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Thank you for pitching in on this, cth515. It does make sense that decoupling the “noise making device” (the microcontroller) better would help cure the noise…although I’m pretty sure that I tired this with the noisy unit that i had and it didn’t help…but i was using a lower capacitance (around 220nf) so it makes sense that a much higher capacitance would make more of a difference. The board version shouldn’t make a difference of how well this works. The ground planes and power distribution path are very similar on both board versions. The ground planes are separated (digital and analog), but there are other ways for current to get through.
I’m really glad that you found a solution that works for you! Good work!
Mike353…yes, please go ahead and try this. The cap you linked to is much too large of a capacitance…use one of these:
https://www.taydaelectronics.com/capacitors/electrolytic-capacitors/nichicon-1uf-50v-105c-radial-electrolytic-capacitor-5-11mm.html
https://www.mouser.com/ProductDetail/KEMET/ESL105M100AC3AA?qs=HXFqYaX1Q2x0RWu%2FYCFzZA%3D%3D
https://www.digikey.com/product-detail/en/rubycon/50YXJ1M5X11/1189-1421-ND/3134377
Ideally you want a cap with a relatively low ESR (equivalent series resistance) which gives the noise a low impedance path to ground, but i’m not sure how practically important that is in this application.
Here is a page with a graphic of the Atmega328p IC’s pinout:
http://www.learningaboutelectronics.com/Articles/Atmega328-pinout.php
You can see that pin 1 is near the divot on top of the chip. Pin 1 is also closest to the dot on the IC (although it’s not shown in the graphic). Pin 1 also has a square solder pad, where as the rest of the pins on the IC have round pads. From pin 1 count the pins down to 7 and 8. Please note the graphic is a picture of the IC from the TOP, but you will be soldering the cap to the BOTTOM of the IC, on the solder side of the board. So keep that in mind when finding pins 7 and 8 on the bottom of the board.
Once you think you’ve found pins 7 and 8, test them to make sure you are correct. Pin 7 should be connected to the other 5v pins around the board and on the voltage regulator. Pin 8 should be connected to ground.
Remember electrolytic caps are polarized so the positive lead (the long lead) should be soldered to pin 7 (aka 5v) and the short lead (the negative pin, with the white stripe on the body) should be soldered to pin 8 (ground).
Cut the leads short and lay the body of the cap down on the solder side of the board so the leads are touching pins 7 and 8…then solder the cap leads to the IC’s solder pads. You may want to hold the body of the cap to the board with some hot glue or something to keep it from rattling around so the solder joints don’t eventually break.
Please let us know how this works for you.
Good luck!
-BrachJust to be clear, since your pedal is out of phase with itself…when the red led is on you do not hear the tremolo and when the red led is off, you do hear the tremolo…Correct?
The tremolo is supposed to be heard when the red led is on, and the effect is bypassed when the red led is off.
I’m not sure how the bypass switch could be out of phase, so let me know if this is the case.
-BrachThat’s great! I’m glad you are enjoying your VPM-1!
Please spread the word…we can use as much promotion as possible!
Thanks for the feedback.
-BrachWell that was an easy fix! I’m a little hesitant to say it’s totally good because it may start doing that again because we never found out the cause…but for now i’m glad it’s working well.
Take care and enjoy your Quaverato!
-BrachThank 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.
-BrachClive,
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.
-Brach
