Dirtbag Troubles

[madbean]

You can turn up GAIN1 and GAIN2 to counter-balance the effects of the mod for more oscillation.

[tenwatt]

You can turn up GAIN1 and GAIN2 to counter-balance the effects of the mod for more oscillation.

Does it have to oscillate during the biasing process?  That's where I'm getting the distortion.  It sounds good and clean but then I turn up the GAIN pots and I get some distortion.

[RonaldB]

Maybe a silly question but do you mean by omitting R10, leaving it out and don't place anyting back?

[LaceSensor]

iIve compromised and made R11 12 and 42 as 22k
Now its kinda there.

Dont think this fix is the be all end all personally however.

[MadeByMike]

iIve compromised and made R11 12 and 42 as 22k
Now its kinda there.

Dont think this fix is the be all end all personally however.

I'm confused, as far as the up to date document is concerned I thought we were supposed to still use R11,R12 as the 47K specified for the 3205s?

There is also no mention in the document of changing R42 from 11K to 22K, I thought this was just something Scruffie suggested during this debug?

Did you still have dirty repeats with the pedal stock except for changing R21 and C14 to 100K?

Brian - when you made the above two circuit subs did you get your v3205 build all biased up and sounding good?

I've just started populating my board and unfortunately have already soldered in R11,R12,R21,R42 after hearing that the fixes were just those 100K subs. Am I going to end up experiencing the same issues?

Has anyone had success with their build as stock with only those 100K subs on top of the 47Ks in R11/R12 as documented?

[madbean]

Brian - when you made the above two circuit subs did you get your v3205 build all biased up and sounding good?

I've just started populating my board and unfortunately have already soldered in R11,R12,R21,R42 after hearing that the fixes were just those 100K subs. Am I going to end up experiencing the same issues?

Making the 100k resistor subs completely solved the distortion issue for me and I was able to bias the two BBDs easily. I have not tried tweaking R42, though.

[MadeByMike]

Brian - when you made the above two circuit subs did you get your v3205 build all biased up and sounding good?

I've just started populating my board and unfortunately have already soldered in R11,R12,R21,R42 after hearing that the fixes were just those 100K subs. Am I going to end up experiencing the same issues?

Making the 100k resistor subs completely solved the distortion issue for me and I was able to bias the two BBDs easily. I have not tried tweaking R42, though.

Thanks for the reply - That all sounds good to me then, sounds like I can continue with my build in hope!

[LaceSensor]

Mike. Check your email.
Probably too late now.


The fixes of 100k for R21 and C14 do have an effect, but as another user pointed out, soon as you crank the gains to get any semblence of more than 2 repeats (clean) the thing starts distorting again.

Sorry but I have to voice these concerns otherwise more people might be in the same situation and all this troubleshooting would be for nothing.

All I can say is the combination of the madbean fix, and scruffies suggestions, has got me to a point where I can put a full stop on this. However, I am still not 100% happy with it.

[LaceSensor]

Making the 100k resistor subs completely solved the distortion issue for me and I was able to bias the two BBDs easily. I have not tried tweaking R42, though.

was this on a production board or a prototype?
were you able to tune gain 1 and 2 after biasing bbd 1 and 2, to get runaway feedback, without distortion (other than the obvious) and by this i mean tweaking to get to that point, then backing off the Feedback control.

When I do this, and back of the feeback control, because of the extra pre and post gain required for self oscillation, the isolated repeats at lowered feedback amounts are suffering distortion.

Hence leading me again to start messing with Scruffies suggestions.

Anyway, after much desoldering and dismantling I am chalking this up to experience and hopefully this discussion will help others. If the stock values work for them then great, but it seems mine and Tenwatt's experiences beg to differ, unless you are happy with 1 or 2 repeats only.

Footnote - I am sorry if my words appear negative but I feel I must voice them. No offense intended. With respect, LS.

[madbean]

If you are having to turn the gain pots up so much to counteract the input signal and this is causing distortion, then the best way to proceed is to modify the voltage divider created with the two 100k resistors. Hopefully you have those socketed. Try 47k for R21 to start and leave C14 at 100k. Or, you could temporarily hook up a 100k pot as a voltage divider and then tweak it to the optimal setting, Then it's just a matter of recording the resistance between the outer lugs and the wiper to get the correct resistor values. But, I don't think you will have to go to that far. Simply experimenting with lower values on R21 should be enough to balance the input signal with GAIN1.

[madbean]

Another approach would be to leave R21 and C14 as they were before (1k/33n) and instead tweak the value of R13 from 24k up to 51k - 100k. I'll give this a try today and see if it is any different from the posted fix from earlier.

[LaceSensor]

If you are having to turn the gain pots up so much to counteract the input signal and this is causing distortion, then the best way to proceed is to modify the voltage divider created with the two 100k resistors. Hopefully you have those socketed. Try 47k for R21 to start and leave C14 at 100k. Or, you could temporarily hook up a 100k pot as a voltage divider and then tweak it to the optimal setting, Then it's just a matter of recording the resistance between the outer lugs and the wiper to get the correct resistor values. But, I don't think you will have to go to that far. Simply experimenting with lower values on R21 should be enough to balance the input signal with GAIN1.

Seeing as how confident the fix appeared to be I didnt socket C14, I just put the 100k resistor in. I do have r21 socketed however.

[MadeByMike]

Yikes. I've already soldered a 100K into R21 since it seemed this was confirmed as the fix. C14 is empty so I'll socket that for sure in case.

I guess I'll hold off doing anything else at all until this is all sorted out. I'll wait for more feedback from Brian about the state of his production board with the current R21/C14 100Ks and whether this needs to be reverted and other values installed elsewhere.

Upsettingly R13 is already soldered on my board too. I was really hoping not to have to start pulling out components already.

[madbean]

Seeing as how confident the fix appeared to be I didnt socket C14, I just put the 100k resistor in. I do have r21 socketed however.

Well, if it appeared confident it's because it worked for me. I'm doing my best to help you 

[MadeByMike]

Can you post your IC voltages with your trims adjusted? Maybe this will help LaceSensor to see where he's differing to you?

You're not getting the problems he is with not getting oscillation unless the trims are so high the delays are gritty?