LSC - Feedback Issue??

[Janglin_Jack]

I have had some trouble with my LSC running away with feedback. I am using the drive switch on and the Drive and Gain knobs about 12 oclock. I don't think that is a huge amount of gain. I tried goosing it with an overdrive pedal, and it just goes crazy with feedback. You just let the strings go and it starts wailing.

Is this a bad preamp tube or the nature of that lead channel? Up til now, I hadn't tried OD pedals on the lead channel, but I was trying for a bit more aggressive sound and I was surprized at the uncontrollable noise.

No issues with the clean channel with my OCD AND my Barber LTD Silver AND my Katana Clean boost. I run the OCD or the Silver LTD with the lead channel and look out.

Suggestions?

Jack

 

[jbird]

A bad pre-amp tube will exhibit microphonic squealing even when nothing is plugged in! I believe you may just be overloading the circuit! Try lower gain settings to see if it diminishes!

 

[rockhound76s]

I ran into a little of the same thing with my LSC, although I am not boosting it. One thing I can suggest, (which I remember reading in the manual) was that Mesa recommends keeping the drive control lower than the gain. You mentioned that you have both at 12'oclock. Try bringing the drive down to, say, 10'oclock. If that doesn't give you the "ooomph" you need, leave the drive where it is, increase the gain to taste, and back off the treble to compensate. The treble control dumps more gain into the mix and can cause feedback at high gain/drive settings. Hope that helps.

 

[BottyGuy]

You might want to check if it is Reverb feedback, several people have had reverb feedback problems with the LSS. If it goes away when you cut the reverb level to 0 its in the reverb circuit/pan (you can do that when you hear the feedback). If so contact Mesa.

 

[Janglin_Jack]

I did say that the gain and drive were both at 12, but it is probably more like Drive at 11 and Gain at 1. I also have the treble up high, (around 3 oclock).

What settings are you guys using to get a nice overdriven tone that still cuts? As I turn the gain up where I want it, (say AC/DC overdrive) it is too dark. I thought I found the settings that worked but turning up the treble and presence, but maybe that is adding too much gain in the signal.

Any settings suggestions would be appreciated. I love the clean channel and I was trying to duplicate the sound with added gain. I am using warm reverb switch, 100w diodes, full power with thick switch. Mids around 11 and Bass around 10. :shock:

Thanks,
Jack

 

[JoeVFR]

Jack,
When you turn up the treble, you are dumping more gain into it. Also, as you have probably read, when you crank the gain, you lose some of the tonal controls. I think your gain at 1:00 is okay. Maybe turn down the mids and bass a little instead of cranking the treble.
I also use a TS-9 to for leads, I run the gain at about 11:00. If I run much more, I get the feedback as well and it loses a lot of clarity. I can get feedback when I want it by turning towards the amp.
Hope this helps...
Joe

 

[Mr_You]

My guess would be either a microphonic tube or a pickup has gone bad.

 

[Janglin_Jack]

Jack,
When you turn up the treble, you are dumping more gain into it. Also, as you have probably read, when you crank the gain, you lose some of the tonal controls. I think your gain at 1:00 is okay. Maybe turn down the mids and bass a little instead of cranking the treble.
I also use a TS-9 to for leads, I run the gain at about 11:00. If I run much more, I get the feedback as well and it loses a lot of clarity. I can get feedback when I want it by turning towards the amp.
Hope this helps...
Joe

I will try reduce the mids/bass and keep the Gain down. Maybe it is just really sensitive to an overdriven signal from the OD pedal. I will try with my clean boost and work with the settings.

Thanks,
Jack

 

[Janglin_Jack]

Well, I spent some time with the controls and might have stumbled onto something I should have tried long ago. I switched off the Drive circuit and cranked the gain. I set it to 50watts, tube rectified, I added the Thicker switch and seem to be getting some nice Marshall tones. I think the drive circuit is adding the noise due to the additional gain stages.

Does anyone know what tube is used for the "Drive" circuit? Has anyone tried a lower gain tube in that spot, (like a 5751 or 12AT7)??

Jack

 

[Cheez]

"Thick/Thicker" is not engaged unless you're using the drive... Also, I asked mesa the same question about signal path, and the sent me the schematic - both channels run through V1 and V2. Channel 2 WITH DRIVE ENGAGED uses the A side of V1.

so Ch1 is: V1B -> Ch1 EQ -> V2B -> (V4A&B if verb is on) ->V2A, etc.

Ch2 no drive: V1B -> Ch2 EQ -> V2B -> (V4A&B if verb is on) ->V2A, etc.

Ch2 w/ drive: V1B -> V1A -> Ch2 EQ -> V2B -> (V4A&B if verb is on) ->V2A, etc.

 

[Janglin_Jack]

Cheez,

Thanks for the feedback on the circuits. That was good information, I will try different preamp tubes in V1 to see what happens.

Are you sure the Thick/Thicker switch doesn't work without the drive engaged. I don't have my amp with me to verify, but I think it works without the drive stage engaged. It only works with CH2.

Jack

 

[BottyGuy]

The Thick/Thicker switch works with or without drive engaged, it is merely switches in different capacitors for the treble section of the tone stack. Thick adds adds in 250pf Thicker adds in 500pf. The rest of the tone stage is the standard Fender style.

The tone stack of the Lone star is directly after the drive stage.

 

[Cheez]

Are you sure the Thick/Thicker switch doesn't work without the drive engaged.

...nope, false memory . Guess I should read the manual monthly.



...now I gotta go flick a switch up & down for a half hour!