PT2399 problems...

[tommycataus]

Hey everyone,

I've just built Merlin's PT2399 Equinox reverb from the vero layout at tagboard effects and it sounds lovely.

One problem though - most of the time I turn it on, it makes a hideous screeching oscillation sound which I can only get rid of by repeatedly switching the 9V supply on and off, or lifting one of the PT2399 chips and re-seating it.

I've built other pedals with PT2399s and every one of them is glitchy in some way which makes them completely unsuitable for gigging, since you never know when they are going to stuff up.

I also know about the pin 6 problem and that it can be fixed by changing resistor values, but I haven't heard of that problem having resulted in horrifying noises.

My question is, is this a known issue with PT2399s (the terrible noise), and is there a way of making these chips reliable? Or will they forever be relegated to the bedroom domain, never to be savoured by a proper audience?

Thanks in advance

[merlinb]

A screeching reverb is usually a sign that the feedback loop has too much gain, causing it to oscillate. Not sure how that can be happening in this case though. Suggest you double check your component values.

[tommycataus]

Thanks Merlin, it worked Ok on the breadboard so maybe there's a short somewhere... I'll give it a good going over and let you know. 

[tommycataus]

Found the problem. It worked a dream first time, no issues whatsoever...

I have a cheap power supply that adds a lot of noise with high gain pedals, so I created a filter for the high frequencies. There is something wrong with this filter causing the equinox to squeal like nothing I've ever heard before! Without the filter it is fantastic. Seems like I can eat humble pie and go back to the drawing board with the filter.

Thanks Merlin, amazing effect

[samhay]

If the supply voltage of the PT2399 sags much below 5V, it sounds pretty nasty.
If tamed, it can be put to good use - this is how the 'Little Angel' works.

[tommycataus]

Thanks Sam, it's another lesson I think.  The 9v regulator had gone west as when I'd built it, I had no heat sinks. All fixed now.

I'll remember that tip though as it may come in handy incidentally the little Angel is already on the build list!

Cheers

[garcho]

I've built other pedals with PT2399s and every one of them is glitchy in some way which makes them completely unsuitable for gigging

That's an exaggeration. I've been gigging with an Echo Base for years and not one problem. Plenty of problems with my earlier Little Angel builds, with no doubt that my lack of skill was to blame. I'm not saying that's the case with you, I'm just saying that while having some issues with PT2399s, they occur in inverse proportion to my skill with the iron and breadboard and PCB design, etc. My last Angel hasn't had problems of any kind in 2 or 3 years. I'm guessing many cheapo brand delay pedals have SMT PT2399s and it's hard to imagine "every one of them is glitchy in some way". Belton bricks are made of PT2399s. I've noticed a few people mentioning their desire for a PT2399 upgrade IC. 2400?    I'm certainly interested but experimenting with new digital delay chips is just one more thing on a super long list of things to do. Anyway, what kind of pedals gave you problems?

[pinkjimiphoton]

i still have yet to find a stable pt2399 based ANYTHING.

i had a rebote i built that i loved... until i tried to run it on a battery. i did a stupid pedal tricks video on it... when the power dips below a certain point, the circuit freaked out. apparently the low voltage fried the regulator when the bat died, and after that even replacing components i could never get the dang thing to work.

i built a little angel too... sounded boss. until i turned it off. them damn chips latch up once, and they smoke something internally i think.

[tommycataus]

Well the original question was, I guess, whether they were giggable... turns out my major issue was the power supply filter. I knew that it would be down to me (as it always is) but the effect was working partly and I just couldn't work out why it was doing what it was doing.

Jimi I know what you mean.  I've not had the chips latch up irreversibly although I have had sporadic issues.  It's nice to hear decent first hand feedback from you garcho, the abductor delay it is then!

[tommycataus]

*That probably should have read "none of MY PT2399 builds are giggable", in hindsight 

[merlinb]

This is all very mysterious. I've designed four or five PT2399 circuits, and played with a lot more on breadboard. I've never had a single problem (except when it was my own wiring mistake).

[deadastronaut]

^ me too, never had a problem with pt2399's...(even from different suppliers)

i always use a good psu ...never batts.

[tommycataus]

Gah! I'm so awkward! Note to self... don't reply via smart phone during lunch break!

It was my power supply filter causing problems all along, sorry for the confusion - it seems like the issues I was having with the PT2399s were actually caused by the voltage regulator in my testing power supply filter blowing... so all the PT2399 projects I've been working on in the last 3 or 4 weeks (nearly every PT2399 project I have started) have been affected by this.

It's the only IC that made a godawful screeching sound when plugged in, so I thought it might have been a problem with PT2399s in general given that:

-No other pedals plugged into this power supply exhibited any issues, only those with PT2399s
-When building the Equinox, the problem went away when I reseated IC1, which led me to believe that my wiring was OK
-I read about the issues with latching as well as pins 3-4 having to be linked

So, up until building this one I was stuck looking for my mistake. Once the heatsinks arrived I forgot to put one in the filter. Eureka! When I measured the voltage on the power supply it read about 7.4V. Perhaps PT2399s are more sensitive to this.

The Equinox is working like a dream!

So... It WAS my mistake. Nothing new there.

You guys are always so helpful, thanks!

[merlinb]

Once the heatsinks arrived I forgot to put one in the filter. Eureka! When I measured the voltage on the power supply it read about 7.4V. Perhaps PT2399s are more sensitive to this.

What is you filter? 7.4V is not enough to run a 5V regulator reliably. The 7805 will probably have been dropping out of regulation. You really need 8V input for reliable operation of a 7805.

[tommycataus]

I have a cheap 9V power supply which hums. The filter is based on the circuit on the SmallBear website with two caps and a voltage regulator, and is used to filter out unwanted frequencies.

The regulator went west, so without the filter (just the cheap power supply directly into a pedal) 9V was being supplied with the hum. With the filter attached, it was providing less voltage.

[garcho]

Have you worked with digital ICs before? They're not always intuitively troubleshot. Glad you got it working, cheers!

EDIT: it really pays to have a regulated PS on your bench, to weed out variables. You don't have to get a $300 giganto thing, a One Spot will do nicely.

[allesz]

Come on merlin, you are more skilled than the average diyer! Say it right.

I toyed a little with the pt2399 too, (I am not an expert, nor a professional) and I had experienced more troubles compared to transistors and simple IC designs.
The regulator gave me problems some times (once I had the idea to try a simple voltage divider... but was not man enough to try it ), and maybe, as a partial noob I make little mistakes, that I am unaware of, that tend to give noisier or worst overall performances.
Sometime I have to breadboard the circuit three times, before getting something working decently... but I admit that I always like to depart from designs and experiment a little.

And thanks for the informing pt2399's "augmented" datasheet.... we should call it "the real one".

Note: my opinion of this IC was almost like the one of pink jimi.... then I tried some bbds.... 

[tommycataus]

As far as regular diyers go, I'm pretty far below the bell curve! I believe this is my first foray into working with digital ICs. I stocked up on a bunch of components a while back and I'm slowly using them up - every penny is being saved at the moment although a decent isolated power supply is most definitely near the top of the wish list!

You guys are so helpful as always.

[merlinb]

a decent isolated power supply is most definitely near the top of the wish list!

Get yourself an old laptop or computer power supply for free, and a cheap LM317 kit to bolt on. Bench PSU for practically nothing!
http://www.ebay.com/itm/LM317-Step-Down-DC-5V-35V-to-1-25V-30V-DIY-Kit-AC-DC-Power-Supply-Module-/371079822657?pt=LH_DefaultDomain_0&hash=item566614bd41