Shoot the moon Tremolo help

[shay1510]

Hey folks,
Need help on Shoot the moon Tremolo (based on the tremulus lune). Built on vero using http://tagboardeffects.blogspot.co.il/2013/04/culturejam-shoot-moon.html.

When powering it, the inner led starts working. The two knobs (depth, speed) as well as
the wave switch work fine (you can tell by the way they change the led's behaviour.
However there is very little effect even when the DEPTH knob is at maximum (and the led goes all the way from off to on).
Also tried to play with the GAIN trimmer but no change.

Do you have any idea where should I look for the problem?
Btw - there is a slight volume drop when the effect is engaged.

Thanks a lot.

[samhay]

The LFO is working, which narrows it down. What kind of LED/LDR combo or a vactrol did you use?

[shay1510]

3mm red led+tayda's ldr wrapped together in a heat-shrink tube.
Btw- i didnt have a 330pf cap so i connected 3 1nf caps together in series.

I'm assuming that the problem is based on a defective part or wrong value.

[midwayfair]

3mm red led+tayda's ldr wrapped together in a heat-shrink tube.
Btw- i didnt have a 330pf cap so i connected 3 1nf caps together in series.

I'm assuming that the problem is based on a defective part or wrong value.

The little pF cap is just to help prevent ticking.

Your gain trimmer isn't working, and your LFO isn't changing the audio path. This means your op amp isn't functioning. Post your voltages, and start looking around there for your solution. Audio probe pins 1, 5, and 7, and see if you have amplified signal anywhere.

pictures of both sides of the board may help.

[shay1510]

midwayfair, I'll change the opamps and check connections.

UPDATE: I've found out that the 6 220k resistors are actually 200k (Tayda's fault. Put me the wrong value in the bag.)
Changing them from 200k to 220k will make the difference?

[nocentelli]

Unlikely: Post the opamp voltages.

[shay1510]

IC1 (tl072):
1 - 200mv
2 - 200mv
3 - 4.7v
4 - 0v
5 - 4.8v
6 - 530mv
7 - 530mv
8 - 9v

IC2 (tl062):
1 - 3.5v-5.5v (keeps changing on the voltmeter)
2 - 3.5v-5.5v
3 - 3.5v-5.5v
4 - 0v
5 - 3.5v-5.5v
6 - 3.5v-5.5v
7 - 2v
8 - 9v

[samhay]

At a guess, I would say that you need to use a larger gain pot - I doubt you can pull your LDR much below 10k. Do you have an A100k pot you could try.

Edit - I'm off my game today. Can you measure the resistance across the LDR with the depth at min and max?

[midwayfair]

At a guess, I would say that you need to use a larger gain pot - I doubt you can pull your LDR much below 10k. Do you have an A100k pot you could try.

no no no no no.

10K is a HUGE amount of output boost in this pedal's setup. I use a 5K, but 10K is perfectly fine (if excessive).

OP: Your voltages on 1, 2, 6, and 7 are way too low. They should be about 4.5v. Can you post pics of both sides of the vero?

[shay1510]

when depth is at minimum (led on) resistance is about 7k ohm
when depth is at maximum (led cycling off->on) resistance is changing from 0 to a few k ohm (my Multimeter is not fast enough).

[shay1510]

I'm not sure if the photos are helpful. I must apologize in advance - This is one of my worst soldering jobs. My soldering Iron is defective and has to be replaced. Also replaced a 10uf electrolytic cap with a tantalum. connected 3 resistors and 3 caps in series to get the values I needed.
* on the top row there is continuity, so don't worry about how it looks.

[shay1510]

Hey guys - GOOD NEWS!
Since Jon P has pointed out that the voltages on IC1 were too low, I've replaced it again with another tl072.
It works great! though I cant figure out why do I have so many defective IC's lately.
I'd like to thank all of you for directing me to the right part/problem.
You're awesome.

[midwayfair]

Hey guys - GOOD NEWS!
Since Jon P has pointed out that the voltages on IC1 were too low, I've replaced it again with another tl072.
It works great! though I cant figure out why do I have so many defective IC's lately.
I'd like to thank all of you for directing me to the right part/problem.
You're awesome.

Yay! Glad it worked out to be something simple (bad part is always a tricky debug).

Enjoy one of my favorite tremolos.