Dual Rec - Class A Sensitivity

[RR]

... and the Blue Angel

8)

... and the Maverick

And the Express

tiktok is correct. The rest of MESA are "Vox AC30 Class A Type" (Aiken) not necessarily TRUE CLASS A regardless MESA advertise as "Pure Class A"

 

[simonich]

As far as the Class A and A/B thing, what most people call Class A is sort of a misnomer as *true* class A is single ended and not accomplished with a pair of tubes; rather a single power tube. But that's splitting hairs rather thin for most.

Well, not true. (Read Randall's paper on this topic, here is the link... http://www.mesaboogie.com/US/Smith/ClassA.htm) Class and configuration are different.

First is operating class of the tube. It's kind of hard to explain if you're not familiar with how a tube works, so this is a bit simplified. Class A means the tube is setup such that DC current is flowing all the time. Meaning that when your guitar volume is at zero, the power section is still burning a nominal amount of watts (you don't hear anything because there is no AC current present). Not very efficient. Class AB means the tube is setup such that when idling, there is very little current flowing, i.e. the power draw at idle is very low (though not zero, were it zero you'd have class B, which sucks for sound amplification). The upside of class AB is more efficiency.

Second is the configuration, which refers to how tubes are connected. "Single-ended", "push-pull", and "parallel" are what we usually talk about. In single-ended, the entire signal runs through a single path and is amplified by one tube at a time. In "push-pull" the signal is split in half with each half being amplified by different tubes. In both cases one can bolt on additional tubes in parallel. (Though in push-pull you have to bolt on additional pairs of tubes.)

So, contrary to the quote above, it is entirely possible to build a class A push pull power section. The LSS has one (and also the single-ended option). Though all Class AB designs are push-pull.

There are other things going on like biasing method, negative feedback loop or not, triode or pentode, etc.

Randall's paper does a good job on the details. Though it is a pretty technical article.

 

[RR]

As far as the Class A and A/B thing, what most people call Class A is sort of a misnomer as *true* class A is single ended and not accomplished with a pair of tubes; rather a single power tube. But that's splitting hairs rather thin for most.

Well, not true. (Read Randall's paper on this topic, here is the link... http://www.mesaboogie.com/US/Smith/ClassA.htm) Class and configuration are different.

Randall's paper does a good job on the details. Though it is a pretty technical article.

... VS Aiken Reference. Who effing cares? If an amp sounds great, who cares what Class it is. :x

 

[simonich]

... VS Aiken Reference. Who effing cares? If an amp sounds great, who cares what Class it is. :x

:shock: Don't get tense man.

I don't think anyone is suggesting sound isn't the important thing. But some people are interested in understanding the differences in these amps. What's wrong with that? When people want to know about the differences, I see no problem with people posting the info. And when posted info is wrong, it's fine to post a correction.

And of course those that don't care don't have to read the thread. 8)

 

[CoG]

I have to admit that as much as I love my MkIIIs, my Valve Jr is incredibly fun to play because of the crazy responsiveness. The "Class A" setting on my Marks doesn't feel the same. I think it's really a shame that a lot of more "experimental"-type guitarists go digital, because there's an incredible number of really neat sounds in a Class A amp.

I have a feeling that a Carr Vincent or something like that is likely to show up in my noodlin' studio after I'm 40.

 

[tiktok]

Who effing cares? If an amp sounds great, who cares what Class it is. :x

Usually, the sort of people who take the time to write a thousand posts on an amp-oriented message board.

 

[RR]

Who effing cares? If an amp sounds great, who cares what Class it is. :x

Usually, the sort of people who take the time to write a thousand posts on an amp-oriented message board.

Yeah, I guess with the internet "the information highway" we absorb so much information we over analyze music gear.

Amplifiers and guitars are instruments to make music.

I suppose when we hear a cool guitar solo or guitar riff we could say: "Ah, listen to that Class A amp at work, nice tone." :evil:

 

[fishyfishfish]

So, instead of reading this I should be playing guitar?

 

[twostring]

So, instead of reading this I should be playing guitar?

Nah...

There are many things that are related, but distant enough to be independent. Being a guitar player is one thing, being a tone seeker is another. You don't have to be a perfect guitar player to enjoy messing with different tones. I've known many players that are simply amazing, but they don't know how to get a decent tone to save their life. There are tons of tone seekers that can tell you why a given guitar/amp/pedal sounds good and how it does what it does, but they make the whole show sound horrible. I love to play, but I also love being a gear head.

That put, I'm still wanting to order the parts to expand my valve jr. and make it parallel into one EL-84 tube and one 6V6 tube. It sounds great with the few mods I've done to it (Hammond 125ESE tranny, "fender" mods, upgraded filter caps and a "tweed" style tone control). I think I'll do that first to get my feet wet...I've been itching to build a Trainwreck Liverpool clone for the longest time now.

I would be very interested to see what Mr. Smith could cook up in a small single ended type package.

 

[fishyfishfish]

Agreed on that. I just think that the Dual is not the right animal for Class A type sensitivity, It's more of a stadium beast on the other end of the spectrum.

 

[MrMason]

... and the Maverick

And the Express

tiktok is correct. The rest of MESA are "Vox AC30 Class A Type" (Aiken) not necessarily TRUE CLASS A regardless MESA advertise as "Pure Class A"

I don't claim to know any of the technical aspects of what makes True Class A, but I DO know that the Express' "Class A mode" is wired differently than a lot of what's out there claiming to be Class A but not 100% Class A; hell, it even has a separate transformer for that mode of operation, and has a different output wiring configuration (running on a single tube, btw). All I know is that it SOUNDS great 8)

 

[MikeK]

... and the Maverick

And the Express

tiktok is correct. The rest of MESA are "Vox AC30 Class A Type" (Aiken) not necessarily TRUE CLASS A regardless MESA advertise as "Pure Class A"

Nice article. One thing that it explains quite nicely is that a push-pull configuration can still be true Class A. Also while cathode biasing doesn't make an amp Class A, Class A amplifiers can be cathode biased. What it doesn't do is prove that the LSS in Class A mode is the only Mesa to have true Class A.

 

[nomad100hd]

I think the big argument about Vox's not being true class A is when pushed the drift into AB somewhat. Funny thing is most people mod'ding there VJ's on SE bias them so the go into class AB slightly. One dude says it gives the amp hair! Mesa did at one point make a "class A" rectifier amp. Sounded a lot different i can't remember where I heard the clip. One thing to point out is the rectifiers preamp is class A!

 

[coppa]

can everyone please stop sayign class a its making my head hurt.


there is single ended,cathode biased and you can have as many valves running that way as you want

you can even run single ended with a fixed bias

there is cathode biased push pull again as many vavles as you want as long as its in multiples of 2

and fixed bias push pull same deal as above

I really dont see the big deal. The way the power section operates has a lot less to do with the sound than what the amp was built to sound like. forget about all that junk and just listen and choose your amp based on that.

A recto has plenty of dinamics and you can roll off and get a clean sound too the key is to use the distortion from the power section rather than the preamp.

All the smaller cathode biased or single ended amps get their sounds from the power tubes. That likely has a lot more to do with that touch response than the way the power amp operates.

 

[nomad100hd]

coppa the class and type of the PA is part of how the amp is voiced. The power supply has a lot to do with how the amp responds. You are right especially with the VJ, power amp distortion is a big key to the response. The PA distortion from my mesa is far different than the PA distortion from my VJ. It's more important i guess to a builder than to most guitarist, but understanding how an amp works to get it's tone will help in picking out an amp and mod'ding one. Besides if your not interested than why post on this thread.

 

[coppa]

It just seems like class a is too much of a buzz word for selling amps more than anything else. Its not very specific.
An amp that runs the tubes in pushpull with fixed bias can be just as sensitive and just as fast as a single ended amp.
A trainwreck clone by Komet (based on the trainwreck) is one of most sensitive amps as far as touch response and that Push pull and with a fixed bias. So its really up to the design of the circuit.

 

[nomad100hd]

i've heard clips of a trainwreck a little bright for me but good tone overall. Trainwrecks are designed so the everything clips from last to first. Maybe that is the secret to touch response, that is defiantly how my VJ is set up. What sucks about GC is i doubt you can go in and crank anything enough to see what the PA distortion is like besides a VJ.

I guess try your Rect cranked to pa distortion with a low pregain setting and see how responsive that is. An attenuator might be needed in order to do that!

 

[coppa]

IF you get the recto to pa distortion and roll back it works. really. try it.

 

[RR]

I recently purchased an amp that has a Class A power section that uses EL34s. The touch sensitivity is amazing. Is it possible to get this type of sensitivity from a Dual Rec? Is it possible to convert a Dual Rec power section to Class A from A/B? Anybody but me ever thought about this?

Hey kramerxxx, care to disclose which Class A amp you bought? There's not many Class A amp I could think of other than Boutique amps such as Matchless Chief-something, Bad Cat model, ... or maybe an Orange Model that are Class A.

I think a lot of that touch sensitivity you experience has to do with driving the power tubes and possibly the lower power output transformer.

Not sure you could do that with a Dual Rectifier other than trying the THD yellow-jackets if that gets close what you are trying to achive.

I don't claim to know any of the technical aspects of what makes True Class A, but I DO know that the Express' "Class A mode" is wired differently than a lot of what's out there claiming to be Class A but not 100% Class A; hell, it even has a separate transformer for that mode of operation, and has a different output wiring configuration (running on a single tube, btw). All I know is that it SOUNDS great Cool

MrMason, o-kay, I did not realize that the Express at 5 watt is single end like the LSS. Having a separate output transformer (is it a separate winding housed in the same output transformer?) in this case is actually good. Some of the lower power tube amp "mojo" tones comes the output transformer.

coppa the class and type of the PA is part of how the amp is voiced. The power supply has a lot to do with how the amp responds. You are right especially with the VJ, power amp distortion is a big key to the response. The PA distortion from my mesa is far different than the PA distortion from my VJ...

What is PA distortion?

i've heard clips of a trainwreck a little bright for me but good tone overall

I agree, but I do like the "Dumble Tones" whether its a clone or real thing.

 

[nomad100hd]

PA = power amp. Also i still get the touch responsiveness with my VJ even though i put in a 15W transformer. It added a bigger bass response but didn't rob the response. I don't however get transformer saturation distortion now.

I bet the class A switch just mutes the input of one of the power tubes after the PI. That's how it's normally done to switch back and forth.