Hey all
I'm just starting to put together a MusicPCB tap tempo tremolo.
I was just giving the board the once over to make sure I had everything I need and noticed 2 small solder pads that are unlabeled.
One is under the opto coupler and the other is under the TL072 chip.
Does anyone know what they are for? I can't find anything in the build doc.
Here's a photo, the pads are ringed in red.
(http://img.tapatalk.com/d/13/10/20/u5uda7uv.jpg)
They are vias, used to link a trace from one side of the board to the other. Ignore them.
Ahh, thank you.
I've not come across these before, thanks for the info.
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Next question:
The build doc says to use 22k trimpots but on the board the are labeled as 10k.
Anyone know which value is correct?
Thanks.
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You will have more range if you use 22k or 20k trims
BTW this is mine experience with it that I have post in the building thread on DIYSTOMP:
-First thing I didn't do is build it with waveform pot and that was mistake because I couldn't stop thinking about that option :D , so at the end I did add that pot and it gives you really more versatility.
-Second thing is about NSL-32, I have tried 4 of them and they all had problems with ticking and that drive crazy 'cause I could rid of it, so I grab those GL5516 ldr's that I got from ebay and wrap mine own optocoup. with white led and I got best results with them and no ticking..
-Third thing is that with those GL5516 I have noticed that you have more output if this is something interested to someone.
-Fourth thing is about that 330pF cap, raising value of this cap really helps with ticking and adding buffer in front of the pedal can remove ticking in bypass (at least in mine build)
-Finally This Tremolo is not ticking in the FX loop of the amp even when used with those NSL-32
Hope this will help you
Brane
Wow. Thanks for all the info. Really appreciate it!
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I've just hooked the circuit up to my test rig and there's a problem. When engaged there's no sound. The tempo indicator LED is working as it should and the knobs effect how fast/deep the LED lights up but there's just no sound. I have sound in bypass.
Anyone have any ideas on what the problem might be?
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Sounds like you might have something shorting to ground somewhere. Check for solder bridges and if you're using board-mounted pots, make sure they're not accidentally touching the PCB anywhere.
Thanks man. I've had a look and trimmed a few stray strands of wire but the problem persists.
Here are some
photos. Can anyone see anything obvious that I've missed?
(http://i.imgur.com/ez3DtE5.jpg)
(http://i.imgur.com/DLSd6hg.jpg)
For reference (ignore the red circles)
(http://i.imgur.com/HT6wREo.jpg)
It's so disheartening. I was so careful when putting this one together. I was certain it would work first time.
Thanks guys
Don't give up! I don't see anything immediately suspect in your soldering, so I'd say the thing to do now is bust out your signal tester and see what's going on. Don't take anything for granted - start at the input wire and work your way through. If you get signal all the way through the output, then your circuit works fine and something's probably grounding out somewhere outside of the PCB.
Cheers. I've not really had much luck doing this before. I can't read schematics so will need to brush up on this.
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I would definitely check if your input and output is grounded. Next thing could be tl072..
this circuit has very simple dry path so you will find error very fast.
Quote from: brejna on October 25, 2013, 12:21:01 PM
I would definitely check if your input and output is grounded. Next thing could be tl072..
this circuit has very simple dry path so you will find error very fast.
Thank you. Please could you explain how to check they are grounded? I know this is incredibly basic stuff but I've just never managed to get my head around debugging.
Do you have DMM? if you have one set it to check connections/diodes, then put one lead on the GND connection and the other on the input and repeat same thing with output. if input or output are grounded you should here that from the DMM multimeter if a form of bip.
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.
Also I'd check to make sure your resistor values and cap values are all good.
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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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
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.
(http://i1122.photobucket.com/albums/l524/guitarmageddon9/signalpath.jpg)
Let me know how that goes.
Thank you for such a detailed reply! I'll have a go through everything you have said asap.
Thanks again!
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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.
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.
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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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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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.
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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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?
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)
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.
(http://img.tapatalk.com/d/13/10/30/uzery2a7.jpg)
Going off what you say I'm guessing it needs to be in th diagonally opposite corner?
Well that's likely going to be your problem.
Dot should be top left, where the "+" sign is.
Carefully desolder it and see where you're at.
Still no signal at point 9 I'm afraid. No grounding shorts from 9 through to 13 either. I think it's screwed :/
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I'm assuming you flipped the opto?
It might be toast. Do you have another one or an LDR and a LED you can use instead?
One other thing, that trimmer beside the opto is the opamp gain control, you've tried adjusting it?
Also, while the opto is out, try tacking a jumper across 8 and 9 then audio probe to see if signal reaches the output.
Yep I flipped the opto and I've adjusted the trimmers but still nothing.
Good news (I think). I snipped the opto out and joined points 8&9 together as you suggy and I got clean signal at both points.
I don't have another opto so I soldered an LED to two of the opto pads (the pair with the + sign) and it lights up and goes out in time with the external rate LED. Unfortunately I'm out of LDRs so will need to get some new ones ordered before I can find out if this will solve it. Do you know what tolerance I'll need?
Cheers!
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I'd go with any old thing, they're not especially well calibrated in my experience. Anything that goes 100ohm-1M should cover it. Tayda has them.
When speed and a particular range is necessary designers tend to specify an optocopouler like the VTL in this build, but I've built plenty of good trems with LDR/Led combos.
I've got a few LDRs here, pm me your address and I'm send you a couple of candidates.
That's incredibly kind. Thank you. PM on its way!
If you're ever unsure which leg of an optocoupler is the cathode, use your multimeter on the diode setting. The LED will give you a forward voltage only when you have the cathode to the black probe. Or you can stick it on a breadboard and put a resistor and LED in series with it. Flip the vactrol until you get the LED to light up. Then you know which direction the current is flowing.
Great tips! Cheers Jon.
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