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PostPosted: Sat Jul 23, 2016 4:34 pm 
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Mark III

Joined: Tue Dec 22, 2015 12:15 pm
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The bias point determines what class the valve is operating in. 95-100% (though Weber claim 90% too) is what class A valves are biased to. It's all there in the links. I didn't want to state it again.

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PostPosted: Sat Jul 23, 2016 4:36 pm 
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Mark III

Joined: Tue Dec 22, 2015 12:15 pm
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Could a Mark 4 owner perhaps post the plate voltage and grid current of their inner valves. That would probably help.

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PostPosted: Sun Jul 24, 2016 12:06 pm 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
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.

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Old friends I sometimes miss:
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PostPosted: Sun Jul 24, 2016 3:40 pm 
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Mark III

Joined: Tue Dec 22, 2015 12:15 pm
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So basically then, Mesa are lying and Simulclass is just mismatched class AB. With 6L6's one pair biased cold cold and the other pair biased hot.
It makes sense I suppose, two 6L6's or EL34's in class A don't knock out 45watts. That is firmly class AB.
EL34's and 6L6's give about 25 watts each.

I've a headshell landing tomorrow. When the chassis is out, I'll re-check my bias measurements. Make sure I've got every variable down.
As it stands now, (cos I note everything from every amp I work on) my mk5 has the inner sockets running at

Variac, 42ma inner 28-30ma outer.
Full power 52ma inner 38ma outer
So yeah in full power 70% of max on the outside. 95% of max on the inside, in full power mode. Which Mesa say not to use with EL34's
Those were JJ's matched quad from Hotrox used about 5 times before I tried them.
I'll re-test tomorrow. But in Variac power that is nowhere near class A.

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PostPosted: Tue Jul 26, 2016 6:38 am 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
Mesa is not lying, Simul-Class has always been in this form. Besides, how could you run a pure class A circuit in parallel to an A/B ? This has baffled me. Extended class A region of the push pull (A/B) makes sense. However, the manual has a few references that makes you think the 45W mode is class A. There is no way possible unless the schematic is wrong, definitely is A/B in 45W and 90W. In 10W mode, only one side of the power amp is used, It still uses two power tubes (one inner and one outer). When you switch to 10W mode, the relays will change how the power tubes are wired. Quite an intelligent design in all respects. The simul-class was what moved me into Mesa, fixed bias was the other reason, along with quality of workmanship and materials, and of course the tone and character of the amp. I find it hard to believe I started with Mesa some 29 years ago.

Thinking about features, what would be cool if possible, keep the simul-class but also have a switch to change to a traditional class A/B. That would be possible since the ground leg on voltage divider on the grid of the inner tube gets unconnected. In essence, you get pure class A at 10, and two modes for high power (simul-class 45W/90W, traditional A/B 50W/100W) Since each type of power section offers its own characteristic.

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TC-50, JP-2C, MK V, Roadster, RA100
Old friends I sometimes miss:
Mk III (blue stripe), Mark IVb-WB


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PostPosted: Wed Jul 27, 2016 1:37 pm 
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Mark III

Joined: Mon Sep 29, 2014 12:17 pm
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Location: Canada
I was under the impression that only 90W was SimulClass(Class AB outside tubes paired with am extended Class A pair). 45W disables the outside tubes, and just runs the Extended Class A tubes. Then the 10W mode runs a true single-ended class A. So you could possibly toggle a 100/120W true Class AB power section, but that would involve some Bias changing, wouldn't it?

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PostPosted: Thu Jul 28, 2016 6:19 am 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
Keep in mind the 45W power mode is a Class A/B power amp, it is just biased differently. Also, with that in mind, the signal also flows though the same grid circuit, the signal path into the outer tubes only has a series resistor to limit current flow, the inner pair has a voltage divider on each grid (pulls the bias voltage more towards ground which in result drives the inner pair hotter (extended class A region, does not mean the amp is class A in 45W).

It would not be difficult to alter the Simul-class extended class A to a traditional push-pull A/B circuit with a few relays and a few extra parts. This could be done with the same bias circuit as once the voltage divider resistor connected to ground is disconnected, the bias voltage on all 4 tubes would be very much the same (however the series resistor on each grid may be different as well as the screen resistor, would not be too difficult to use relays to switch in additional parts to balance things out).

What I would like to know if this be true, does the JP2C sound as good in the clips as it does in first person point of view?. I found that I do not care for the Mark V tone when the EQ is off. What I have seen in some of the demo videos, turning on and off the EQ did not seem to make the amp sound worse with it off. In case of the Mark V, it sounds lifeless and lacking power without the EQ (preset or sliders), but with it on, it sounds much better. In pale comparison to the RA100 or Roadster, both sound incredible without EQ. I have the Mesa 5BEQ pedal and I actually prefer the amps without it. Sure, it is all about tone stack, how it is managed, where in the circuit is it, etc... Roadster drives it with a Cathode Follower, RA100 does not (closer to the Mark V in method).

I have been looking into the JP2C more now, I believe that may be what I have been looking for, but yet still want to wait and see what comes out of Mesa next (if anything).

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Current amps:
TC-50, JP-2C, MK V, Roadster, RA100
Old friends I sometimes miss:
Mk III (blue stripe), Mark IVb-WB


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PostPosted: Fri Jul 29, 2016 1:36 am 
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Mark III

Joined: Sat Apr 25, 2015 1:22 am
Posts: 274
Location: MO
bandit2013 wrote:

What I would like to know if this be true, does the JP2C sound as good in the clips as it does in first person point of view?. I found that I do not care for the Mark V tone when the EQ is off. What I have seen in some of the demo videos, turning on and off the EQ did not seem to make the amp sound worse with it off. In case of the Mark V, it sounds lifeless and lacking power without the EQ (preset or sliders), but with it on, it sounds much better.


The clips do the amp no justice. I've yet to hear any clips really truly capture the magic in the JP2C. I agree 1000% with you on the V without the GEQ. In fact, imho, the V sounds god awful without the GEQ. When I bought the JP2C, I assumed it too would sound like crap without the GEQ engaged. I was very wrong. It sounds wonderful without it. I can't belive how well I get along without the GEQ on the JP. Basically, the character of the JP2C is very different from the V. The V has that honky nasty midrange, the JP has none of this. It's more scooped, so it sounds smoother and feels bouncier, which, to me, feels more lively. Where that nasally, honky midrange in the V makes it feel tighter, or stiffer, and that makes it more unforgiving to play. And I agree with you that that sounds lifeless, and I think it feels lifeless. The JP2C was truly refreshing to play. No more fighting with my V to get it to loosen up its midrange stranglehold and trying to get it to breathe. Now I've got the JP2C, and it sounds like the mark tone has been perfected.

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PostPosted: Fri Jul 29, 2016 2:10 am 
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Mark III

Joined: Tue Nov 08, 2011 10:48 am
Posts: 235
SamuelJ86 wrote:
...I agree 1000% with you on the V without the GEQ. In fact, imho, the V sounds god awful without the GEQ. When I bought the JP2C, I assumed it too would sound like crap without the GEQ engaged.


I strongly disgree. With e.g. EHX preamp tubes the V sounds phantastic without the GEQ, fluid, full and singing. The only thing you have to do is add some bass with the GEQ.


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PostPosted: Fri Jul 29, 2016 6:42 am 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
Posts: 2558
Location: North Carolina
I have experimented with many different preamp tubes, 12ax7: From EH, TS, Mullards (both LP and short CV4004), Preferred series and a few others, 5157 NOS JAN GE, also including 12AT7. Same with Power tubes. My issues with most of the tubes brokered by New Sensor seem to create more noise in certain positions than others. If I can get past the low frequency hum or high hiss I would love them. What was noise free (almost) were some old Mesa Chinese tubes I have (square foil getter) that really liven up the amp. Best tube for V2 if you want that heavy healthy punch for the crunch. I tried a few of the ECC 803S JJ tubes (very nice sounding and not as dark as the ECC83s used by Mesa. The Mark V does react quite well to different preamp tubes. If you want to change things up, NOS 12AT7 in the V4 and V5 pushes CH3 into a different world. Perhaps less gain but quite a different character. If I play without the EQ I could get used to it, but turn it on and its Nirvana.

Speaker choice is another thing that helps. I converted to a Combo so I could experiment with different speakers and love the Celestion Crème ALNICO 90W. Sounds really great with stock Mesa Power tubes, could not stand them in the V before the change. JJ 6CA7 or Gold Lion KT77 are also amazing. Will have to try some other brands of the 6CA7 as the JJ tube had some issues that were not related to plate voltage, more so quality issue due to open lead wires inside the tube causing intermittent function.

I still want to get a JP2C, would like to get one before they become discontinued as it seems that Mesa drops the amps that I like. I have no plans now to let go of my V, it is a keeper at the moment. What I would love to get my hands on would be a JP2C combo 2x12 but doubt that would ever become a reality.

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Current amps:
TC-50, JP-2C, MK V, Roadster, RA100
Old friends I sometimes miss:
Mk III (blue stripe), Mark IVb-WB


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PostPosted: Sat Jul 30, 2016 10:22 am 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
Posts: 2558
Location: North Carolina
What would be cool is two FX loops, each buffered with their own tube circuit as well as independent switching and volume control. There are times you want to run a parallel patch especially with delays and reverb pedals. When they are run in series, it gets muddy but in parallel it sounds much better (had to do this with the TASCAM recorder and did not use any effects on the amp for that reason alone). Also you could assign each loop to a specific channel or use both simultaneously or just one. If two loops are not enough, add a few more (similar to the Line 6 helix).

Add midi control as requested by the OP, Cab clone (would be better with improved cab simulation based on assumption as I do not have the cab clone, perhaps some DSP with down loadable IR ).

Let's not forget about the coffee or beer dispenser while we are at it. Okay I can do without that, it is the thought that counts. I can understand wanting to be challenged with a set of what may seem impossible to pack into a small enclosure along with preamp and power tubes. Perhaps we have not given enough challenge to the master amp engineer. Preserve what was done and add what was not done. Why only stick with 3 channels, when we can have 4. Blend the JP2C with the Mark V ;Perhaps use the JP2C clean on CH1 but add the tweed for some grit, CH2 could be the IIC CH2, CH3 with same features as JP3C CH3 and CH4 the Mark V (mkIV, extreme, and little Mark III blue stripe). What ever would make sense and be yet feasible to accomplish. Still have to find the place to put in the Mark 1. recap that, Mark 1, Mark IIC(in the form of the JP2C), Mark III, Mark IV, Mark V (tweed and extreme) with the possible power amp switching for pure class A (10W), Simul-Class power (45w/90w) and more traditional A/B power used on JP2C (50W/100W) with a twist to include two 5U4GB that can be used at all power settings.

As always, I am looking forward to what ever it is that will be released to production.

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Current amps:
TC-50, JP-2C, MK V, Roadster, RA100
Old friends I sometimes miss:
Mk III (blue stripe), Mark IVb-WB


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PostPosted: Sat Jul 30, 2016 9:54 pm 
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Mark III

Joined: Thu Feb 07, 2013 10:45 pm
Posts: 221
I think Mesa will try and get at least 10+ years out of the Mark V before we see a Mark VI. The Mark V has been out for 7 years which is not very long for a flagship tube amp. I can imagine a revision at some point but not the next generation of the Mark Series.

With that said, I think integration with pro audio equipment is something Mesa has wisely deemed important. I think they will continue in that direction as long as guitarists want to record music.


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PostPosted: Sun Jul 31, 2016 7:17 am 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
Perhaps you are right about the time line when a new Mark would be in the works. I am sure something is in the planning stages for a new product.

I have one last request and this would be applicable to all Mesa amps,
A footswitch chassis that does not vibrate at low frequencies. The Mark V footswitch controller seems to resonate the most at certain low frequencies when compared to that of the RA100 or Roadster. If you have the space to distance the footswitch away from the speaker enclosure it is not an issue.

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Current amps:
TC-50, JP-2C, MK V, Roadster, RA100
Old friends I sometimes miss:
Mk III (blue stripe), Mark IVb-WB


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PostPosted: Sun Jul 31, 2016 8:16 pm 
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Mark III

Joined: Thu Feb 07, 2013 10:45 pm
Posts: 221
bandit2013 wrote:
Perhaps you are right about the time line when a new Mark would be in the works. I am sure something is in the planning stages for a new product.

I have one last request and this would be applicable to all Mesa amps,
A footswitch chassis that does not vibrate at low frequencies. The Mark V footswitch controller seems to resonate the most at certain low frequencies when compared to that of the RA100 or Roadster. If you have the space to distance the footswitch away from the speaker enclosure it is not an issue.


I do not think it is hard for Mesa to create a new product. I think the challenge is making that product affordable, marketable, and profitable.

Mesa redesigned the Rectifier Recording Preamp's footswitch fairly recently. The only reason I know that is because I happen to need a new footswitch for that Preamp. The new one looks really nice! The only pieces of plastic on it are the LED covers. So you never know, maybe Mesa is redesigning all their footswitches as we speak.


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PostPosted: Mon Aug 01, 2016 5:00 am 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
Given To Fly wrote:
I do not think it is hard for Mesa to create a new product. I think the challenge is making that product affordable, marketable, and profitable.

Mesa redesigned the Rectifier Recording Preamp's footswitch fairly recently. The only reason I know that is because I happen to need a new footswitch for that Preamp. The new one looks really nice! The only pieces of plastic on it are the LED covers. So you never know, maybe Mesa is redesigning all their footswitches as we speak.


Designing a product to meet the demand and yet make it affordable, marketable, and profitable is every engineers challenge. That is one of the difficult challenges I face every day at work. Shoveling a load of features and functions and control surfaces into a small box in attempts to meet a cost target. "wait a minute here, you want this and expect it for that? Are you nuts? I may think that but usually respond with " 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".

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Current amps:
TC-50, JP-2C, MK V, Roadster, RA100
Old friends I sometimes miss:
Mk III (blue stripe), Mark IVb-WB


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