Trying to figure out what is wrong with my DIY delay pedal and someone suggested my voltages at my TL 072 look way too low, so I looked on youtube on how to check it. I put the multimeter on diode setting and put one lead on the output A pin and one on the input A as well as the other input A. Did the same thing on the B side. On the A side, the meter read 0.732 for both and on the B side it read OL for both. Does this give any indication that the chip is no good?
using the diode measuring setting is not how you test an op amp, especially since an op amp is not a diode...
testing an opamp is simple, first there is the buffer method, for wich you need a breadboard and a (digital) multi meter.
configure the opamp in this configuration:
(https://i.postimg.cc/8jGFdFfC/buffer-tester.png) (https://postimg.cc/8jGFdFfC)
all the voltages on all the pins should be the same, if not, its probably bad.
if you want another method and you have an audio probe.
configure the both op amps in this configuration:
(https://i.postimg.cc/BtVYX0jN/test-oscilator.png) (https://postimg.cc/BtVYX0jN)
the audio probe should reveal a frequency near 1.5kHz on both the output and at a lower volume at the inverting (-) pin, if you can't get it to work, its probably broken.
i have a simple perf-board with two sockets for both methods, for both dual and singe opamp pinouts to test opamps i suspect to be wrong, but a normal breadboard is also a good tool to test opamps in a less permanent setup.
(now i think of it, this might be a good 'tool' to design a PCB kit for or something,)
cheers, Iain
You set your meter to DC voltage, range just above your power supply,
on my meter 20v is the next value over 9v.
You stick (or clip) the black probe to ground of your circuit
and check the various pins with the red one.
If you are testing it in a powered circuit with 9v you should *usually* see:
0v on pin4
9v on pin8
all the other pins should *usually* read around middle voltage, more or less 4.5, although the inputs may be "loaded" by your meter and read a little low.
What circuit are you looking at?
IDY...I was wondering if the TL 072 chip is bad for some reason based on the voltages I got before
You should have continued this in the first thread you started. The chances your delay isn't working because of a faulty op amp are very small. The low voltages around that op amp are clues to finding improper solder and wiring. Considering you're very new to this hobby, the chances you erred in your soldering are 99.9%. "Bad parts" make up about 0.1% of the problems around here.
Garcho...i bet you are 100% correct in that today I took new readings and I was getting half of the input on most pins and one at 5 volts...i made an audio probe today and found i get audio in most plavces, some loud and clear and some not so clear. Did see that some resistors have sound on one end but not the other..same with some other components. I was trying to clean up the solder on my switch but not haveing much luck..wotking with solder is such a pain. not having a schematic isnt making things much easier.
Question for you all....when using an audio probe, should I get audio signals from every single end of every single component? Or are there certain things that do not get tested with the probe?
Quote from: rdhj on December 26, 2020, 04:05:24 PM
Question for you all....when using an audio probe, should I get audio signals from every single end of every single component? Or are there certain things that do not get tested with the probe?
Well, you typically try to follow the signal path, and in time that will come fairly naturally. If you probe power pins, you'll get a 'click' (provided you DO have a capacitor in your probe!) and then nothing as it blocks DC. Ground same, as well as the leg of any component connected to power or ground. If there is noise in your power supply sometimes you can hear that (if it's bad or a cap is missing or dead).
Otherwise, signal chain, from input thru the device to output > next device or effect out. You'll get the hang of it...
It's also helpful to have a 'signal generator' for testing effects, which provide a signal so you don't have to pluck the guitar constantly (tho we all do sometimes). That can be a simple oscillator, or even a recording from an MP3 player or some such thing. Learn the probe first, next project, a simple signal generator ;)
But it's always good to have a schematic/diagram to follow signal path.. :icon_wink:
(it should be more easy to locate "series" and "shunt" items..)
Checking the DC voltages in the *original circuit* is often a good starting point for testing an opamp. The original circuit *is* the test circuit so there's no need to specifically set-up test circuits. If the DC voltages look OK it's highly likely the opamp is working and it's probably best to consider other avenues. After that you can check AC voltage with a signal generator and oscilloscope - the step below that is testing with an "audio probe".
Yes, what Rob says. My info was 'generic', answering your question about using an audio probe. Voltages will tell you a LOT about the opamp your typical dirt box! And quick & easy!
I have traced the audio signal from the input jack all the way to the Op Amp...Had to reflow some solder on a frew caps and resistors to get that far. Only getting a signal from one pin on the amp and its not as loud or clear. Is this normal. I've been cleaning up joints alot but still no good.
A lower signal on a pin that's used in the feedback loop can be expected to have a lower level; being present is what counts. But 'missing signal' at the other 2 would indicate either that the opamp is toast, or maybe something else isn't connected right. Reporting what pin you get results on is traditional, so we can help you out more... :) If you have a multimeter, this is a good time to just list the DC voltages at each pin, too!
Yes, you need to specify which pin you are measuring! And voltages!
My most common error is a biasing resistor not soldered well enough. It looks fine but the + input (3 or 5) is not getting its proper (middle, around 4.5) volts. So the op-amp does nada. You find a signal at pin 3 or 5 and nothing coming out...
Unless the op-amp is getting a proper DC voltage to that pin it will appear to be dead. I have experienced this too many times, and it has always been a resistor not soldered well enough. And the resistor always looks just fine even under a magnifying glass....
Are we talking about any particular circuit or we're just guessing..??
^ it's basically the PT2399 datasheet delay, some variation with a layout but no schematic, sold in kit form. For some reason the OP is resisting following the troubleshooting guide or much of any advice and being oddly parsimonious with any information, so good luck!
QuoteI have traced the audio signal from the input jack all the way to the Op Amp...Had to reflow some solder on a frew caps and resistors to get that far. Only getting a signal from one pin on the amp and its not as loud or clear. Is this normal. I've been cleaning up joints alot but still no good.
The lack of schematic makes is difficult to judge the results because it's not possible to see the "lay of the land" so to speak.
Here's a collection of common circuit patterns using opamps,
http://www.add.ece.ufl.edu/4924/docs/TI_SingleSupply.pdf
The circuits in figures 3, 4, 8 and 8 are pretty common. Although you will often find R3 = 0.
Unfortunately there's a few bugs like the lower example in Figure 3. The opamp + input should have an extra resistor to Vcc/2, more like Figure 6. Also, it's common to put a cap in series with R1 (those parts can then wire to ground or Vcc/2).
For the inverting amplifier case, top of figure 3, you would find the opamp+ pin and opamp- pin have no signal. This is normal. If you see signal on the opamp- pin the opamp could be clipping, so drop the test signal level.
For the non-inverting case, bottom of figure 3 + fixes, you would find the both the opamp+ and opamp- pins have signal. In this case the signals are less than the output signal; as GibsonGM mentioned.
FWIW, the PT2399 chip has a number of opamps inside. You need to get the datasheet to see what pins they connect to.
If possible try to trace out the circuit around the opamp(s) you think aren't passing signal. Try to match-up the circuit with common circuits in the PDF link I posted. Then try to judge what you would expect based on that circuit. Without doing that it's very hit and miss because you don't know what you are dealing with and can't know what you should expect to see.
I have been read trying to follow the debugging pages to the best of my ability. Somehow, after all the messing with it and resoldering the joints, I actually got it to work. However, when I hit the guitar strings harder or play a chord, I am getting a somewhat distorted sound, not clean like it should be. Could this also be a bad solder joint that i didnt get yet.
QuoteI have been read trying to follow the debugging pages to the best of my ability. Somehow, after all the messing with it and resoldering the joints, I actually got it to work. However, when I hit the guitar strings harder or play a chord, I am getting a somewhat distorted sound, not clean like it should be. Could this also be a bad solder joint that i didnt get yet.
You did well pushing through.
Well, it is quite possible the units working and it just does that. It's a bit of a fine line. It becomes hard to judge without a schematic, or, without an oscilloscope to see how large voltages are before the circuit starts clipping. You could keep pushing to see if you can improve things.
FWIW, here's the what I understand is the original thread,
https://www.diystompboxes.com/smfforum/index.php?topic=126028.0
Possibly the TTone Delay kit.
There's this one called Tweaked Tone Delay
https://forrestwhitesides.com/tweaktone-delay/
Well it might be worth comparing against these,
http://revolutiondeux.blogspot.com/2012/01/mad-professor-deep-blue-delay.html
https://the7line.clan.su/_pu/0/92883033.gif
There's a gain of 2 before the delay and a gain of 1/2 after to improve the signal to noise. Perhaps that's the cause of the overload. Maybe pre-emphasis (boosting highs before) and de-emphasis (cutting highs after ) is a safer scheme to improve signal to noise with out risk of overload. The inverting input stage might not be the best for that but anyway ...
This is the Landtone delay kit that I got off off amazon. I think it is the same as the TTone kit.
So, what are DC voltage readings on all TL072 pins..??
(black probe on power supply ground and red probe on pins - DMM set on VDC..)
TL072 pin numbering..
(https://i.imgur.com/koEoKEu.gif)
For some reason, when I put the black probe to the ground on the 9V jack, it wasnt iving me the right readings. So, I stuck the probe on the fround of the output jack and got the following voltages.
1 1.468
2 4.16
3 4.09
4 0
5 3.95
6 4.06
7 6.97
8 8.09
Quote
1 1.468
2 4.16
3 4.09
4 0
5 3.95
6 4.06
7 6.97
8 8.09
Your pin 2, 3, 5, 6 look reasonable for a working opamp.
The pin 1 and 7 voltages are close to the power rails and might explain the lack of headroom you are seeing.
It's not possible to judge beyond that if those voltages are normal for the circuit.
It would be worth looking into why pin 1 and 7 are so close the supply rails.
It's virtually impossible to debug further without a schematic. At this point experienced debuggers
would draw out part of the circuit as it's the only clear way forward.
can you exlain "lack of headroom" and "close to the supply rails"?
Lack of headroom: the signal can't get more gain without distorting (which may or may not be good, depends on what you're building.)
Close to the supply rails: the voltage of a certain area is nearly the same as the power supply voltage, which normally for guitar/bass pedals would be +9v and 0v (ground)... but since your power is at around 8v (as we can see from pin 8 of the op-amp), pin 7 (7v) is too close to the supply (8v) in which we would probably be expecting distortion... also the voltage on pin 1 (1.5v) is too close to ground (0v) this may give some volume problems... but again, without a schematic we can only guess...
Thanks. I emailed the chinese company to ask for a diagram. Lets hope they can supply me with something.
Based on the above about headroom and the rails, would you expect that the TL072 may be bad? I can order a new one from ebay and try it.
Quote from: Rob Strand on December 30, 2020, 06:56:57 PM
It's not possible to judge beyond that if those voltages are normal for the circuit.
When you are probing the non-inverting input, your meter may be dragging the voltage down that is set by the voltage dividers because it may have an input resistance on the order of megohms which may change the voltage at the voltage divider if the divider is high resistance.
When you are probing the output / inverting input, you have a low-impedance source and meter loading will be negligible. If you have a second meter, leave one on the inverting input while you probe the inverting input. They should read the same then.
If you want to test the full functionality of the op amp so you can measure all of the characteristics on the datasheet, that requires a number of setups and a lot of test equipment and most of the setups are shown on the datasheet.
was messing around with it today. Here is what I got now:
1. Bypass mode works totally fine and LED light is lit up
2.Hit switch and led gets brighter....with repeat knob all the way down yu can hear the guitar signal but it is weak
3. as you turn the repeat up it gets loud and noisy like it is keeps repeated and getting louder as you turn the knob.
Does this happen to tell us anything....maybe issue with the delay IC?
Audio probe?
Pictures?
(I think tracing the board would be a *quicker* way to get a schematic...)
The delay IC seems good to me... again, inexperience speaks...
Just found this which is the same exact kit and issue that I am having..
https://www.reddit.com/r/diypedals/comments/b2ozqn/delay_pedal_kit_problem/
For some reason I have trouble with imgur,
(https://i.imgur.com/0EQtdT0h.jpg)
That's the only image I see. (Sometimes imgur shows more than one.)
Weeding through some threads I got these,
(https://i.imgur.com/HCaPqtIh.jpg)
(https://preview.redd.it/o9e2iaj5zlm51.jpg?width=640&crop=smart&auto=webp&s=5e73906d82e924aa57f199ee9d8f00e9dfc23bbd)
It's looking a lot like this one, but there are some differences,
http://3.bp.blogspot.com/-bEMBMvJwA5Y/TwrbbnpmzoI/AAAAAAAAAbw/EQ70PKQOFes/s1600/seaUrchin_Schematic.gif
- The opamp has the A and B parts swapped: Input opamp is pin 5, 6, 7, output opamp is pins 1, 2, 3
- Input opamp has resistors 510k in and 510k feedback. So gain of 1 not gain of 2 on this one.
It also has 240k in series with pin 5; which does nothing but add unnecessary noise.
- Output opamp has input resistor 24k and output resistor 24k; correctly matches the gain of 1.
It also has 1k in series with pin 3.
Opamp is powered from 9V and the VB supply is made from two 12k resistors.
So getting back the opamp voltages. The measurements on pins 7 and pins 1 look wrong.
I think the cause is around the input opamp, pins 5, 6, 7. Pin 1 is wrong *because* pin 7 is wrong.
For the overlay pic I posted, the top left has a 1M, 82n and 510k, close to the 240k.
It seems if the 82n was faulty or there was a short across the 82n then we would probably see pin 7 having a high voltage.
Both sides of the 510k should be about 4.5V (DMM loading can screw that up) if one side is at a lower voltage than the other it could be due to a fault in this area.
It could well be this one,
https://aionfx.com/app/files/docs/vector_legacy_documentation.pdf
If you look at the Rebote 2.5 variant parts list - sort of close. The values in the parts list are different to the schematic. The values in the parts list match-up with the values in the kit (sort of).
The extra opamp resistor was on the Rebote 2.0,
http://www.matsumin.net/diy/jisaku2/vin_delay/Rebote2Delay.pdf
when you say 82N are you referring to the capacitor labled 823? If so, i took the voltage readings on each side. One side was 3.9 and the other was giving me a voltage in millivolts that was different each time I checked it.
Quotewhen you say 82N are you referring to the capacitor labled 823? If so, i took the voltage readings on each side. One side was 3.9 and the other was giving me a voltage in millivolts that was different each time I checked it.
Yes, that 823 cap. So your measurements look normal.
It might be worth measuring the voltages on the two 12k resistors located just below that group of components (510k, 510k, 240k, 82n). Also measure the voltage on each side of the 240k . For sanity you could re-measure voltages on the opamp, pins 5, 6, 7.
Based on your 8V supply, one of the 12k's should have 0V and 4V, the other 12k should have 4V and 8V. The 240k should have about 4V on each side.
If those check out but the pin 7 voltage is still 7V, I'm struggling to see how the opamp (pins 5, 6, 7) can produce 7V. It's like the pin 6 input is damaged by leaking current to ground.
(https://i.postimg.cc/HJPGh2f9/F3-AE578-D-A394-4487-81-C7-C3-C998-C169-A2.jpg) (https://postimg.cc/HJPGh2f9)
Here is what I got. Everything looks normal except for pin seven is 6.3 V
The 3.78V measurement on the 510k resistor should match the 6.3V on pin 7. If you look at the PCB tracks the two points are connected so they have to be at the same voltage. When voltages don't match like this it's a sign of a connection issue. A faulty IC cannot do this.
It's worth checking those again. It's also worth check the pin 7 voltage from the bottom of the PCB and on top of the pin of the IC. All the points should be at the same voltage.
Perhaps touch-up the soldering on pin 7 and the 510k resistor.
If the pin 7 voltage is different on the top of the IC then it's likely pin 7 of the IC is not connecting to the socket. That can be because of a dirty IC pin or dirty socket pin (these things can develop oxide coatings). So try cleaning those up.
If you can get those two voltages to match and they settle on 4.0V then it should work and you can check pin 1, 2, 3 which should also match. If they settle on 6.3V then there's still a problem, perhaps pointing to the IC.
I redid a bunch of the joints in that area and it looks like I still have the same thing going on. I was still getting 6 V. Should I just replace the two chips and see what happens? Also is there anyway to add a video attachment to this posting? I would like to take a video and share what it is doing to see if that would help any
QuoteI redid a bunch of the joints in that area and it looks like I still have the same thing going on. I was still getting 6 V. Should I just replace the two chips and see what happens?
To fix the 6V problem you only need to replace the TL072. It's a quick way to short-cut a lot of testing and perhaps get an immediate result.
Maybe no need to replace the PT2399 yet but if you have to factor in shipping and we end-up having to replace it anyway then it's up to you.
QuoteAlso is there anyway to add a video attachment to this posting?
Not that I'm aware of. People tend to upload to youtube then link that. I think someone uploaded a video to imgur but it didn't work for me.
Oh, checkout Reply #16 of this thread by Kipper,
https://www.diystompboxes.com/smfforum/index.php?topic=111503.0
Good part values matches to the kit.
Kipper's schematic has a bug on the filters (the Kit PCB is OK):
- move C9 to where R13 & R14 join
- move C10 to where C9 was (where R12 and R13 join)
Similarly,
- move C11 to where R17 and R18 join
- move C12 to where C11 was (where R16 and R17 join)
- C12 value on PCB is 22n not 27n
Here is an update on my never ending issues.
I got the new Op amp today and installed it and when the pedal is on everything seems fine minus some static noise which I guess is normal. But now I have a different issue. When I switch it to bypass mode, the signal is cutting out for some reason (bypass was totally fine before). Then if I unplug the 9V power supply line, it is fine. Seems like it is now using the circuit in bypass mode.
Does this tell you anything. Took it apart and looked for broken or crossed wires but found no issues.
QuoteHere is an update on my never ending issues.
I got the new Op amp today and installed it and when the pedal is on everything seems fine minus some static noise which I guess is normal.
Good news then.
QuoteBut now I have a different issue. When I switch it to bypass mode, the signal is cutting out for some reason (bypass was totally fine before). Then if I unplug the 9V power supply line, it is fine. Seems like it is now using the circuit in bypass mode.
Does this tell you anything. Took it apart and looked for broken or crossed wires but found no issues.
Wiring, wire connection, or the switch are the likely cause. Once your in bypass the circuit doesn't have a say in the matter.
You can check the switch contacts with your multimeter conductivity tester. You might be better off connecting to the ends of the wires that go to the switch instead of the switch itself. The switch could be damaged, due to say heat, and pushing the meter leads down on the switch can fix the problem but only temporarily. You could also poke down on the switch contacts with small plastic handled screwdriver to see if the poking helps.
I think someone mention the LED wiring early in the thread. That can short onto the signals and cause trouble. Maybe it's happening at the switch contacts.