Mesa/Boogie Amp Bias/Mod...help?

[CapoFirstFret]

So I consulted with Bob at Eurotubes.com and he concurs that my amp badly needs a bias mod to get rid of some flabby low end (on top of a complete retubing with JJ's)....well

I've never had a bias adjusted before! how much will it cost? and will my switch for EL-34's still work or will it have to be readjusted if I try EL-34's? anyone know?




or is there anything I can do on my own to fix this? (yeah I know, doubtful since I don't have the proper tools and gauges but I do have a rudimentary working knowledge of electronics!)

 

[MDS]

Re: Mesa/Boogie Amp Bias/Mod...help?

Mesa's are fixed bias, so if you want to change it you need to convert it to an adjustable bias. Not usually that big of a deal, but I'd recommend letting a tech do it. It isn't super hard, but if you've never modded an amp before I wouldn't suggest starting on a Mesa.

Mike

 

[STRATDELUXER97]

Re: Mesa/Boogie Amp Bias/Mod...help?

Bascially you are replacing a fixed set resistor with an adjustable cermet pot...You need to know what resistor to sub with and what value cermet pot you need...It's not that expensive of a job for any competent tech to do for you though..

When you replace to an adjustable or variable bias pot,the amp is now called "fixed bias" still,but you now can change the bias settings...Kind of an oxy moron...Adjustable Fixed Bias....

 

[JeffB]

Re: Mesa/Boogie Amp Bias/Mod...help?

Your recto should have a "bias switch"...that allows you to switch between a fixed bias for MESA's 6L6 tubes or MESA's el34s....if you use thier tubes it should be real close...but some folks have an adj bias put in so they can use various other tubes.

 

[CapoFirstFret]

Re: Mesa/Boogie Amp Bias/Mod...help?

well mine does have a switch...but many it's flabby and farty as hell on the low end...and all the reviews I've read say that that is not a speaker issue..but that's a bias issue...not enough power getting to each tube.....Mesa/Boogie biases their amps very coldly, and it needs a warmer bias to really tighten up that low end (so the reviews and Bob and eurotubes.com say)

 

[FretFire]

Re: Mesa/Boogie Amp Bias/Mod...help?

well mine does have a switch...but many it's flabby and farty as hell on the low end...and all the reviews I've read say that that is not a speaker issue..but that's a bias issue...not enough power getting to each tube.....Mesa/Boogie biases their amps very coldly, and it needs a warmer bias to really tighten up that low end (so the reviews and Bob and eurotubes.com say)

Mesa amps ARE biased very cold, and that's one reason you have a bit of leeway in the grade of tube you can drop in without having to worry about blowing something :laugh2:. For instance, after talking with Bob I replaced the 4-5 year old stock Mesa tubes in my newly bought Rectoverb with some JJ ECC83S preamp tubes and 6L6GC power tubes. I've since changed the first 3 preamp tubes to a GT Mullard reissue and 2 9th gen Chinese tubes out of preference, but the point is I've had absolutely no trouble with amp with these tubes without having bias adjustments/mods done, and I'm very happy. I'm sure it would be even better if I got the adjustable bias done, but I have ZERO techs around here I'd let in the same room with any of my gear.

I say if you can do it, go for it, it probably won't do anything but improve the amp! Good luck bro.

 

[MDS]

Re: Mesa/Boogie Amp Bias/Mod...help?

I'll second the concept of putting different tubes in without a rebias. I put some JJs in my DC-5 and tried some EHs for awhile too. While I could probably benefit from being able to adjust the bias, my amp definitely improved with the JJs without me changing the bias.

Mike

 

[JeffB]

Re: Mesa/Boogie Amp Bias/Mod...help?

well mine does have a switch...but many it's flabby and farty as hell on the low end...and all the reviews I've read say that that is not a speaker issue..but that's a bias issue...not enough power getting to each tube.....Mesa/Boogie biases their amps very coldly, and it needs a warmer bias to really tighten up that low end (so the reviews and Bob and eurotubes.com say)

Ahh I see what you are saying now....

My experiece with the rectifiers is pretty much the same (flabby low end), though I do think that the V30s they are paired with normally, does contribute to that problem. Does with the F30 combo as well.

Though as you say that may not be the main problem.

Do you run it in the tube rectifier mode? or the SS rectifier/s?

 

[Lewguitar]

Re: Mesa/Boogie Amp Bias/Mod...help?

John and the guys are right! I too recommend getting your amp modded so you can adjust the bias with a pot. My Mark I was modded for adjustable bias and it made a big improvement in the tone to be able to use any tubes I wanted to and to be able to set the bias to my own tastes.

Just do it. No big deal. Any genuinely competant tech can perform the mod in under an hour.

Lew

 

[JeffB]

Re: Mesa/Boogie Amp Bias/Mod...help?

Just do it. No big deal. Any genuinely competant tech can perform the mod in under an hour.

Lew

The thing that has kept me from doing it on my MESA F-50 is that it does void your warranty. I was going to have Trace at Voodoo install it. However, I'm glad I didnt do it cos the speaker blew on my F-50 a month or so after I bought it.

Of course if the amp is out of warranty, like Lew said, no big deal.

 

[Lewguitar]

Re: Mesa/Boogie Amp Bias/Mod...help?

The thing that has kept me from doing it on my MESA F-50 is that it does void your warranty. I was going to have Trace at Voodoo install it. However, I'm glad I didnt do it cos the speaker blew on my F-50 a month or so after I bought it.

Of course if the amp is out of warranty, like Lew said, no big deal.

Good advice from Jeff. I rarely buy anything new so I don't worry about warranties. But you don't want to void your warranty so wait until it goes out of warranty before doing anything that will void it. Lew

 

[Jeff5]

Re: Mesa/Boogie Amp Bias/Mod...help?

How do you have your Boogie EQd? I ask this because Mesas are bottom heavy amps to begin with, and its a common problem ( or feature I guess ) for the bottom end to flub out when too much bass is dialed in. I find that the bass in most boogies is more of a thickener than actually adding bass. You can get that "thunk" without dialing in much bass at all. I'd try playing with the EQ a bit, less base, more mids/highs etc.

 

[FretFire]

Re: Mesa/Boogie Amp Bias/Mod...help?

Do you run it in the tube rectifier mode? or the SS rectifier/s?

Rectoverbs only have an SS rectifier.

 

[Lewguitar]

Re: Mesa/Boogie Amp Bias/Mod...help?

How do you have your Boogie EQd? I ask this because Mesas are bottom heavy amps to begin with, and its a common problem ( or feature I guess ) for the bottom end to flub out when too much bass is dialed in. I find that the bass in most boogies is more of a thickener than actually adding bass. You can get that "thunk" without dialing in much bass at all. I'd try playing with the EQ a bit, less base, more mids/highs etc.

I sold mine a while back. Boogies and Mesas are just not my cup of tea, and for some of the reasons you just stated. I like hearing other guys play through them but not me. I just can't relax with the tone...it's never quite "right". Lew

 

[CapoFirstFret]

Re: Mesa/Boogie Amp Bias/Mod...help?

Jeff that's actually what I'm working with now man...I'm dialing back the bass a bit....you're talking to a reformed Fender player here (I had a couple Fender amps, a 1971 Marshall super bass (Which I sold to get the mesa), a traynor ycv40, and a peavey classic 50)...none of their bass knobs were quite as "hot" as this bass control is.....I'm just having to rework my tone by dialing it back a bit...I'm getting pretty good tones out of it now.... I've got 4 and a half years left on my warranty...*sigh*...I'm not gonna do it til it runs out so I'm gonna have to find the most usable tone and I'm also gonna have to retube the sucker! JJ's should open this thing up a bit and tighten up the low end......thanks guys...this place is definitely the most helpful forum I've ever seen..I got almost no useful responses on a few other boards

 

[JeffB]

Re: Mesa/Boogie Amp Bias/Mod...help?

How do you have your Boogie EQd? I ask this because Mesas are bottom heavy amps to begin with, and its a common problem ( or feature I guess ) for the bottom end to flub out when too much bass is dialed in. I find that the bass in most boogies is more of a thickener than actually adding bass. You can get that "thunk" without dialing in much bass at all. I'd try playing with the EQ a bit, less base, more mids/highs etc.

Agreed. I rarely run the bass past 11 o clock on my F-50, cept on the clean channel.

Tone controls on MESA amps IME are considerably more "sensitive". Not like a Marhall NMV where ya can nearly dime everything and it will still sound pretty damn good Or even better that way.

Once I learned how interactive the tone controls were, I was able to dial out the "fizzy top" and "flabby" bottom end many complain about, without sacrificing anything in actual useful EQ. Did the same on the Dual rec heads I tried at the store too. I still couldn't get it as tight as the F series/Marks, but it was much less "recto" sounding.

And Fretfire, thanx for the info. I was not aware the combo only had the SS rectifiers (all I would use personally on a recto).

 

[CapoFirstFret]

Re: Mesa/Boogie Amp Bias/Mod...help?

yeah I almost bought a F-50...in some ways I wish I did, but in some ways I'm glad I didn't...I'll probably end up getting one it was cheaper than my recto too!!!

And Fretfire, thanx for the info. I was not aware the combo only had the SS rectifiers (all I would use personally on a recto).

Actually it's just on the rectoverbs and solo 50's...they're a single rectifier, and the only single rectifier they have is the solid state one...it's on the dual and trip rectifiers that you have a choice...

 

[Burkwieser]

Re: Mesa/Boogie Amp Bias/Mod...help?

Have your amp switched to adjustable bias!!! I am having my Mesa modded with adjustable pots and some test points. It just makes for easier self biasing.

 

[CapoFirstFret]

Re: Mesa/Boogie Amp Bias/Mod...help?

wow, I also just found out from bob at eurotubes that using anything other than Mesa tubes will void my warranty!! sheesh!

 

[MDS]

Re: Mesa/Boogie Amp Bias/Mod...help?

I think a lot of the issues people have with Mesa's come from not knowing how to use them. People get really used to the counter-intuitive(IMO) fender EQs and start applying that experience to the far more flexible, sensitive, and ultimately more usefule Mesa EQs. I think people generally aren't used to an amp that actually has some mid-range too(Marshall users excepted, of course). On a Mesa a little goes a long way and an astounding number of tones are available once you get to know your amp. I've had my DC-5 for 10 years and I'm still finding new ways to use it. One of the best combos ever. Add a couple of distortion pedals(Fulldrive and Tone Bone HB in my case) for some different colors and you have an extremely wide palette from one simple rig.

Mike