PT 2399 Build Question

[mikepurcell]

I just finished a build of the crap-fi delay - just a simple PT2399 delay. It didn't work, so I started checking voltages to see if I could locate the problem. When I was checking the PT2399, I bridged pins 2 & 3 and it started working. I disconnected the power and reconnected and it didn't work until I bridged 2 & 3. I noticed that when I first apply power before bridging the pins, the voltage regulator and 2399 start to get really hot. I can put a meter on the battery feeding the board and literally watch as the voltage drops down .01 volts every second. When I bridge those 2 pins, everything returns to normal and the circuit works as it's supposed to until it's power cycled.

The voltages on the chips are the same before and after I bridge those 2 pins, I'm getting 5.01 volts on pin 1, 2.55 volts on pin 2. I thought that I may have lost the ground on pin 3, but I'm showing a good ground path on pin 3 and pin 4 of the 2399. The voltage regulator is showing 5.1v on the output.

This is my second PT2399 build with these chips that I've had a problem with, first one was a cave dweller II and output was mostly white noise with the effect way down in the noise floor.I figured I'd try something really simple that's hard to screw up to check these chips, but I'm having a different problem. I've tried 3 different chips from this batch of 10 and they're all behaving the same.

I got the chips off eBay. They were priced comparable to other suppliers, so I didn't really think that they may be problematic.

Does anyone have any insight into what may be causing this? Looking at the schematic, I'm wondering if the 100u electrolytic between the voltage regulator out and ground would have something to do with this? Or is it something with the chip?

I followed the layout exactly but used tantalum 100n for the caps across PT2399 9/10 and 11/12. Positive side to 9 and 12.

[garcho]

There should be a cap from pin 2 to ground, try 47uF

[anotherjim]

When the chip started to be exploited for FX, nobody connected pins 3&4 together and all was good (although it would have done no harm to connect them together in the first place). Something changed in the chip (it is supposed -the datasheet says nothing) and we find they don't all work unless we do connect them together.
When you search for schematics or layouts, you will tend to find both connections depending on how old they are.
Edit - yikes, I thunk we was talking about the two 0v pins!

[bluebunny]

I think Jim is confusing 2&3 with 3&4 (which are both "ground").  But Gary is right: pin 2 shouldn't be unconnected.

[anotherjim]

Yeh, I see my mistake now,
Note though, that this "Crap-Fi" design may rely on leaving pin2 without a bypass cap. Letting it float should allow all kinds of nasty interactions between the various sections of the chip.

So, shorting out pin2 to the ground pin may have cleared a lockup in the chip. The lockup might have many causes, but an injection of static electricity during handling or from an ungrounded soldering iron tip could be responsible.

[duck_arse]

it's like they always say - can we see photos of your build, please?

cap or no cap on pin 2 shouldn't affect operation. what is your supply voltage into the regulator? also post the voltages on all other pins, if you would.

[mikepurcell]

Thank you - I’ll try the 47uf on pin 2 to ground.

Regulator:
I 9.1v (edited)
G 0.08mv
O 5.1v

PT2399
1 5.1v
2 2.49v
3 0.08mv
4 0.08mv
5 3.41v
6 2.46v
7 1.10-1.14v
8 1.08-1.15v
9 2.51v
10 2.49v
11 2.49v
12 2.51v
13 2.49v
14 1.13-1.21v
15 2.49v
16 2.49v

[mikepurcell]

47u to ground from pin 2 fixed it.

Thank you!

[anotherjim]

Pin 13 should not be disconnected. You can connect it to pin 14.

[duck_arse]

cap or no cap on pin 2 shouldn't affect operation. what is your supply voltage into the regulator? also post the voltages on all other pins, if you would.

well I'm happy it works and I'll stand for corrected. but, those ground voltages you posted worry me, they should be 0.00. a reading hints at a connection fault, somewhere.

[mikepurcell]

Yeah, I wondered about that voltage on the ground too. I ended up bagging it, too noisy. I chose this one for the size, but the trade offs just aren't worth it.

[garcho]

I ended up bagging it, too noisy. I chose this one for the size, but the trade offs just aren't worth it.

The size obsession in guitar pedal world is a thing, ain't it? It really does make building working pedals difficult. In my opinion it's not worth it, because performing with dozens of 1590A pedals also isn't worth it. Consider - for a delay pedal anyway - a larger enclosure/layout. Just my 2¢.

crap-fi delay

They tried to warn you! 

[mikepurcell]

I had a 1590bb that had already been drilled for something else which I ended up using a different enclosure - not really an obsession with small circuits, just trying to find a delay circuit to work within existing size parameters.

I'm not really into things that would fit into a 1590a, I prefer circuits that are more feature rich. I figure you're spending close to the same money for the switch, the jacks, and the enclosure, might as well make something with more than one knob.