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Hey everyone,
I recently finished building the Quaverato and it has quickly become one of my favorite pedals on my board. Tonight I was messing around with pedal placement(quarantine boredom) I noticed my Quaverato had stopped working. Now when engaged, the pedal doesn’t pass any signal at all. Although while bypassed, everything works just as it should. All LEDs function just as they did before, and tapping in a tempo works as well. I have gone through and verified that all voltages are within spec that the troubleshooting guide describes. I also have re-flowed any solder joints that looked suspicious.
What really boggles me is that the pedal was working without any issue, and then all of a sudden it stopped working. Maybe moving something around caused a short, but I would think taking it out of the enclosure would rectify any issue of that nature. I took some general photos of the pedal, but if there is any key areas that you would like me to highlight I am more than happy to take more.
Photos:
Photo 1
Photo 2
https://ibb.co/VQ23WHx
https://ibb.co/FqrmbHd
https://ibb.co/GMx047m
https://ibb.co/Fw2mzv8
https://ibb.co/9cFJL0f
https://ibb.co/0JSXz3R
https://ibb.co/2PqVYbr
https://ibb.co/HKRtQvC(Small note, I had the paper under the second row of pots off only for the photos. I have reinserted the paper and there is no grounding issue between the pots and any solder joints.)
Maybe I’m missing something obvious (which I hope is the case!), but right now I’m pretty stumped. Thanks for taking a look!
Alex,
I’m sorry we didn’t see this post until now. I guess it got caught in the spam filter. Sorry about that.
It’s odd that it was working for at least a little while and then it stopped working suddenly…at least i’m assuming it suddenly stopped working. Does the bypass LED turn on and off as expected? I’m assuming that you can hear the relay click when the bypass button is pressed?
Thank you for the photos. At first glance, the only thing that comes to my attention are that the leads on the “standing up” resistors are exceptionally long. You want to keep those as short as possible so they don’t short out against each other. Check to make sure none of them are touching.
Test the relay circuit by working through step 5-C of the troubleshooting guide.
When the bypass LED is on (and the guitar and amp are plugged into the pedal), turn the volume knob all the way up…can you hear any hiss being modulated by the tremolo circuit or is it completely quite?
Let me know what you find.
-BrachHey Brach,
No worries! Since I originally wrote this post little while ago I’ve made some progress and found some new things. First, I have tested the relay along with the status LED and everything works exactly as it should. There is an audible click every time I use the switch along with the LED turning on and off. Second, I went through and did my best to shorten down all the standing resistors leads but it didn’t make any different sadly. Third, I’ve remeasured the voltages against those provided in the troubleshooting doc and I think I may have found the culprit; The TL074 has voltages of 1.5v~ on all pins besides the power (which hovers around 9v), so I think something might be wrong with it. Fourth, today I decided to plug in my guitar again in to test pedal and there was actually output! Hooray! Granted, it sounded like a gated fuzz (a sound a I normally enjoy but wouldn’t expect from a trem pedal) but I’m still happy. I’m not exactly sure what is making this “broken” fuzz sound, but my guess is something with the bias in the op-amp isn’t working correctly. I had a fuzz pedal that when you turned the bias all the way it produced a similar sound. Anyways, I recorded a quick demo of this sound on my phone, let me know what you think. Thank you so much for your help!
https://drive.google.com/file/d/1Gqa-9lGDaR5IXtrtgN0MAF6RawTmzNo3/view?usp=sharing
(Small note, after I engage the pedal the faint buzzing noise is me pressing the volume pot on the pedal with my finger)-Alex
Alex,
Your guess is correct, the bias is way off on your opamp (the TL074). Each pin should be biased to around 4.5 volts (half the supply voltage), but for some reason it’s a at 1.5v. In these types of situations the opamp doesn’t usually go bad or break, the issue usually is that the circuit sending the bias voltage got messed up somehow. You need to check (re-flow) the solder joints on R9 and R10 (the junction that the 4.5v is comes from) and also C15 (also make sure this cap is installed in the correct orientation). Also check that C10, C11, and C16 are soldered correctly. It kind of sounds like something is partially shorted to ground…like the paper insulation under the pots might have been punctured by a lead and is touching the back of one of the pots. In a rare case, it is possible that the opamp went bad and needs to be replaced. If you can’t seem to get the bias voltage back up to 4.5V by doing the things i just suggested then we’ll have to assume that the problem is the opamp.
Good luck.
-BrachHey Brach,
I re-flowed all the solder joints you suggested and I have verified that C15 is installed is correctly orientated. Sadly, I’m still getting around 1v to 1.5v on the TL074. I noticed that the lead from R10 that’s supposed to be 4.5v is also 1.5v~, which would lead me to believe that it isn’t the TL074 creating the issue but once again I’m not sure. I have also lifted pots up and I made sure that none of them are shorting on anything. I never had a TL0XX opamp break on me, so it does seem unlikely that’s the problem but at this point I’m not sure what else it could be. Also, now when I play through the pedal it doesn’t even do the “gated” sound it was producing before as no sound is able to get through at all. Hopefully if the TL074 gets replaced all will be well again. Thank you for your continued help!
-Alex
Alex,
Thanks for checking those things. The fact that all the pins on the opamp (not just one section) are low indicates to me that something other than the opamp is draging the bias voltage to ground somehow. With the power off, what is the dc resistance to ground from pin 10 of the TL074 (that pin is connected directly to the bias voltage)?
Let me know.
Thanks.
-BrachHey Brach,
I checked the resistance of pin 10 of the TL074 against ground (which I assumed to be pin 11 from the datasheet) and got around 11k ohms.
-Alex
Thank you for checking that. What you are saying is essentially that the resistance across R9 is 11K. The power was off when you measured this, correct? Can you please double check to make sure R9 and R10 are really 100k.
Also, please turn all the dip switches to the off position and re-measure the voltage on the opamp pins (when the power is back on).
Other than these things, please use your magnifying glass to look for little solder balls or other things that could cause shorts on (both sides of) your board.
Let me know about R9 and 10. If none of these things solves the issue then you might want to move towards replacing the TL074.
-BrachHey Brach,
Sorry for the late reply, work and school have kept me very busy for the past days. Out of frustration, I had a friend come take a look at the situation and see if he could spot anything I had turned a blind eye to. I turned away for a moment to get something to drink and when I came back he was reading 4.5v on all pins on the TL074! I’m not sure how he fixed it (and he isn’t even sure) but the pedal works exactly like it did before. Thank you very much for all your help!! I’m off to use my Quaverato!
-Alex
