ADA FLanger - Clock noise - need suggestions

[jmasciswannabe]

So I am no stranger on this build. I jumped on the pcbs that moosapotamus offered back in the day and have built a few flintlocks as well. My latest one has an issue, though. It is what I suspect to be clock noise. In the upper part of the sweep, noise comes in (sounds like a crackly wave when sweeping.) Happens in both modes, I can use the manual control to isolate it. Very strange and I don't ever remember having this issue before (although I will say for anyone building the thing to avoid the charge pump, just use a dedicated power supply!!) So I built up another. Wouldn't you know it, that one does it too. Now I use the frequency meter and bias a al moosapotamus instructional youtube videos to set them up. I've compared working opamp voltages and everything checks out. I am ordering all chips from mouser this evening. The only thing I can't poop out are the SIL opamps. So, I am looking for suggestions in the meantime to experiment with to try and make it go away. I started a post over at MB a bit ago and Scruffie chimed in (for which I am very grateful) but the problem persists. I don't have the smarts to be able to look at the schematic and know what could potentially be the issue. Any suggestions will be tried and appreciated. Oh, and I have ran it straight with two 9 volts in series and regulated to 15 to see if it was a power supply issue. No dice.

There are some differences in the schematics between moosapotamus and lectric fx flintlock with regard to the bias and bbd sections. No one has reported this particular issue with the flintlock circuit and again, I don't recall it in previous builds I have done, but I am willing to adapt it to the moos if someone believes it might help. Again, not educated enough to draw those conclusions I've posted links to both below.

https://lectric-fx.com/wp-content/uploads/2015/07/FlintlockFlangerV1.2.pdf
http://moosapotamus.net/images/FlangerClone_SCH_rev5_MN3007_jan2010.gif

Thanks for your time and input!!!

[Mark Hammer]

The Flintlock has a pair of 2k7 resistors on the outputs of the BBD, while the Moosapotamus just gangs the two BBD outputs together directly.  Many higher-quality BBD-based devices will use a trimmer on the outputs of the BBD to balance them in order to cancel out clock noise.  Maybe if you can retrofit a ten-turn 5k trimmer in their, you can balance the outputs.

I say this not having any idea about what resistance is required to provide "ideal" balancing, or whether some batches are more prone to "output imbalance" than others.  But the fact remains that some circuits use it and some don't.  Maybe circuits that employ more lowpass filtering of the delay path rely on that without feeling the need to diddle with output balance.  The A/DA circuit uses very little lowpass filtering of the delay signal, so maybe it can use a little help.

[jmasciswannabe]

I inquired about those and scruffie reported

"The extra resistors are to do with clock cancellation, it's slightly better than connecting the BBD outputs straight to each other but not quite as good as the 5k trimmer you find on delays, but without a scope, probably not an audible change."

I can definitely try that. Here's the thing. I can set the pedal to where the manual goes into the noisy zone. Maybe if I do the multiturn and slowly go through it I will be able to hear it without the use of a scope.

Also, from an old thread StephenGiles offered:

"I didn't bother with the gate - the noise is all part of a flanger to me. Try changing R13 to the BBD bias trim to 4k7 which should provide a better range to trim out the distortion."

Might give that a shot also.

[Mark Hammer]

All useful info.  Incidentally, haven't seen you here in a while, so welcome back. 

[Fender3D]

I think this is not an usual clock noise issue, since you said it happens

In the upper part of the sweep

The noise Mark is referring to comes in in the lower part of the sweep
I think VCO is going too much high so that the BBD can't work properly.

You can try lowering the max clock frequency and check if it disappears...
It might be the BBD used or the clock buffers or the VCO itself...

[Mark Hammer]

A sensible response.  Yes, clock noise shouldn't be audible if is above the audio range.  So the "handoff" between stages may be corrupted at highest clock frequencies.

But I thought the A/DA's use of a buffer/driver got around that?

[jmasciswannabe]

Mark, I never left, just haven't posted in a while. Grad school and kids have been occupying a lot of my time. Regardless, DIYSB has always been my go to for helpful and knowledgeable folks and I'm glad it's still available fifteen years later from when I began my pedal building journey.

Fender3d - thanks for the input. You helped me out years ago when I modded one to switch between wave forms. Anyway, Tthe chips in both builds are more than likely from Tayda and the MN3007 from Polida. I am sourcing parts from Mouser and elsewhere in an attempt to see if I might have got a bad "batch," although it is worth mentioning I have never had issues from Tayda...or issues with mn3007 chip from Polida and I've bought many, however, I have received other defective parts from that supplier. We'll see what happens

In the meantime, pretty much anything over 750khz starts getting noisy and it increases the closer you get to 2.6.

[StephenGiles]

The Flintlock has a pair of 2k7 resistors on the outputs of the BBD, while the Moosapotamus just gangs the two BBD outputs together directly.  Many higher-quality BBD-based devices will use a trimmer on the outputs of the BBD to balance them in order to cancel out clock noise.  Maybe if you can retrofit a ten-turn 5k trimmer in their, you can balance the outputs.

I say this not having any idea about what resistance is required to provide "ideal" balancing, or whether some batches are more prone to "output imbalance" than others.  But the fact remains that some circuits use it and some don't.  Maybe circuits that employ more lowpass filtering of the delay path rely on that without feeling the need to diddle with output balance.  The A/DA circuit uses very little lowpass filtering of the delay signal, so maybe it can use a little help.

One of my ADA Flanger builds used a trimmer on the BBD output, and I remember that it did reduce clock noise slightly at the bottom of the sweep.

[StephenGiles]

I had a rummage in our attic amongst the bag of old boards, but no trace of it.

Got to be 14-15 years ago so I'm wondering if it was a breadboard version?

[jmasciswannabe]

Replaced the chips. Thought things were good until I got the output level set. I can still hear some crackly fizz at the top end of the sweep, but the gate feature goes a long way getting rid of it. I may be being too picky for my own good at this point. In a mix you'd never know and if I nudge my guitar volume down a bit it cleans up. I've turned into the guy complaining about too much noise in the memory man, lol.