GGG PT-80 problem

[Curranm]

So I bought a GGG PT-80 kit last week and have assembled it. The delay level is super low and when I crank the level all the way up it starts a high pitch squeal. I have checked my wiring layout but i have not had a chance to check voltages yet. I do have the charge pump in the circuit and I am using a BOSS stye poiwer supply that works with all of my other pedal. Any ideas right off the bat?

[mp3j3rk]

I realize this is a stale thread, but this is the closest to my issue that I have found anywhere.  I started the PT-80 project around the same time the OP created this thread.

I am having similar issues.  Same setup (pt-80 w/ charge pump).

At first I was using a dc adapter with the polarity reversed and my charge pump got extremely hot.  I found another supply with correct polarity and got the circuit to engage with led on and sound with no effect but with a newly developed squeal.  Sweeping pots makes no difference.  Checking voltages on the charge pump I was getting ~9.4v on pin 1 and 8 (n.c. boost and V+).  According to the MAX1044 spec sheet that voltage is well within normal parameters.  I also checked voltage on both sides of the voltage regulators, and got surprisingly low voltage, but I cannot recall exactly what.

I even purchased a new set of ICs (PT2399, MAX1044, TL072, 571) and tried those with similar if not slightly better results.  Still no effect but no squeal.

Were you ever able to troubleshoot your build?

One strange-ish thing that I have noticed on the schematic is that the MAX1044 pin 2 (capacitor +) is connected to the negative lead of the capacitor.

[mth5044]

A few things that are going against you here.

It is helpful to provide a link to the schematic since we don't have these things memorized:
http://www.generalguitargadgets.com/pdf/ggg_pt80_sc.pdf

Check out this debugging thread to get the most info for help (can also be found sticky'd under the main 'Building your own stompbox) forum:
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0
The voltages that were surprisingly low would be helpful!

Finally, this post is under the Digital & DSP subforum. I guess the PT2399 is digital, but you might get more help in the main forum as that area seems to has more visitors!

A high pitched squeal usually seems to be associated with a charge pump. When that happens, connecting pins 1 and 8 double the squeal of the frequency out of hearing range. It seems Mr. Sleep at GGG had thought ahead and already bridged them for you. The MAX1044 can be very sensitive to overvoltage. The datasheet does say 10V, but I've also read people not being able to put in more than 9.1V. You could try a 9.1V zener like an IN4739 that only allows 9.1V to pass.

Not 100% sure if the negative side of the cap connecting to pin 2 is correct, I use a different layout for voltage doubling, but the PT80 has been built by a ton a people, so I imagine if there was a mistake in the layout or schematic, it would have been caught years ago.

You should be getting probably a bit under 18V on the inputs of both the 12V and 5V regulator, then their respective voltages on their outputs. Check that you have a 1k resistor coming off pin 6 from the PT2399. If resistance is too low off of that pin, the PT2399 will lock up and cause you problems as well.

[mp3j3rk]

I would have posted those voltages however, I took the measurements last night and I am at work so I can't take the measurements again until later.

Your suggestion that >9.1V on the MAX1044 V+ is intriguing because my 9V DC adaptor measured out at just shy of 9.5V which could prove to be a problem.  I think I have some zeners around and will check if I have the IN4739s to put inline between +9v and the charge pump.

Will hopefully have my list of measurements to share soon.

[mth5044]

Also forgot to ask, are you using a PCB from GGG or your own layout?

[mp3j3rk]

Bought the PCB from GGG.

[Govmnt_Lacky]

Might help.. might not... but it is worth a look and some discussion.

The project follows the standard datasheet setup for a voltage doubling circuit BUT..... if you notice, the GGG project schematic has no connection from MAX1044 Pin 5 to GND. This "error" is in the GGG schematic AND in the etchable layout. On the Maxim datasheet, you can see that Pin 5 is supposed to be grounded. This has been around for a while and was never fixed.

If you have a GGG board, check to see if Pin 5 of the MAX is grounded. 

[mp3j3rk]

I will definitely check that, thank you!

[mp3j3rk]

I've taken measurements of the IC pins and v-regs, but haven't taken measurements of all pins like I know I'm supposed to do.

Max1044
1 9.43V
2 4.68V
3 0
4 0
5 0.19V
6 4.69V
7 4.11V
8 9.43V

TL072
1 0.42V
2 0.42V
3 0.44V
4 0
5 0.22V
6 0.4V
7 0.41V
8 0.86V

PT2399
1 0.84V
2 0.42V
3 0
4 0
5 0.46V
6 0.08V
7 0
8 0.81V
9 0.68V
10 0.72V
11 0.04V
12 0.05V
13 0.05V
14 0.05V
15 0.03V
16 0.02V

SA571
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
10 0
11 0
12 0
13 0.68V
14 0.01V
15 0
16 0

78L05
1 0.63V
2 0
3 1.38V

78L12
1 0.55V
2 0
3 1.38V

2N5088
1 0.01V
2 0.24V
3 0.54V

[mth5044]

Oh boy, lots of wrong voltages there, but it could all stem from a single problem. Lets start with the where the power is going.

Pin 1 and pin 8 of the 1044 are getting the right voltage, but either the chip isn't doing it's job, you have a solder bridge somewhere, or you have something messed up in the two IN914's/10u electros feeding into the regulators. Both the diodes and the caps have an orientation, make sure that they are abiding by them!

It's a little odd that the pin 8 of your TL072 doesn't match up with either of voltages on the 12V regulator since it's being fed directly by it. Did you reverse the regulators at all? Whenever I've done it, I find they just short circuit and pass full voltage, but you don't seem to be having that problem, which makes me thing it stems back to the 1044 or the stuff between it and the regulators. If you have the TL072, PT2399 and SA571 in sockets, I suggest you take them out before messing with the power supply. The only real danger is passing the full 18V to the PT2399, but better safe than sorry I guess.

Getting 18V to come out is what I would try to accomplish next, so focus on those diodes and caps (IMO).

[mp3j3rk]

You called it with the 914s.  There was one of them that was dead (the one connected to pin 1 of the 1044 one of the 10uF caps).  They were all oriented the correct way, and I had thought maybe that was the problem a while back and so checked and double checked them, but it wasn't until just after I posted the voltages that I tested the diodes and found that one wasn't working at all.

At one point, I believe I had used a power source with the wrong polarity so that poor 914 took the full hit and gave it's short life for the caps.  I changed all the chips (although I kind of suspect most of them are probably still good...that remains to be seen), and was starting to look at caps and diodes following the "I think i fried my pedal" guidelines.

The next problem was several of my hookup wires were breaking off at the pcb because I'd been moving it around a lot and they'd taken a fair amount of abuse so once I replaced/repaired those everything works dandy!

Now I just need to figure out how to complete my finish...any ideas on how to do white text and details?  I'm going to head over to the relevant forum and see if there is anything in there, but if you have had any experience with that, I'd appreciate it.

[mth5044]

Nice! Glad it's working now.

When I need something in white, I get my printing done by pedalpartsplus.com who can drill, powder coat and print enclosures. You send them the design and they print it for $20.

Alternatively, you can try using white labels (water slide, photopaper, etc) so that the white text will be white from the paper, not ink. It's been done very successfully.