- This topic has 14 replies, 2 voices, and was last updated 4 months, 3 weeks ago by
.
-
Posts
-
Hi all.
I got the VPM-1 kit a while back. The mod is pretty good but I have one major issue. As I rock the pedal back to the silent position, the sound gets a “frying” sort of crackle to it. As a result, I’ve had to put in a shim that stops the footplate before it rocks back to the silent position which isn’t ideal. It’s like there’s a problem where the circuit doesn’t know whether it should be open or closed so it oscillates between the two states, causing the fry. I’ve tried all sorts of calibration approaches but I can’t get rid of the problem.
Any ideas?Cheers,
Neil.Neil,
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.
-Brach
I am experiencing a similar issue.
I recently got a second hand VPM-1 that was the ready to install version.When I rock back the pedal to the silent position slowly, it get a slightly distorted sound in the last 5% or so of volume decrease.
When I rock the pedal back quickly to go silent before then swelling up another note, it takes about a second for the signal to truly go silent even though the pedal is all the way back. I am recording my guitar straight into my interface with no extra gain. I’m also using headphones so I can hear this clearly. When I use my analog volume pedal this doesn’t happen of course and it clearly goes silent immediately.
I have done the stereo calibration as well as tried several taper calibrations ensuring that the “0” point is not all the way back. Any ideas?
I love this mod for it’s low noise and for the perfect taper for slide playing but the lack of true immediate silence doesn’t work for what I’m doing.
Tyler,
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?
-Brach
Thanks Brach
I bought it from someone and was told it was a ready to install kit where the PCB was populated by you guys.
Serial is ZD46226I used it a bunch last month and I don’t recall this happening but I wasn’t wearing headphones as much so maybe it didn’t stick out. It’s a pretty subtle but I definitely notice it compared to using other volume pedals.
So when I fade up very slowly while playing there’s the subtle distorted sound like a incredibly fast tremolo.
Then, when I kick it back quickly it takes about 1 second for the very low signal to fully go silent almost as if the voltage is taking a second to drain from the circuit or something.
Oops! ZD4626
I’m going to jump back in here. I’ve had a look at the schematic and I can see that there are 2 optocouplers in the circuit, one directly in the signal path. I reckon this is where the issue might be, if the circuit gets to a state where signal is so low that the optocoupler can’t work out if it should be slightly open or closed, so it oscillates between the two states. Could there be a mod that would correct this?
Neil.Tyler,
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.
-Brach
I’m having the exact same issue with my ZD7160 build.
I built the Quaverato kit and it works flawlessly and sounds incredible. I loved it so much, I went out and bought a VP Jr for the express purpose of building and installing the VPM-1.
Although I wouldn’t disagree with the “frying” descriptor, I personally would describe the effect as irregular volume modulation with distortion….a sort of “glitchy” sound that occurs from zero to roughly 5% of max volume. When actuation the pedal quickly, the effect manifests as a sort of jump or dead spot. But the treadle can be kept stationary at the spot where the distortion/modulation is apparent, and the effect will remain persistent indefinitely.
It is apparent to me that the effect is not caused by the hall effect sensor since the exact treadle position in which the effect occurs changes slightly depending on which taper setting is selected.
Hopefully, my comment can add to this discussion and help eventually lead to the resolution of this issue.
Brach, are you confident in the fix regarding the capacitor across the legs of the optocoupler LED? Which one? Both? What capacitor value?
Fanyo,
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.
-Brach
I think I can help add some clarity here! I just installed the prebuilt ready to install vpm1 into my vp jr yesterday.
I’m getting that same distorted/sputtery sound at the initial part of the sweep. I’ve attached a video to demo it. I also throw on a drive just to make it a little more obvious.
I’ve also noticed that in the off position there is some signal pass. Not really a deal breaker but I wish there wasn’t. I’ve experimented with the treadle position several times during calibration to make sure the treadle isn’t all the way down at the start of calibration and still no difference. I agree with the other poster about the signal taking a few seconds to get completely quiet at the bottom position too. It is still audible though.
The distorted noise is my biggest thing. I do a lot of swells and I can hear that initial distortion/sputtery sound when I swell in notes. Even with washy reverb and delay added.
Couple considerations…
– I did disengage my comp, the sound is still there, so even if I put my comp before the volume pedal (which I don’t want to do), I know it’s still going to be there.
– I understand that the pedal being all the way down the sound is insanely quiet and probably not a factor, I still want it to cut out completely.Matt,
Thank you for the video. I hear what you are talking about.
The volume not cutting out all the way tells me that you have a lot of gain after the volume pedal. On the VPM-1 the volume is guaranteed to get reduced to something like -70dB or so (I can’t remember the exact specs). So the signal is never completely gone, but just reduced by a whole lot. This is the way all volume pedals work, even the EB Jr, but in the case of passive pedals the volume is reduced much more, because it gets really, really close to ground level…so it would take tons of gain to make it audible again. With active volume pedals, depending on the volume reduction technology, the volume can only be reduced a finite amount. So in this case, the reduced signal is getting boosted back up again by the following pedals and amps in the chain. We mention in the manual to only use as much gain on or after the pedal as necessary. Unfortunately, because of the gain structure of this pedal, it’s not an exact drop-in replacement for the passive EB pedals…some signal chain gain adjustments may need to be made for it to operate optimally. It’s one of the limitations of the particular technology, I’m sorry about that.
After hearing it, I think the distortion sound is caused by what I was speculating in my previous post. This happens on the very first of the 256 volume level steps. This happens on all VPM-1s but most of the time it’s inaudible because the gain structure is lower. I think a possible mod to help it be less audible is to add a small value capacitor across the LEDs of the optocouplers. I’ll try to look into this when I get a free moment. But I’m sorry for the annoyance and trouble with these issues.
-Brach
Thanks for the follow up Brach.
After gigging with this I realized my frustrations really didn’t matter in a live band setting whatsoever… funny how that works. I’ve been wanting to move to an expression pedal controlled volume pedal with something like the vertex boost.
I bought the expression mod with this unit. I assume all the issues I listed wouldn’t be a problem at all if I went that route right?
Matthew,
That’s correct, you shouldn’t notice any of this weirdness when using the VPM-1 as an expression pedal because it uses different circuitry for that function.
I did have some time the other day to play around with this distortion issue. I placed 10uF capacitor across the LEDs of both optocouplers and it seemed to fix the problem. That was just the only value of caps I had laying around, so it may not need such a high value, but it did seem to work. Theoretically, the bigger the cap, the longer it will take for the sound to decay when you turn the volume off in the heal down position (it works somewhat like a sample and hold circuit). But practically, even 10uF didn’t cause any noticeable delay at reasonable volume levels.
If you do this mod, you just need to be mindful that the square pads are at 5V while the round pads are close to ground potential…so if you use polarized electrolytic caps, make sure the positive lead is on the square pad. You probably could use 0805 sized surface mount MLCC (multilayer ceramic caps) that would fit directly between the leads…and they are not polarized, so their direction doesn’t matter.
-Brach
