PT-80 questions

[J.D.]

 Hi, I'm trying to build GGG's PT-80 delay http://www.generalguitargadgets.com/pdf/ggg_pt80_lo1.pdf
1) My problem is that  the 12v reg is only putting out 5.82v--I have 7.28v coming in---I'm not sure if this is a bad reg or if something else could be effecting it?
I have a 12v reg wall wart--couldn't I just jumper the 70L12 in-put & out-put and use that? It says in GGG's text to use a 15-18v wall wart and leave the 12v reg in but if the wall wart's all ready regulated I not sure why I couldn't use it(but then I'm new to this stuff and there may be a reason).
2) Also I swapped the TLO72 and used a LF353n because I couldn't find the TLO72 I had for this project(I'll find it next year when I clean up the garage I'm sure).
  Thanks

[geertjacobs]

1. The regulator used in the PT-80 is a 7812.
The datasheet of the regulator shows that you need at least 14.5 input voltage.
So your 12V regulated wallwart will not work for the PT-80, unless you remove the regulator and bridge the pads with a piece of wire.
2. at first sight they seem to be pin-compatible.

[J.D.]

 Hey thanks for the reply--OK so so much for that-- I'm using a LM78L12 and the MAX1044 charge pump so shouldn't  the 1044 be boosting the voltage up on one its of pins?( I'm still searching for that data sheet )

Here's the readings I'm getting on the 1044
pin 1) 8.92      pin8) 8.92

pin2) 8.91       pin7) 8.00

pin3) 8.36       pin6) 7.2

pin4) 1.06       pin5) 1.13

Guess I'll keep checking my work out

[Michael Allen]

Well, Pin 3 should be grounded so there should be 0V on it. The junction of the second 10uF cap and diode should be around 17 V and then the regulator should cut it down to 12V. On the layout, the bottom pin of the regulator should be 12V and the middle pin should be 0V, the top pin should be around 18v. For regulators to regulate they need a few volts more than they put out, thus the need for the 18V supply.

You could use the 12V wall wart and jumper the 12V regulator (keeping the 5V regulator) but you'll get a more consistently stable voltage if you use the wall wart -> MAX1044 -> 12V regulator.

P.S. I think if your input voltage on the MAX1044 is 12V the output may be around 20V or so, don't be confused if you get more than 18V since that circuit is designed for 9V.

Check your parts and wiring around the MAX1044, make sure no pads are touching or solder bridges are in place. Also make sure the IC is in the right way.

[J.D.]

 Yeah thanks Michael I was checking it out and ground trace to pin 3 on 1044 didn't have continuity to ground(trace is there but continuity just quits @ one spot) so I just made jumper to closest pad to ground(- side of 47uf cap). Now I have 15.2v @ 7812 input- but only 3.69 @ output so there are other problems. I need to go through the whole thing and check it out as I stayed up way to late last night putting it together.
   Also I'm only getting 15.52 @ second 10uf cap so perhaps there are more problems around the 1044.

[Michael Allen]

I think the voltage out of the MAX1044 may depend on the voltage drop over the diodes. What type did you use? Make sure your 7812 is oriented correctly and that there is nothing shorting the power rail to ground. You're getting closer! I'm firing mine up next week, waiting for the ICS to come in so I hope mine fires up quick!

[J.D.]

 Used 1n914 diodes--as per the BOM @ GGG,---My 7812 is oriented right--but somethings not right,the 7812 seems to be a tad warm, I'll work on it some more in a while. I'm no EE  or Tech so troubleshooting's a long trial & error process for me.

[Michael Allen]

the warmth is indicator of a short. Make sure that all the traces are clean and you have continuity between each pin and the other parts connected to them. You must have a short somewhere. Might even be a bad cap or something shorting out.

[miqbal]

Ok,

IMHO, LM7812 is just too big for such project. We are dealing on a very small current circuit. Better use 78L12 regulator, it's TO-92 in package, just like a tiny ordinary transistor.

The circuit should work with 9V (batteries or wallwart) WITHOUT 78L12 (for 12V source) without any problem. The output level only seems a little bit lower to my ears. Try to bypass all the charge pump and 78L12 circuitry and feed the 9V source, does the fx ok?

To check the 78L12 regulator is simple. Put it out of the circuit, feed a positive voltage from your wall wart set at more than 16V to the input  pin, ground voltage (0V/minus) to ground pin. The reading at the outpin should be a nice 12V. You can use breadboard for ease of use, or alligator clipper, or simply solder the wall wart cable to the regulator.

If you feed 9V to input of the chargepump, the output should produce approximately a nice 18V, and will be higher if you increase the input (higher than 9V).

[head_spaz]

The circuit was designed to run on a 9Volt battery. The datasheet states that the MAX1044 has a MAXIMUM input voltage of 11 volts. It's more than possible that your 12 walwart fried the max1044.

[J.D.]

 Yeah Headspaz  I wasn't real clear in my post, I am using a 9v wall wart. Just was wondering why couldn't I use a 12v wallwart instead of the charge pump(because I have 1 laying around not doing anything).I'm going to try what miqbal suggested and by-pass the charge pump and jumper the 78L12 and see what that does---but I'm pretty sure there is something else going on so I thinking that it still won't work.