Circuit diagram

[Masterof1angel]

Does anyone know where to find the Mark V circuit diagram? I need to compare the mark IV and Mark IIC+ mode circuits.

Yours Truly,
Angel

 

[phyrexia]

Good luck; it has not been sent even to dealer service centers yet to my knowledge. all repairs are going back to petaluma.

 

[niilz]

here:

http://www.sendspace.com/file/lan84p

let us know to which conclusion you came! ;-)

 

[Azrehan]

Good luck; it has not been sent even to dealer service centers yet to my knowledge. all repairs are going back to petaluma.

That's funny. Mine was repaired by the Mesa repair tech in South Australia and it took 4 days, so I doubt it went to the other side of the world in that amount of time. He also said that Mesa emailed him the schematic.

 

[phyrexia]

oh you guys are different.

i stand corrected!

thanks for the info.

 

[Masterof1angel]

That's very interesting because my amp tech had one in his garage and is going to do the cap swap for me. I'm just trying to figure out if it's worth it because the iic+ tight mode is great and I'd love to have the high end clarity with a bit looser bottom, but the IV mode has a softer high end and I'm trying to figure out if it's the bass cap that does that too and how different the circuits are. Ideally, I'd like to have the IIc+ tight mode AND Original GEQ mode too.

-Angel

:edit: I'm confused on where the lead circuit is. im not too good at these and this amp is so different schematically than the others.

 

[mejoshee]

That's very interesting because my amp tech had one in his garage and is going to do the cap swap for me. I'm just trying to figure out if it's worth it because the iic+ tight mode is great and I'd love to have the high end clarity with a bit looser bottom, but the IV mode has a softer high end and I'm trying to figure out if it's the bass cap that does that too and how different the circuits are. Ideally, I'd like to have the IIc+ tight mode AND Original GEQ mode too.

-Angel

:edit: I'm confused on where the lead circuit is. im not too good at these and this amp is so different schematically than the others.

i could see why you'd be confused. there are bits and pieces all over the place. mesa likes to do the serpentine schematics. not too familiar with the "bass cap" value and what it's connected to (preamp tube interstage bypass/coupling?). is it part of the geq circuit, or in the preampe section? do you know what the value was on the original iic+ vs. the ones in the v?

i have a sneaking suspicion this is it

but correct me if i'm wrong about understanding the function of the bass cap. looking at the schem, in m7 (mode 7=mark iic+, according to pg. 1 of schem), then it'll switch in the 2x 2.2uF and switch out the 15uF. sound right? or am i totally off?

 

[mejoshee]

correction. i read the manual and i'm fairly sure this is it, actually:

this pair of caps still engages via the rym7, relay for mode 7, iic+ mode. according to the manual,
"There was actually a difference between the EQ model and those non-EQ models. It all came down to a coupling capacitor at the end of the EQ circuit that feeds the driver. In the EQ model, it was a great big cap that let a lot of sub-low pass, slowing down the sound and making it fatter. In my amp - a non-EQ version - this cap was smaller and didn’t let as much sub-low through - which speeds up the sound and makes everything tighter and more urgent. There it was, a simple part…but it made all the difference in the time domain."

labels for the mode next to the switches or relays on the schematic indicate that's when the mode is selected, so the "m7" is by the side that would engage the .22u cap, while not in m7 mode (mark iv/extreme) selects the 10uF.

it's probably polarized only because of how large a value it is--10u is not a what is usually considered a common coupling cap value since it's probably about 2 decades larger than the "normal" range (i.e. 100x). in marshalls for instance the coupling caps are on the order of .022 or .1 depending on the models and circuits. usually this can distinguish between the "vintage" 60's/70's plexi and the modern ("harsher") circuits of the 80's or later.

however, note that the caps in the previous post right next to v6a also engage with the same m7 relay, so there's more than one cap swap when the switch is thrown. keep this in mind it's not "just one" part.


anyone else out there concur?

 

[DaveDaveDave]

Yep, I concur with your synopsis mejoshee.

I had a lot of fun reading the schematics too, and comparing them to the Mk IV. It REALLY looks identical to the Mk IV when set in that mode, with the exception that the "gain" resistor network that replaces the gain post is set to 450/550ohms - which is probably like setting the equivalent Mark IV gain pot to 6 or so. I should measure a 1M pot some time and check, but prolly not worth the time.

That is pretty weird about the EQ output cap being polarized though - isn't it? That's a pretty hot set of transistors in the EQ too : +24v. I'd always thought that you'd never want polarized caps in the signal path. I'm pretty sure that no matter what you do, that cap will cause an asymetrical signal, wouldn't it? Thoughts?

As for the cathode coupling caps at V6A wyou mentioned earlier - I understand that these caps do two things - they stop feedback and they create a low shelf RC filter that affects the gain structure. With two cathode ground cap options under V6A (4uf (2x2uf c104) or 15uf (c106)), having the 15 being employed in IV and extreme modes we're balancing the way V6A is driven (c104) with how much bass you let out (c99) of the EQ.

Really though, I'm thinking that bumping the GEQ sliders is going to have the same effect on things as increasing the EQ output cap. After all, at this point we're dealing with a solid state output stage. Am I missing something here? Is it just that they'll be combing/shelving filtering differently?

I dunno - I find this amp sounds so amazing all around - I wouldn't change a thing. If you really want to tweak tones, it's a lot easier to find an older handwired amp like a Traynor or a kit like a Ceriatone and mess with it.

Cheers,
Dave

correction. i read the manual and i'm fairly sure this is it, actually:

this pair of caps still engages via the rym7, relay for mode 7, iic+ mode. according to the manual,
"There was actually a difference between the EQ model and those non-EQ models. It all came down to a coupling capacitor at the end of the EQ circuit that feeds the driver. In the EQ model, it was a great big cap that let a lot of sub-low pass, slowing down the sound and making it fatter. In my amp - a non-EQ version - this cap was smaller and didn’t let as much sub-low through - which speeds up the sound and makes everything tighter and more urgent. There it was, a simple part…but it made all the difference in the time domain."

labels for the mode next to the switches or relays on the schematic indicate that's when the mode is selected, so the "m7" is by the side that would engage the .22u cap, while not in m7 mode (mark iv/extreme) selects the 10uF.

it's probably polarized only because of how large a value it is--10u is not a what is usually considered a common coupling cap value since it's probably about 2 decades larger than the "normal" range (i.e. 100x). in marshalls for instance the coupling caps are on the order of .022 or .1 depending on the models and circuits. usually this can distinguish between the "vintage" 60's/70's plexi and the modern ("harsher") circuits of the 80's or later.

however, note that the caps in the previous post right next to v6a also engage with the same m7 relay, so there's more than one cap swap when the switch is thrown. keep this in mind it's not "just one" part.


anyone else out there concur?

 

[kiff]

I'd always thought that you'd never want polarized caps in the signal path. I'm pretty sure that no matter what you do, that cap will cause an asymetrical signal, wouldn't it? Thoughts?

many circuits use polarized/electrolytics for coupling when there's a positive (+V/2) bias on the signal. from the pic that's posted, the transistors aren't bipolar, so it would make sense that the signal is (biased)

 

[chipaudette]

Hi DaveDaveDave,

Your comment about the GEQ transistors being "hot" at 24V...well, the other boogies actually run their GEQs at higher (absolute) voltages...

EQ Supply
----------------
Mark V: +24V
Mark IV: -30V
Mark III: -42V
Mark IIC+: -42V
Mark IIB: -47V
Mark IA: -37V
-----------------

So, what I actually find surprising is that this is the first boogie to use a positive voltage supply instead of a negative voltage supply for the GEQ. This means that they had to swap all of their transistors from PNP to NPN and vice versa. To me, that's really interesting. The GEQ has been one of the most stable portions of the design since the Mark series began.

I wonder why they chose to do that?

Chip

 

[chipaudette]

Notice that Randall got rid of his long-beloved vactrols/optocouplers/LDRs. Wow. All his switching is now done by relays and (gasp) J-FETs.

Not that I care either way...it's just another one of his original fingerprints on the Mark series that has now passed into history.

Chip

 

[phyrexia]

LDRs haven't been used in a new Mesa design for a while now. The Mark IVs did because they weren't going to redesign the whole amp a third time.

 

[mejoshee]

LDRs haven't been used in a new Mesa design for a while now. The Mark IVs did because they weren't going to redesign the whole amp a third time.

that and they've probably run out of them. or perhaps it was a financial choice based on comparative analysis.

maybe that's also why it took them so long to do a new design after the iv...

 

[LPJunky]

Excuse my ignorance on Mark electonics history but what are LDRs? Lethal Dose of Radiation? :lol:

I spent a fun time surveying the different schematics, IV, V and IIC+withGEQ but could not find a IIC+nonGEQ schematics if only to read the famous capacitor value.

 

[mejoshee]

Excuse my ignorance on Mark electonics history but what are LDRs? Lethal Dose of Radiation? :lol:

I spent a fun time surveying the different schematics, IV, V and IIC+withGEQ but could not find a IIC+nonGEQ schematics if only to read the famous capacitor value.

nothing lethal not the best article http://en.wikipedia.org/wiki/Light_Dependent_Resistor

here's another one that's more visual (and a little silly) http://www.technologystudent.com/elec1/ldr1.htm

application of light on the ldr causes it to change resistance. in this way it can be used as a switch. hope that answers your question

sorry to go a on a rant here. just a warning. re: the cap values. can someone chime in on this? frequency response makes sense given the cap values, but can anyone honestly tell the difference between the two versions (w/ the geq off) if the parametric tone settings are the same? a 1:1 a/b comparison is probably very difficult to make since you'd need two mark iic+'s with the same power tube configuration, the same transformer part numbers, etc. and there's no way to know at this point in the iic lifetime whether all the components have aged the same. everyone's always sniffing around for new tweaks. can't we be happy with the iic+ mode? :?

oh, and "tone boy" did mention he thought people wouldn't be used to the tighter non-eq tone. so, perhaps this is something we need to get used to? or maybe continue tweaking the eq settings until you get closer. granted 3-band parametric and 5-band geq are not very very exact, but if you're worried that much about the frequency response of a single cap value, why don't you spend the money on a rackmount graphic eq, with 30 bands. even the good ones are probably going to be cheaper than the bill from your amp tech fiddling with the electronics. ok rant over.

 

[domct203]

Does anyone have a MKV footswitch schematic, or know the pin-out config?

I'm looking to trigger the FX Loop and Reverb via MIDI.

Thanks,
Dom

 

[MerlynMetal]

Hi,

Here's the foot switch pinout:

1- gnd (when channel selector is on FS)
2 - +5V
3 - channel
4 - EQ on
5 - Solo
6 - mute
7 - Reverb
8 - FX loop
shield - EQ fsw

By the way a friend of mine has some channel switching issues so if anyone can share the switching part of the schematic (which according to rumors is 18 pages(!) with several revisions) it will be greatly appreciated.

 

[alezuniga]

Any clue of the circuit diagram for the Mark V 35?
Is there any out there?

 

[xenonaut]

Hey MerlynMetal

How are the pins numbered? Is it 1-7, going clockwise when you're looking at the pins, with 8 in the middle? I also want to control all functions over midi, but don't want toscrew anything up, as pin 2 is hot...