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Fanyo,
I have never heard of this issue before. There is nothing uncommon about the input or output impedance of this version of the Quaverato, so that’s not the issue. My only guess is that it has something to do with the frequency response of the Quaverato. If you have drives or other pedals that are sensitive to the frequency response of the input signal, they may be boosting those particular frequencies more than others. Have you tried changing the order of the pedals in your chain? Most people run modulation effects like the Quaverato toward the end of the pedal chain, partially for this reason…modulation effects often have a tendency to shift the phase of different frequencies. Another thing that might help is to keep a non-true bypass pedal directly after the Quaverato…like a tuner pedal or a buffer pedal or something.
I’m sorry about this issue. I hope you can find a solution that works for you. I’m sorry that I can’t be of more help.
Take care.
-BrachFanyo,
I think your issue may be a different than Tyler. If you are experiencing a “dip” in volume as you move the treadle, that is caused by the volume level table in the microcontroller not being populated correctly. If you run the stereo setup routine, that will re-populate the table and is likely to fix it.
To directly answer your questions, my suggestion about adding a capacitor was only theoretical. I have never tried it myself. It will take some experimentation to find the exact capacitor because I can’t remember the exact frequency of the PWM, but I think it’s around 30kHz.
-BrachTyler,
Thanks for the serial. Yes, we did build that one with the expression mod.
In dealing with 8 bit control, there are only 256 discrete steps of brightness on the LED (controlling the LDR). We’ve done some processing magic to acquire a few more steps toward the bottom of that range…which, I believe is what is causing the frying or distorted sound, as the final step flickers on and off. I don’t remember experiencing this before, but that is what I think is happening. Theoretically this distortion is at the lowest possible volume level of the pedal (without being turned all the way off). So this artifact should be rather quiet, but if there is a lot of gain added to the signal after the volume pedal then this sound will get boosted more into the audible range. One thing you can do is to change gain structure of your pedal board/amp set up. Keep the gain on the pedal only as high as necessary. Also keep the gain as low as possible after the pedal or change the location of the pedal in your signal path. If you are going straight into your audio interface, be mindful of keeping the gain low on that signal path too (be very careful when using compressors). Doing this will also help with the long turn off time you are experiencing.
If that doesn’t help or is not practical to do, then you might be able to mod the circuit hardware to help smooth out this fast switching of the LED. If you add a very small capacitor between the LED pins (on the both optocouplers) then that should delay the turn on time so that this artifact is less audible. This cap should be very small. I can’t remember off the top of my head what frequency the PWM controlling the LEDs is, so I can’t say what value of cap might work…but you can experiment by trying a variety of capacitors in the range of 100pF to around 5nF. Maybe start with the larger values and work down to see if that noticeably changes anything.
I’m going to be out of town for the next week so I probably won’t be able to respond right away, if you have any questions.
Good luck.
-BrachTyler,
I’m sorry that you are experiencing this trouble. I have some questions for you…
I’m assuming that you built your VPM-1 from a kit…is this correct?
Has it ever worked correctly, in that the volume quickly decays instead of slowly fading out in the heal down position?
What is your pedal’s serial number?
-BrachThat is true, you have to have a midi controller to recall the presets on the Quaverato. Good luck with the kit. Thanks again for your interest!
-BrachCnpcnp,
Thanks for your interest in the Quaverato.
I’m not an expert with the Vox repeat percussion effect, but from what I’ve heard (from demos on youtube) the Quaverato should be able to get pretty close to it. As with any very old piece of gear, and especially cheaply made gear like the repeat percussion (and all guitar effects from that era), you will find a good amount of variation with how each unit sounds. This is because of the high tolerance components and large variation in transistor characteristics from that era…not to mention component values drifting over the years. From my experience, each piece of vintage gear has its own unique tonal characteristics and “sound” compared to other units of the same model, from the same era. So, if you are trying to match a particular repeat percussion unit, I can’t say if the Quaverato will have the same exact tonal characteristics, but it can definitely get very close to the type of sound the designers of the repeat percussion were trying to achieve.
That’s just some thoughts…
Take care.
-BrachYes, you can run that jumper from C11 to C10, it’s all the same node. But I was expecting you to run these jumpers on the solder side of the board. Use very fine wire (i use 30 gauge), which you can acquire from the inside of old vga cables or something similar. These traces should be run close to the circuit board surface. You should just bend up the mix pot and solder the wire to the correct pad and then bend the pot back down on top of the wire and insulation paper. But to answer your question, you can run the jumper from anywhere on that node.
The resistor should also be placed on the solder side of the board.Jason,
I wrote the troubleshooting guide to be followed from step 1 onward. …as a flow chart of sorts as you answer the questions. It’s probably not the best course of action for troubleshooting, but it’s a starting point. So based on your symptoms, hopefully there is a point in the guide that will deal with that problem. The voltage chart is for reference as the troubleshooting guide directs you to measure certain points on the board.
Let me know if you have questions.
-BrachBen,
I’ve never done this mod, but theoretically it shouldn’t alter the sound. The gain will be different, so you’ll have to adjust the gain trim pot again by ear. But it shouldn’t affect the bandwidth or frequency response. The signal through the optocouplers will be going into a higher impedance (less load), so the response of the LDRs may be slightly different, which you could adjust with the tone trim pots.
-BrachBen,
From looking at the schematic in the assembly manual, you can see 2 noninverting opamp stages and one non-inverting…resulting in an inverted output….so you are correct. If you want to mod your Quaverato, you can turn that last inverting opamp stage into a non-inverting stage by cutting 3 traces, running 2 jumper wires, and adding 1 resistor (10K ohm, or so). The first picture shows the traces that you need to cut (in purple) and the jumper wires you need to run (in green). The second picture shows where to solder the resistor (sorry for the horrible artwork)…soldered to pin 9 from the V/2 rail.
Let me know if you have any questions.https://zeppelindesignlabs.com/wp-content/uploads/2024/05/noninverting-quaverato.jpg
https://zeppelindesignlabs.com/wp-content/uploads/2024/05/noninverting-quaverato-2.png
https://zeppelindesignlabs.com/wp-content/uploads/2024/05/ORIGINAL-MODDED-circuit.jpgBenjamino1979,
Email me and I can give you the latest Arduino code package…info “at” zeppelindesignlabs “dot” com
-BrachNeil,
I’m sorry about this trouble.
I’m not sure what is happening here. Does the frying sound happen when the treadle is stationary, or just when it is moving through the lowest part of its action? There are some interesting things that are happening at the very lowest volume setting that may be causing some sonic artifacts. I’ve never heard of this happening, but I suppose it’s possible.
A question that follows is how much gain are you using on the VPM-1 or after it? If you use a lot of gain, then some of the normally inaudible artifacts might be more audible if the volume is turned up enough.
Also, it may help to re-set the volume level table in your pedal’s software by running the “stereo setup routine” discussed in step E-3 of the troubleshooting guide (if you haven’t done this already).
I hope this is helpful.
-BrachMathias,
I’m sorry about this noise problem. This problem has to do with some of the PWM frequency leaking into the ground path of your power supply. Certain power supplies, (mostly regulated switch mode power supplies) don’t have much filtering on their output, so these frequencies can leak into the audible part of the circuit. Other power supplies (like linear powers supplies) help filter these frequencies out of the audio path. You can verify that this is a power supply issue by using a battery to power up the Quaverato (with a 9v battery snap to barrel adapter). So one thing you can do is try a different power supply. I recommend using a linear power supply for this application.
Another thing that you can do is add a filter capacitor across the microcontroller as described in this post: https://zeppelindesignlabs.com/forums/topic/extra-noise/page/2/#post-25412
This capacitor helps filter the frequency at its source.
Another thing you can do is make sure all your solder joints are not too large and then clean off the flux from the circuit board (as described in another post on that same forum).
I hope this is helpful for you. Please let me know if you have any other questions.
Good luck.
-BrachI’m glad to hear you were able to get the new one working…although I still think you could have successfully repaired the first one. There is a table in the owner’s manual that shows the crossover frequencies based on the dip switch settings. When the phase switch is on the “in” setting, the crossover frequency doesn’t matter because both sides are going up and down the same…there are no frequencies crossed over. But you still can determine the amount of highs and lows you hear based on how the trim pots are set.
I hope that answers your question.
Enjoy your Quaverato!
-Brach
