ticking and oscillation on Dirtbaby in relation to the c/v rate

[z11111]

Hey y'all, been a lurker here for a long time. Have built a few handfuls of Madbean boards and I love all of them (& thanks Brian for being a fantastic designer )

So, I built myself a Dirtbaby and didn't seem to have any issues running it with my test rig, until I boxed it up and I don't really know what went wrong.

When both bypassed or engaged, regardless of anything being plugged into the input (and trying both a onespot and a PP2+), my Dirtbaby has a strange and VERY audible ticking directly correlating to the chorus/vibrato rate pot. When in vibrato mode with the rate all the way up, the pedal starts oscillating. This happens regardless of the rest of the settings on the pedal and likewise is still 100% audible during bypass.

I tried three different PT2399s, each with different markings (one of them definitely being a counterfeit, two of them being from apparently genuine sources) and that didn't change anything.

I got the TL062s from Tayda and they all measure around 0.1 ~ 0.2v lower than the recommended voltages in the build doc. I know Tayda has some genuine ICs in stock but also some more questionable parts so maybe this is the issue? I swapped each one at a time for a TL072 to see if that would eliminate the issue but it did not (however, I did not swap out ALL of the 062s, just one at a time).

Here is a youtube video of the issue: https://youtu.be/_giVXCTf5CM

Any help would be appreciated! I have no clue what happened here. All other functions work fine, aside from irritating ticking...

edit: I should also note that I used a b100k for the delay pot instead of a b50k just because it's what I had on hand BUT this issue happens regardless of the resistance on the delay pot. Also as mentioned, this didn't seem to be happening before I boxed up the pedal.

[midwayfair]

It's not related to the PT2399, it's from the LFO for the modulation. LFO ticking is not uncommon in all sorts of pedals.

The easiest fix is usually a low current chip, like the LM1458. You can also try increasing the power filtering (both for the whole pedal and for the LFO) though that's rarely the cause of the problem.

However, the ticking is usually fairly quiet. If it's loud -- like as loud as the guitar signal -- then you have something else wrong.

[z11111]

It's not related to the PT2399, it's from the LFO for the modulation. LFO ticking is not uncommon in all sorts of pedals.

The easiest fix is usually a low current chip, like the LM1458. You can also try increasing the power filtering (both for the whole pedal and for the LFO) though that's rarely the cause of the problem.

However, the ticking is usually fairly quiet. If it's loud -- like as loud as the guitar signal -- then you have something else wrong.

I figured it was the LFO rather than the PT2399 because the PT2399 is getting the proper voltages across the board. The ticking I am experiencing is DISTRACTINGLY loud, very close to the level of the guitar signal to the point where the pedal is unusable. As mentioned; it also happens in bypass mode presumably because the i/o jacks are board mounted at a similar distractingly loud level.

A friend recommended replacing C3 (2u2, coming off the vibrato/chorus in the schem) so I am going to try that with another 2u2 and see what happens.

[Boba7]

Maybe pics could help too...

[z11111]

Alright, problem mysteriously solved.

Replaced C3 with a MLCC (still 2u2) and brought down the ticking a little bit.

Turns out (still blows my mind) that the wire I had going from the tip of the input jack to the PCB was causing the problem. When it was close to the PCB, the LFO ticking was super present, but when I moved it away the ticking was almost inaudible. I blame the wire as the insulation must have been poor quality and maybe created some sort of capacitance issue () (replaced it with higher quality wire and everything was all set), but I've NEVER had this happen to me before and I've built some odd 30~ pedals!

Put an old LM358 in IC3 for the LFO and it sounds quite a bit nicer to my ears. Will also try a LM1458.


edit: I should note though; I can slightly hear the delay motorboating at slower speeds. I tried swapping in the three different PT2399s I had on hand and it didn't seem to make a difference, but this might be normal? Not entirely noticeable.

I also rewired the jacks directly to the 3pdt instead of through the pcb and that made quite a difference with noise as well.

[madbean]

Wire acting as an antenna for LFO ticking is a very common problem. What you did is exactly what I would have suggested- move it out of the way or re-route it away from the IC.

The motorboating can be a problem with PT2399 when it is pushed over 500ms (remembering that these chips are only spec'd for 300ms of delay). A common mod for the Dirtbaby is to increase the filter cap at the delay output from 4n7 to 47n (C13). This will darken the delay some but it should quiet down the motoring quite a bit.

On the next order of DB boards I'm going to add an additional filter at that spot to make it more of a permanent mod.

[z11111]

Wire acting as an antenna for LFO ticking is a very common problem. What you did is exactly what I would have suggested- move it out of the way or re-route it away from the IC.

The motorboating can be a problem with PT2399 when it is pushed over 500ms (remembering that these chips are only spec'd for 300ms of delay). A common mod for the Dirtbaby is to increase the filter cap at the delay output from 4n7 to 47n (C13). This will darken the delay some but it should quiet down the motoring quite a bit.

On the next order of DB boards I'm going to add an additional filter at that spot to make it more of a permanent mod.

thanks for the info Brian!!

I'll try a 47n in C13. I like a darker delay anyway so this sounds like a nice modification to pursue.

[Boba7]

Glad it's working!

I wanted to see pics just to check on your wiring. I've had this issue a couple times, and moving the wire/re routing it worked each time.

I tried to raise C13 but didn't really like the result. Instead I raised C10 to 1,5nf and it was good.

Additionally (though not necessary) I raised C12 to 150nf and R4 to more than 30k to compensate (a higher value for C12 raises the wet volume)

I REALLY like the result of those mods, I highly recommend them!

[midwayfair]

I blame the wire as the insulation must have been poor quality and maybe created some sort of capacitance issue ()

Insulation is not shielding. Shielding is a faraday cage around the wire carrying signal. All insulation is is a way to prevent the wire from shorting against something else metal.