VTL5C4/2

[petemoore]

Im building the DOD 440 Env Filter from JD's site.
 Could this be a Red LED and a couple photocells?

[petemoore]

Well I just couldn't wait so I put in the RED LED, and the two photocells..
 However I'm having trouble getting the LED to light.
 I'm using a TL082, also Im not using the /4k7 and indicator led/.
 I took these pin voltages from the opamp:
 1.   4.56v
 2.  4.56v
 3.   4.48
 4.   Gnd 0v
 5.   4.45v
 6.   4.57v
 7.   4.57v
 8.   9.15....battery voltage
 The knobs having no effect.
 Anyway maybe someone could take a look at these readings and tell if at least the OA voltages look right.
 Other experience that would apply with this type ckt would be helpful!

[jsleep]

I think the voltages to the opamp are ok.  I had the same problem with this and the only thing I could get to work properly is the VTL5C4/2.  That's not to say you won't get something else working as good or better.  

I got one of those "bright" LEDs to light in the circuit and I got a standard LED to light up by lowering the value of R6 down to 4k7 or something like that.  But I just never found the magic combination of tweaks to get it to honk.  I experimented a lot with the VTL5C3/2 with no luck.

Good Luck,
JD

[petemoore]

I'm thinking of trying to test the DOD 440 envelope filter using some type of variable resistance where the two photocells [of the vactrol] are situalted [just above the two 220k resistors in the schematic from GGG.
 What range of resistance [if anyone knows or could guess] would be required to get the filter to sweep? Even a little bit of sweep would verify that the Filter part of the ckt works.
 Then I would get the required vactrol, or maybe use a dual ganged pot or something. Switched resistors...