Penfold "Light Metal Effects" ring mod - anything wrong with this schematic?

[Taylor]

http://experimentalistsanonymous.com/diy/Schematics/Ring%20Modulators%20and%20Frequency%20Shifters/Light%20Metal%20Effects%20Penfold%20Ring%20Mod.pdf

I was planning to build this, and have ordered all the parts. I was trying to find someone on here who has actually built it, but the only person I could find who's built it says it never worked. I'm wondering if anyone can see something in the schematic that seems wrong or that would create a problem. I'm also going to try to get RaceDriver205, who built one with no luck, to give his thoughts here. I'll probably build it, since I bought the parts, but if anyone sees anything fatal in the schem, let me know.

[StephenGiles]

i couldn't get the trigger to work for starters. Is that Lee van Cleef in your picture?

[soggybag]

I have all of the parts for this in a bag. I never got a round to making it. Maybe I'll give it a try, we can compare notes.

[Taylor]

i couldn't get the trigger to work for starters.

Hmm, that seems like it would be one of the simpler aspects of the project to me. Perhaps I'll try grafting a trigger from something else in. I'm also building the E&MM harmony generator, which has a trigger out. 

Is that Lee van Cleef in your picture?

Yep.

[Taylor]

Bump, and does anyone know of a PCB trace for this? I don't think I want to tackle this on perf.

[rackham]

Bump, and does anyone know of a PCB trace for this? I don't think I want to tackle this on perf.

Isn't the PCB image on that PDF you've linked to in your first post?

Should be easy enough to duplicate I'd have thought?

[col]

I've not built this one but I've built the one in Penfold's book "Practical Electronic Musical Effects Units" and that one works perfectly but is quite different to the one you've shown. It's still built around an LM13600/13700 though. You can get soem very nasty noises out of it!

[Taylor]

Isn't the PCB image on that PDF you've linked to in your first post?

Should be easy enough to duplicate I'd have thought?

It needs to be traced. I was hoping one of the couple of people who built it might have made a ready-to-etch layout, but I may just have to do it myself.

I've not built this one but I've built the one in Penfold's book "Practical Electronic Musical Effects Units" and that one works perfectly but is quite different to the one you've shown. It's still built around an LM13600/13700 though. You can get soem very nasty noises out of it!

Does that one track your note as well? Or is it the usual static oscillator? Could you scan the project? The only copy of that book I could find was $97. 

[sean k]

I've got the penfold book and I can't see a ring modulator but there is the metal effects unit which "generates frequencies that are not harmonically related to the input frequencies. The output from an oscillator in the effects unit is heterodyned with the input signal to produce sum and difference frequencies."

Is this what you are after?

[Taylor]

Yeah, that's what a ring modulator is. The Light Metal Effects is unique in that it also has an oscillator that tracks the input frequency, instead of the oscillator's frequency being set with just a knob.

If anybody can do a better scan of the layout than the one in the OP, it would be great. I've been tracing it and it's really difficult because of the quality.

[soggybag]

Redrew the schematic for this so that it would fit on perf board. I did this from the bad scan of the magazine article.

I curious about the alternative effect from the book. Though it sounds like this a regular ring mod type effect, and does not include the oscillator tuning feature.

[Taylor]

Do you by any chance still have your redrawn layout?

[Taylor]

And the debugging begins... I have this thing all put together, and I'm getting some sounds coming out of it, but not the right ones (I think/hope). I seem to have the right voltages at all the ICs. I'll try to audio probe it, but I won't really know what to listen for.

When I first fired it up, IC11, a 4001be, got really hot, then it cooled off. I thought I killed it, but the doc says the LED is lit by IC11, and the LED does light a lot of the time (the light seems to depend on whether the osc. is locked on a pitch or something?)

The settings of the trim pots appear to be incredibly finnicky. I can occasionally zero in on something that sounds promising, but changing the other trims throws everything out of whack.

I can sometimes get the oscillator oscillating, and sometimes the pitch changes with my playing, but it doesn't seem to be tracking pitch as much as tracking amplitude. The oscillator is very buzzy; sounds like a pulse wave. Kind of a bummer, pulse wave ring mod isn't my favorite sound. May try to filter the oscillator if I get this working better.

There's usually not any ring modulation happening, but sometimes it's vaguely there. There's a lot of debugging necessary, but it will be pretty difficult since the functioning of this circuit is pretty perplexing to me.

If anybody else wants to try this, I can post the PCB layout I did.

[Taylor]

Well, not sure anybody's listening, but I still can't get this to work. Tracing through with an audio probe is not particularly enlightening for a few reasons:

The article doesn't explain the functioning of the pitch tracking - he just says, "this is the same as the Guitar Tracker" but I can't find any info about the guitar tracker. Secondly, there is so much going on that I really can't tell what I'm supposed to be hearing anywhere.

I have to boost the signal to hell before going into the LME to get the VCO's pitch to change according to my playing, and even then, it doesn't track pitch so much as amplitude.

I don't think there's any ring modulation going on. I have swapped the LM13700 for another, and no change. The oscillator is always running, even when I don't play. Also swapped out the 4001be, no change.

I'm just afraid that there is some error in the layout I copied from the doc, and that it's not possible to get this working as is. Anybody have any thoughts?

[fredmerts]

I built the Penfold Tracker. Do a search, it was posted here. There were several things wrong with the schematic and parts layout. One thing that I can remember was the 5V voltage regulator (for the VCOs) was upside-down and had to be replaced after the first one was ruined. It eventually worked, but didn't track very well.