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