PT80 Problems High Pitch Ringing

[TheTornOne]

Hello All,

I am currently debugging a PT80 board that I purchased from GGG (I purchased the PCB from GGG and have purchased all of the parts separately).  I have assemble the board according to what the GGG instructions said for running it on a 9V operation.  When the effect is off, I get signal through the box and when the effect is turned on I still get signal but a terrible high pitch, constant ringing.  I have checked for shorts on the underside of the pcb, have double checked the wiring for errors, and have looked for broken or cold solder joints and have not found anything.

Here are 2 questions to start:
What is the hole on the board that goes to pin 3 of the MAX1044 supposed to be hooked up to?
Is there supposed to be a jumper in the place where it says jumper? - This might sound stupid but the picture on the GGG instructions does not have a jumper here and I have seen pictures on this forum of boards with them in place. I have one in place.

Here are the readings for the ICs with a 9V battery reading 8.73:

MAX1044
Pin 1: 8.73V
Pin 2: 6.93V
Pin 3: 0V
Pin 4: 2.43V
Pin 5: 2.47V
Pin 6: 5.61V
Pin 7: 3.46V
Pin 8: 8.67

TL072
Pin1: 2.76V
Pin2: 2.76V
Pin3: 2.77V
Pin4: 0V
Pin5: 1.39V
Pin6: 2.76V
Pin7: 2.76V
Pin8: 5.53V

PT2399
Pin1: 5.02V
Pin2: 2.49V
Pin3: 0V
Pin4: 0V
Pin5: 2.54V
Pin6: 2.50V
Pin7: 1.10v
Pin8: 1.16V
Pin9: 2.51V
Pin10: 2.51V
Pin11: 2.51V
Pin12: 2.51V
Pin13: 2.51V
Pin14: 2.51V
Pin15: 2.51V
Pin16: 2.51V

NE571N
Pin1: .97V
Pin2: 1.81V
Pin3: 1.81V
Pin4: 0V
Pin5: 1.32V
Pin6: 4.63V
Pin7: 4.63V
Pin8: 1.82V
Pin9: 1.82V
Pin10: 4.67V
Pin11: 1.28V
Pin12: 1.30V
Pin13: 5.44V
Pin14: 1.81V
Pin15: 1.81V
Pin16: .36V

78L05
6.91V
0V
5.02V

78L12
6.9V
0V
5.41V

I am really excited to finish this one off and would love some help.  I am pretty green at this still so any explanations that are very broken down would be preferred.

Thanks!

[.Mike]

I've never built one of these, but...

What is the hole on the board that goes to pin 3 of the MAX1044 supposed to be hooked up to?

It doesn't look like it connects to anything. If you look at the layout and the build instructions, there is nothing connected. It appears as though it is an extra connection to ground.

Is there supposed to be a jumper in the place where it says jumper? - This might sound stupid but the picture on the GGG instructions does not have a jumper here and I have seen pictures on this forum of boards with them in place. I have one in place.

It appears as though you should use a jumper there. It looks to me like that jumper provides V+ to the TL072.


OK, for the voltages. There's definitely something wrong.

The MAX1044 is being used as a voltage doubler. It uses two diodes and two capacitors to put out roughly 17 volts, which you should be able to measure at your 78L05 and 78L12 (pin closest to edge of board). I believe you are getting 6.9V.

I would first start checking in that area. Make sure you have the MAX1044 oriented properly, make sure you have the diodes and capacitors oriented properly, and make sure your regulators are oriented properly.

I hope that helps!

Mike

[TheTornOne]

So I checked the orientation of all the caps by the MAX1044, the MAX1044, the diodes, and the voltage regulator and found that I had a 10uF cap reversed.

I swapped it out and put it in correctly, and there is no audible change, I still get this terrible high pitch ring coming out.

Any other thoughts?

Thanks

[jacobyjd]

You're going to want to replace that cap if it was reversed--it's likely that its usable life is seriously diminished now. I doubt that will solve the ringing--just something to note regarding elecro caps.

[MarcoMike]

wasn't there some kind of thing to do to make the MAX work at higher frequency, out of the audible range? maybe there's something wrong with that, and you hear its switching noise...

[TheTornOne]

Josh, thanks for the info, I have replaced the electro cap.
Marco, the high pitch ringing is low when the effect is switched off, and gets incredibly loud when switched on.

[jacobyjd]

I agree that it sounds like it might be related to the 1044. You may want to try adding an RF filter cap to each power output.

[TheTornOne]

Josh - Out of curiosity, if I needed to do this wouldn't everyone who did this build have to do the same?  I am not trying to disagree with any help, because I really do need it, but I feel like the issue would be due to an error of mine as opposed to needing to add extra components.  Is if I am reading your post correctly that's what it sounds like, maybe I am wrong.

Do you have any other suggestions?

Thanks

[oldschoolanalog]

wasn't there some kind of thing to do to make the MAX work at higher frequency, out of the audible range?

Connect pin1 to pin8.

...maybe there's something wrong with that, and you hear its switching noise...

Go to GEO & search MAX1044.
Read the entire article on "Higher V from a 9V Battery".
Good reading there.

[jacobyjd]

Josh - Out of curiosity, if I needed to do this wouldn't everyone who did this build have to do the same?  I am not trying to disagree with any help, because I really do need it, but I feel like the issue would be due to an error of mine as opposed to needing to add extra components.  Is if I am reading your post correctly that's what it sounds like, maybe I am wrong.

Do you have any other suggestions?

Thanks

I've found that due to any number of variables (parts tolerances, certain wall warts, etc.), things like hiss, high-frequency noise, etc. like you're dealing with can come to light in some builds but not others. So yes, you may have the same build w/ problems that others might not have.

In this case, it sounds like the whine is from a clock or switching power supply, etc. With the right caps, you can cancel that out, but it'll affect your signal a bit.

Have you tried running it from a battery?

I also second OSA's advice to read that GEOFEX article. There's good stuff to be learned there.

[TheTornOne]

Josh - I apologize, the variation in parts and specs does make perfect sense as to why the are variations from build to build resulting in different sounds, problems, etc.  I am currently running this from a battery.

Dave - Looking on the bottom of the Rebote 2.5 board and testing for continuity, pin 1 and pin 8 are connected via the PCB.  The extra circuit that is discussed in the GEO article, would i be adding a 2n3906, a 1K and a 6.8K resistor into the circuit.  I am pretty green so a breakdown would be great.

Thanks

[jacobyjd]

Josh - I apologize, the variation in parts and specs does make perfect sense as to why the are variations from build to build resulting in different sounds, problems, etc.  I am currently running this from a battery.

No problem, man It's good to see you think through the debug--it's by far the best way to learn how all this stuff works.

[TheTornOne]

I took a look at the ratings on the electros and saw I had put in 15V caps.  I swapped those out for 25V.  No change. Any more thoughts?

[.Mike]

I took a look at the ratings on the electros and saw I had put in 15V caps.  I swapped those out for 25V.  No change. Any more thoughts?

After you turned the electrolytic capacitor around, did you check to make sure you were getting proper voltages before and after the regulators?

[TheTornOne]

Here are the readings retaken:

78L05
6.55V
0V
5.0V

78L12
6.55V
0V
5.05V

[TheTornOne]

Would hving that 10uF cap backwards have damaged any other components?
Would having 16V caps in plave before have damaged any other components?

If I understand correctly, I am supposed to have the 12V when it gets to the regulators, so it would have to be between the battery (my power source) and the 78L05.

Is that correct?

[jacobyjd]

It seems like it...the input voltages look pretty low there (I can't remember the operating specs of the regulator atm...can't look it up at work). Have you tried using a fresh battery?


I need to check out the schematic on this one so I can be of more help If I get a chance this evening...*sigh* too much to do

[oldschoolanalog]

First; your V's at the input of the regs are way low. This thing eats batteries. Use a power supply.
Do you have a power supply? If so, what V?
My choice would be to use a 15-18V power supply with the regulators on the board. Ditch the charge pump & associated components. At least try testing it w/out the MAX.
I have 2 of these. One is powered at 9V.  No charge pump. Sounds great. The other is set up like this:
http://www.generalguitargadgets.com/pdf/ggg_pt80_lo2.pdf
Try removing the MAX and hook up your DC in as shown in the above link.
Don't have a 15-18V power supply? Read the last page of the build notes at GGG. Jumper the in & out of the 12V reg. Then you can test it w/a 9V power supply or a fresh 9V battery if you must.
BTW, the max input V the MAX1044 can take (according to the Maxim datasheet) is 10.5V. Be careful if using a wall wart with the MAX.
More stuff later...

[head_spaz]

The MAX1044 should be putting out roughly 17 volts to the regulators.
Double check the polarity on your diodes, and check their continuity, they may have been damaged.
Try removing the regulators from the circuit to see if they are damaged and perhaps pulling down the output of the MAX1044.

Semiconductors are rather delicate unless they are used within the specifications of their precise operating parameters.
Installing the caps backwards, and using caps with insufficient voltage ratings are mistakes. It's likely there will be consequences for those mistakes.
The MAX1044, your diodes, your caps, and both regulators are suspect now. Treat them as dead until you can verify otherwise.
And DON"T replace the MAX1044 until you can positively verify that all the other parts are in good shape, or you might damage the new charge pump too.

Good luck.

[oldschoolanalog]

The MAX1044, your diodes, your caps, and both regulators are suspect now. Treat them as dead until you can verify otherwise. And DON"T replace the MAX1044 until you can positively verify that all the other parts are in good shape, or you might damage the new charge pump too.

+1
Excellent advice.