My PT80 works but with no ECHO!!

[RonaldB]

I made the PT80 but it doesn't echo
And here's the strange thing. When i measure it with the audio probe before the 10K (see image) iand i turn the speed knob i here the delay changing from fast to slow when i turn it. But when i put the audio probe after the 10K res. (at point X) i get only signal but the speed knob doesn't function the way it did before the 10K. What's the deal here?
I changed to an other PT2399 but that didn't made any difference. I allready resollederd the hole board and especially the points at the 10k res.

Can someone please help me, i will post the voltages of the IC's later but they seam OK especially the TL072 has good voltages. So i have signal and good volume but no echo.

Thanks for reading
Ronald

[Scott Swartz]

Ronald,

Its first thing in the morning after a late gig, so hopefully I am analyzing this properly...

The point you marked X is the "-" terminal of the output mixer.  This stage is an inverting amp, and the "-" is a so called virtual ground, so you will not get anything with an audio probe.  Another way to look at it is, an opamp will always work to make the signal on the + terminal the same as the - terminal via the feedback components, and since the + is at Vr (a ground at 1/2 the 12 VDC supply) the - terminal will probe the same, about 6 VDC and no audio signal.

Based on what you're saying about getting delay on the other side of the 10K resistor, it sounds like the delay section is working.  Do the repeat and delay pots function as they are supposed to when checked on the upstream side of the 10K resistor?

Also there is another 10K resistor missing from your screen print (the dry signal) below your "X", I assume that got wiped out on your screen print but it exists on your PCB?

And, have you checked if delay signal is present on the output pin of this opamp stage? 

[RonaldB]

He Scott,

Thanks for the quick reply.

I checked if the level and repeat pots work before the 10k and yes they are working here, the level pot gets a bit distorted here
O buy the way i put 50K log pots in here and by acident but i'm replacing them with 50k lin this week. Is this maybe the problem?
But i did the audio probe thing after the op amp pin1 and the repeats level and speed pots don't work here.

I here also have the voltages for the IC:

TL072
1:6.7
2:4.6
3:4.6
4:0
5:2.1
6:2.8
7:2.8
8:0

PT2399
1:5
2:2.2
3:0
4:0
5:2
6:2.3
7:0.7
8:0.7
9:2.1
10:2.1
11:2.1
12:2.1
13:2.1
14:2.1
15:2.1
16:2.1

SA571

1:0.9
2:1.3
3:1.8
4:0
5:1.8
6:6.7
7:6.7
8:1.6
9:1.8
10:3.1
11:1.8
12:1.8
13:9.3
14:2
15:1.8
16:1.1

And i'm using the 9volt powersuppley.

The 10k you mean that's not on the picture is in the layout of mine only got lost on the picture.

Thanks for youre help and i hope you can help me.

Ronald

[oldschoolanalog]

TL072/pin 8 = 0V.  Something is wrong here. That's the pin for the positive (+) supply voltage.
I'll open mine up tomorrow and compare voltages if this isn't solved by then.
All the Best.

[RonaldB]

oops, soory did that wrong.
Pin 8 of the TL072 is 9.3 volts.

[RonaldB]

Does someone has an idea how to solve this???

Thanks Ronald

[Painkiller]

I think some of the voltages on the TL072 is wrong. If I remember correctly, I have only one pin with around 2.2v. The rest are either 0, 4.5 or 9

I don't remember which ones, but I'll see if I can check it out tomorrow.

[oldschoolanalog]

Too obvious; but I have to ask anyway. 1: Is the 10k resistor good? Check it with your DMM. Also make sure it  is 10k. Bad resistors are very rare. However, strange things have been known to happen. 2: Is the op amp good? If it's socketed, try a different one.
I'll check the V's on mine tonite and post any inconsistencies later.
Stay Cool.

[BubbaKahuna]

I've built a couple ReBote 2.0 using the BYOC boards & sourcing my own parts.
My OpAmp voltage readings are as follows on all 3 of my delays:
pin 1 = 4.7vdc
pin 2 = 4.7vdc
pin 3 = 4.7vdc
pin 4 = 0vdc
pin 5 = 3.8vdc
pin 6 = 4.7vdc
pin 7 = 4.7vdc
pin 8 = 9.5vdc

Also make sure your regulator is getting 9v in, 0v at ground and putting out about 4.5v to 5v.

I had a problem with a wrong value resistor in my input buffer stage that was dumping all my signal to ground. It seems I have trouble reading thin colored lines in bad light! Go figure.   

As tedious as it is, go over all your resistors to make sure you're not allowing all your echo signal to drop to ground by not having enough resistance somplace. It's happened to me twice now.

Cheers,
- JJ

[oldschoolanalog]

PT-80 using an Ibanez AC109 wall wart. 8.9 VDC output. I used a TL082. No problem.
1: 4.38 VDC
2: 4.38 VDC
3: 4.38 VDC
4: 0 VDC
5: 3.94 VDC
6: 4.38 VDC
7: 4.38 VDC
8: 8.75 VDC
Re-check values of components associated with the 072. Check the chip. Clean the board real well and check for cracks/solder bridges/etc. Use a magnifying glass for this. Hope some of this helps.
All the Best!
osa

[runmikeyrun]

stupid question- isn't this a 24v circuit?  you are using 24v supply right?

[RonaldB]

He guys,

Thanks for all the reply's. I will go trought my board today to look at bad resitors etc.
i'm using the 9v power suppley on this one. It looks like i have a problem with the TL072.
I swaped in a new one but that didn't made any differance.

Thanks for all the help and keep it coming

Ronald

[jasonsmusicgear]

Hi RonaldB

I was wondering if you ever got your PT80 problem fixed.  I just built one and am having a similar problem.  The echoes are very soft, I also used log pots instead of linear but I really don't think thats the problem.  How did you fix yours?

http://www.diystompboxes.com/smfforum/index.php?topic=64239.0
Jason

[RonaldB]

Hello,
I just made a new PCB, i got sick by tracing the board.
I was getting no echo, the pots where not the problem.

I would check al the solder joints and check if you didn't put in a wrong value resitor or cap.

RonaldB

[Mark F]

stupid question- isn't this a 24v circuit?  you are using 24v supply right?

Not so stupid. It is a 24 volt circuit. Well, actually I think it is a 12volt (or 15, I forget) & a 5 volt circuit but Scott reccomends a 24Vdc supply to be used. So if a 9Vdc supply is used it will not be enough for the 12 volt regulator to function as designed.

[miqbal]

Hi Jason,

How is your soldering?

[jasonsmusicgear]

My soldering is pretty lousy, I didn't think about cleaning the PCB again before populating it and I'm guessing that I have several bad solder joints.  I have stared at the solder joints for too long now and cannot find anything, I will probably do a whole new PCB like RonaldB said.

Jason

[miqbal]

Jason,

As long as you had good PCB traces, I think you don't have to start it over again. Simply re-solder them, soldering-grease is a must. Just hold it a little longer than usual while soldering until the solder iron looks melted/flow.

[jasonsmusicgear]

What is soldering grease, is that the same thing as having the flux already inside the solder?

[miqbal]

>What is soldering grease, is that the same thing as having the flux already inside the solder?

Yes: flux; stannol; soldering grease; they are the same and sold in a separated can package. Do not use more soldering iron, simply just use the flux and re-solder them, the result should be shinier and more amalgamated solder.