PT80 problem please help, no repeats

[Wales]

I made the PT80 digital delay from ggg http://www.generalguitargadgets.com/diagrams/pt80schem.pdf  [url=http://]]]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.

[RonaldB]

It looks like your voltage at pin5 of the TL072 is not correct. THis needs to be about 4.5volts.
Please check that.

regards
Ronald

[Wales]

Thanks, a little drunk right now but I'll check that in the morning. Oh maybe not till sat. but i'll report back. thanks for the area to look in.

[anchovie]

I'm pretty sure that I read on this forum somewhere that bias voltages at op-amp pins can be measured incorrectly by some multimeters. Even if it was a problem it wouldn't kill just the repeats, the whole delay signal would be affected.

The repeat pot is in parallel with the delay level pot which is why you measure a lower resistance in-circuit. This should be really easy to isolate given where the repeat pot is located:

Check that the middle lug of the repeats pot isn't shorted to ground (though I'd expect the single echo to be killed/quieter if this was the case).
Check that there is continuity between the middle lug of the pot and the 1uF cap.
Check that there is continuity between the other side of the 1uF cap and the 22k resistor.
Check that there is continuity between the other side of the 22k resistor and pin 12 of the SA571.
Check that the 22k resistor does measure 22k.

[WLS]

It looks like your voltage at pin5 of the TL072 is not correct. THis needs to be about 4.5volts.
Please check that.

I agree that the voltages  don't look correct. You're working with an inverted amp the end results will be on the tl-072 that your pin voltages will be half your suppply voltage except for the pin coming from your jack. this will be lower.

The one side of the amp feeds to the other side mixing the wet and dry signal. Use an audio probe and check pins 7 and 10 of the SA-571.

I'm using my pda so I can't look at the schematic but I worked with this circuit a few weeks ago and it can be a bit tricky.

SA-571's pin 6, and 7 carries the signal over to the pot and then onto pin 12,  12 also ties to pins 14, 15, and 16. Sending the signal back down to the PT-2399 to come up through the transistor to pins 2 and 3 of the SA-571. Right before the collector their is a line feeding it back to the amp.

But your amp doesn't look right.

If you would like, later I post some final readings of a healthy circuit to give you some benchmarks to go by.

If I can find them.

[Auke Haarsma]

You've received sound advice, but I think you should first look at something else.

1) Pin 1 of the PT2399 should have +5V. It is directly connected to the 5V regulator. Check what is coming out of the reg and check what is going into the reg.
2) Pin 4 of the PT2399 is directly connected to ground. You read 2.49V, this should be 0V. Check for shorts here
3) The MAX1044 seems incorrect. Pin 1 and 8 are connected to Vcc (battery/adaptor) so should be around 9V.

I'd start with 3). But I am sure it is not just an error around the chargepump. Looks like you have some shorts across the board.

[anchovie]

You've received sound advice, but I think you should first look at something else.

1) Pin 1 of the PT2399 should have +5V. It is directly connected to the 5V regulator. Check what is coming out of the reg and check what is going into the reg.
2) Pin 4 of the PT2399 is directly connected to ground. You read 2.49V, this should be 0V. Check for shorts here
3) The MAX1044 seems incorrect. Pin 1 and 8 are connected to Vcc (battery/adaptor) so should be around 9V.

I'd start with 3). But I am sure it is not just an error around the chargepump. Looks like you have some shorts across the board.

I think the PT2399 is fine, as there is the single delayed signal without repeats - looks like the pins were measured in the wrong order! e.g. Pin 1 of PT2399 is V+, Wales measures 5v at pin 16, pins 3 & 4 of PT2399 go to ground, Wales measures 0v at pins 13 & 14, etc.

Here's what Wales has told us:
The dry signal is fine.
The delayed signal is fine.
There are no repeats.

Therefore, the obvious part of the circuit to worry about is the bit that does the repeats!

[WLS]

Here are the voltages off my build a few weeks ago:

2N5087                   J-201

10.85   Collector        10.47   Drain
5.22   Base             10.43   Source
4.73   Emitter          10.96   Gate


TL-072CP

Pin-1    5.37     Out #1
Pin-2    5.36     (-) IN #1
Pin-3    4 .77    (+) IN #1
Pin-4    0        VCC (-)
Pin-5    5.31     (+) IN #2
Pin-6    5.32     (-) IN #2
Pin-7    5.32     Out #2
Pin-8    10.67    VCC(+)


SA-571IN

Pin-1     .72    Rec Cap #1        Pin-9      1.78    THD Trim #2
Pin-2     1.78   Rec In #1         Pin-10     5.94    Output #2
Pin-3     1.78   AG Cell #1        Pin-11     1.78    Res R3 #2
Pin-4     0      VCC (-)           Pin-12     1.78    Inv, IN #2
Pin-5     1.78   Inv, IN #1        Pin-13     10.51   VCC (+)
Pin-6     6.64   Res R3 #1         Pin-14     1.78    AG Cell #2
Pin-7     6.64   Output #1         Pin-15     1.78    Rec In #2
Pin-8     1.78   THD Trim #1       Pin-16     1.22    Rec Cap #2


PT-2399

Pin-1     5.03    VCC         Pin-9      2.52       OP1-OUT
Pin-2     2.51    REF         Pin-10     2. 52      OP1-IN
Pin-3     0       AGND        Pin-11     2. 52      OP2-IN
Pin-4     0       DGND        Pin-12     2.52       OP2-OUT
Pin-5     4.68    CLK_0       Pin-13     2.52       LPF2-IN
Pin-6     2.51    VCO         Pin-14     2.52       LPF2-OUT
Pin-7     .82     CC1         Pin-15     2. 52      LPF1-OUT
Pin-8     .82     CCO         Pin-16     2. 52      LPF1-IN


Hope these benchmarks helps!

[solderman]

Hi
Don't trust your PCB transfer . This shortage in a PCB costed me 5 hours of trouble sooting and gave me gray here. It is the PT80 and the pad is all to close to the trace and will cause a Short circut when making your own PCb:s. It's nearly impossible to find. I spent at least 3 of the 5 hrs looking at the solderingside with my magnifying goggles on before i got it. the result was similar to yours. But I agree that the pin1 voltage and the MAX voltage is prio 1 but probably not the whole solution.

 
 

//Solderman

[Wales]

Thanks for all the help folks. I found I had a copper trace that had been nicked by a knife and broke continutity between pin 12 of the 570 and the 22K, but that isn't the whole problem. The problem is somewhere in the power of the circut, because I get a reading of 0.02V on the ground. [color=blooks like the pins were measured in the wrong order! e.g. Pin 1 of PT2399 is V+, Wales measures 5v at pin 16, pins 3 & 4 of PT2399 go to ground, Wales measures 0v at pins 13 & 14, etc.
lue][/color] this is very correct sorry I posted them all backwards for the PT2399, however there is still 0.02v on the ground pins.

Also the voltages on my voltage regulators are incorrect
2N5087                   J-201
C - 8.71V               C - 8.71
B - 0.03V               B - 0.03V
E - 5.00V               E - 7.94

I'm givin it a good goin over tonight so I'll report. Oh I swaped out the TL072 for a new one and the voltage on pin five was even lower.

[WLS]

So, do you have this on PCB?

If so, whose template did you use?

Bill

[Wales]

Yes i made it from a pcb template from general guitar gadgets http://www.generalguitargadgets.com/pdf/ggg_pt80_pcb.pdf  From the picture solderman posted it looks like the same board. I actually caught that possibility for a short when i was drillin the holes. There must be a cold solder or short that I'm missin somewhere.

[Wales]

I am starting to think I have my 12v regulator in backwards. I have a L7812cv regulator and when i looked at the data sheet i couldn't quite tell which pin was which. From the data sheet I couldn't tell if the diagram was the front or back of the regulator. When i went to install it i assumed that if you were looking at the numbers on the front of the regulator that left most pin was the output.  I hope that makes sense and hope that someone know to read the datasheet better than me http://www.st.com/stonline/books/pdf/docs/2143.pdf Thanks

I noticed that posted this earlier, I don't know why i put it 2N5087 its my five volt regulator and the J-201 is my 12v regulator the C should be the Input and the B the ground and E the out
Also the voltages on my voltage regulators are incorrect
2N5087                   J-201
C - 8.71V               C - 8.71
B - 0.03V               B - 0.03V
E - 5.00V               E - 7.94

[solderman]

I am starting to think I have my 12v regulator in backwards. I have a L7812cv regulator and when i looked at the data sheet i couldn't quite tell which pin was which. From the data sheet I couldn't tell if the diagram was the front or back of the regulator. When i went to install it i assumed that if you were looking at the numbers on the front of the regulator that left most pin was the output.  I hope that makes sense and hope that someone know to read the datasheet better than me http://www.st.com/stonline/books/pdf/docs/2143.pdf Thanks

I noticed that posted this earlier, I don't know why i put it 2N5087 its my five volt regulator and the J-201 is my 12v regulator the C should be the Input and the B the ground and E the out
Also the voltages on my voltage regulators are incorrect
2N5087                   J-201
C - 8.71V               C - 8.71
B - 0.03V               B - 0.03V
E - 5.00V               E - 7.94

Hi
The pinout of the 78lxx is the same as for yours. So if you put the flat side the same way as the heat sink you are safe. Se the pic of my PT-80
Sorry for the size. Am at work and cant scale down.


//Solderman

[Wales]

Thanks! Ok mine must be in backwards then my flat side is in the opposite direction of the 5V reg's flat side. My regulator isn't the shape that looks like a standard transistor, both sides are technically flat on mine but there is one obvious flat side where the pins come out the bottom. If mine was like a regular transistor the writting would be on the curved side.

I'll start heatin the iron 

[WLS]

It sounds like a 220 package. Look at the data sheet. It will tell you the pin configuration.

Bill

[Wales]

I'm starting to go crazy with this one. I think I need to step back and clear my head for a while. On my ground rail I get 0.01V where the wires leave and as I move further away from that area the voltage will climb to 0.02V. I can't find why pin 5 of TL072 is so low. Also my voltage on my transistor is weird I used a 2N5089 rather than the 2N5088 that was called for but I don't think that should matter. The voltages are E-1.59V B-1.90 C-4.31. I don't know anymore

[WLS]

...
I used a 2N5089 rather than the 2N5088 that was called for but I don't think that should matter. The voltages are E-1.59V B-1.90 C-4.31. I don't know anymore

When I bread boarded mine I also used the 2n5089 and had no problem with the circuit. That is once I got it right.

What is your voltage at pin 5 and without staring at the template is this the one that the input from the jack enters???

If so, referring back to my voltages I posted for you the one pin in my case pin #3 was at a lower voltage than the rest.

But you have a short somewhere your negative rail should be zero. Upon looking at what you wrote, you  may have found a way to find your short. You said that their is a difference of voltage readings where you check on the rail. I have not been into this very long but their is resistance in any line. So I would think that the higher the reading the closer you are to the short.

Bill

[Stomp]

I just finished this one, & its working correctly.  Dont know if this will help or not, but its a layout I drew from the same schematic for point to point soldering, might be something to double check connections.  I use a number system for wire connections. 

http://i204.photobucket.com/albums/bb235/whathefuk_photos/JEFFSPT80-DELAYjpg.jpg

Here are my voltages from a 7.8v battery:

Max1044             TLO72                 PT2399             SA571
1. 7.8V                1. 5.57                1. 4.97              1.04
2. 3.7                  2. 5.53                2. 2.48              1.76
3. 0                     3. 5.51                3. 0                   1.76
8. 7.82                4. 0                     4. 0                   0
                          5. 2.76                5. 2.36               1.76
                          6. 5.5                  6. 2.48               6.48
                          7. 5.5                  7. .68                 6.48
                          8. 10.96               8. .76                1.77
                                                    9. 2.48               1.77
                                                   10. 2.49              7.37
                                                   11. 2.48              1.74
                                                   12. 2.48              1.78
                                                   13. 2.49              10.69
                                                   14. 2.48              1.77
                                                   15. 2.78              1.77
                                                   16. 2.48              1.08
                                                   

[anchovie]

Wales,

Just to confirm, is your only issue now that you don't get repeats, just one delayed signal?

Does your dry signal sound fine?
Does the single delayed signal sound fine?

Stomp has a working build, with a lower voltage at pin 5 of the op-amp. I really don't think this is the showstopper and I'm still inclined to believe it's this multimeter quirk that I've read about before. I've seen this happen on my own builds of overdrives/distortions and whilst it seems strange if the pedal doesn't sound bad then I don't lose sleep over it.

I don't think you should stress over measuring 0.02v on the ground rail of the board - this is 20mV which I think a lot of people would be happy to call zero in this situation. There's going to be PCB trace and wire between your measurement point and your star-ground point and this is going to have an (albeit small) resistance of its own. You could even set your DMM to measure ohms and see what it is. Likewise measuring 0.01v where the wires leave the board is simply telling you that your wire is a very, very, very, very low value resistor. It's not a problem.

If your answers to my questions above are all "Yes!", then you just need to get checking around that repeats pot like I've said earlier in the thread. Don't do your head in over this if all the other aspects of the circuit are now fine as far as your ears are concerned.