Squeal / Squealing

[Brianiac5150]

I've read the few somewhat related posts here, however, thought it useful and/or beneficial to create another post with specific details I've not seen elsewhere. Feel free to direct me to any I may have missed which cover this exact subject.

When connecting directly to my Mark V head I'm now getting a squeal when I have the EQ on (preset or sliders) and am not holding the strings in any way. It is amplified when my right hand gets closer to the bridge PUP and is audible when playing and for the split seconds when the strings are not being touched. This is true with multiple guitars and cables and, again, is only an issue when the EQ is engaged.

All issues go away when the guitar is first connected to the Eleven Rack and/or POD HD500, then the Mark V. The Eleven Rack is usually connected via the front AMP OUT jack and the HD500 is usually 4CM.

This leads me to believe there is some type of "buffer" introduced via these connectivities, along the lines of having a reduced input jack as some amps do.

Ultimately, my concern is that my amp does not have an issue which will become worse and/or cause other problems if not attended to sooner than later.

Any advice regarding this subject would be greatly appreciated?

 

[MrMarkIII]

Prime suspect is a microphonic pre-amp tube. If you do anything other than trouble-shoot or change them one-at-a-time, you are in for days and days of endless fun trying to figure out which tube is the culprit, since you may very well replace a perfectly good "old" tube with a perfectly bad "new" tube.
One-at-a time.
Second suspect is extreme gain and/or EQ settings, since that's when the squealing happens.

 

[Brianiac5150]

It does increase with gain/EQ and I understand how that would be a potential issue, however, I'm still curious about the fact that it does not do any of these things when connected through the 11R and/or HD500, no matter how extreme the gain or EQ settings. I would think if it were solely a tube issue, it would be present all the time, unless there is a decrease in input signal gain via said devices. I do not know for certain there isn't a decrease, however, tone quality does not change +/- with any of the three connections.

I do agree that changing all tubes, as opposed to troubleshooting the specific tube, would be a big time savings.

 

[bandit2013]

If it is tube related, you may be able to invoke the amp into squeal by bumping the top of the amp. Knock on it like you would a door but not too hard. If it sounds like you are tapping on an acoustic guitar (do it with the reverb off) likely one of the preamp tubes has become sensitive to vibration which is also indicate one or more tubes may be mircophonic.

Any device placed between the guitar and amp will compress, alter, attenuate the signal into the amp. Some pickups can produce over a volt, typical amplitude of signal when pots are turned up is between 400mV and 800mV (depends on pickup position, distance pickup is from strings). Another culprit could be a resonating cavity behind the pickup. Filling the air gap behind the pickup will reduce uncontrollable feedback or squeal.

The 5 ban EQ (sliders or preset) will operate as a gain stage. If you select the slider mode, set the EQ sliders at the center point and see if the feedback or squeal is eliminated. (sliders on Center position will not amplify the signal).

You may want to drop the pickups farther away from the strings. I have one guitar that is sensitive based on the cavity behind the pickups and how the routing was made for the wires, Also had the pups too close to the strings. Without touching the guitar strings, just turning up the volume I would wind up with the guitar playing itself. Cured that with foam behind the pups, and dropped them away from the strings just enough to prevent induced string oscillation. Also cured the squeal I would get when playing through the Mark IV lead mode with high gain and drive settings (found it more sensitive than the V).