Vibrobot distortion

[Diynot]

Calling @DGWVI and @Mentaltossflycoon and anyone else who might have thoughts. Mkay, not the reason I thought I was going to open this thread, but while my vibrobot is trem-ing, it has some distortion/fuzziness on the signal. After chasing rabbits before lifting pin 6 I am 99% sure of parts values. During the no trem witch hunt I also have reflowed joints, cleaned the board, the voltages look good, the ICs aside from the 8038, that I got from Robert, came from Mouser, I have messed with the trimpot, but can’t get the signal clean. Obligatory board pics in case I missed something and also a vid for listening purposes. My initial suspicion would have been the TLC2262 except with the depth all the way down the clean is clean. I guess that leaves the 741, 8038, or the 2N7000, but are those actually seeing/producing an audio signal? The vid was made using my p-90 loaded Reverend in the bridge position, but I also tried with my tele and although there is less, the distortion is still present.

 

[Mentaltossflycoon]

That's a bummer, I wish I had something helpful to offer but I do not. Mine just had a little grit to the sine/saw setting that I easily dialed out with the trimmer. It never had anywhere near that much dirt.

 

[Nostradoomus]

Did you…solder your dpdt switch?

 

[Diynot]

That's a bummer, I wish I had something helpful to offer but I do not. Mine just had a little grit to the sine/saw seeing that I easily dialed out with the trimmer. It never had anywhere near that much dirt.

All good. you provided me with confirmation that it isn’t supposed to sound like that

 

[Diynot]

Did you…solder your dpdt switch?

Ha, yes. I am pretty sparing with the solder on switches, no flooding the pads here for potentially easier removal if needed. Continuity checks out and I have access to all 3 waveforms

 

[DGWVI]

I had this issue with both I've built, solved with adjusting the trimpots. It's a very small window to hit, so gotta go kinda slow with it

It's been a while, but I also kinda recall having to audition mosfets on one of em

 

[Diynot]

I had this issue with both I've built, solved with adjusting the trimpots. It's a very small window to hit, so gotta go kinda slow with it

It's been a while, but I also kinda recall having to audition mosfets on one of em

Good to know. I have tried to dial in the trim and it is a very tiny % of rotation from no trem to quiet muffled trem to louder, clearer, but still noisy trem, back to clean. Maybe I should try using a multi turn trimmer…. Did you still use a 2n7000, or a different one altogether?

 

[DGWVI]

Good to know. I have tried to dial in the trim and it is a very tiny % of rotation from no trem to quiet muffled trem to louder, clearer, but still noisy trem, back to clean. Maybe I should try using a multi turn trimmer…. Did you still use a 2n7000, or a different one altogether?

Pretty certain I used 2n7000, but may have used bs170

 

[Mentaltossflycoon]

Mine has no substitutions. Pretty sure everything but the enclosure and ICs came from tayda.

 

[Diynot]

Mine has no substitutions. Pretty sure everything but the enclosure and ICs came from tayda.

I have been slowly working my way through the same pink baggie of 2n7000s for awhile now. I don’t want to go too crazy chasing this down. Think I’m going to try a multiturn

 

[chris.knudson]

I guess that leaves the 741, 8038, or the 2N7000, but are those actually seeing/producing an audio signal?

A multi turn may help, but to answer your question -- while these parts aren't directly in the signal path, the definitely affect the signal path. All of the suspect parts you listed could be introducing the distortion, but you can eliminate them by adjusting the depth control. If you get distortion at both ends of the depth control, these semiconductors are not your problem, which just leaves the TLC262. If you only get the distortion with the depth control engaged, then any of them could be the problem, with the 2N7000 being the first place to start.

 

[Diynot]

A multi turn may help, but to answer your question -- while these parts aren't directly in the signal path, the definitely affect the signal path. All of the suspect parts you listed could be introducing the distortion, but you can eliminate them by adjusting the depth control. If you get distortion at both ends of the depth control, these semiconductors are not your problem, which just leaves the TLC262. If you only get the distortion with the depth control engaged, then any of them could be the problem, with the 2N7000 being the first place to start.

Yeah, signal is clean with the depth/mix down so it’s something in that LFO(?) block. I may (shudder) put in a socket to try different mosfets. The 741 was swapped in previous troubleshooting efforts so don’t think it’s that.

 

[chris.knudson]

I may (shudder) put in a socket to try different mosfets.

If you have another 8038, you could try that first, but the mosfet seems a likely candidate.

 

[Diynot]

If you have another 8038, you could try that first, but the mosfet seems a likely candidate.

I have but the one 8038

 

[Diynot]

Tested all the 2n7000 I had, all with more or less the same result. Can dial it out enough to be ok with single coils, but anything else is grit city. It’s not an unpleasant grit, just not what you want on a trem per se

 

[Robert]

Can dial it out enough to be ok with single coils, but anything else is grit city.

Coincidentally the Frantone product writeup for the Vibutron says "Designed with the single coil player in mind" ...

I wonder if the MOSFET is clipping the signal, similar to how they're used as clipping diodes in the Zendrive/OCD/etc...

 

[Diynot]

Coincidentally the Frantone product writeup for the Vibutron says "Designed with the single coil player in mind" ...

I wonder if the MOSFET is clipping the signal, similar to how they're used as clipping diodes in the Zendrive/OCD/etc...

She does seem to play a lot of Strat for her demos…… it’s not an unpleasant clipping and if you are using od anyways, meh?