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PostPosted: Tue Aug 02, 2016 6:03 pm 
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Mark III

Joined: Tue Dec 22, 2015 12:15 pm
Posts: 283
Think about Class definition.
Taken from Duncan Amp pages.

CLASS A
"The distinguishing feature of class A is that the valve is conducting current at all times. Note the the "Out" current never drops down to the zero line at any time....."

CLASS B
"What about class B? In the diagram on the right, we have set the bias point to where the valve has almost stopped conducting.

Note that the input signal is a lot larger now in order to drive the valve hard enough. Also, the output current is only for half of the waveform.

To make any use of this, we have to have a "push-pull" output stage which employs two valves (or two banks of valves) so that each side amplifies each half of the waveform. While the first output valve provides the output current as shown on the right, the second valve fills in the gap which follows it."

CLASS AB

"By now, you have probably guessed what class AB is - it's somewhere between class A and class B. Where exactly, is up to the imagination!

In our class AB diagram, a small amount of bias current is flowing through the valve. For the output valves in a typical class AB guitar amplifier, this would amount to around 30-40mA, with peaks of approximately 250-300mA.

In the push-pull output stage, there is a little overlap as each valve assists it's neighbour during a short transition, or crossover period."

So in class A, the valve is conducting all of it's current all of the time. Whether that is a single valve or six of them. If that valve ever shuts off, it's not class A, it is then class AB.
Where a class B valve conducts no current unless needed, it completely cuts off and lets it's partner do the work for half of the time.
A class AB valve conducts some current all of the time, not all of it's current like a class A circuit would.

http://www.duncanamps.com/technical/ampclasses.html

Therefore, there is no extended class A, there is simply hotter class AB bias, where the valves are on more than the regular class AB, outer pair.
What I won't do is deny the results of it, no matter how Mesa dress it up in words. It sounds really good. I wasn't a fan till tonight. When I plugged my amp into a Peavey Valveking 4x12. Cheapo speaker cab and the thing sounded divine. If their 2x12's sound as good, I'm having one.

Those readings of 42ma on the inner valves in Variac mode is about 65% bias, colder than I'm used to, firmly class AB.
The 30ma reading of the outer pair in Variac mode is stone cold but still class AB at 45%.

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PostPosted: Tue Aug 02, 2016 8:24 pm 
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Mark III

Joined: Thu Feb 07, 2013 10:45 pm
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bandit2013 wrote:
Given To Fly wrote:
" I will see what I can do to meet the cost target, but if we are dealing in low annual quantities that may not be possible".


:lol: I love this response! Every profession has its own unique way of saying "No."


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PostPosted: Fri Sep 16, 2016 2:58 pm 
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Mark II

Joined: Sun Sep 27, 2015 2:50 pm
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Location: Good ole England
I think that progressive linkage thing would be great. I'd love to be able to run CH1 and 2 EL34 and CH3 6L6. Or any other options it may reveal. Is that what it does? Love tweed with EL34's and CH2. CH3 is also great with EL34's but the option would be incredible. The bigger coupling cap for iic+ mode is a no-brainer along with the bigger transformer too. MIDI as well. And the drive control. Could drop my clean boost then! I like Bandits multi fx loop idea as well. Series and parallel loops both have their pros and cons. Big form factor head as well, changing Pre amp tubes is a nightmare.

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PostPosted: Sat Sep 17, 2016 4:35 am 
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Mark III

Joined: Sat Apr 25, 2015 1:22 am
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Location: MO
bandit2013 wrote:
Is it really that important to debate the method by which Mesa biased the Mark V? The only time the Mark V operates in pure class A mode is in the 10W power setting, amp is reconfigured to operate at a cathode bias and uses one inside tube and the outside tube next to it. In 45W mode, the amp is operating in class A/B (push pull) but the operating point of each side is biased closer to class A than it should be for class A/B. 90W mode just pulls in the outer pair also in Class A/B. Quite similar to the Mark IV but does not have a 10 W mode. If I recall, the differences were in the plate voltages, screen resistors, and the voltage divider network on the pair of tubes. Too bad I deleted the schematics for the Mark IV after I sold the amp (you can find that one doing a search). I still have the schematics for the Mark V (not complete as it is missing the relay control circuits and logic for the footswitch, but is good enough for simple repair if needed). In essence, the Mark V in 45W and 90W is operating Class A/B. If you consider each portion of the Class A/B amplifier, each is composed of a push pull format, extended class A refers to the operating point or load line characteristic of the inner pair of tubes that is closer to that of a Class A but is not a true class A amplifier, it is a push pull or A/B. How this differs from a traditional class A/B amp is that the inner pair of tubes have a lower bias voltage than the outer pair. Inner pair of tubes have a -43.6V on the grid, outer pair have -46.6v on the grid. If you feel the Mark V is operating in Class A in the 45W mode, you are mistaken.

If you want it in writing by the manufacturer, look at bottom of page 3 of the Mark V manual.

copied from the manual:
45 WATTS turns off the outer pair of 6L6s so only the middle two are running. These are the ones with the lowered bias so, while they are still Class AB, their Class A region is extended. In Channel 3, they can be switched to run in Triode configuration which cuts their clean headroom roughly in half.
Combining these two opposite styles of wiring in one amplifier gives you the best of vintage and modern amplifier styles. Headroom and power are there when you need it… but there is always a naturally pleasing and musically curvaceous quality to the sound that
Overview: front panel (Continued)
PAGE 3
is magic to your ears and to your hands. Simul feels great and is inspiring to play!
10 WATTS reconfigures the whole set of 6L6s so that the two nearest the 5U4 run pure Class A, single-ended—no longer push-pull. This is the ultimate low wattage output circuit that duplicates the essence of the best really old vintage circuits. Here, the second harmonic (an octave above the note played) is NOT cancelled out (as it is in push-pull circuits) and provides a magical halo surrounding the notes. Onset of clip is so gradual that it’s hard to pin down the transition from clean to overdriven.

I was under the impression that the 45W mode was class A as well. It is not.


What about the other mark amps with the "class A" switch? If it's anything like the simul-class circuit the V uses then it's not class A, it's still A/B. Isn't that a bit misleading if that's the case? I thought the V was the first Mark with a true class a circuit. Is mesa telling the truth with that class A switch on the other marks?

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PostPosted: Sat Sep 17, 2016 9:02 am 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
The other Mark Amps that have the Simul-Class use the same circuits. Class A is in reference to the push/pull only. In essence it is two class A circuits each out of phase. What it should state Class A push/pull. When I think of Class A, I think single ended, not in terms of push/pull circuit. All of the preamp tubes operate class A single ended, including the PI tube. Most of the products I design do not use negative power supplies as there is not much of a need for that so I have forgotten most of what I learned back in college. I can still remember most of it so I have not lost what was learned. Having a good definition what is Class A, what is Class A/B, what is push/pull and single ended Class A. How does it all work....? This can be found on the internet if you are interested. Perhaps I too should read up on it as it has been more than 23 years since I had designed any audio amplifier circuits.

I think I am getting a better understanding of all of this....
Mark V operates in true class A only in 10W mode only. However, the 45W mode is not a single ended class A, it is a push/pull similar to A/B but not. Center tubes will be operating class A (sort of) but will be 180 degrees out of phase of each other. Still class A as it were but the cross over point when signal is above or below the load line that tube will be amplifying the signal, there is no cut-off at the cross over region, actually there should be no cross over region with the push/pull Class A circuit. In essence this will require the center pair to have a hot bias compared to the outer pair of tubes. Class A/B works differently as such that signal above the bias voltage will cause one tube to conduct and the other will be off, and when the signal drops below the bias voltage the roles switch. This will result in cross over regions. When mixed together, the outer pair of tubes will be operating in A/B mode and the inner pair is class A push/pull. It is finally making sense to me know.

If you ever had any background in electronics and amplifier circuits, term called load line is used. I simplified this by stating bias voltage but it is more in depth than that. In other words, the traditional A/B amplifier uses a horizontal load line (not it will have a slight angle but it is more horizontal) signal that drops below the load line is cut off. Consider it as a half wave signal. For simplicity the A circuit amplifies the positive going signal, and the B circuit amplifies the negative going signal. Class A or extended Class A uses a load line that is ideal at 45 degrees. It will amplify positive and negative swings (signal above load line would be positive, below load line will be negative) Extended class A may refer to push/pull as once circuit is 180 degrees out of phase to the other. Both tubes in the 45W mode are always amplifying the signal and there should be no cross over distortion. The outer tubes when turned on (90w), will only amplify part of the signal. Simul-class blends both together. Sort of neat trick once you mull it over. I never really bothered to understand all of this as it was not important to me.

Now when it comes to the JP-2C, characteristic is very similar to the 90W simul-class sound. I beg to wonder if it is a traditional Class A/B circuit or is there something different in it. I guess I have read over the manual and read the stuff I skipped over as it was the same story provided with all the manuals. Roadster and RA100 are traditional Class A/B amplifiers. Both seem to have their own character that has been difficult to replicate with the Mark V and vice versa. Perhaps the monstrous OT of the JP-2C may have a major role in its character. Now I wonder.....

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PostPosted: Sun Oct 16, 2016 3:43 pm 
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Location: Seattle
Working on my gig rig and just wishing that Mesa would drop a Mark V update with the JP-2C features. ESPECIALLY MIDI CONTROL.

At the moment I'm trying to figure out how I'm going to fit a mini amp gizmo (which I do not own yet) on to my pedal board. It's looking grim.

PS: Midi-selectable channel modes would be hot.

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PostPosted: Tue Oct 18, 2016 9:00 am 
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Mark III
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dlpasco wrote:
Working on my gig rig and just wishing that Mesa would drop a Mark V update with the JP-2C features. ESPECIALLY MIDI CONTROL.

At the moment I'm trying to figure out how I'm going to fit a mini amp gizmo (which I do not own yet) on to my pedal board. It's looking grim.

PS: Midi-selectable channel modes would be hot.


Here is my RJM unit cable tied to the metal screen. I connect the proper cable (RJM cable) when needed between the Gizmo and the amp's switch jacks. I think I need to attach the cable permanently by tying it down with cable ties rather than connecting / disconnecting.


Something you may want to consider for you setup (I'm assuming your pedal board is away from you amp):

With the Gizmo attached to your pedal board, the RJM cable will be a long run back to your amp. Considering the RJM cable is 'specially made' I'd protect this cable as priority and keep it as a short run by attaching the Gizmo to the amp instead, similar to how I have. Having the Gizmo attached to the amp the RJM cable is short and tucked away. You only need to run one standard midi cable from your pedal board to the Gizmo. A standard midi cable is a lot cheaper if it get's damaged with overly excited feet.


RJM unit cable tied. Power lead shown with hooks that I installed. The hooks are simple clothes hooks I bought from a hardware store. I don't understand why Mesa doesn't have hooks to wrap the power lead nice and neat. My Peavey JSX has moulded hooks as standard.
Image

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PostPosted: Fri Oct 21, 2016 9:15 am 
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Blaklynx wrote:
dlpasco wrote:
Working on my gig rig and just wishing that Mesa would drop a Mark V update with the JP-2C features. ESPECIALLY MIDI CONTROL.

At the moment I'm trying to figure out how I'm going to fit a mini amp gizmo (which I do not own yet) on to my pedal board. It's looking grim.

PS: Midi-selectable channel modes would be hot.


Here is my RJM unit cable tied to the metal screen. I connect the proper cable (RJM cable) when needed between the Gizmo and the amp's switch jacks. I think I need to attach the cable permanently by tying it down with cable ties rather than connecting / disconnecting.


Something you may want to consider for you setup (I'm assuming your pedal board is away from you amp):

With the Gizmo attached to your pedal board, the RJM cable will be a long run back to your amp. Considering the RJM cable is 'specially made' I'd protect this cable as priority and keep it as a short run by attaching the Gizmo to the amp instead, similar to how I have. Having the Gizmo attached to the amp the RJM cable is short and tucked away. You only need to run one standard midi cable from your pedal board to the Gizmo. A standard midi cable is a lot cheaper if it get's damaged with overly excited feet.


RJM unit cable tied. Power lead shown with hooks that I installed. The hooks are simple clothes hooks I bought from a hardware store. I don't understand why Mesa doesn't have hooks to wrap the power lead nice and neat. My Peavey JSX has moulded hooks as standard.
Image


I agree that this is the way to go. I'm planning on ordering one by the end of the month.

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PostPosted: Mon Oct 31, 2016 12:00 pm 
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Mark I

Joined: Mon Sep 29, 2014 9:07 am
Posts: 49
dlpasco wrote:
Working on my gig rig and just wishing that Mesa would drop a Mark V update with the JP-2C features. ESPECIALLY MIDI CONTROL.

At the moment I'm trying to figure out how I'm going to fit a mini amp gizmo (which I do not own yet) on to my pedal board. It's looking grim.

PS: Midi-selectable channel modes would be hot.



I solved the problem for my small-ish/backup rig by putting the RJM switcher into a small, 4U rack that also houses the effects that go into the loop and are also switched via midi.

Image[/URL]

For a "Mark 6" I think there have been plenty of suggestions here. I personally figured the Mark V wasn't for me so I'd like to see something that is closer to the Mark IV again. Maybe with a Mark IIC+ mode from the JP2C. And yes, Midi would be great. Dual EQ would be the winner. So basically a 4-channel JP2C with the 3 channels from the Mark IV plus one of the JP2C gain channels. And all that in a more traditional Mark design, skirted buttons, wicker and all. And no famous-person-endorsement logos and stuff please.

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PostPosted: Wed Nov 16, 2016 5:58 pm 
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Mark III
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Here is my idea for the Mark VI: The Mark Modular.

This would be a Mark "chassis", that would accept preamp "modules". The chassis would contain the power amp, fx loop, GEQ, and reverb. There would be slots which would allow you to pop in preamp modules, with each module being its own preamp channel. There might be several versions of the chassis, which would allow either one, two, three, or (why not?) 4 modules, depending on how many channels you wanted. They could also have a "high power" chassis (6L6/EL34) and a low power (EL84). There could be many preamp modules available, allowing the user to customize their setup, and even change it around, based on different needs.

Remember the Seymour Duncan convertible amp back from ~20 years ago? I had one of these for a while, and I think it was a brilliant design. Mesa could go crazy offering various preamp modules, having a module for every sound from every amp they've ever built. (Speaking of signature amps, they could have signature modules...) Imagine having 30 preamp modules to choose from! Also, you could have a stereo setup by adding a simple 1-module-chassis, similar to the Satellite amps they built in the 90s.

I really feel that this would be the best of all possible worlds. The flexibility would be amazing. No more compromising! You could choose the exact preamp sounds you like, the exact number of channels you want, and could change it around from gig to gig, depending on the needs. And Mesa could spend the next 10 years developing new and exciting preamp modules!


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PostPosted: Mon Nov 28, 2016 4:19 am 
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Mark III
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cho wrote:
Here is my idea for the Mark VI: The Mark Modular.

This would be a Mark "chassis", that would accept preamp "modules". The chassis would contain the power amp, fx loop, GEQ, and reverb. There would be slots which would allow you to pop in preamp modules, with each module being its own preamp channel. There might be several versions of the chassis, which would allow either one, two, three, or (why not?) 4 modules, depending on how many channels you wanted. They could also have a "high power" chassis (6L6/EL34) and a low power (EL84). There could be many preamp modules available, allowing the user to customize their setup, and even change it around, based on different needs.

Remember the Seymour Duncan convertible amp back from ~20 years ago? I had one of these for a while, and I think it was a brilliant design. Mesa could go crazy offering various preamp modules, having a module for every sound from every amp they've ever built. (Speaking of signature amps, they could have signature modules...) Imagine having 30 preamp modules to choose from! Also, you could have a stereo setup by adding a simple 1-module-chassis, similar to the Satellite amps they built in the 90s.

I really feel that this would be the best of all possible worlds. The flexibility would be amazing. No more compromising! You could choose the exact preamp sounds you like, the exact number of channels you want, and could change it around from gig to gig, depending on the needs. And Mesa could spend the next 10 years developing new and exciting preamp modules!


Been there, done that....

http://www2.randallamplifiers.com/Amplifiers/MTS-Heads/

http://www.guitar.com.au/amplifiers/ele ... dules.html


The Egnater M4 is another one:

https://www.youtube.com/watch?v=uqWrOUVw0Co

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PostPosted: Mon Nov 28, 2016 6:29 am 
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Mark III

Joined: Tue Dec 22, 2015 12:15 pm
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One thing is becoming clear. Any 'improvements' would be pretty minor in the grand scheme of things.
I think Mesa may have hit the pinnacle with the Mark V.
More channels, just more of the same.
More vintage correct whatever, buy a vintage amp.
Midi, yeah ok, good call.
There's really not much that could be added that hasn't been done before and available elsewhere in the series.
There's a maker of amplifier DIY kits in the UK. Who offers a valve amp kit that doesn't distort but has exceptionally wide ranging eq controls. Perhaps that's the next step for Mesa. An amplifier that doesn't distort.

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PostPosted: Mon Nov 28, 2016 11:19 am 
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Mark III
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Blaklynx wrote:
Been there, done that....


Yeah, but Mesa hasn't done it! Who wants to buy a Randall or Egnater? :lol: This would allow the wide range of Mesa customers (from blues to rock to metal....) to customize their own Mark amp.


Last edited by cho on Tue Nov 29, 2016 8:14 pm, edited 1 time in total.

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PostPosted: Mon Nov 28, 2016 3:55 pm 
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Mark III

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Why would Mesa want to do that. When there's a million people out there thinking you need a specific amp for certain types of music.

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