Tap Tempo Tremolo

[lincolnic]

You've got this on your test rig, right? Are you using plastic jacks in there? If so, you'll have to connect their grounds. Metal jacks, as long as one of them has a sleeve connection, will ground to each other through the enclosure.

I have a sneaking suspicion that your build is actually fine, and there's just some ground issue going on here. It's happened to me before.

[jimilee]

Also I'd check to make sure your resistor values and cap values are all good.

[Guybrush]

Cheer guys. I'll give everything the once over again.

My test rig has metal jacks. I've used it for all my other builds so pretty sure that this isn't the problem. That being said I'm not sure my audio probe is working as I'm not 100% sure how to use it. I hope you're right about it being a grounding issue though Lincolnic.


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[Guybrush]

Well I've spent the weekend going over the circuit and I'm still no closer to finding the issue. I'm not even sure that I'm using my DMM and audio probe correctly.

Would anyone be kind enough to have a look at it for me? I know it's a cheats way out but I've just come to the end of my knowledge on how to fix it. I really don't want this circuit to end up on the scrap heap. I'll post it out and buy you a couple of beers for the trouble.

I'm desperate to get this circuit working. I even sold my vintage EH pulsar to fund this build

If someone would be willing to give it the once over for me I would be enormously grateful.

Cheers

[Guitarmageddon]

The flashing led tells us the LFO is working, so it's probably a problem in the audio path. As Brejna pointed out, it's quite short so it shouldn't be too hard to find where the problem lies.
I can look at it for you, but before that happens, get a 6" piece of wire, solder a 1uf cap on the end (neg leg to wire), this is your audio probe.
Connect the board to your test rig and power it up, connect a guitar to the input, an amp to the output, but leave the effect output wire disconnected from the test rig. Connect the audio probe to the test box output instead. We can now use it to eavesdrop at various points in the circuit.
With this rig plugged in to an amp, and while strumming the guitar, touch the probe tip (+ leg of cap) to the points I've numbered in pink. Start at the input, you should hear effected guitar signal.
Proceed through the numbers, looking for where the signal stops. If it's a cap or resistor it's most likely a cold solder. Reflow it.
If it stops at the opamp, it could be a few things, power supply to the opamp, a bad opamp, bent leg...etc.
We'll deal with that if necessary.
If it stops at the opto, double check it's in the right way.

I've found that Taylor's boards, being multi-layer, aren't as robust as  Brian or BYOC's dual layer boards. They don't like to have parts desoldered. If you need to desolder be very careful and check for continuity afterwards. If you've already done some desoldering to this board inspect those areas carefully too.



Let me know how that goes.

[Guybrush]

Thank you for such a detailed reply! I'll have a go through everything you have said asap.
Thanks again!

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[Guybrush]

Ok. I've run the audio probe over the points you indicated and this is what I found.

I get clean (no tremolo) signal at points 1, 2, 3 and 4. The signal goes dead at point 5, the TL072. I've had a look and there don't seem to be any bent legs.

As a side note I did find that I got clean signal from pin 1 (point 7 on your diagram) of the TL072. Not sure if that helps.

Any suggestions on how to further progress would be again enormously appreciated.

Thanks.

[Guitarmageddon]

Cool, you'll find that audio probe invaluable!
Do you have signal at points 8 and 9?
Also, can you post the opamp voltages.
To do this, set your DMM to DC, put the black probe to ground and red probe to each of the opamp legs.
You should have 9v at pin 8, 0 at 4 and about 4.5 at the others. If you have a spare, try swapping the opamp too. Make sure it's correctly orientated, dot/indent toward the left as pictured.

[Guybrush]

The audio probe is a little miracle.  I actually built one into my test rig but I've somehow managed to wire it up wrong. I'll use your one from now on!

I'm at work at the moment but will check the signal at points 8 and 9 and get the voltages read. I really hope it's just a faulty chip.

Thanks again.

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[Guybrush]

Well I just hooked it back up to my test rig to start probing again and one of the resistors (the 10R next to the diode) burnt out. I tried to replace it but lifted the solder pad and I couldn't save it :-(
I'll just have to order another board and start again. Grrrr.

Thank you for all your help. I've learned loads and will hopefully be able to begin debugging on my own on the next attempt!

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[bcalla]

You might be able to salvage this.  You can run the resistor lead through the hole and solder it to the next connection point.  Probably worth a shot.

[Guybrush]

What do you know it worked! I've soldered one leg directly to the neighbouring diode then run a length of wire from the other leg across to the 9vt across the other side of the board. It won't win any beauty contests but whatever works I guess!

Thanks for the tip. I was about to bin it!

Right, back to the probing.

Jeez, I really hope I get this thing working after all this!

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[Guybrush]

Ok.

I have clean (no tremolo) signal at point 8 on the diagram but nothing at point 9

The voltages of the TL072 are:

1 - 4.66
2 - 4.66
3 - 4.62
4 - 00.3
5 - 4.62
6 - 4.66
7 - 4.65
8 - 9.31


Do they seem right?

[Guitarmageddon]

Those voltages look fine.
Point 9 is where you'll hear the tremolo.
Between point 8 and 9 should be the LDR part of your optocoupler. It has 4 legs, two at one end are the Led anode and cathode, the other two are the light dependent resistor.
Three possibilities strike me.
1. bad solder joint at #9, try reflowing it.
2. Opto is in around the wrong way. The VTLxxx have a dot on the case to denote the positive leg of the led.
Triple check it's orientation.
3. Something may be shorting to ground in the signal path at 9 or beyond, use the continuity setting of your DMM to see if there is continuity to ground at 9 (there shouldn't be)

[Guybrush]

Thank you.

The dot on the octo coupler denotes positive? When reading up about them I'm sure I found that it denotes negative. That's how I've wired it up so if you're right this will hopefully the issue.

As it is the dot is located here.



Going off what you say I'm guessing it needs to be in th diagonally opposite corner?