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You can test if the LDR is working by unsoldering the jumpers (JP3 and JP4) and measuring the resistance across TP3 and TP4. Keep the depth knob off and the resistance should be relatively low (when the power is on). But you should have already done this when you calibrated the pedal, so I would guess that it’s still working.
When you measure the resistance between R15 (the pin of R15 closest to pin 1 of U2) and pin 3 on U2, what do you get (with the power off)?…I’m wondering if S5 is working properly.
Also, what DC voltages do you get on the pins of U2A, pins 1,2, and 3?The problem seems to be with your bias voltage (called V/2 in the schematic). Pin 10 is directly connected to V/2 and you measured that voltage to be 0V, it should be half of the power supply voltage (9V/2)…around 4.5V. You can see the bias network in the center of the page on the schematic…it’s a voltage divider consisting of R10 and R9, along with C15, C10, C11, and C16. Make sure the pins of C15 aren’t bridged. Also make sure none of the other pins are bridged to anything and everything is soldered correctly.
-BrachThat was quick.
So that tells us that the digital side of things is working properly, so we know the issue is with the analog circuit.
When you turn the gain trimpot up all the way (counter clockwise) do you notice the LFO noise getting louder? I’m just trying to see if that component/part of the circuit is working properly.
It would also be helpful to know the DC voltages of all 14 pins on the TL074, with the depth knob all the way down and no audio signal in the input jack.
By the way, do you hear the relay click when you press the bypass foot switch?
Thanks and good luck.
I probably won’t be able to respond more until tomorrow or monday.
-BrachOk, good.
Now check to see if the LEDs in each optocoupler are working by making a tiny incision on the heat shrink close to the LED’s leads….just a tiny cut, no bigger than 1mm long…just enough to see if the LED is working.
Let me know what you find.
-BrachI just have to ask…are the jumpers soldered properly? Sometimes people accidentally skip that step, or just solder them wrong.
Another thing i wanted to make sure of…are you able to tap out a rhythm on the tap foot switch? …Just to make sure the microcontroller is working properly.
The faint pulsing you hear is probably just the LFO leaking through to the audio or ground path. It’s normal when the volume is all the way up.
Let me know about the jumpers.I’m just now seeing your post from the 12th. I’m sorry that I haven’t been more available to help you. I’ve been so busy with trying to get a new product released, taking care of a very sick 6 year old, and staying up with my baby who’s not sleeping well that i haven’t had time to help you (or anyone else that i’m currently in the process of helping) troubleshoot anything for the past few days. I’m sorry that you took my busyness as “blowing you off”. We are not obligated to help our customers build their kits, but we do it because i have a passion for helping people understand their gear. When someone gets a kit (instead of a ready to play product) part of the process of building it is troubleshooting, which takes a lot of patience. I will do my best to help you, but i can’t guarantee anything because a lot has to do with your skills and knowledge. In our previous posts i think maybe i was assuming too much…I’ll try not to assume anything.
Now, let’s get on to troubleshooting…
I don’t want to assume anything or be condescending, but it would be helpful for me to know if you can read and understand the schematic in the back of the assembly manual. And (also not to be condescending, but) if you don’t understand anything i’m asking of you please just let me know and i’ll explain…we’ll save a lot of time and frustration that way.
The high frequency signal path works, but the low frequency path doesn’t. We’ve narrowed down that the digital side of things is working…the low opto led is lighting up. So we know the issue is in the analog path. You said you corrected the jumpers and now they are soldered correctly. To be sure of that, (with the power off) please test the continuity between pin 1 on U2 (the TL074) and TP3 (they should be connected, test them with your meter’s beep test). Also test the continuity between TP4 and R5 (the pad closest to R19 and R20). These tests will tell us if the jumpers are soldered correctly. Sometimes when the jumpers are heated up too much one of the little rectangular pads can come off the board.
Please make those tests and let me know what you find.Thanks for your interest in the VPM-1.
We don’t do anything to the actual pedal hardware. On the 20 or so units that I’ve modded on used Ernie Ball VP Jr pedals, all of them seem to behave properly…the treadle stays in place when it’s set in one position. It sound’s like your VP Jr may be too worn out to use this way. When I get some time I’ll take the treadle off of one of them and see if there is any adjustments that can be made to tighten the axel up.
-BrachEven in calibration mode there is still no low frequency sound?…after turning up the trim pot? Keep the depth knob fully counter clockwise all the way off when you test the calibration mode.
Make a tiny incision on the heat shrink in the back of low side optocoupler (with your xacto knife), near the the leads of the opto’s led. No longer than 1mm long. In calibration mode, with the harmonic mix knob on the low side, look to see of the opto’s green led is lighting up. If not, turn the low side trim pot all the way up (clockwise 20 times) to see if you can see it light up. If it does light up then you have a problem with the analog signal path, if it does’t light up there is a problem with the led or it’s driving circuit.
Let me know what you find.
-BrachThanks for checking that stuff. That is good information to have.
Are you sure the jumpers are jumped correctly? JP1 and JP2 aren’t connected, are they?Yes, I agree…the loudness is probably just the gain pot over adjusted.
When the pedal is engaged, does it sound different than in bypass (other than it being louder)?
On the middle pin of depth knob…Are you getting a variable DC voltage between 0 and 5V as you turn the knob?…or is it always at some low voltage, close to 0V?
Are Q1 and Q2 installed properly?
Are you hearing both channels (high and low) fine in calibration mode?
-BrachMake sure all the tube pins are making good connection in their sockets. Sometimes it’s easy to over-loosen the sockets when assembling. If pin 2 (the plate) wasn’t making good connection then the screen (attached to the 2k2 resistor) would start drawing too much current. So tighten all the tube sockets.
…But I’d start by turning on the amp without the tube in the socket to see if the problem is just related to the tube and/or socket.
Keep me posted on what you find.
Good luck.
-BrachWhat is your Quaverato’s serial number?
Just as an experiment, try to use a linear power supply instead of a switch mode power supply. In the past we’ve had good luck using liner power supplies or even a battery (with a barrel-to-9v-battery-snap adapter) to get rid of noise issues. If the noise changes when using a different power supply it will help with troubleshooting.
-Brach
