Tim OD squealing when gain and boost are maxed.

[lasermonkey]

Hi, I'm having some issues with a Tim OD that I have just built, using the layout on the main site. When the gain and boost controls are maxed out, it starts squealing at just over unity gain. I have made sure the leads are a short as possible, tried shielded cable and even a buffer, which improved things somewhat but not really enough.

I built another Tim (using the same layout) a few years back and don't remember having the same issue. Certainly, the guy who now has it never mentioned it!

Anyone else encountered the same problem and did you find a cure? I'm completely at a loss now. Any ideas grateful received.

Cheers,
Mark.

[Kitsune42]

Glad to know it's not only me! I've been scratching my head for the last month trying to solve this on the TS808 + timmy tone build.

[lasermonkey]

The only thing I found that worked was a Klon buffer added between the input jack and the footswitch. With that, there was no squealing whatsoever, even at full volume. Placed after the footswitch, the squeal came back at higher volumes, although it's probably fair to say that it had a good, usable range before the squeal occurred.

I thought that the buffer sounded completely transparent, but the guy I was building it for was adamant that it should be true bypass, so the project got shelved.

I still don't know how to explain why the position of the buffer is so important, but the results kinda speak for themselves. It has to be worth a try.

Good luck!

[luc.tonnerre]

Might be interesting to know that the same thing happens with the Animal: https://tagboardeffects.blogspot.com/2013/07/rockett-pedals-animal.html

It seems to be because the buffer was omitted from the original layout if I remember rightly. A buffer in front of the pedal fixes the issue for me, but someone in the Animal comments fixed it by swapping out components: https://tagboardeffects.blogspot.com/2013/07/rockett-pedals-animal.html?showComment=1375548298902#c869991209471127897

[lasermonkey]

Thanks for the info. It’s been a while since I last poked around with the circuit. I did try shielded cable, but that made no difference at all. Only a buffer situated between the input jack and the footswitch removed the squealing.
I suspect that it’s the cable run length that must be the problem. On the first build I did (which worked fine) the jacks were physically closer to the circuit and footswitch, though not by a huge amount. The guy who I was building the pedal for specifically wanted a layout which meant longer cable runs.
Anyway, the guy went quiet on me in the end, so I’m officially abandoning the project. I’ll repurpose the enclosure and salvage the useful components from the stripboard. Life’s too short!