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nicolasoto,
Sorry for the Quaverato trouble.
To be clear, the tremolo effect is supposed to be engaged when the red “effect on” light beside the bypass foot switch is on. Is that not happening with your pedal?
Is the momentary switch not functioning correctly according to the user manual description? Let me know.
-BrachThis is a very strange issue. It’s strange that it is only happening on the high side, but it could be that both sides are affected the same, but the LPF is filtering out the noise on the low side. The fact that the noise seems to change characteristics with the rate knob makes me think that it has something to do with the microcontroller, although I can’t imagine how it would be behaving this way. If you have a USBTiny programmer, you may consider re-flashing the microcontroller to see if that changes anything. If you happen to own an oscilloscope you can scope the PWMs coming from the microcontroller on each side (high and low) and compare the wave forms.
One more thing I wanted to ask is if it behaves any differently when the mode switch is flipped.-Brach
Since you said the sound was coming through only on the high side of circuit (with calibration mode), it must be responsive to the high trim pot. Are you able to manipulate (lower) the volume level of the noise with that trim pot?
I’m sorry for the delay in responding. I just got back in town.
This is a very strange issue. It almost sounds like the PWM from the microcontroller is making its way through the optocoupler to the signal path. My initial thoughts are to ensure that all the components are installed correctly (proper orientation) and to ensure all the solder joints around Q1, opto1, and the trim pot are solid and not shorted to anything. Also ensure that the solder joints don’t have too much solder on them; sometimes this can cause the joints to act as antennas, broadcasting the signal to other parts of the circuit. Also make sure all the components are installed correctly.
Are you testing this with the sine wave function? You should be for these tests.
You mentioned that you adjusted the high trim pot. Please move it in the opposite direction that caused the purring sound. It could be set too high. Ensure that it is working properly; you should be able to turn the high signal off by adjusting it all the way in one direction (25 turns). Does purring sound go away when you adjust it to where all the high signal is gone, or does the purring stay the same or get louder?-Brach
The first thing to try is to do the stereo setup routine, as described in step D-3 of the troubleshooting guide. If that doesn’t fix it then make sure the magnet is placed in the correct orientation, making sure the sticky tape is placed on the side with the black mark. You can also try to take out the sensor board (with the pot block) and use a different magnet to change the volume…move it closer and further away from the sensor as you listen to the volume. Remember the polarity of the magnet matters. That test will at least show you if your magnet is backwards and if the sensor is working properly. Other than those 2 things, I’m not sure what to tell you. I’ve never had this issue before. Hopefully the stereo setup will work.
Good luck!
-BrachPhilip,
Thanks for the questions…
I don’t recommend using a jack/socket for the piezo connections because of its very high impedance. Jack connections will get oxidized over time and that will limit its conductivity. When dealing with extremely high impedance devices, the tiniest bit of resistance on their connections will severely degrade the signal. Remember, high impedance devices have lots of voltage but hardly any current to push through impedances in the signal path. That’s why it’s always best to use hard wire connections in dealing with piezo sensors.There are some complications involved with using Plastidip to insulate the disc. The main thing you need to be mindful of is that the dip will flow away from the edges of the disc causing this area to be susceptible to electrically connecting with the copper tape. This also causes the disc to be slightly domed shaped or beveled. These days I suggest using electrical tape or Kapton tape. But to answer your question, you can use plastidip to coat the disc when it is finished. If you coat it well enough, it will be waterproof and can be used as a hydrophone.
I hope this helps. Good luck!
-BrachIs the Quaverato the only thing in the signal path or are you still using your loop switcher? I remember when we talked last, that switcher seemed to have some weird things going on with it, so you may want to test the pedal without that in the signal path, if you haven’t yet.
I highly doubt that that the Quaverato’s voltage is the cause for the distortion. It currently uses 9 volts, biased to half supply (4.5V), so the signal would have to get pushed beyond those rails (+/-4.5Vpp) to distort. Guitar signals are usually much less than 1Vpp, so it’s very doubtful that an unamplified guitar signal would run out of headroom. Most likely, (if the distortion is happening internal to the Quaverato) the problem is related to an issue with the opamp (TL074) circuit. Check the ins and outs of those opamps to see if they are biased correctly around 4.5V. The schematic in the back of the assembly manual is useful for tracking down signal and voltage problems.
If you really feel compelled to use higher voltage in the Quaverato, 12V will probably be ok to use. The only thing to watch out for is the 5V regulator. If, after a while it starts getting hot, go back to 9V….I can’t remember off the top of my head what the max voltage differential (or wattage) that regulator can stand.
Good luck.
-BrachThanks for telling me about that. That stuff seems like it would make a good grill for some other amps…future projects.
I’m glad you enjoyed the amp building experience! Hopefully you’ll eventually get into designing your own amps…that’s where the real fun is!
Take care and good luck!
-BrachRomeo,
I’m glad to hear you are enjoying your Percolator. It looks really good.
What type of screen are you using for your grill? Did you paint the screen, or did it come that way? It’s really nice looking.
Thanks for sharing your work!
-BrachScott,
Thanks for getting back to me. The resistors that make up the voltage divider are R8A (1k) and R9A (100k). They are located under the output jack, so you’ll have to remove that to access them. Look in the troubleshooting guide to see how to properly remove the jack.
If the pedal that you put after the volume pedal to reduce the volume level was set to unity gain, you might be able to measure the resistance of its volume knob to get an idea of what the voltage divider resistance values should be. Otherwise, you can make note of the signal level change by using an oscilloscope.
With tube amps, the preamp tubes don’t usually offer much tonal change between loud and soft volume levels…this is because they are able to handle a lot of head room giving a relatively clean tone. The real tone (increased odd harmonic distortion) comes from pushing the power tubes hard…but the volume level from the speakers usually gets really loud before they really start sounding good. This is why “power brakes” are used…to attenuate the already distorted tone from the loud power tubes. In your application, you were just attenuating the hot preamp signal, which has too much voltage headroom to break up nicely, while leaving the signal getting to the power tubes relatively low. Since from a tonal perspective, it doesn’t matter if the preamp is turned up or not, I suggest leaving it relatively quiet, so the signal hitting the volume pedal is lower. This way, it won’t bleed through as much when in heal down position.
I hope that makes sense.
-BrachScott,
That is correct about the gain knob, it is not a volume knob, so it doesn’t reduce volume. The circuit itself, does have a slight drop in amplitude when the gain knob is at fully the counterclockwise position, but it’s only a few dBs. The opamp circuits in the pedal are non-inverting, so they cannot lower gain, the lowest they can go is unity. But I’m not sure that lowering the volume/gain level of the pedals is going to solve your problem. It sounds like you are asking for a wider dynamic range of the pedal, which lowering the gain setting will not give you.
You can test if this by adding another pedal (with a volume control) to the effects loop after the VPM-1, and with that pedal set to unity gain, adjust its volume control lower. This will at least give you an idea of weather lowering the VPM-1’s output gain will solve your problem. If that helps the problem you are experiencing, then you could modify the voltage divider circuit on the VPM-1’s output. I can tell you what resistor to change when and if that time comes.
I think what will work better for you is if you do what i was suggesting in the previous post about setting the treadle calibration differently. If you set it to where the volume on the VPM-1 is at 25% in the heal down position, then set the preamp on the amp for a nice sound at a quiet level. Then you’ll have the entire range of treadle movement to turn up the amp. You are already using the VPM-1 in this way, where you get a sound that you like in the heal down position, but if you set up the calibration this way you won’t hear the noise artifacts at the low end of the treadle position anymore.
-BrachBob,
I’m so sorry that I missed this post until now. I’m out of town right now on vacation, so I’m a little distracted.
Anyway, thanks for asking about a pickup for your bass. The Coratado MkII kit sounds like it might be a good fit for you. You might consider modifying it by replacing C1 and C2 with bigger caps…try 12 or 15nF, to allow better low frequency response…it will pick up low harmonics better. I wouldn’t suggest getting much larger than 22nF or so or it will start sounding too big and muddy in the lower frequencies.
Also, you might want to try to add another piezo sensor in parallel to the first one (just make sure they use both the same wiring configuration or you’ll get phase issues). That way you can add one to somewhere around each side of the bridge to get a better frequency pickup range.
In my experience, this should work pretty well for your bass, as long as there aren’t a lot of things rattling around inside of it. Good luck!
-BrachFanyo,
I’m sorry about this annoying journey. In finding out that this same issue happens with another pedal, I’m thinking that there is something fishy going on with your PXL. Normally the footswitch popping occurs when there is a DC offset on one side of a bypass capacitor. When the pedal is engaged the bypass cap allows some of the DC voltage change to momentarily flow through the cap, causing the pop. Pull down resistors can be used to help keep the charge from accumulating on one side of the cap.
If you just need a Boss style buffer, they are really easy to build. You can just follow the schematic from one of their service manuals (look at the TU-2 service manual, for a very simple schematic). You just need one FET and one BJT and a few other supporting passive components. You may consider trying to build one yourself, on some perf board. It would be very small and you could even install it inside the Quaverato chassis, so you could use the Quaverato’s 9V rail to power the circuit with. Perhaps a better solution would be to find out what kind of circuit the PXL is using and modify that. You could even install the buffer circuit in the PXL chassis so this problem doesn’t occur, no matter what tremolo pedal you use.
…I’m just throwing out ideas here. I hope your Quaverato ends up serving you well, despite this annoying issue.
Take care.
-BrachScott,
I’m not sure I totally follow you, but if you want full range of motion with the treadle there is a trick you can do…
You can calibrate the pedal by pressing the first 2 or 3 points at the bottom of the treadle position (heal down) and then equally space out the other points between the bottom and the top of the treadle motion. Each point is 25% of the full range…the 5 points are 0%, 25%, 50%, 75%, 100%. So, if you put the first 2 points at the bottom of the range of motion and then space the other 3 points out equally between the heal down position and the toe down position, then the heal down position will be 25% of the volume, going up to 100% when in the toe down position. Hopefully, 25% of full volume (the heal down position) will set your amp to a level just before it breaks up. I hope that makes sense…and is helpful for doing what you want to do.
-Brach
