Squealing/howling - how to prevent

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mace

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Hi,

Tonight at practice the TC-50 was up to bat. All was well in channel 2, gain at noon, tight, crunch heaven. Channel 3 however, was having issues. My guitars (a PRS with Seymour duncan Mark Holcomb pick-ups, a JP IX with the Liquifier/Crunchlab set up) would both howl around when not being played, even with strings fully muted. The only other time I've experienced this was with the Rectoverb cranked, I figured it was a Rectoverb thing. When the guitars were being played, there wasn't any problem, just when stopping and holding the strings the guitars would howl.

The settings (o'clock): EL34 tubes, Channel 3 Tight, Gain 2:00, Master 1:30, Pres 1:00, Treble 12:00, Mid 10:30, Bass 9:00 , Output 10:30. Amp was on a concrete floor in a double garage. I was maybe 5-10 feet away from it. I put EL34s in before practice because I figured the extra power (vs. 6V6) would be needed with these guys (GnR, old school Metal 80s-90s). Room was pretty solid (brick, cement etc.)

Yes, the amp was loud, but not overly so. With the Mark V it can be much louder with no howling around.

Any ideas of what settings to modify (without reducing volume) to prevent the howling? I did knock the bass and mids down a bit when it first started howling, but it didn't help much.

At any rate, I love the tones out of the TC-50 so I'd like to get this to work in the future. Thanks,

Mace
 
I had a squeeling with a guitar that had really hot pickups. Im not familiar with your pickups but maybe it could also be a microphonic preamp tube. Have you tried another guitar?
 
I believe it is the tight mode causing the feedback issue. It works about the same as the Mesa grid slammer but is not adjustable like the pedal is.
You may need to adjust gain and presence to find the happy median. I have been getting feedback with the tight mode on CH3 so I generally do not use it. If you do need it, you may have to adjust your settings to compensate for the gain structure change.

Pickup potting (typically a wax) used on the coil if not sufficient could lead to similar issues. You could always try the foam pad behind the pickups (which would cut down on body resonance behind the pickup that may cause feedback issues. I have a Koa guitar that rips but will feedback without the dead space filled with foam pad behind the pickup. Open cell type works well, compresses easily and does not push back on the pickup unless you pack too much in the cavity. If you have a bleed capacitor on the volume pot, try removing it and see if that changes anything.

Your guitar cable can also play a role, if it is one of those high dollar cables like the Mogami Platinum cables, sound great but makes everything much brighter than I prefer, much easier to get feedback with it so I do not use it very often.
 
Hi,

Thanks for the replies. Always helpful!

Pickup potting - I did that a few years back on an old Japanese 1970's vintage Epiphone I borrowed while living in Germany when it was doing the feedback/howl like this. However, that was at much lower volumes. The potting helped a bit, but it really just changed the frequency of the feedback, made it lower.

The thing about the PRS and Music Man guitars is that I have cranked the living crap out of the Mark V 90 watter Ch 3, Mark IV and IIc+, BRIGHT on, with no issues with these guitars (albeit a different practice room, which was actually smaller, but not as boxy and cement walled as where the TC-50 was howling). The Mark V was with a more or less classic "V" curve (more like a check mark, with the high side on the left) on the EQ and gain at about 1:30-2:30, presence 12 noon, treble maybe noon to 1:00.

Once, months ago, the Music Man was howling with the Rectoverb 25 MODERN cranked (I do not remember the dial settings). So, it must be that the TC-50 Ch3 TIGHT and Rectoverb Ch2 MODERN have something in common as far as the frequency band distribution.

I'll have to do some more experimenting with a couple other guitars with less "hot" pick-ups and also dialing the settings a bit, but this type of aural abuse is something best not done at home. haha

One last questions: Do any of you guys get feedback (with the strings muted silent) with the settings I posted? Just curious.

Mace

PS I always wear custom molded earplugs when practicing, just so y'all don't think I'm a glutton for punishment.
 
I have gotten feedback on CH3 in tight mode, muted strings and not using hot pickups. I chose one of two options, dial back on the volume control or just not use the tight mode (unless the gain was reduced).

It is a bit more aggressive than the Mark V:90W and the frequency response is also different. well lets say before the Saturation mod, I could not dial the gain above 10oclock on the V without instant feedback unless the strings were muted, the second I would pull away though, ouch.
 
To be honest, I think your channel master is too high. My basic settings are: EL34 tubes (stock), Tight, Presence 10:00, Ch. master 11:00, Gain 1:30-2:00, Bass 2:00, Treble 11:30, Mid 1:00 and my Global master is set around 10:30-11 depending on venue/home use. Mine is dead silent with no feedback at all. My main guitar at the moment is a 2017 Charvel San Dimas with a Seymour Duncan JB & 59' in it. Now, mind you I have the head version and am running it through a Recto 4x12 cab, so that will make some difference, but I really think if you lower the channel master a bit you'll notice a big difference. There really isn't any practical or utilitarian reason to have the channel master up past noon. That would be my first recommendation. Hope you solve the problem man, it's a fantastic amp.
 
Daxman73 said:
To be honest, I think your channel master is too high. My basic settings are: EL34 tubes (stock), Tight, Presence 10:00, Ch. master 11:00, Gain 1:30-2:00, Bass 2:00, Treble 11:30, Mid 1:00 and my Global master is set around 10:30-11 depending on venue/home use. Mine is dead silent with no feedback at all. My main guitar at the moment is a 2017 Charvel San Dimas with a Seymour Duncan JB & 59' in it. Now, mind you I have the head version and am running it through a Recto 4x12 cab, so that will make some difference, but I really think if you lower the channel master a bit you'll notice a big difference. There really isn't any practical or utilitarian reason to have the channel master up past noon. That would be my first recommendation. Hope you solve the problem man, it's a fantastic amp.

Thanks for the input. Not sure if I mentioned it but I'm running the stock combo.

You could be right. I was noting that the TC50 sounds a bit thinner than other amps and it was suggested (I think by Bandit) that the channel masters be raised, which might beef it up. Maybe that worked in spades (as evidenced by the incessant howling)!

My old Epi SG has a Duncan JB in the bridge, so I'll try your settings (and suggestion) with the SG and other guitars and see what happens.

Mace
 
the channel master and the gain work together. You could adjust the gain to compensate if needed, this can make things difficult if you are tying to balance channel levels. You can even use the gain as a volume control as I found that the gain setting dramatically influences output volume and or the master volume influences the gain characteristic. Tight mode does change the response in the midrange and upper frequencies as well as the bottom frequency. With the CH2 a boost in bass and reduction in treble reduces the thin character. CH3 tight mode does pose its challenges and I have had some difficulty getting past the howling issue when using it. Finding a setting that works for you may be different that what others may have due to differences in guitars, pickups, etc...
 
I thought I'd add that I have had some howling a couple of times and turned off the reverb and that killed it.
 
Does the howling stop when you turn down the guitar volume? If it continues to howl with the guitar volume down the problem is the amp, most likely a microphonic preamp tube. V1 is the most critical tube.

If it does not howl with the guitar turned down at the settings you want to use, it is either a microphonic guitar pickup or a feedback loop between guitar and amp. Touch the guitar pickup with your pick - does it make a thud, a click or a metallic ping? The latter would indicate a microphonic pickup.

Some pickups may work well under moderate gain and volume but howl with high gain and high volume. Since you don't want to back off on volume, the only other solution is to back off the gain on the amp or the guitar volume.

Good luck
Stephan
 
You can change V1 all you want, this will not effect CH2 or CH3. The key is V3 and V4 on the TC-50 and TC-100. V3 is the tube position for the first gain stage of CH3 and CH4. Note that the TC series has two separate preamp circuits and does not cascade through V1 or V2. If you have a microphonic tube it would be V3 unless you are having issues with the clean channel. Also if you tap on top of the amp an hear a pinging noise it is preamp tube related. (changing channels should not create a pinging noise either if you hear it with the guitar volume all the way down or unplugged). Culprit will be V3 with the TC series amp not V1 unless you are getting the issue with the clean channel too. If this amp was identical in design to the Royal Atlantic, then I would agree with the V1 being the issue. It is a bit different as the roles of the tube positions have changed location.

When using tight, I would recommend dropping the presence control all the way if necessary. Dial in your tone with the tone controls and gain setting and adjust the presence control last. The presence control is not your typical feedback circuit like other amps employ as it is a high pass filter tone control. Look at the manual on tone controls and presence control settings. You can easily dial in a brittle settings if too much presence and treble are used, this will definitely encourage uncontrolled feedback. If you play too close to the speaker cab this can also play a role in your issue. The last option would be not to use the tight mode as this can be an issue with some guitars especially with active electronics.
 
bandit2013 said:
You can change V1 all you want, this will not effect CH2 or CH3. The key is V3 and V4 on the TC-50 and TC-100. V3 is the tube position for the first gain stage of CH3 and CH4. Note that the TC series has two separate preamp circuits and does not cascade through V1 or V2.

Thanks for clarifying this - have not seen the schematic of that particular amp.
 
All you need is the tube task chart that is in the manual. I have not seen the schematics of either TC or RA so nobody leaked those. That is fine with me. I can look inside and figure them out. Many will assume it is a typical cascade set up like a mark series amp. It is but the difference being the two independent preamp circuits and does not share a common input gain stage. That is what is cool about it as well as the Royal Atlantic that it is based on, you can change preamp tubes for the gain channels without affecting the clean channel. Often times I have seen similar comments on the Royal amp but in that case V1 is the first stages for the gain channels and v4 is the fist stage for the clean. V5 on the TC is the FX loop 12AT7 and with the RA it is V3. Just rearranged positions but very similar circuit. I am almost tempted to compare the internals of each to see what can be modified in the RA, probably not worth the effort though.
 
On the weekend at band practice I got a bit of howling and squeal with the TC-50 Channel 3 TIGHT (not while playing). I turned the gain down just the slightest smidge (from maybe 1:30 to 1:15 or so) and all was well.
 

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