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This sounds like there is a bad connection in the signal path somewhere…possibly a short or an open somewhere. Judging from the fact that reflowing some solder joints fixed the testpoint readings, it seems likely that you probably have some other bad solder joints somewhere. I’d very carefully re-flow all the joints on the board, particularly in the signal path. Take your time with this because pads can easily get bridged.
Good luck.
-BrachI’m sorry, that’s got to be frustrating.
It can be kind of tricky the first time you try soldering these jumpers. Try using more solder and quickly rubbing the tip of the soldering iron across both pads until they stick together. You’re basically scraping across the surface of the PCB very lightly and quickly while you add more solder.
You can always just use a very short piece of wire too, like a lead that you cut off a resistor earlier, to jump between them. Use a very short length (about 1/8″ max), hold it with some tweezers as you bridge the jumpers.
Sorry for the frustration, and good luck.
-BrachOn those test points you are measuring the LDR’s resistance with the LED on, so if you have no reading it could mean that the LED is not on, which would make the LDR’s resistance very high (practically open). So make sure your LED is actually on. Measure the voltage across it with the depth knob fully counter clockwise (it should have around 1.8v dropped across it…compare it to the LOW side LED). Make sure it’s installed correctly. (When it’s off) Use your multimeter diode checker to test if it has the same reading as the LOW side led (make sure you measure both LEDs the same way…red on square pad, black on the round pad). Make sure all the solder joints are solid and there are no opens or shorts anywhere in that circuit.
Let me know what you find.
-BrachAssuming the solder jumpers are open, when you measure across the test points, you are actually measuring the resistance of the LDR in the optocoupler. When the LED is off the resistance should be very high (practically open) and when the LED is on the resistance should be relatively low depending on how bright the LED is (which is determined by the trim pot). If the resistance won’t get above 1K then this tells me there is most likely something wrong in the optocoupler circuit. Make sure everything is installed correctly and all the solder joints are very solid (and noting is open or shorted) in that circuit. Make sure the jumpers are open too, that would really screw up your readings. It is possible that the trim pot is bad, but that is not likely. If everything else looks good then you can check your trim pot by measuring the resistance across it’s outer most pins while the power is off. You can check your readings against the LOW trim pot resistance measurements to see if they are similar.
Let me know what you find.
-BrachAaron,
How are you measuring the resistance of the trim pot? Is it in the circuit or is it out? Are you measuring across test points 1 and 2?
The clicking you hear happens when the trim pot is maxed out in one direction or the other. It’s normal.
-BrachMark,
It’s great to hear that you are enjoying your Quaverato. Let me know if you have any more questions.
-BrachThank for the post Mark.
Yes, what you’ve discovered is expected for the Quaverato. This happens because the high frequency signals have much less impedance going through the pedal input and U2A (the first opamp stage) than the low frequencies. You should be able to adjust the HPF and LFP trim pots (while testing it inline with a buffer pedal) to make it sound more natural. If you want to go deeper, a mod you can do to reduce this effect a buffer has on the brightness of the pedal is to add a capacitor in parallel to R3, which will allow the high frequencies to pass around U2A without being amplified/buffered.
That may be more information that you wanted to hear, but hopefully that answers your question.
Take care.
-BrachTimTom,
Thanks for bringing that manual discrepancy to our attention, but upon reviewing the manuals i’m not sure what written instructions and image are referring to in the manuals. We definitely want to make the manuals as clear a possible so I’m really interested in making these changes…so let me know what image and pages you are referring to.
It sounds like you will have to play around with the HPF and LPF trim pots to get the tone you are after. Just to make sure both optocouplers are working correctly, start up the pedal in “calibration mode” with the depth knob off (fully counter clockwise) and adjust the harmonic mix knob so that you can tell if both optos have signal going through them. It sounds like they are probably both working because of the issue of it sounding very bright when driven by another pedal…but just double check, if you haven’t already. But the brightness thing is an interesting issue. I think this is happening because the high frequencies have much less impedance getting into the pedal than the low frequencies (because of C1). You should be able to adjust down the HPF trim pot to make up for this. Another fix would be to put a capacitor in parallel with R3 to keep the high frequencies from being amplified/buffered by U2A. If you want to try this (it shouldn’t be necessary) , a 1nF cap would roll off at 15kHz, that would probably be a good value to start with.
Good luck…and please let me know about that manual discrepancy.
-BrachWow! That certainly is an anomaly.
My first thought is a power supply issue…try getting power from a different source.
Something else to check for is microphonic components. With the Quaverato plugged in to an amp, tap on various components on the PCB with a (non-conductive) plastic pen or something to see if you can hear ringing.
Has it always done this or did it start recently? Have you tried unplugging your guitar from the cable to make sure it’s not somehow the guitar? Just to be safe, have you tried a different input cable?
Keep me posted.
-BrachIs the Quaverato powered on when you are taking these measurements?
You are actually measuring the resistance of the LDR (not the trim pot) when you measure across TP3 and TP4. The trim pot just adjusts the maximum current going through the LED controlling the LDR.
-BrachThe Fender Brownface used around 150Hz for the low pass and around 700Hz for the high pass.
Good luck!Thank you so much!
I’m really looking forward to playing with these things. The links you provided are really getting me inspired to start designing some new things with piezo film. I’ll make sure to use a heat sink when soldering them. Thanks for the heads up. Please keep us posted with how these work in your application of drum mics with the Cortado. I fear they may have too much gain, but there are ways around that.
Thanks again and good luck!
-BrachWow! Certianally! Thank you very much for the offer.
Our address is:
Brach Siemens
Zeppelin Design Labs
2950 N. Western
Chicago, IL
60618I’ll play with them and see what I can figure out. I’m noticing the datasheet has some interesting information presented as experiments that the manufacturer has done. What devices do you harvest these things out of?
Thanks again!Russek,
I actually haven’t tried that, but theoretically it should work. One thing to be mindful of is that often time PVDF piezo sensors are is more sensitive than PTZ piezo sensors, depending on the application. So you may have to reduce the incoming voltage via a voltage divider to account for the possible higher voltage input to the Cortado.
Now that you’ve got me thinking, I’m going to get some film piezo sensors and do some experiments when I get the chance. Thanks for bring it up.
Good luck.
-Brach
