Mesa Walkabout Megathread!

[Vic]

That's the way I was seeing it.... but I've been wrong so many times before

K

Well, if you're careful not to turn it up too loud, sure, anything can be made to operate safely... I can drive a Ferrari Enzo on the city streets too, but you KNOW what's gonna' happen someday, which is why I drive a Mazda. No chance that THAT amount of potential power is gonna' get me in trouble.

P.S. Hey K, yeah, I posted in that cab thread, cool potential there, I'll be watching to see what LDS does for sure...

 

[tombowlus]

In other words, again, when Tom was pushing the tar out of that one speaker config, he was basically "over"pushing that cab to get the SPL he wanted, so I think he was beyond the efficiency range of that config, so he was really demanding a lot of both the amp and speaker cab, which is why the amp got so hot.

That's my working theory.

 

[junglebike]

Interesting thread... Remember, it's current, not power, that heats up electrical components. Let's see if this makes sense...

P=IV ; Power (W) = Current (Amps) * Voltage (Volts)

V=IZ ; (Z=Impedance, ohms)

P=I(^2)Z

So... halving your impedance (4 to 2 ohms) at the same power output will quadruple your amp's current draw, and thus also quadruple resistive heating of its components! *this is assuming a 100% efficient power amp...

BUT...

SPL~P*Efficiency

Two cabs generally increase efficiency by 3db, right? Which is equal to approximately a doubling in electrical power. So you'll turn your amp down by 33% to get back to your original SPL, reducing resistive losses some, but not all.

BUT BUT BUT...

It doesn't really work that way, because amps aren't 100% efficient (or else they wouldn't need cooling at all...duh...). So the less efficient your amp is, the more dramatic the increased resistive heating due to lower impedence cab.

 

[Vic]

Interesting thread... Remember, it's current, not power, that heats up electrical components. Let's see if this makes sense...

P=IV ; Power (W) = Current (Amps) * Voltage (Volts)

V=IZ ; (Z=Impedance, ohms)

P=I(^2)Z

So... halving your impedance (4 to 2 ohms) at the same power output will quadruple your amp's current draw, and thus also quadruple resistive heating of its components! *this is assuming a 100% efficient power amp...

BUT...

SPL~P*Efficiency

Two cabs generally increase efficiency by 3db, right? Which is equal to approximately a doubling in electrical power. So you'll turn your amp down by 33% to get back to your original SPL, reducing resistive losses some, but not all.

BUT BUT BUT...

It doesn't really work that way, because amps aren't 100% efficient (or else they wouldn't need cooling at all...duh...). So the less efficient your amp is, the more dramatic the increased resistive heating due to lower impedence cab.

Except for "Two cabs generally increase efficiency by 3db" part (which I didn't realize, and is very interesting), this is the more detailed version of what I was getting at, but from the perspective of voltage. For a cone to move a certain amount, the amplitude of the voltage has to be a certain value, and at a lower impedence, requires more current (as you point out, if voltage stays the same and impedence goes down, current goes up).

However, this adding cabs to add efficiency thing is what KJung was talking about, which I didn't think would be as significant as you pointed out... interesting... so, even though you're moving more speaker material and hence more air, and basically increasing the amount of physical work being done, that doesn't much factor in?

 

[JJBluegrasser]

Okay guys, I just thought of an idea. My rig 2 iterations ago was some 'stuff' into a PLX1602, into my EA cabs. I've still got the 1602 in a PA setup along with compressor, and 31 band EQ.

I could buy a 4ohm 2x10 or 4x10 for use with the Walkabout at lower (non transistor melting) volumes, and if I ever wanted to crank it, I bet I could use the DI on the Walkabout into the 1602 and use that as a slave SS power amp.

Since the DI on the Walkabout is post preamp, I guess I should get the same Walkabout tone just replicated in the PLX. I'm not sure about the gain on the DI output, but since it's got it's own knob, I ought to be able to do this. Anyone tried this?

Interesting... I'll try it tonight and report back.

 

[Vic]

Okay guys, I just thought of an idea. My rig 2 iterations ago was some 'stuff' into a PLX1602, into my EA cabs. I've still got the 1602 in a PA setup along with compressor, and 31 band EQ.

I could buy a 4ohm 2x10 or 4x10 for use with the Walkabout at lower (non transistor melting) volumes, and if I ever wanted to crank it, I bet I could use the DI on the Walkabout into the 1602 and use that as a slave SS power amp.

Since the DI on the Walkabout is post preamp, I guess I should get the same Walkabout tone just replicated in the PLX. I'm not sure about the gain on the DI output, but since it's got it's own knob, I ought to be able to do this. Anyone tried this?

Interesting... I'll try it tonight and report back.

It should work, in fact, because the DI is wired completely stupid, it should work well.

Basically, the output of the DI changes if you change ANYthing on the amp... yep, including the master volume (as well as the gain, eq, and DI control). IMHO, it definitely should not alter when you adjust the master (which should be stage volume ONLY.)

If the DI was wired "right", you'd use the DI control for the PLX master and the master to control the Mesa. However, in your config, the master would be an overall master, with the DI being a "trim/balance control" for the PLX, which might be convenient.

 

[SnoMan]

I'm confused.

see if this is correct.

I set my stage volume up on the mesa. Lets say, keep the DI at noon. Could I then turn the DI down/up to suit the system?

 

[Vic]

I'm confused.

see if this is correct.

I set my stage volume up on the mesa. Lets say, keep the DI at noon. Could I then turn the DI down/up to suit the system?

yeah, but the "problem" is, if you change your master volume because you want to be a little louder on stage, the DI output ALSO increases.

In a NORMAL config, the DI is BEFORE the master volume, so you can "set/forget" for the production staff and adjust ONLY your stage volume as needed using the master withOUT affecting the front mix from the DI.

On the Walkabout, you can't do this. Period.

 

[SnoMan]

Thanks.


This will work for me.

My plan is to have my Mini12+airheadWalkabout Combo(Jorg's assymbling it now) and run it into a schroeder 310212 airhead with a poweramp.

I could use the master on the Walkabout to control that entire setup.


I'll just buy a regular DI box and run it through the FX loop on the walkabout to run to FoH.




it'll work for my purposes at least

 

[JJBluegrasser]

Vic,
I wonder if Mesa was thinking about this possibility when they designed the DI circuit?

Jason

 

[Vic]

Vic,
I wonder if Mesa was thinking about this possibility when they designed the DI circuit?

Jason

They should have been, but clearly weren't. Why I'm (so obviously) frustrated is, with all their practical experience, they should've known better.

If I were to guess at "why", I'd say it boiled down to ease of design, as opposed to ease of use and real-life practicality, which was a mistake. You design once. Your customers use repeatedly.

It's not annoying enough for me to sell the head of because of it, but it's annoying enough that I'll probably use its DI out as little as possible.

All this said, I wouldn't be nearly as cranky about it if I didn't really love the head, so keep that in mind while I'm bashing it as well. All you fellow Walkabout owners out there, I'm still a huge fan of the head. I just wish...

 

[Vic]

Oh, here's the other part to it I forgot to mention. I think I also found out adjusting the master volume changes the output of the effects send, which basically makes the effects loop extremely hard to use. I'll have to double check this, but I think that's also the case.

In my case, that's not a huge problem because I rarely use pedals, and when I do, they're before the head anyway, but as long as I'm rubbing salt in my own wound here...

 

[junglebike]

If you read the Mesa Walkabout manual, it mentions the reasoning behind the variable send levels. They say they'll mod the amp for you so that it functions "normally" if you wish, but it will compromise the tone of the amp. I think it has to do with the tube preamp circuit, but the manual is kind of vague about this.

 

[Vic]

If you read the Mesa Walkabout manual, it mentions the reasoning behind the variable send levels. They say they'll mod the amp for you so that it functions "normally" if you wish, but it will compromise the tone of the amp. I think it has to do with the tube preamp circuit, but the manual is kind of vague about this.

Yeah, I know about the mod, but I consider a "solution" that compromises tone to not be a solution, and I won't do it on mine. There's no justifiable technical reason why it has to be this way. There's great tube and hybrid designs out there that don't. Eden is one I know of, I believe Demeter is another, most likely Ampeg, SWR, and very probably MANY others.

No excuse. IMHO, they simply screwed up and their workaround is unacceptable... at least for me.

Pobody's nerfect, tho, and I am still generally very happy with the head. That DI thing is just (clearly) a thorn in my side. That's all.

 

[JJBluegrasser]

I'm kind of excited about the mistake Looks like it will work really well for my needs

J

 

[Vic]

Here's the text from the manual...

NOTE: The DIRECT OUTPUT signal is derived from the driver stage and the MASTER control is active at this point, affecting the overall signal strength available from the DI LEVEL control. While this may, at times present an inconvenience under certain live performance applications, the added tonal benefits of this toneful stage at the DIRECT OUTPUT are well worth the occasional compromise. If you must have true independence between these two controls - and cannot learn to work with the stock scheme, contact us directly and we can fax you a simple modification you can do that will remove the MASTER and its associated stage from the DIRECT signal path. However, this will result in degradation of the sweet tube character and while you will gain independence of the controls...you will trade a substantial measure of tone.

So the way this reads to me is, they're deriving the DI off the output side of the power amp driver tube which is controlled by the master control, and therefore is strictly variable.

I believe this tube's job is specifically to get the amp to sound as much like it had a tube power amp as possible.

I'd take this to mean that, if you did their mod, it wouldn't sound as good as it currently does, but might still sound as good as other amps which tap the DI before this final gain stage (or otherwise have a different design where there's no benefit to be had by moving the DI tap point).

A lot of assumptions here, but if they're all true, then I can see their point, but I'm still not sure I'd prefer this design... then again, I do more live performance than recording, too. My primary concern would be that, if it still sounded very good, but not "as good" (in at least their opinion), then I'd accept the mod, but I'd probably do it myself and make it switchable so I could have it either way any time.

 

[JJBluegrasser]

So I just tried the experiment I mentioned above. It seems like it worked just fine. No horrible noise and the volumes seemed pretty matched with the same Wattage going from the QSC to each 8 ohm EA Cxl 1x12. I'm assuming all 3 speakers in this experiment were getting the same power.

Scout internal speaker: 300W @4 ohms <-Walkabout
EA Cxl 1x12: 300W @8 ohms <-right channel of PLX 1602
EA Cxl 1x12L: 300W @8 ohms <-left channel of PLX 1602

Test done with:
American Precision w/ Lindy Fralins and 2 month old TI Superalloy Strings
American Jazz Deluxe w/Antiquity IIs and 3 week old TI Superalloys.

Nothing sounded bad, so I believe I'm calling the experiment a success. However, I think I've pretty much come to the conclusion that the EAs are not for me. I tried various tweeter settings, and it all just sounded so much more brittle than the Scout.

I bought them originally because I was playing a lot of upright, but now that I'm playing electric more and more, I keep going back to the sound coming straight out of the Scout. I'm hoping that the Mesa 2x10 of 4x10 I'm searching for will give me what I want.

Tom, now I understand why you have so many cabs. I don't think the EAs are bad, they're just not my sound. I guess you really do just have to try EVERYTHING!

Jason

 

[junglebike]

Yeah... I was wondering how a passive mid control could possibly be boost/cut. Does that mean that 5:00 on the mid control is flat?

In re: the effect of the DI mod affecting tone very adversely, anyone else think the manual might not be so accurate?

In addition to minor things such as a few grammatical and spelling errors, there’s that major gaffe about the passive mid knob being boost and cut, and in re-reading the section one the active tone controls recently I was left wondering if it was fantasy – supposedly as you boost the frequency range broadens only to a point at which it stays fixed while the level of boost increases, and if cutting it acts differently and on a different frequency range than the one affected if boosting. Not saying it can’t be done, but that seems very unusual to me and a bit unlikely for such a simple and small amp.

 

[tombowlus]

However, I think I've pretty much come to the conclusion that the EAs are not for me.

Well, if you are only basing that upon the audition of the CxL-112, then I'd say that it's more accurate to say that the EA CxL-112 is not for you. IMHO, the CxL-112 is my least favorite EA cab (though I know that others really like it), and I think that some of the other cabs, like the Wizzy and NL-210, sound far different (and pair up better with the Walkabout, too).

But as always, personal preference rules the day.

Tom.

 

[KJung]

MID: This is the only passive style control in the string of rotary tone controls. This scheme was chosen for its inherently musical blend and for the way the passive style midrange control, with its wide spread and smooth taper, fills in the holes. Unlike the BASS, this control is a boost only, and while it can competently remove this broad spectrum of midrange from the mix, it cannot provide the extreme attenuation of an active style control.

"

There is a post somewhere on this thread explaining that 'passive' mid control. It's not what most of us consider totally passive (i.e., cut-only), and the 'flat' setting on the mid control on the Walkabout is definitely not 'all the way up' or 'all the way down'. It is actually a 'boost' passive control, which is kind of counter-intuitive, but the explanation posted a while ago made a lot of sense. It came from a discussion a TBer had with a Mesa tech.

Sorry that I can't remember the technical description, but it is an unusual 'boost' passive control. There's a more technical description vs. the more 'marketing oriented' blurb posted above from the Mesa documentation.

Maybe someone can post the correct scoop on this, since that mid control IMO really does define the Walkabout's tone in my experience with it.