PT2399 motorboating problem with new ICs

[LaceSensor]

I bought the ICs from the following suppliers;

Banzai (good, but I have not bought recently)
Tayda (all good)
Goodbuy7888 (Ebay seller) Noisy, but ok on shorter delay times. At least they're usable in some form
Thaishopetc (Ebay seller) Total rubbish and unusable.

I'm not suggesting that the vendors know how good or bad these ICs are - they're just commodity items being passed around the world. Unfortunately I left good feedback for the worst ones before I tested them.

Now, it's OK claiming guarantees, exchanges or refunds, but the return postage from here in England is excessive compared to the 'free' postage sending them out from Thailand, Hong Kong, China or Singapore. It just isn't worth sending them back.

The main question is; are they just cheap, or cheap for a reason? There has to be a certain defect threshold in the factory and a number of rejected components for whatever reason. You would think that the ICs would fail prior to being marked up, but are they finding there way out of the back door and getting printed up with PTC markings?

I can accept that we're swimming with sharks on Ebay, so I have to blame myself to some extent. Buy cheap, buy twice, as they say (or three times, ten times or more if you're buying ICs).

Must say though, it's the first time I've ordered of Tayda and they've supplied excellent products.

As above I have 20 from tayda that are junk...so it seems to be pot luck...

[Maudibe]

Steve @ Doctor Tweek here.

Test circuit built, based on Princeton circuit / Rebote ... last batch checked and they all motorboat when given more than about 75% feedback 

I have another batch to check later today... fingers crossed.... otherwise these will be binned too.

Meanwhile, I have refunded the couple of customers who got caught with the bad batch 

I have been in touch with Princeton Technology direct and can source from their Europe agent no problem, however the cost is significantly higher and the minimum quantity buy is, shall we say, 'significant'. I have yet to ponder on the outlay required    I can soak some of the price increase, but I am concerned that I will be left holding a monster stock for a few years!

Ah, joy 

[grrrunge]

I'm thinking that it may be possible to design a delay line to accomodate these motorboating chips by adding a high-pass filter section after a PT2399? Maybe a second or third order active high-pass filter with a corner frequency around 200hz could do the trick without being too invasive on the resulting sound?

Edit: I have one of the motorboating IC's in my Echo Base. The oscillations are most apparent on delay time pot at minimum available and again from 12-1 o'clock and forward, Feedback settings doen't matter at all.
At minimum delay time, the chip oscillates at around 88hZ, but the frequency drops rather fast on the first part of the pot. At max delay time the oscillations seem to be in the 20hZ area, and is apparent as small but very obvious pulse sounds. Maybe it's enough to add a filter around 100-150hz?

[LaceSensor]

Steve @ Doctor Tweek here.

Test circuit built, based on Princeton circuit / Rebote ... last batch checked and they all motorboat when given more than about 75% feedback 

I have another batch to check later today... fingers crossed.... otherwise these will be binned too.

Meanwhile, I have refunded the couple of customers who got caught with the bad batch 

I have been in touch with Princeton Technology direct and can source from their Europe agent no problem, however the cost is significantly higher and the minimum quantity buy is, shall we say, 'significant'. I have yet to ponder on the outlay required    I can soak some of the price increase, but I am concerned that I will be left holding a monster stock for a few years!

Ah, joy 

Thanks Steve good to know in a way that we weren't going nuts,
It's put me off making some ace pt circuits.

Hopefully supplies get sorted out.

[Mick Bailey]

Just received another batch from Tayda and they're perfect.

[Maudibe]

  PT2399 Chips now Quality Checked @ Doctor Tweek  

Just to let the board know that I now have the Rebote test bed circuit built and all PT2399 that are sold are now tested to check for quality and correct performance.

This should make for happy bunny people  

If anyone wants mild fails (motorboating at +70 feedback) for a chorus project then I have a few from the 'bad' batch going for just the postage and packaging (£1.70 to anywhere). Just ask at info@doctortweek.co.uk

I have about a dozen or so, so hope I can help some folks out - only one per person     while they last.

Best, Steve

PS MICK BAILEY  - contact me for your free good checked one as a way af saying thanks for bringing this to everyones attention 

[Mick Bailey]

Steve,

Thanks, got it - will put it to good use in a pedal for my own use.

Mick

[Mark Hammer]

Happily, there is the Equinox reverb circuit, which can make productive use of a motorboating chip that shuts the motor off at very short delays.