Shoot the Moon Tremolo Debug

[neutronarmy]

Friends,

I'm working my way through a Shoot the Moon tremolo build that is giving me the worst of frustrations. I have it all built and assembled and the oscillator that drives the vactrol is not oscillating. I've double-checked all of the connections and triple-checked for bridges between traces. The TL072 section in the signal path seems to be functioning just fine - gain control works as I'd expect - and here are the voltages:

1 - 4.6V
2 - 4.6V
3 - 4.6V
4 - 0V
5 - 4.5V
6 - 4.5V
7 - 4.5V
8 - 9.1V

However, the RC4558 that drives the oscillator is giving me nothing but trouble. The speed and wave controls seem to do nothing at all and the depth control makes the volume quieter (by dimming the LED in the vactrol - so that works). The IC voltages are all kinds of not right, but I can't quite deduce what might be causing it. Here are the RC4558 voltages with the IC in circuit:

1 - 2.5V
2 - 2.5V
3 - 2.5V
4 - 0
5 - 2.4V
6 - 6.2V
7 - 1.5V
8 - 8.08V

And the voltages on the socket without the RC4558 in circuit:

1 - 4.1V
2 - 4.1V
3 - 4.2V
4 - 0V
5 - 4.2V
6 - 4.1V
7 - 4.1V
8 - 8.43V

I am using the Tagboard Effects layout located here: http://tagboardeffects.blogspot.com/2013/04/culturejam-shoot-moon.html and the schematic located here: http://www.forrestwhitesides.com/node/111. The only major difference I could see was the RC4558 in the schematic and the TL062 in the layout but to the best of my knowledge they are interchangeable.

The only modification I included that is outside of the schematic is the use of a switched jack on the speed pot. The future recipient wants to use an expression pedal. Other than that it is bone stock. I've attached two photos of the build to hopefully help any troubleshooting. I apologize for the slightly messy track side; I've been troubleshooting to the point of a less-than-my-standards-of-cleanliness build.




Thanks in advance for any help; you all rule,
Chris

[mistahead]

Is the TL062 a single or a dual opamp?

I've heard certain opamps function better in these circuits than others, for variety of reasons depending on the circuit... food for thought, not much else.

[midwayfair]

Is the TL062 a single or a dual opamp?

I've heard certain opamps function better in these circuits than others, for variety of reasons depending on the circuit... food for thought, not much else.

It's the low current draw version of the 072. I regularly use the 072 in this oscillator without issues.

Op: see if you can isolate just the first half of the oscillator. The second half is just a buffer before the depth. There are only about six parts in the first half, so check them all with the multimeter against the schematic for proper continuity. Once you have moving voltages pin 1, then move on to the depth control.

[neutronarmy]

Is the TL062 a single or a dual opamp?

I've heard certain opamps function better in these circuits than others, for variety of reasons depending on the circuit... food for thought, not much else.

It's the low current draw version of the 072. I regularly use the 072 in this oscillator without issues.

Op: see if you can isolate just the first half of the oscillator. The second half is just a buffer before the depth. There are only about six parts in the first half, so check them all with the multimeter against the schematic for proper continuity. Once you have moving voltages pin 1, then move on to the depth control.

midwayfair: I'll do that very thing. I made the same realization about the half of the TL062, but still couldn't manage to get it to work. I'll give it a thorough going through shortly and update. I was hoping it would be easily apparent and under my nose as I've been fighting this thing for some time. I'm sure it's something dumb. Also - the Bearhug rules; I built it for a friend who loves it.

[Lurco]

are you really sure that all the trace-cuts are really cut through all the way? In the picture, some of them look a bit suspicious.

[GP]

I would also suggest you start by knocking out that huge solder bridge between the 5th and 6th track (from the bottom).
Run a sharp knife between all of the tracks.

[duck_arse]

[2c_worth]I use a larger diameter drill to cut vero tracks, without going through the board. it makes the pointy cut edges further apart. I haven't seen many of the hole-thru boards about.[/2c_worth]

[mistahead]

[2c_worth]I use a larger diameter drill to cut vero tracks, without going through the board. it makes the pointy cut edges further apart. I haven't seen many of the hole-thru boards about.[/2c_worth]

Razorblade tip in the hole, rotate and shave until you have a nice cut was my way, then I discovered that the shaped grinders in my rotary toolkit were faster and neater.

I have drilled as suggested but found it to lack the control of both above, and hence took longer to get to the same outcome.

[duck_arse]

I used to have a genuwine "vero spot face cutter". dunno where it went, but now I have a 3.5mm drill jambed into a cut down dishbrush handle. works like a bought one. and then I go over with a mag glass and a snap blade knife, for shyts and giggles, I think they say.

razor blade tip? yr a braver man than me.

so where are we with the debugg?

[neutronarmy]

For years I used a Radioshack pin vise with a slightly larger drill bit to take care of the hole cutting. Unfortunately I lost the pin vise. This time around I used a Dremel drill press and a bit and the results weren't what I was hoping for. Posting debugs is always a little embarrassing because you are sharing the work that didn't really live up to your own standard of quality. I was just trying to get a quick build for a friend and it turned into a real headache. Thanks for all of the help! I knocked out the solder bridge (which was actually just a little chunk of solder that fell onto the board) and tried my best to isolate the problem. It still persists, but admittedly I haven't had the time to properly debug as a local music festival happens in my hometown this weekend and I've been crazy busy. I'll get back on the game early next week. I can't thank you all enough for the help.

[duck_arse]

a closer look at your underside pic.

first cut from the top: cut eighth row: both cuts 13th row: probly both cuts 14th row: all look bad to me. and looks like a copper whisker 7th row, first cut.

12 row, 4th hole from left doesn't look 100%, and a couple of other scattered, but I'm guessing you'll be going over the whole board next?

and those plastic jacks never seem to switch quite the way I want or expect them to ......

[neutronarmy]

So, I have come upon the strangest of luck (of the unlucky sort). I decided that because of the regular working and reworking on the board that I could no longer trust it. So, I decided to rebuild the whole board as it is rather simple. I was certain to take my time this time around and decided to cut the tracks by hand and not run through the entire board. Weirdly, after assembling this new board I have the exact same problem. Properly functioning TL072 stage and the same voltages values on the TL062/RC4558 stage. The only parts I reused were the vactrol and the off-board components. Tomorrow I'm hoping to finish this project, so I'm going to go through the offboard wiring with a fine tooth comb and double check all of the various component values surrounding the oscillator stage. Hopefully, that will get to the bottom.

[Pojo]

Totally going off a guess here, but I looked at the tagboardeffects layout and it calls for TL062 and TL072 which are both jfet input opamps. Maybe the circuit depends on the jfet inputs?

As of now, I know very little about LFOs but I'm hoping that will change in the coming weeks as I dive into learning as much as I can about them.

Another thought is maybe there's an issue with the mod. Have you tried it stock?

[neutronarmy]

As embarrassing as this is going to be, I figured I'd let those who helped know the real problem: 500R pot for the wave control rather than 500K. I double checked nearly every value except for the pots. Well, you live and learn I guess. Thank you all for the amazing suggestions and help!

[duck_arse]

Weirdly, after assembling this new board I have the exact same problem. Properly functioning TL072 stage and the same voltages values on the TL062/RC4558 stage. The only parts I reused were the vactrol and the off-board components.

you had solved the problem, but you didn't know it. one for the sherlock holmes method (qv).

ans well done, now you've got 2 trems.