General Tso Not Compressing / LEDs too Dim

[lumberjack]

Hey gang, just finished a General Tso tonight and everything seems to be working other than the fact that the LEDs associated with the LDR barely engage when playing, so I get no noticeable compression from the circuit. The biggest strum gets a very faint glimmer from them, almost imperceptible, so I double checked the resistors associated with the LEDs and they are indeed 1.5k to ground as called for. If I run a boost in front of the compressor you can see the LEDs light up a bit more, but I'm not sure what a realistic fix would be, or what's wrong. It's like the signal voltage the LEDs "see" from the guitar signal is too low to light the LEDs, perhaps the transistors associated with them aren't doing their job properly? I got them from Tayda and Mouser, and I haven't had any trouble sourcing components with them before.

The op amp seems to be working fine, as the volume knob generates quite a bit of boost, and the "sustain" control increases the volume as well in both modes, but again it just makes everything louder, not compressed. Would this be something as simple as running lower resistors to ground in place of the 1.5k? It seems like something else must be wrong though, as there's plenty of people who have built this and they used 1.5k for the LEDs.

Note: trimmer at right is for power LED brightness, and the tied resistors are just to get the right values.

 

[lumberjack]

Awesome, thanks for the heads up - I'm definitely going to give that a shot then.

 

[mkstewartesq]

Yup, just dropped them in with no other changes. The OG Dinosaural schematic has 2.2K current limiting resistors in that part of the circuit instead of 1.5K like the Tso, and I wasn’t sure if those would need to be changed too (such a small change but I wondered if Thorpy picked 1.5K for a reason). I didn’t feel like I needed to even experiment after testing it just changing out the vactrols; it sounded great.

Thanks for this information. I tried a Thorpy Fat General and loved it and so will be starting on a General Tso shortly (actually a 2-in-1 build with the Kompromat (Keeley clone) on the other side for times when I need a little more "squish") - but I was dreading the trial-and-error of working with LEDs and LDRs and so thought buying some VTL5C4s would be worth it just for peace of mind. I know the VTL5C4 was used in the original Dinosaural but I didn't get a chance to open the Thorpy to confirm they were also in the newer pedal - and some around here have stated that, going by specs, the VTL5C4 might be too slow. So it's good to have your anecdotal report that they not only work in the Tso but also work well.

M

 

[DeadAirMD]

I have two General Tso's (ordering mistake), so I thought I'd try a vactrol in place of the photo resistors. Put in the VTL5C4 yesterday and I like the way I had it before, actually compresses way more in my experience before the VTL5C4. I have a few NSL-32/NSL-32R laying around that I'm going to try out today. Socketed the VTL5C4 just in case.

 

[lumberjack]

I have two General Tso's (ordering mistake), so I thought I'd try a vactrol in place of the photo resistors. Put in the VTL5C4 yesterday and I like the way I had it before, actually compresses way more in my experience before the VTL5C4. I have a few NSL-32/NSL-32R laying around that I'm going to try out today. Socketed the VTL5C4 just in case.

Thanks for sharing! Let us know how the other vactrols go? I realized the ones I had weren't the VTL5C4 after all, but were the VTL5C3, so I haven't tried them. I'm pretty satisfied with how things turned out with the KE-10720 LDR and LED combo; good compression with a bit of character and "juice" as it were, but not overwhelming by any means. It's a great comp.