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Strange volume pedal behaviour

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Strange volume pedal behaviour

Postby insch » Mon Feb 10, 2020 11:12 pm

I have a new issue and I don't know why it's started happening. I have two volume pedals in my pedalboard and each controls a different path. They both share the same initial pedals of the board. What has started happening is that if I have one pedal down I get a decent level out of that path into my amp. The same applies for the other pedal. But when I have them both down volume level gets sucked out of the output overall. It's like the second volume pedla is working in reverse - down reduces the volume overall. It doesn't matter which way round I do this - the second volume pedal is always reducing to the overall output of the board. Any ideas anyone? This didn't use to happen. My pedalboard setup is:

SHARED PATH
Lehle 3@1 (to switch between inputs)
TC Electronic Bona Fide buffer
TC Electronic PolyTune
Digitech Whammy 5
Electroharmonix Freeze
Dunlop Wah
Electroharmonix Small Stone Nano
Maxon compressor
Wampler Tumnus

to

Lehle P-Split II then to

PATH A:
Voodoo Lab Micro Vibe
DOD 440 Envelope Filter
Guyatone Flip Vintage Tremelo
Boss FV-300L volume pedal
to Fender Deluxe Reverb (Vibrato channel)

PATH B:
Boss 500H volume pedal
Strymon Timeline
Neunaber Immerse II
to Fender Deluxe Reverb (Normal channel)
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Re: Strange volume pedal behaviour

Postby Hugh Robjohns » Mon Feb 10, 2020 11:41 pm

Thats a heck of an elaborate pedalboard setup!

I'd bet my chips on the problem being the output of path B being in the opposite polarity to the output of path A, probably because one (or more) of those pedals inverts the signal.

The challenge for you will be identifying which one (or more than one) it is!

One way, if you have a DAW, would be to record both paths on separate channels and compare the waveforms. Try tapping a string against the pickups to generate an impulse waveform which should reveal any polarity issues more easily.

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Re: Strange volume pedal behaviour

Postby CS70 » Tue Feb 11, 2020 12:03 am

insch wrote:I have a new issue and I don't know why it's started happening.

Did u recently changed/moved any patch cables?
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Re: Strange volume pedal behaviour

Postby insch » Tue Feb 11, 2020 12:13 am

Thank you. That makes total sense. I have re-jigged things on the board recently- changing the order of a few pedals and adding the Neunaber and Bona Fide buffer. I wonder how the polarity got switched - I’ll get looking. Really appreciate your help.
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Re: Strange volume pedal behaviour

Postby Wonks » Tue Feb 11, 2020 9:27 am

The polarity of the signals needs to be different, as the two channels of a Fender Deluxe Reverb inherently produce output signals of opposite polarity within the amp (one channel has an extra triode stage). This isn't an issue when just using one channel, or using an A/B switch to select between either channel, but putting a signal of the same polarity into both inputs will result in severe phase cancellation when the two pre-amp signals are mixed and feed into the power section.

This was brought up a couple of years back in this thread https://www.soundonsound.com/forum/view ... 8&start=40

Where the solution was an Orchid isolating transformer and a polarity reversing lead.

You can't simply use a polarity reversing lead because both the signal positive and negative sides will both be tied to ground, so you will need as isolation box in the output to one side of the amp.
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Re: Strange volume pedal behaviour

Postby Hugh Robjohns » Tue Feb 11, 2020 11:01 am

Ooh! Well done Wonks -- I didn't know that about the Fender Amp, but having looked at the schematics I can see the extra triode stage in the Vibrato channel. Oops!

So the amp's two inputs actually have opposite polarities, and hence if you put the same polarity of signal into both channels at the same time they will tend to cancel each other out.

This implies that the two outputs of the OP's pedal-board are currently of the same polarity, and so one needs to be inverted if both outputs are needed at the same time.

The solution described by Wonks will work with a bit of custom wiring, but it may be that a pedal can be found that inverts anyway (or one removed or reassigned within the current signal chain).

It seems there are inverting pedals a-plenty, as this thread on the Gearpage documents:

https://www.thegearpage.net/board/index.php?threads/list-the-pedals-that-invert-phase.796444/

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Re: Strange volume pedal behaviour

Postby Wonks » Tue Feb 11, 2020 11:05 am

Hugh Robjohns wrote:It seems there are inverting pedals a-plenty, as this thread on the Gearpage documents:

https://www.thegearpage.net/board/index.php?threads/list-the-pedals-that-invert-phase.796444/

H

But you'll want one that always inverts (as most only invert when 'on'), which does severely limit the selection. So just those with the dark blue comments.

And you won't want two inverting pedals in the same branch!
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Re: Strange volume pedal behaviour

Postby Eddy Deegan » Tue Feb 11, 2020 11:07 am

Hugh Robjohns wrote:I can see the extra triode stage in the Vibrato channel. Oops!

Ahh the familiar old "extra triode stage in the Vibrato channel" thing. Yep, I should have spotted that immediately. Kicking myself!

Excellent insight Wonks! :clap:
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Re: Strange volume pedal behaviour

Postby Wonks » Tue Feb 11, 2020 11:10 am

I just remember these things. I didn't know about it myself until DC's post two years ago (which only seems like a few months back to me).
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Re: Strange volume pedal behaviour

Postby insch » Tue Feb 11, 2020 11:28 am

Wow - you guys are great - thank you so much.

The strange thing is that I have been using this setup for years without issue but I think I have found a solution (and maybe the cause). When my chain splits into the A and B legs it does so through a Lehle P-Split splitter box https://v3.lehle.com/_data/products/P-S ... -II-EN.pdf and that box has the option of inverting one of the outputs by 180 degrees. I have now done that and my problem has gone away. I guess this switch might have been inadvertently changed at some point which caused the problem. But either way, now the issue is gone.

Thank you for your help :thumbup:
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Re: Strange volume pedal behaviour

Postby Hugh Robjohns » Tue Feb 11, 2020 11:39 am

:clap: Ah yes... the old polarity inversion switch trick... :lol:

Well, at least we identified the right cause and a host of possible solutions!

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Re: Strange volume pedal behaviour

Postby Wonks » Tue Feb 11, 2020 11:56 am

I thought it must be something basic like that, but without knowing the kit in detail, it's very hard to know. And you may have added a pedal or something since you last used it when working. But glad to know it's all sorted and working again. Next time, you'll know exactly what to do!

If you ever swap to using use two amps instead of one, then you'll probably want to swap the reverse polarity switch back again, though it may still depend on the amps and if they have reversed polarity with respect to each other. You won't get the same volume drop as before, but still worth experimenting with the polarity switch to see what sound better to you, as one position may sound rather 'sucked out' compared to the other.
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Re: Strange volume pedal behaviour

Postby insch » Tue Feb 11, 2020 12:07 pm

I do hope to go to two amps at some point and will def play with the polarity when I do. Thanks again.
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Re: Strange volume pedal behaviour

Postby Wonks » Tue Feb 11, 2020 12:07 pm

:thumbup:
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