Ordered TL072 instead of TL022

[xorophone]

I've just built the Coral Chorus from Tonepad, but I accidentally ordered a TL072 instead of the TL022. I still put it in the circuit, but it didn't work. The guitar signal goes through the circuit, but no chorus is applied. Since I'm not using the right op-amp, I don't want to start the fault diagnosing process before I know if the TL072 will even work the slightest. I'll of course order the right chip and replace it as soon as possible, but if something else is wrong with the pedal, I'd like to fix that while I'm waiting.

I've included every mod on Tonepad's PDF. None of the potentiometers (including the depth) make any difference to the sound, but when I touch the lugs on the depth pot, it generates a hum that I can control the volume of by turning the knob. The bass and chorus intensity switches don't change the sound at all either, but as soon as i deactivate (or activate?) the vibrato switch (when I disconnect R21), the guitar signal goes away completely.

Could these issues be related to the chip, or do I need to start fault diagnosing the rest of the circuit? If anyone has a list of measured voltages from IC's etc, I'd love to see them, but I can probably find them easily through a Google search.


Edit: When I look at the schematic, I understand why the signal goes away when I disconnect R21. I'm basically just disconnecting the dry signal and since there is no wet signal in the circuit, nothing is going to the output.

http://www.tonepad.com/project.asp?id=53

[niektb]

Do you have a schematic where we can refer to?

Verstuurd vanaf mijn Lenovo P2a42 met Tapatalk

[xorophone]

Do you have a schematic where we can refer to?

Verstuurd vanaf mijn Lenovo P2a42 met Tapatalk

Sorry! Forgot to link it.

Here it is: http://www.tonepad.com/project.asp?id=53
Scroll down and click the pdf link under "Layouts".

[robthequiet]

It would be good to have images of your build, front and back and large enough so that we can read the component values and verify the wiring. Also, do you have an audio probe to check where the signal gets lost?

[xorophone]

It would be good to have images of your build, front and back and large enough so that we can read the component values and verify the wiring. Also, do you have an audio probe to check where the signal gets lost?

I can upload some images and voltage measurements tomorrow. Yes, I have an audio probe, but I'd like to know if the TL072 will create any significant problems before I get too deep into the audio probing, since that might be the only problem with the circuit. But if no one knows, I'll start audio probing it while I'm waiting for the new chips and hope for the best.

The wiring should be fine, since the input, output, ground, power and bypass are working.

[smallbearelec]

Hi--

I can't help with the debug, can assure you that the TL072 is the way to go. It's pin-for-pin compatible with the long-obsolete TL022 and is known-to-work in the Coral.

Regards
SD

[xorophone]

Hi--

I can't help with the debug, can assure you that the TL072 is the way to go. It's pin-for-pin compatible with the long-obsolete TL022 and is known-to-work in the Coral.

Regards
SD

Thank you so much! That's really good to know! Then I'll just have to start debugging it tomorrow. I know how to do that, but I'm still pretty bad at it, so I'd love some voltage measurements if someone has them. It just makes it a bit easier if I know where I should expect signal.

Oh, and on the - input of op amps I shouldn't be able to hear any signal while audio probing, right? Is it the same on any other places in the circuit? (except ground and power supply tracks of course.)

[GGBB]

If you look through the builds reports for the project on the Tonepad site, you'll see that many use the TL072 instead of the TL022 - and some think it sounds better.

[armdnrdy]

Since when is the TL022 obsolete?

http://www.mouser.com/ProductDetail/Texas-Instruments/TL022CP/?qs=tJ5HNKWh3OXMoEOaPjTJiA%3D%3D

The TL022 and the TL072 may be pin for pin compatible....but in many builds with multiple op amps or an LFO...the TL022 is used for it's lower current draw. (65 uA TL022 compared to 1.2ma TL072)

[blackieNYC]

+1. You may be barking up the wrong tree, worrying about the '22. Maybe post some voltages?

[xorophone]

+1. You may be barking up the wrong tree, worrying about the '22. Maybe post some voltages?

Voltage measurements with all pots at around 12 o' clock:


IC1 (RC4558P)

1. 4.33v
2. 4.33v
3. 4.33v
4. 0v
5. 4.33v
6. 4.33v
7. 4.33v
8. 8.86v


IC2 (TL072. TL022 in project file)

1. Modulation between ~1.5v and ~7.5v
2. Tiny modulation around ~4.4v
3. Modulation between ~2.5v - ~5.5v
4. 0v
5. Tiny modulation around ~4.4v
6. Tiny modulation around ~4.4v
7. Modulation between ~2.5v - ~5.5v
8. 8.86v


IC3 (MN3007)

1. 8.83v
2. 0v
3. 1.42v
4. 0.05v
5. 0v
6. 8.83v
7. 8.81v
8. 8.81v


IC4 (MN3101)

1. 8.83v
2. 8.83v
3. 0v
4. 0v
5. 0.01v
6. 0.02v
7. 8.83v
8. 0.19v


I'm guessing the TL072 is used as the LFO, which describes all the modulation that's going on. Something that worries me a bit is that pin 1 on the MN3007 chip is connected to 9v, but on the pinout that's supposed to be the ground pin... Please tell me if I should measure any other components, for example the transistors.

Something I have noticed is that my 3007 and 3101 chips look very salvaged or even fake. The mn3007 chips have solder left on the pins, suggesting they're salvaged. The mn3101 chips look relabeled because they've got a square around the label on the top. The salvaged chips might still work, but the relabeled ones are really worrying me. I don't want to buy new chips before I know if they work though. I've done that before.

Here are some pictures of the circuit board and the possibly fake chips. As you can see, the etch really didn't turn out nice this time, but I've checked the obviously unreliable connections and they seem fine. I might of course have missed something though. It was hard getting a good picture of the chips, but you might be able to see that the right chip (MN3101) has been relabeled or something and that the pins on both chips have blobs of solder and crud on them. I ordered 4 chips and the MN3101 I have in my circuit didn't have the dirt and solder on the pins.

[anotherjim]

Something that worries me a bit is that pin 1 on the MN3007 chip is connected to 9v, but on the pinout that's supposed to be the ground pin...

This is a P-channel device. Convention is for these to be shown as positive ground, negative supply. So the + supply is marked as 0v or Ground and the - supply is Vdd. To use in a normal negative ground, positive supply circuit, the chip Gnd is +9v and the Vdd supply pin is connected to 0v. That keeps the polarity correct.
Confusing isn't it

[xorophone]

Something that worries me a bit is that pin 1 on the MN3007 chip is connected to 9v, but on the pinout that's supposed to be the ground pin...

This is a P-channel device. Convention is for these to be shown as positive ground, negative supply. So the + supply is marked as 0v or Ground and the - supply is Vdd. To use in a normal negative ground, positive supply circuit, the chip Gnd is +9v and the Vdd supply pin is connected to 0v. That keeps the polarity correct.
Confusing isn't it

Ah, I understand! (almost )

So the mn3007 voltages look right?

[xorophone]

I just did some audio probing and I'm hearing the signal all the way to pin 3 on the mn3007. All other pins are quiet. I also fixed a suspicious looking solder joint and checked some continuity. Everything looks right to me. Can someone please take a look at the voltage measurements and tell me if they look good? Is there something else I should check before I conclude that the chips are fake?

[robthequiet]

Theoretical question: If there is no output from the BBD, it means that there is no clock to pulse the signal across the 1024 stages for output?

If the clock is coming from the 3101, would we not hear a fizzy noise on the 3007 pins 2 & 6?

Will the 3007 pass some kind of audio even if the clock is not present?

Just thinking out loud here. 

[xorophone]

Theoretical question: If there is no output from the BBD, it means that there is no clock to pulse the signal across the 1024 stages for output?

If the clock is coming from the 3101, would we not hear a fizzy noise on the 3007 pins 2 & 6?

Will the 3007 pass some kind of audio even if the clock is not present?

Just thinking out loud here. 

Those are actually good questions. If the 3101 provides the clock and there's no output from the 3007 without the clock source, it might as well be something wrong with the 3101 (or the wiring around it), rather than the 3007.

Still need someone to take a look at my voltage readings.

[robthequiet]

To me, IC1 and IC2 look pretty happy. Also, the fluctuations on IC2 suggest that the LFO is doing something. Need to consult datasheets for the BBD chips, but maybe there is a forumite who has the answer...

[xorophone]

To me, IC1 and IC2 look pretty happy. Also, the fluctuations on IC2 suggest that the LFO is doing something. Need to consult datasheets for the BBD chips, but maybe there is a forumite who has the answer...

Yeah, IC1 and 2 look fine, but I've never used BBD chips before, so I don't know how they're supposed to work. I think the thread subject might make a lot of people ignore it too, since the topic has changed completely. I don't know if there's any rules regarding thread subject changing and stuff though.

When I get home today I'll check if the LFO from IC2 makes it all the way to the 3101. Knowing that should help me a lot. Don't know why I haven't checked that before.

[robthequiet]

Yep. What I was looking for was the clock signal getting from the 3101 into the 3007 -- my fear is that the 3101 is stalled, but checking for clock signal with a meter is not straightforward -- if you have a meter that measures frequency it should show some activity on both pins (MN3101 pins 2 & 4). If you put it on AC and measure each pin you should get some kind of reading on both clock pins, not hard Vdd on one and ground on the other. If you had access to an oscilloscope you would find out rather quickly what the status is.

Just for kicks, you could check for continuity (power off) on the clock pins:

MN3101 -> MN3007
pin 2      -> pin 6
pin 4      -> pin2

Looking forward, it may be worth considering getting sockets and new chips after we rule out any other component or PCB issues.

[xorophone]

Yep. What I was looking for was the clock signal getting from the 3101 into the 3007 -- my fear is that the 3101 is stalled, but checking for clock signal with a meter is not straightforward -- if you have a meter that measures frequency it should show some activity on both pins (MN3101 pins 2 & 4). If you put it on AC and measure each pin you should get some kind of reading on both clock pins, not hard Vdd on one and ground on the other. If you had access to an oscilloscope you would find out rather quickly what the status is.

Just for kicks, you could check for continuity (power off) on the clock pins:

MN3101 -> MN3007
pin 2      -> pin 6
pin 4      -> pin2

Looking forward, it may be worth considering getting sockets and new chips after we rule out any other component or PCB issues.

I made some measurements again, with some very interesting results. First I checked continuity between the pins you suggested. They were fine.

I did have an oscilloscope which I used to measure the clock signal from the TL072, until I got to R36... then it stopped working... (the oscilloscope) I continued measuring with my multimeter, which worked pretty well. I realised that there was clock signal up until the anode on D1, but not on the cathode. Instead I measured about 8.7v (which seemed to have a tiiiiny 0.01v modulation). Looking at the schematic, there isn't supposed to be 9v in that part of the circuit, right? It's supposed to go through both R52 and R38 and get lowered quite significantly, if I'm understanding it correctly. I checked continuity between the cathode of D1 and the cathode of D7, but there is no continuity. I'm just getting really confused at this point.

The reason I didn't use sockets was because I have to fit the circuit board under the 1/4" jacks. I could have used them on the 3007 and 3101 side of the circuit board though... I don't know why I skipped them. At least I used one for the TL072.