ROG Trivibe with volume drop and rate led not working

[Marcos - Munky]

I built a Trivibe some time ago, and now I'm finally putting it into an enclosure. But I found 2 problems: first, there's a huge volume drop when the effect is engaged. I initially used an JRC4558 for the buffer IC. After a little search, I found out that some people solved the volume drop problem using an NE5532 for the IC, but I tried this and the volume drop is still there.

Also, the rate indicator led doesn't work. I'm using a clear blue led for the rate led and a colored lens red led for the lfo, as called for at ROG's page. If I connect the rate led, the lfo stops, and the lfo works when I disconnect the rate led.

Any clues of how can I solve those problems?

[Aph]

I had the same problem when I tried a TL072. Here's how I modded the output stage to work:



When I used a 5532, it worked fine with the original schematic, but I did this to make sure I could adjust the output:




Here's how I did the LED:

[Marcos - Munky]

Thanks for your led wiring, I tried it and it worked without affecting the lfo. I tried the 100K trimpot, but the volume was below unity even with the trimpot at maximum. So I tried a few resistors and ended up with a 220K resistor, way bigger than the original 47K one . Now the volume is about unity, actually it's a little bit lower, but probably imperceptible when used in a live situation.

[Aph]

There must be something wrong somewhere else in the circuit, or the opamp is bad, etc.

[Marcos - Munky]

I tried two opamps with the same results. I'm thinking about to rebuild it using a different layout.

[ElectricDruid]

+1 agree with Aph. I doubt that the problem is the layout. 220K should give you 220K/47K = x4.7 gain on that final amp. If that's not getting you back to unity, something is wrong somewhere. Either you're losing a lot of level before that op-amp, or something is shorting the output and dragging everything down after it. An audio probe would probably tell you which of those is going on. It's probably nothing serious, just something you haven't spotted yet.

[Marcos - Munky]

Yeah, it's probably something simple. But to tell the truth there's some things I'm not very happy with at this build, so I'm etching a new board today using a different layout.