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Clive,
That’s great! Very practical! Thanks so much for sharing.
Are you making this an open source project? Do you have a blog or anything where you are planning on sharing the code?…just curious.
-BrachAlex,
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.
-BrachYes, you can just short the pins/pads of J4 with solder or a small piece of wire. But if you ever plan on installing the expression upgrade then use the provided 2-pin header and jumper to short these pins together. When the expression board is used, the jumper on the header needs to be removed because there is a switch on the expression board that handles the tuner output functionality instead of this jumper. All this jumper does is complete the signal path to the tuner jack…if it’s not shorted then no signal gets to the tuner jack, unless you are using the expression upgrade board, which that routing is controlled by a dip switch on it.
I hope that makes sense.
-BrachAlex,
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.
-BrachAlex,
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.
-BrachYes, it is odd that it stopped working after it was working. Most likely it’s something simple.
I’m assuming all the switches on the dip switch are in the off position, correct?
I’m also assuming the ribbon cable is installed the correct way around (not twisted)…and has been calibrated AFTER it has been installed correctly. If it was calibrated when it wasn’t connected correctly then the microcontroller will have bad data and it won’t pass signal.
I’m also assuming that the jumpers, J5 and J6, are installed.
Just to make sure the jacks are working correctly…while the main board is in the chassis and the pedal is powered and plugged into an amp and guitar, try to firmly wiggle the input and output jacks as you play guitar….just to see if the signal jumps in and out.
Please check out those things and let me know.
Good luck!
-BrachI’m in the process of writing a troubleshooting guide for the VPM-1…but it’s been hard to finish due to the pandemic and me not working at the lab much.
As far as the volume not turning off…check the optocouplers (especially on the LED side) to make sure that one of the heat shrink tubes didn’t pop open, or has an “optical” leak that could let light in. If so seal it with some opaque material…like caulk or even sticky tack (poster putty). I use black hot glue for this.
You can also try to re-setup the microcontroller’s memory registers by running through the stereo set up procedure. To do this jump together the 2 pads of “CAL1” as you plug in the power. Once the power is on you can remove the jumper…i just use my metal tweezers to short the pads together upon power-up. The red LED will start flashing for a couple of minutes as it re-writes the registers. It will flash 256 times, if you care to count. When it is done writing, the green LED will start flashing, letting you know that you can unplug the power and remove the jumper if it’s still on.
As far as it not working anymore, what do you mean? Does the LED turn on? If not, check your DC jack to make sure the wires are still intact. Then check to make sure the voltage regulator is putting out 5V, which powers the microcontroller, which light up the LED.
As always, check for solder shorts with your magnifying glass.
Let me know what you find.
-BrachMark,
Have you worked your way through the trouble shooting guide? If you haven’t, that would be the best place to start.
I’m sorry, but right now I am very busy and don’t have time to accept any kits to troubleshoot. But if your Quaverato was working for a while then it’s probably not too far away from working again. The noise could be caused by a lot of things. Once it’s working again we can try to troubleshoot where it’s coming from. But for now, start with the troubleshooting guide and see if you can make any headway with that.
Good luck.
-BrachRichard,
His readings were way off. Use the troubleshooting guide voltages for the correct values (found under the “documents” tab of the Quaverato page on our site”.
To use a multimeter to measure DC voltage (all the voltages to measure on the Quaverato are DC) first make sure the meter is set to the DC voltage (V) setting, not milivolts (mV) (if your meter has a “mV” setting).
Put the black probe (the negative probe) on a 0 volt point in the circuit…we call this the circuit “ground” or “common”. You can use the fist pin of the input or output jacks (the pin closest to the part of the jack with the hole for the guitar cable). Or you can use the point on the pcb that the ground lug wire is soldered to.
Put the red probe on the point you want to test. The voltage difference between these 2 points will be given by the meter.
When you test the voltages on the pins of the IC make sure to not be touching 2 pins at once. Place your red probe on the IC pins right where it comes out of the IC’s body. Make sure the depth knob is all the way counter clockwise. That’s the only knob that needs to be in a particular position.
Good luck!
-BrachVery nice! I like how you implemented the dip switch idea, along with the long press foot switch to change the total number of presets. I’m looking forward to seeing how it all comes together in the box. I love watching ideas like this come to life!
I forgot to address the solder shorting out your power jack issue…
Are you sure that the pins of the power jack are shorted together by the solder? This would be very unlikely…the solder would solidify as soon as it hit the board, which would keep it from flowing under anything. I don’t know which pins you found connected, but 2 of the pin are supposed to be connected on the jack when nothing is plugged into it. Try plugging a power cable into the jack (DO NOT plug the other end into the wall yet…we don’t want power in the circuit yet) and then re-test continuity between all the pins on the power jack. Hopefully they are not connected anymore.
You should be able to peel off the solder drop that fell on the board without much problem. If not, send me some detailed, in-focus photos.
-BrachCraig,
I’m sorry to hear about your jumper trouble. First of all, do not use a conductive pen to try to fix this. You need to just bypass the jumper pads with a jumper wire. It appears that you have your iron set to a much lower temperature than you should…i keep my Hakko FX-600 set to 575 F, which is around 300 degrees C. With the temperature set this much higher you’ll probably need to adjust your soldering technique. It should only take you about 1 second or less to thoroughly solder most of the joints on this board (the components with more thermal mass, may take a bit longer…like around 1.5 seconds). I wasn’t able to see your picture that you posted (sorry for the forum limitations) but you may want to re-flow the joints on your board with a bit of added flux (preferably the “no-clean” type).
To bypass JP3, solder a wire from pin 1 on U2 to TP3. Use the thinnest wire you can find. I use “wire-wrap” wire for these types of jumpers…which is either 28 or 30AWG. You can use the wire found in a cat 5 network cable or wire from an old VGA monitor cable…that stuff is usually thin enough, from my experience. You’ll need to tin the ends of the wire first; and also tin pin 1 of U2 (solder the wire to the pin right as it exits the body of the IC). Try to fit the other end of the wire inside the TP3 hole and then solder it. If you can’t fit in in the hole then just lay it across the top of the hole and solder it down…in which case you may want to use a tiny drop of super glue to hold the wire in place on the surface of the board, but make sure you don’t get glue on the solder joint.
If you have other jumper pads that are bad, just fix them the same way. You can find out where the jumpers wires are supposed to go by looking at the schematic in the back of the manual.
Good luck!
-Brach
