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You didn't say which package you are using.  Is it the 150mil of 300 mil SOP?
I've only used the 300 mil which is the pt2399-S.  I haven't had any problems with anyone I've done work for with that package.

I'd also try them from a reputable supplier if you haven't already.

That being said, there is some variability between chips and some changes over time which are not disclosed.  Some batches have more quirks than others, in my experience.

Josh

It's 150mil, and it's from Tayda.
The resistance between pins 9 & 10 and 11 & 12 is around 5k - not that far from '4.7k'
BTW as I turn the rate pot, it works fine up to about haif way, then as soon as you turn up from there it's into full on feedback meltdown into crackles.....

Do you have a picture of the SMT chips you are using?  There are some fakes out there.

Here it is...

Hi!
I'm David, from Rainger FX guitar pedals, making my first post here! I'm wondering if anyone can shed some light on my recent problem with the PT2399 chip.

I've used the thru-hole version successfully in the past, and have recently been using the SMT version - the PT2399s. I've got this to work well too in the past, but with the current PCB project I'm working on, as I turn up the rate pot to longer delays, an out-of-control feedback quickly builds up and disappears into just crackling noises.

Meanwhile my breadboard thru-hole version works well. So one pin at a time I disconnected the SMT chip, reconnecting to the breadboard version and testing as I went, until finally the PCB was entirely connected only to the thru-hole chip in the breadboard... Working totally fine!

So then - using an SMT 'conversion board' - I replaced the thru-hole PT2399 on the breadboard with the PT2399s... And the problem occurred. I repeated this test with several chips of both kinds, confirming the situation; the bigger thru-hole works well in this circuit, and the SMT version doesn't.

Does anyone have any idea how to fix this?
Looking online, I find nothing about 'different conditions needed for thru-hole vs SMT'.
As I mentioned, I have got the PT2399s to work fine in the past, but I just cannot find any differences between 'good' and 'bad' layouts, and man, have I been looking....!

On the 'bad' circuits I've noticed the DC on pin 14 (the feedback/output pin) to increase as I turn the rate pot - which doesn't happen on 'good' circuits.

Any help/suggestions are much appreciated!