gives a nice range from noticeable to squash.
gotta try it with an active bass to see if rx is big enough for that one, too, as soon as i have put it in a box (gotta take the one from the g*****n pulsar that still ticks).
i´m also gonna make a shootout then with the punch factory and the carl martin comp.

the cap in the sidechain is 0,33µF now. that sounds perfect with bass, maybe for guitar you need to put a different value (initially, i tested it with guitar and wasn´t very impressed...then with bass it opened up).

i also have not tested it with the double opto´s yet.

one last question: is the switch open (2k7) the 1:10 setting and the switch closed 1:3, or vice versa ?

cheers,
lowstar

[Johan]

UPDATE:
the layout is verified 
the cap in the sidechain is 0,33µF now. that sounds perfect with bass, maybe for guitar you need to put a different value (initially, i tested it with guitar and wasn´t very impressed...then with bass it opened up).
one last question: is the switch open (2k7) the 1:10 setting and the switch closed 1:3, or vice versa ?
cheers,
lowstar

cool that you got it working 
perhaps if you use it for different things, you should try the basscomp.mod. just put the cap straight on the pot..no need to change the layout..
yes 1:10 open and 1:3 closed..that is correct
thank's for the short report too..

johan

[lowstar]

ok, i boxed it up a few hours ago.
i ran into quite an amount of hiss...tried ne5532 instead (even ne5532ap), but that did not help; it only changed the characteristic of the drive pot (with ne5532, Rx probably needs to be bigger, since that op-amp drove the box into too much compression to soon).
apart from that, i did the promised shootout.
the carl martin is very transparent and versatile - there´s basically nothing you can´t do with it - except add subtle coloured compression.
that´s where the two opto comps come in. the punch factory adds some nice subtle punch and thickens up the tone, very subtle. noise-wise it is close to the cm. the la-light is even subtler in how it works, in the first half of the pot travel, it´s even kinda psycho-acoustic maybe. as soon as you can actively hear the peaks being compressed, it´s almost too late. but the hiss is a problem for me. since there is not much in the active signal path, it probably comes from the op-amp itself ? isn´t there some sort of compensation-caps that you can put on an op-amp to eliminate this ?

i also noticed that the la-light sounds better with passive bass, if it´s fed by an active bass, there is less responsiveness (in the "lab", i tried it with an old höfner strat bass, at home into the daw with the active wick).

so much for now !

cheers,
lowstar

[Johan]

cool Lowstar..
you probably need to increase the Rx a little if you get to abrubt compression when it hit..this is one of the reasons I like to make my own vactrols..you can select the LEDs and Rx simply by looking at them..there is no way of knowing what goes on inside a comersiall one..
about hiss..it could be that since the opamp is biased through the pot, when you turn it up it might get too big to supply the current needed ..try a FET input one like those in the TL0x2 family or a simple 4558...
5532's will probably start oscillating ultrasonicly when you get up about halfway on the volpot, wich might show as hiss...there is no reason otherwise that a single opamp stage with a gain of 20 would be too noicy when people regurlarly run opamps at ten times that without problem in their distboxes ...

johan

[lowstar]

hi johan,

my bad. i wasn´t clear enough in my last post.

i´m actually using a tl072; i just tried the ne5532 to see if it would give me less noise.
the drive problem is also just for the ne5532, for the tl072 the rx of 1k is pretty ok.

maybe i´ll doublecheck my board to see if there is anything going on...(hiss-wise)

cheers,
lowstar

[sverige_cruz]

Hej Johan - just wanted to say "TACK" for this project. I recently built one, using my own PCB layout. Cool sounds. I have 2 sets of drum samples run through if anyone wants to host them. They're MP3 format and 2.87MB each. They start out with the original drum track and follow with varying levels of compression.

Here's the inside of the pedal, housed in a RACO electrical junction box:


Mine uses RadioShack wide angle LEDs as well as one of the larger LDRs that comes in an assortment pack. If I were to build another, I'd probably change the PCB layout, as I didn't use a couple pads that I drew in there to begin with. I might also have done something with one of the layouts that other guys posted, with the wire pads all on the edges. It just happened that I didn't see that by the time I had done mine. Thanks again!
-- Jesus