Lectric FC Dandy Horse help

[jwyles90]

Hey all,

I am humbly coming to you again with issues I'm running into on my second Dandy Horse build (honestly I need to just stop building these things).
Basically it seems to be working in the sense that I'm getting some modulation out of it and the modes are "functioning" enough to know that there isn't any issue there, however I'm unable to dial out any of the high pitched whine that should be dialed out with the cancel trimmer.
The cancel trimmer itself seems to only range from "super intense whine" to "somewhat subtle but still present" whine. It's the most pronounced with the trimmer set in the center, and then gradually decreases the further I turn it left or right. I'm also noticing that the gain 1 and 2 trimmers don't seem to have that pronounced of an effect, unless I max out Gain 2 I don't really hear a difference between them.

I started checking voltages and everything looks good except for the 3007s, so I suspect something is up there. On IC3 my readouts are:

15v
7.5v
10.1 (should be 7.8v)
0
0
7.7-9.5v (should be 7.5v)
8.8-9v (should be 8.4v)
8.9v (should be 8.4)

on IC4 I'm getting:
15v
10-12v (should be 7.5v)
9v (should be 6.6v)
0
0
10 (should be 7.5v)
8.6v (should be 7.6v)
8.3v (should be 7.4v)

I've doubled checked all the resistor and cap values around the chips, reflowed everything in that area, and still can't seem to figure out what the issue is or how to get rid of the whine that's there. Any help would be greatly appreciated!!

 

[fontoponto]

I have the same problem with the cancel trimmer.
Anyone else having this issue? The support forum is not really supportive
The pedal itself sounds good. Clean the effects could be a little bit louder.
I tried to tune it with an oscilloscope and that is the only way I can achieve the 10% louder instruction.
The LFO sounds like a square when using it in slower settings. How can this be explained?

 

[neiltheseal]

Try connecting pin 1 and 8 of the lt1054.

I have had charge pumps whine before and this has fixed it for me.

 

[fontoponto]

No it's not related to the LT1054. The cancel trimmer is for the clock noise of the 3007 and it should be less in the middle position of the trimmer but it's not.

 

[Stickman393]

I'm perusing through the manual right now.

Just to confirm: you've completed the previous steps in the setup part of the document, yeah?

Your IC measurements dont look too crazy to me. Not where they're supposed to be, sure, but close.

Looking at the schematic, your trimmers will impact your IC voltage measurements. That cancel trimmer is meant to be a voltage divider for VA on pins 7 & 8 on IC3. What isnt making sense to me is that your IC4 7 & 8 pins are adding up to more than your pin 1 voltage - pin 1 is directly fed from VA. That shouldn't be possible. Can you confirm IC4, pins 1, 7, and 8?

Ic4 pin 3's voltage is going to be directly set by where you have BIAS2 set.

IC3 pin 3's voltage is directly set by where you have BIAS1 set.

 

[fontoponto]

My measurements are like the ones from jwyles90 in regard of the higher voltage IC4 pin 1, 7 & 8 and I think this is ok, I saw this in other posts.

IC3​

1 14,92
3 7,46
4 6,96
5 0
6 7,46
7 7,32
8 7,32

IC4
1 14,9V
2 7,46
3 7,53
4 0
5 0
6 7,45
7 8,16V
8 8,0V

 

[Stickman393]

Hmm. Not entirely sure how voltage behaves with the BBD. Looking at the datasheet, it's possible your bias2 trimmer is influencing the voltage read on pins 7 and 8 as well. Pin 3 is the input, 7/8 are the output: im not seeing anything in there that would block DC.

Both examples are above the quoted voltages from the LECTRIC documents.

Look, you're not in *great* hands with me cause I'm not entirely clear on how BBDs operate. That said: if I was troubleshooting these builds, I would try to adjust bias2 until pin 3 on IC4 is around 6.6vdc.

Then, re-check your IC 4 7&8 voltages. See if that brings those down too.

From there, I'd hook up a scope and fine tune the waveform with BIAS2, then fine tune the cancel trimmer.

I wouldn't worry too much about pins 2 and 6 on either. Those are gonna hop around a bit. It's just the clock communicating with the BBD.

 

[fontoponto]

Ok, I set IC4 Pin 3 to 6,6V by adjusting Bias2 but then the wave form on pad 3 with looks super distorted.
7,5V is the cleanest looking wave form. With 6,6V in the end the effect is less noticable then before.
I mean.. it's there for the Flanger and the Double Tracker and it was there but a bit less and for example in Chorus mode the effect is super weak.

 

[eh là bas ma]

in Chorus mode the effect is super weak

I noticed that when i built it, a few years ago. I managed to dial a good and noticeable chorus modulation after spending some time on the calibration.

I remember i used the vibrato switch to compare the modulated signal with the clean signal. I can't remember if i used Gain 1 and Gain 2 trimmer to adjust the volume to get a 50/50 clean/wet ratio. I vaguely recall that we can't tweak Gain 1 trimmer much, because there's a narrow usable range to avoid distortion. So it was probably mostly Gain 2 and maybe i also tweaked feedback because, (unless i am confusing with another circuit) it acts a bit like a clean/wet control in the first half of its rotation.

 

[tsredman]

Anyone solve the clock whining issue? I am encountering the very same problem.

 

[jwyles90]

Anyone solve the clock whining issue? I am encountering the very same problem.

I did eventually fix it, but I made the silly mistake of not actually writing down what it was that fixed the issue. I think it was one of those instances of "messing around with a few different things combined to solve it". I do think it had something to do with the caps that are used in C43 and 45. i had to experiment with a few different values for each and dial it in each time to really get it right. I also swapped out one of the CD chips (can't remember which one it was ) and believe that helped a bit too.

 

[tsredman]

I did eventually fix it, but I made the silly mistake of not actually writing down what it was that fixed the issue. I think it was one of those instances of "messing around with a few different things combined to solve it". I do think it had something to do with the caps that are used in C43 and 45. i had to experiment with a few different values for each and dial it in each time to really get it right. I also swapped out one of the CD chips (can't remember which one it was ) and believe that helped a bit too.

Hehe. I have a bad habit of not documenting too.

In addition to the loud clock whine, the voltage on pin 16 of the NE570 is high (4.2 vdc) versus what is reported at lectric fx (0.9 vdc). Could the clock whine and high pin 16 voltage be related?

All other voltages check out fine. I reflowed all solder connections. I've double checked all my resistors and they are correct. I am about to double check capacitors.

I am also wondering if the CD4013 and/or CD4049 type might be a factor in the whine?

 

[jwyles90]

I am also wondering if the CD4013 and/or CD4049 type might be a factor in the whine?

I think you might be onto something there. On paper I don't think it actually makes a difference, but, if memory serves, on one of my last polychorus builds swapping out the CD chips seemed to help a bit with the noise.

I'm in the process of putting another one together currently. Fingers crossed this one fires up without issue, but I'll keep you posted if I run into anything along the way.

 

[Feral Feline]

...

I am also wondering if the CD4013 and/or CD4049 type might be a factor in the whine?

Possibly.

I know some circuits based around the 4049 won't work with some brands or production-batches.

NOS is best.

 

[tsredman]

Thanks for the follow up comments. I'll report back when I figure out what is going on. No luck yet though.

 

[beansell]

Hey @jwyles90 @tsredman, I'm having trouble with this project too. Any chance you've figured out the secret sauce? The voltages around IC3 & IC4 aren't quite right on mine as well. Not a whole lot of useful modulation going on, despite my best efforts calibrating with a multimeter.

 

[jwyles90]

Hey @jwyles90 @tsredman, I'm having trouble with this project too. Any chance you've figured out the secret sauce? The voltages around IC3 & IC4 aren't quite right on mine as well. Not a whole lot of useful modulation going on, despite my best efforts calibrating with a multimeter.

What's the sound like on yours? It's very finicky, and the trim pots are all fairly interactive with one another so it can be kind of pain to get just right. I just put together my 3rd one of these recently and I think the caps that you use near IC3 and 4 can play a role in that (as well as where you're getting your BBDs from).

 

[beansell]

I get stuck at the audio biasing section. Sounds like a gentle tremolo (or an artifact of the circuit not working properly) through an audio probe at TP3. No audible delay or significant hiss (as mentioned in the calibration guide). I've tuned for the least distortion at Bias2 & Bias1, but then the Cancel trimmer also gives me weird results. Maximum whine in the center of the trimmer rotation, going down in level along with the dry signal when turned CW or CCW.
My BBDs are XVive MN3007s from Cabintech. I bought 4 total, and have swapped them out to no avail.
Also using Texas Instruments CD chips from Tayda - CD4049UBE and CD4013BE. I saw @tsredman mention that type (suffix?) might be a factor here. I can pick up some from a local electronics supplier that are listed as National Semiconductor and Fairchild. Worth a go?

Also which caps specifically? C42-45 for tuning? Or the caps nearby in the schematic - C11, C13, C18, C19?

 

[beansell]

Update! I went ahead and swapped the CD chips - turns out the supplier just lists datasheets from whoever. The new ones are also Texas Instruments. Silly, but it might have helped.
I followed through the entire calibration process, despite the bias & cancel trimmers doing almost nothing audible to the signal, and it works!
The output has a pretty heavy treble roll off, perhaps that's down to inaccurate calibration (do I really need to shell out for an oscilloscope?)
The effect is wonderful with the blend switch engaged, but it'll need some more calibration for sure.
Thanks for the assistance @jwyles90

 

[jwyles90]

Thanks for the assistance @jwyles90

Not sure how helpful I was, but I'm stoked you got it working! In each of the three builds I've done I've found that there's always something slightly off between what the biasing procedure says to do and what I actually end up doing. I don't think I've ever dialed out the whine completely, and one build basically had it there the entire time. Either way though, they all end up working after some fiddling. Glad yours did too!