La-Lite Opto Compressor

[Jaicen_solo]

Hey guys, I was planning to build one of these today , just as a quick test to see how it sounds. I made a layout for it a while back, but i'm not sure if I want to add mods before I build it, so i'm perfing it. The thing is, after looking over the schematic, i'm wondering if the gain stages are biased correctly. I can see that 1 of the op-amp stages is used to bias the positive signal, however, the gain stages in the signal path appear to be isolated from this bias voltage by caps, is this correct??

http://aronnelson.com/gallery/johan/LA_Light_last_one_001

[Johan]

it will work as drawn as long as you dont connect both circuitground and -V to the same point..as is, it expects the -V to  really be negative . if you want to connect it stompbox-style with a 9volt battery connected to groung, just put decoupling caps on the input/output...
..also, it will accept most common opamps, but not all..some simply has more biascurrent requirement than can be pulled through the 100k pots..5532 is one of them...but since there is only 1 opamp in the signalpath and its lowgain, most noice still comes from the LDR and pot...

johan

[Jaicen_solo]

Sweet. I think i'll have to come up with some sort of arrangement to use it with 9v's then. There's a perf layout for +/- 9v somewhere in the galleries i'll probably use. Gotta be good for headroom too.
Just one other thing, it occured to me there are no values for the LDR's. Do you have a preferred min/max LDR value???

[Johan]

Sweet. I think i'll have to come up with some sort of arrangement to use it with 9v's then. There's a perf layout for +/- 9v somewhere in the galleries i'll probably use. Gotta be good for headroom too.
Just one other thing, it occured to me there are no values for the LDR's. Do you have a preferred min/max LDR value???

..just connect the battery to +v and -v and nowhere else and you'll be fine...( or use blocking caps on the in and out..) and with an TL072 running on a single 9v battery, you can get about 3,5v ac-signal out ( 7v p-to-p) ..and an allready compressed 3,5volt signal is plenty loud...

...it's typacally very hard to get much more than 20db attenuation in any optocomp.thats a 10:1 signal ratio, and with the 68k series resistor that would mean you will need an LDR that can go down to about 6,8k..wich is high..most goes to somewhere between 1 and 2k...since they usualy slow down when aproaching their max and min values, it will be better to have one that can go really low, since it will be faster in responding down to -20db...but basicly, anything you can find will most likely work..

johan