PT2399 Feedback not changing

[subvader12]

Hello everyone, I'm trying to make my PT2399 delay (based on Sea Urchin) oscillate when the feedback pot is maxed out, I've already changed R15 from 5.1k to 20k and 2k testing but it didn't make a difference either way, I changed R16 that goes into the feedback pot from 2k to 1k, and still no infinite repeats. Also, I lowered the pot value from 50k to 10k and still no oscillation. Before I start messing around the circuit more I want to know where should I go from here, what is restricting the repeats?

Here's the schematic I'm based on so you can see which resistors I modified:


Thanks in advance.

[anotherjim]

I think making C13 larger might help. Try 220nF.

[subvader12]

How will this affect tone of the repeats? Because right now its sound is amazing, but I want infinite repeats option if you pull pot all the way up.

[Rob Strand]

With a circuit like this when you change something it affects a lot of stuff and you need to make adjustments to other parts if you want it to stay the same.

How will this affect tone of the repeats? Because right now its sound is amazing, but I want infinite repeats option if you pull pot all the way up.

When you decrease R15 to say 2k2 you need to increase C13 to keep the response (tone) the same.  However, with such a large change, you also need to tweak the filter caps,

For example, to keep the repeats the same,

R15 = 2k2
C13 = 33n
C6 = 6.8n  5.6n better
C7 = 1.8n  2.2n better

That increases the gain of the feedback by 4dB without changing the tone of the repeats.
There is a small effect on the delayed signal response, which is unavoidable.

I don't know if that's going to be enough.

If it's not enough gain you need to change something else, say R16, or R14 or R11.  However you can't *just* change those to keep everything the same you might need to tweak the caps again.   Playing with R14 and R11 will also change the gain of the delayed signal.

And if that's not enough you might have to allow small a change to the feedback tone and increase C13 a bit more.

As you can see it's not as simple as it seems (especially when you don't want to change what it is now).

[subvader12]

I adjusted some values accordingly to keep the tone I had. The reply from anotherjim helped me with the oscillation problem, I made C13 larger and now I got infinites repeats with feedback pot all the way up. Thanks to both of you! This community never ceases to be great and helpful.