You are here

Can a squealing/feedbacking guitar pedal harm an audio interface?

All about the tools and techniques involved in capturing sound, in the studio or on location.

Moderator: Moderators

Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby garrettendi » Wed Apr 22, 2020 9:41 am

I have a pedal that emits a loud squeal when switched on sometimes but not playing. It is tolerable on my amp if I turn the level on the pedal down, but I'm loathe to try it into my audio interface in case I overload something.

This isn't for recording purposes at the moment, just playing around, so the fact its squealing when I'm not playing is not an issue, and its true bypass so no squeals when disengaged. I can fix it properly further down the line, and I can use a VST noise gate in Reaper to help.

Will this loud feedback-y type sound damage the preamps/interface/headphones if its too loud?
User avatar
garrettendi
Frequent Poster (Level2)
Posts: 2326
Joined: Sat Dec 10, 2005 1:00 am
You don't need reverb, just stack two EQs together with a really long cable

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby CS70 » Wed Apr 22, 2020 10:22 am

No, in the interface etc, an excessively hot signal will simply be clipped (which will be perceived as distortion), so you can't really damage audio kit with any audio signal.

A squeal is likely something that's not excessively loud but it just sounds awful (and can damage your ears if you listen to it at too high playback volume).
User avatar
CS70
Jedi Poster
Posts: 7422
Joined: Mon Nov 26, 2012 1:00 am
Location: Oslo, Norway
Silver Spoon - Check out our latest video and the FB page

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby garrettendi » Wed Apr 22, 2020 10:22 am

Thank you kindly CS70! :thumbup:
User avatar
garrettendi
Frequent Poster (Level2)
Posts: 2326
Joined: Sat Dec 10, 2005 1:00 am
You don't need reverb, just stack two EQs together with a really long cable

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby ef37a » Wed Apr 22, 2020 11:06 am

Assuming the pedal is 9V powered the absolute maximum output it could deliver is about 3V rms or 9V peak to peak (with a bang up battery) . Any AI with phantom power must stand the pulse as that juice is connected and removed so no, you won't damage it.

I would also suggest that the whole reason that pedal squeals is BECAUSE it is "True Bypass"!
The input 'load', which is indeterminate, is finnaglled round to the output and there is always the possibility that daft T**Tish designer did not switch a load onto the input when the former was removed.

With a PROPERLY designed bypass circuit you have a buffer and an output circuit and all states remain the same and the switching is done by turning a couple of FETs (sometimes bipolar transistors) on and off.

Rant over!

Dave.
ef37a
Jedi Poster
Posts: 12668
Joined: Mon May 29, 2006 12:00 am
Location: northampton uk

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby garrettendi » Wed Apr 22, 2020 11:08 am

Thanks!

Yup it's 9V powered from a PSU, the pedal is a Behringer HM300.

The AI is the (also) Behringer UMC204HD so has phantom power, although I am of course not using it on the instrument input!
User avatar
garrettendi
Frequent Poster (Level2)
Posts: 2326
Joined: Sat Dec 10, 2005 1:00 am
You don't need reverb, just stack two EQs together with a really long cable

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby garrettendi » Wed Apr 22, 2020 11:10 am

Also just to clarify: the squeal is constant, except when I play the guitar or it is switched off...
User avatar
garrettendi
Frequent Poster (Level2)
Posts: 2326
Joined: Sat Dec 10, 2005 1:00 am
You don't need reverb, just stack two EQs together with a really long cable

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby ef37a » Wed Apr 22, 2020 11:17 am

garrettendi wrote:Also just to clarify: the squeal is constant, except when I play the guitar or it is switched off...

Is the noise independent of control settings?

Dave.
ef37a
Jedi Poster
Posts: 12668
Joined: Mon May 29, 2006 12:00 am
Location: northampton uk

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby garrettendi » Wed Apr 22, 2020 11:17 am

Turning down the level makes it much more tolerable, I haven't tried the other knobs.
User avatar
garrettendi
Frequent Poster (Level2)
Posts: 2326
Joined: Sat Dec 10, 2005 1:00 am
You don't need reverb, just stack two EQs together with a really long cable

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby Hugh Robjohns » Wed Apr 22, 2020 11:34 am

The pedal inherently has a very high gain -- and by your description it sounds like there is an AGC function in there -- so will always be prone to feedback and self oscillation.

You may find that moving the input and output cables away from each other helps to reduce the tendency for self oscillation. Or it could be related to a ground-loop issue with the mains PSU. More likely is that the PSU isn't properly regulating and isolating the supply outputs, so there's either cross-contamination between pedals, or the Behringer pedal is particularly prone to a floppy power supply rail!

It would be worth trying it on an internal battery as an experiment to see...

But there is no need to be conerned about it causing damage to the interface. Your speakers/headphones/ears, on the other hand, is a different story! :-D
User avatar
Hugh Robjohns
Moderator
Posts: 30199
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound
In my world, things get less strange when I read the manual... 

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby garrettendi » Wed Apr 22, 2020 11:35 am

Yes running on battery doesn't cause any sqeualing so I figured it was the PSU. I will upgrade PSU eventually for sure.

Hugh Robjohns wrote:But there is no need to be conerned about it causing damage to the interface. Your speakers/headphones/ears, on the other hand, is a different story! :-D

How can I ensure my headphones/ears are safe with adjusting levels etc?
User avatar
garrettendi
Frequent Poster (Level2)
Posts: 2326
Joined: Sat Dec 10, 2005 1:00 am
You don't need reverb, just stack two EQs together with a really long cable

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby Hugh Robjohns » Wed Apr 22, 2020 11:40 am

Keep the volume turned down!

Interesting that it's quiet on a battery supply. So somehow the audio output is getting back to the input through the supply. You may be able to resolve that by hacking the ground connection in one of the audio cables in the signal chain... But it could just as easily be a problem caused by a contaminated power connection on another pedal, or just a floppy, poorly decoupled power rail.

Does this mains PSU feed other pedals?
User avatar
Hugh Robjohns
Moderator
Posts: 30199
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound
In my world, things get less strange when I read the manual... 

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby CS70 » Wed Apr 22, 2020 11:40 am

garrettendi wrote:Yes running on battery doesn't cause any sqeualing so I figured it was the PSU. I will upgrade PSU eventually for sure.

How can I ensure my headphones/ears are safe with adjusting levels etc?

Always start with all levels down and increase them carefully and with attention.
Have a fast mute option readily available (pulling the plug works in extreme cases).

Basically be aware that every time you turn on a system you may have unwanted noises and be careful accordingly-
User avatar
CS70
Jedi Poster
Posts: 7422
Joined: Mon Nov 26, 2012 1:00 am
Location: Oslo, Norway
Silver Spoon - Check out our latest video and the FB page

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby garrettendi » Wed Apr 22, 2020 11:43 am

Yep, I had aleady planned to let the pedal squeal, and adjust all volumes accordingly form the lowest setting, to ensure that Reaper's Master bus stays green. Then go from there.

Does that sound like the right thing?

Yes the PSU is powering a total of 6 pedals, 5 analogue and one digital (the Boss TU-3 tuner). I have no issues with any of the other pedals, and 3 of the other are also gain pedals, two of them quite high gain.

EDIT: I was also going to mute my headphones until the levels are green in Reaper.
User avatar
garrettendi
Frequent Poster (Level2)
Posts: 2326
Joined: Sat Dec 10, 2005 1:00 am
You don't need reverb, just stack two EQs together with a really long cable

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby Hugh Robjohns » Wed Apr 22, 2020 11:48 am

I suspect what's happening is that one or more of these pedals is allowing the audio signal to modulate the power rail, due to a poor internal design (not unusual), and the power supply unit isn't isolating the power outputs from each other very well (also not unusual).

The result is that the Behringer pedal is receiving a power rail that is being modulated slightly by the audio -- either its own, or from a pedal further downstream, and that audio is then getting back into the high-gain amp's input resulting in feedback and howlround.

A better power supply with properly regulated and isolated feeds would undoubtedly solve the problem.

You might also find that changing the order of the pedals helps, or that removing one particular pedal cures it...

As I recall, there was a discussion here a while back about power supplies and why the good ones are expensive...
User avatar
Hugh Robjohns
Moderator
Posts: 30199
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound
In my world, things get less strange when I read the manual... 

Re: Can a squealing/feedbacking guitar pedal harm an audio interface?

Postby garrettendi » Wed Apr 22, 2020 11:52 am

Yep I will get a better PSU eventually for sure. But for now it's not an option sadly, due to funds.

Will my plans for the setting of level at least protect my headphones and ear? I'll also put a noise gate on the Reaper channel.
User avatar
garrettendi
Frequent Poster (Level2)
Posts: 2326
Joined: Sat Dec 10, 2005 1:00 am
You don't need reverb, just stack two EQs together with a really long cable

Next