Sharkfin: Randomness

[fritz]

My sharkfin build works great and is a lot of fun to play.

However quite often it looses it's randomness over time (e.g. after being engaged for 1 or 10 minutes, that's also random  ) and stabilizes on a fix melodic pattern. Going back to a random behavior can be achieved easily by either re-engaging the pedal or slightly moving the speed pot. So there's a work around. Furthermore to me there seems to be no dependency to any of the tuning settings...

Any idea on how I could mod the pedal so that it permanently stays in a random state?

[Betty Wont]

Ah, the cursed drift. All of the F/SH I've built present this behaviour to some degree. The only solution that has satisfied me is the stomplfo chip from electric druid. The random wave makes for a rock solid and truly random sample hold with no drift or patterning.

[fritz]

Thanks! Does it replace any of the existing chips?

[Betty Wont]

No, unfortunately. The circuit needs to be designed for the chip. The electric druid filterfx project uses the chip to great effect with a Sample Hold and many more waveforms 

[fritz]

what a pity

[nocentelli]

http://me.aquataur.guru/musicstuff/fsh-1.html

aquataur suggests using the b/e junction of the noise transistor (i.e. base to -9v and emitter connected to the opamp) and leaving the collector open. this is a change from the original fsh-1 arrangement, and I can attest that it seems to be a more reliable way to get random blipping from pretty much any old transistor. when I tried out the original arrangement, I had to try out quite a few different types before I got one that was reliably random.

[fritz]

Well, let me translate that for not-so-well-educated people like me.

I "simply" have to twist two legs of the transistor Q4 as marked in the attachment (yellow arrow, lower left corner), right? Whereas I do not have to but anything into the middle hole...

[skyled]

Well, let me translate that for not-so-well-educated people like me.

I "simply" have to twist two legs of the transistor Q4 as marked in the attachment (yellow arrow, lower left corner), right? Whereas I do not have to but anything into the middle hole...

This is exactly right. See my post here:
https://www.madbeanpedals.com/forum/index.php?topic=29884.msg289196#msg289196

[fritz]

thanks. i'll try it today...

[fritz]

... and it works! great!!!

i have the impression, that the type of randomness also changed a little bit. the former one quite often had a sort of "dotted note" aroma. but maybe it's just a matter of tuning...

nevertheless no steady pattern any more or at least only for a very short period of time.