PT2399 delay circuit problem.

[KitShunt]

Hi there.

I'm having trouble with a delay circuit using the PT2399 IC.

I've built the circuit many times before with no problems, but now I have tried to integrate it into a multi-effect unit (VCF, distortion, etc) the chip flatly refuses to work. It's doing my head in! 

Can anyone help me out with this?

Cheers,
James

[ECistheBest]

how did you integrate the PT2399 into your pedal? and do you have DC voltages on each pin? have you tried another chip in it?

[KitShunt]

Hey cheers for the reply.

It's not actually integrated really... it's just on the same board and sharing the same power supply as the other analogue effects.
I have read somewhere that the PT2399 doesn't like sharing a power supply, but I have also read elsewhere that it's not a problem!

I've tried swapping the IC out a couple of times, with the same results.

Unfortunately I don't have it in front of me right now, so can't get the voltage readings from the pins.
I'll have to get onto that later.

[gcme93]

Two main things that I've learnt from Rick Holt (man who's spent a lot of time working on PT2399s):

- The PT2399 "hashes up" the power supply. So I don't think that it doesn't like sharing, I think it provides pretty bad feedback into the power line itself. Maybe have a little power filtering to it? (I'm sure you've tried this)

- The PT2399 is notorious for locking up, never to be used again. This seems to be very hard to predict - circuits that have been working for a few months can suddenly stop until the PT2399 is replaced. The fix was provided on this post on the Little Angel Chorus: http://www.diystompboxes.com/smfforum/index.php?topic=86297.msg774512#msg774512

Hope this helps, be sure to post some build report on it

[KitShunt]

Excellent, thanks!
I'll give that little sub-circuit a go 

So once a PT2399 has locked up, is that it? Dead chip?

[gcme93]

Uhmm... not necessarily? I can't remember what I read from the Little Angel page (there's 40 pages of it!) but try the little subcircuit with one you think might be dead - if I'm honest I have no idea how it works, just that it does. Hopefully it will "unlock" them for you.

At the very least it'll stop it happening in future for certain (if lock up is indeed the problem)

Good luck!

[KitShunt]

Haha story of my life... "How does it work?" "I dunno, but it does!"

Thanks for the help, I'll let you know how it goes

[Pyr0]

Are you testing it with a battery or power supply ?
I've noticed that PT2399 based delays will not work when running from a battery, but will work fine with an external power source that can provide sufficient current. Also if you are using a 78L05 regulator for the 5v supply, some people claim that they do not provide enough current.

[KitShunt]

I've tested with battery and wall-wart power, same result.

As I mentioned, I have built this circuit stand-alone a number of times with no problem, and they were using regulators from the same batch, so I don't think that's the issue. I'm yet to try that little sub-circuit on pin 6, but I'll be sure to post any results.

[slacker]

In my experience when PT2399s lock up they recover after a power cycle, I've never killed one. Unless you have less than 1k of resistance between pin 6 and ground when you power it up it shouldn't lock up, so if you have a pot on pin 6 turn it up above 1k and turn the thing off and on again, if the problem was it locking up it should work.

Have a look at this http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[KitShunt]

Ok, so I've finally got round to having a look at the pin 6 fix.

I notice it's from a chorus circuit that has no control tied to the delay time pin (6).
How would it work with a pot and resistor already connected to that pin for delay time control?

Hmmm.

[Jdansti]

Take a look at the "Application Circuit" in the data sheet and you'll see how they control pin 6. You can also search for PT2399 reverbs, echoes and choruses and see how they utilize pin 6.

Here's the data sheet:  http://sound.westhost.com/pt2399.pdf

[slacker]

What's the minimum resistance between pin 6 and ground, probably set by the resistor, if it's 1k Ohm or more you don't need the fix.
If you need it I think you can just connect the fix circuit between the pot and ground.

[KitShunt]

The minimum resistance between pin 6 and ground is 1k, so I don't need the fix.

I still think it's something to do with the power supply. 
I've built this circuit standalone before with no trouble at all, but now it's on a board with a load of other stuff, it doesn't want to play ball.

[gcme93]

You're probably right, sorry for being hasty with the pin 6 fix thing. I guess I saw "PT2399 problem" and instinctively thought of the lock up issue.

If you can have the PT2399 part of the circuit powered by a separate voltage regulator try that. Also, if you can isolate that part of the circuit to make sure it works on its own without the power being used elsewhere, that would be useful (as an indicator that it is indeed a power line sharing problem)

George

[KitShunt]

Ok... I've isolated the power supply completely.
It worked!... for a bit, and now it doesn't any more again.

All connections are fine, I've triple checked the circuit for shorts, bad joints and component placements.

Time to give up, while I've still got some hair left!

Thanks everyone for the help... I'll probably come back to it at some point.

[Jdansti]

I've had intermittent problems using the 78L05 for powering PT2399s.  Switching to a 7805 corrected this. I'm not saying that this is your problem, but it might be something to consider.  I haven't had to use a heat sink on the 7805 when powering PT2399s, but your mileage may vary. 

[KitShunt]

Hey John.

I am using a 7805... I don't really trust 78L05s for some reason ;-)