PT80 harsh noise trouble

[glenn.b]

I'm still a bit new here, so I hope you all don't mind my lack of knowledge.     I obtained  PT80 from  GGG , and proceeded  to build it as close to layout as possible.  The layout I am referring to is the one that includes the charge pump.  Everything went well in the build, and I am even seeing my "new guy" soldering improve, not to mention my lead dress ( have done a few of these GGG kits, like ITS8 & Dverb)  Anyway, no major hitches.   I get the the PT80 plugged in, and it works, but with a terrible buzz.  The "buzz" sound is not much different than being on a football field after dark with the stadium empty, and hearing the loud droning of the lights far above the ground-only this sound is coming out of my amp.  The sound is also akin to the noise you hear when you plug your guitar into an amp without dumping the volume, 'tho it is steady, and does not go away.                                                                                                                       
             
     Things I have done to troubleshoot:
   1) Checked all parts against BOM-no problems
   2)Double / triple checked all wiring-all good, nothing wrong to be seen.
   3)re-solder joints.  Just to be safe, I went ahead and re-heated all joints on the back of the card, though did not find one connection that was "suspect".
   4) Swapped 3 different wall warts, all of which are known to be good and work with my other effects.


   I would have checked pin voltages, but for this kit pin volts are not listed.  Given the fact that there are 2 -8 pin IC's, and 2 _16 pin IC's, its no wonder there are no values listed.   

       I appeal to anyone who might have good questions to ask, to force me to think of whatever it is that I am missing.  I know my report is a bit "wordy", but I would much rather supply too much info than not enough.  Thanks in advance for any help.  As new as I am, I'm glad to be among y'all.

[oldschoolanalog]

V's from a working build can be found here:
http://www.diystompboxes.com/smfforum/index.php?topic=75455.0
Reply #7 by WLS.
UTSF. It is your friend.

[glenn.b]

I appreciate that!!!  Getting late, but  will make that Job1 for after work tomorrow.

[glenn.b]

1 PM »

I made the PT80 digital delay from ggg http://www.generalguitargadgets.com/diagrams/pt80schem.pdf  ]]http://www.generalguitargadgets.com/diagrams/pt80schem.pdf  http://www.generalguitargadgets.com/pdf/ggg_pt80_lo1.pdf .I made the project with the charge pump and no other substitutions or modifications. The pedal works fine except I only get one repeat no matter were the pot is turned to.  I searched old post on PT80 problems and only one other person had the same problem and for him it was a pot problem. I tested the pot before installation and the swing was 52k. Now that the pot is hooked up I only get a swing of 27K, is this my problem or is this normal because it is hooked into the circut? Here are the voltages I used a battery that was 8.61V, I found it weird that were the 9V+ attaches to the board its only 0.02V.

TL072                     MAX1044                                           PT2399                                       SA571

1 - 4.96                                 1 - 6.23                                     1 - 2.49                           1 - 0.76
2 - 4.92                                 2 - 2.91                                     2 - 0.89                           2 - 1.78
3 - 4.89                                 3 - 0.02                                     3 - 4.08                           3 - 1.78
4 - 0.00                                 4 - 0.15                                     4 - 2.49                           4 - 0.01
5 - 2.26                                 5 - 0.32                                     5 - 0.88                           5 - 1.79
6 - 4.40                                 6 - 1.71                                     6 - 2.49                           6 - 6.51
7 - 4.39                                 7 - 3.32                                     7 - 2.49                           7 - 6.51
8 - 8.72                                 8 - 6.23                                     8 - 0.93                           8 - 1.78
                                                                                            9 - 2.58                           9 - 1.78
                                                                                          10 - 2.51                          10 - 6.02
                                                                                          11 - 2.34                          11 - 1.75
                                                                                          12 - 3.08                          12 - 1.79
                                                                                          13 - 0.02                          13 - 7.50
                                                                                          14 - 0.02                          14 - 1.77
                                                                                          15 - 2.48                          15 - 1.77
                                                                                          16 - 4.99                          16 - 1.20

Any help or thoughts on the subject are greatly appreciated.
« Last Edit: April 02, 2009, 08:33:25 PM by Wales »   Report to moderator     Logged
RonaldB
Posts: 55


 
   Re: PT80 problem please help, no repeats
« Reply #1 on: April 03, 2009, 01:00:13 AM »

I pasted in the above pinouts from the link above.   These are my readings, I am using a wall wart that delivers 10.12 Vdc.  I did try using batteries , however the device would not  fire up at 8.57 vdc.


  TL072-1)5.89
            2)5.90

[glenn.b]

TL72
1) 5.89
2) 5.90
3) 5.90
4) 0.00
5) 0.37
6) 5.90
7) 5.90
11.79

MAX
1) 9.51
2) 4.62
3) 12.0
4) 146.7 MV
5) 0.316
6) 0.485
7) 7.22
9.51

PT2399
1) 4.96
2) 2.47
3) 10.9
4) 10.9
5) 2.92
6) 2.47
7) 1.61
1.62
9) 2.47
10) 2.47
11) 2.47
12) 2.46
13) 2.47
14) 2.48
15) 2.47
16) 2.47

571N
1) 1.16
2) 1.80
3) 1.80
4) 1.90
5) 1.80
6) 6.70
7) 6.70
1.84
9) 1.82
10) 6.22
11) 1.83
12) 1.84
13) 11.79
14) 1.83
15) 1.84
16) 1.39

This is all greek to me. Thanks again for your help.

[WLS]

Is this project breadboarded or is it on pcb? If on pcb did you use GGG template?



Bill

[Blue_Toad]

Looks to me like there is at least a grounding problem,
PIN 4 of 571N should be at 0V, this would cause at least some problems,
PIN 4 and pin 3 of PT2399 should be at 0V as well

I'm basing this off the schematic at http://www.generalguitargadgets.com/diagrams/pt80schem.pdf

Start checking there, also are you using a PCB or a breadboard?

Also to help narrow it down, if you turn the delay level knob all the way down, does the buzz go away? There should still be a guitar sound comming through,

-BlueToad

[WLS]

I wasn't going to say anything till I knew more about what's going on but, just looking at voltages of the PT-2399 if pins 3 and 4 are correct it will surprise me if that chip is still functional. Since 5.5 volts is max for the IC.

And yes pins 3 and 4 are grounds and should be zero.

By not having a ground on the IC may have saved the chip but,

Bill

[glenn.b]

Thank you all for getting back with me so fast!    Ok,  I will answer as best I can your questions.  The whole project is GGG, meaning 100% kit, to include PCB- I  did not etch it myself.   Yes, I agree, in the back of my mind something yells " big grounding problem" but  for the life of me I never found it.  I concur , WLS, the  pins I checked seem wildly out of spec.  Blue, The noise does not go away with the reduction of volume.  Matter of fact, earlier, when I started this post, yes, there was some very underpowered sounding ( weak) guitar behind the buzz.  Now' tho, only have the buzz.  Suspect the IC's have bit the dust?  I will push on over the weekend with this, and thanks again for asking me good questions-   Glenn

[WLS]

...  The whole project is GGG, meaning 100% kit, to include PCB- I  did not etch it myself...

... I concur , WLS, the  pins I checked seem wildly out of spec... 

Glenn,

Then you're saying that you bought a kit from GGG?

Or did you just follow the project 100% and someone else did the etching, but used GGG's template?

Reason being their are known issues involving GGG's PCB template with bad traces. This was brought out by Solderman. If you search the archives on PT-80 looking for the author Solderman their is a picture of one of the bad traces he posted.

Moving on...

It's not that the voltages  are only out of spec. Pins 3 and 4 are ground pins and on your meter should read 0 volts.

You posted that the pins are 10 volts. Two big problems.

1. The PT-2399 is a 5 volt IC an can not handle 10 volts.

2. Sending voltage backwards through the IC.

Both problems on their on will damage the IC.

So, what I'm saying is do not put another IC into the board till these issues are resolved.


Bill

[Blue_Toad]

Hi Glenn,

I'm going to agree with WLS, the first thing that needs to be sorted out is power to the IC's, everything after that is gravy, I'd start with the TL072 as that thing is pretty much bullet proof and based on the voltages you posted before doesn't seem to have anything wrong with it with one exception.

The reason I was asking about the delay volume is that if you turn it all the way down it takes a fair bit of the circuitry out of the mix making it easier to track down the bug. so with the delay volume all the way down and the inputs grounded (guitar volume turned all the way down) on the TL072 you should get the following DC voltages (approximate calculations)

1 - 6V
2- 6V
3- 6V (V+ /2)
4- 0V (Ground)
5- 6V (V+/2)
6- 6V
7- 6V
8- +12V (V+)

From your earlier post it looks like there is only 1 pin that is not behaving properly and that is pin5, I would suggest checking in that area to ensure that Pin5 and its' resistor are proper. Once pin 5 is ready 6V, with the delay level all the way down you should be able to hear guitar loud and clear with buzz, (this will basically be a booster at this point)

Then I would make sure that the power pins on the other ICs are proper before adding those components back onto the board,

Hope this helps, at least for a starting point

Blue_Toad

[WLS]

...  I would suggest checking in that area to ensure that Pin5 and its' resistor are proper...

Not to differ on this but for pin 5 it should be a little low and without my notes on this circuit in front of me. But on this circuit the TL-072 does have one pin that is the starting point of the input for the circuit.

It only consists of a capacitor with a 1 meg resistor tied to it. It's voltage is fairly low and is not consistent with the datasheet information that every pin should be 1/2 the suppply voltage.


Bill

[doitle]

TL72
1) 5.89
2) 5.90
3) 5.90
4) 0.00
5) 0.37
6) 5.90
7) 5.90
11.79

MAX
1) 9.51
2) 4.62
3) 12.0
4) 146.7 MV
5) 0.316
6) 0.485
7) 7.22
9.51

PT2399
1) 4.96
2) 2.47
3) 10.9
4) 10.9
5) 2.92
6) 2.47
7) 1.61
1.62
9) 2.47
10) 2.47
11) 2.47
12) 2.46
13) 2.47
14) 2.48
15) 2.47
16) 2.47

571N
1) 1.16
2) 1.80
3) 1.80
4) 1.90
5) 1.80
6) 6.70
7) 6.70
1.84
9) 1.82
10) 6.22
11) 1.83
12) 1.84
13) 11.79
14) 1.83
15) 1.84
16) 1.39

This is all greek to me. Thanks again for your help.

Pin 8 is so cool...

[WLS]

Here's a link to a previous thread that I posted voltages for this circuit I believe it's post 7.

http://www.diystompboxes.com/smfforum/index.php?topic=75455.0


Bill