Mesa Mark V Schem Available!

[chipaudette]

Hi All,

For any students of the Mesa Boogie Mark Series, I've finally seen a link for the Mark V schematic...the link is available through "The Boogie Board"...

Schem: Attached below

Thread: The Boogie Board • View topic - Circuit diagram

I found it to be an interesting schem to look through. I like seeing what they kept the same and what they changed.

Chip

[defaced]

Very cool. Thanks for posting. I haven't followed the Mark series at all really, but I'm not seeing the typical mute circuit Smith uses in the Rectos to kill the relay pops, and this thing has alot of relays. Am I missing something?

[tboy]

I really hate those file sharing sites with all their popups and annoying ads, so I edited the first post to include the file as an attachment.

[chipaudette]

I'm not quite sure how he does the muting, but here's the most likely option that I see...

Throughout the amp, there are a number of J-FETs that are acting like switches. On the loop/driver page (the page with the phase inverter), there is "J175M1" that, when activated, looks like it would mute the amp. This could be used to stop any popping noises that the amp would make due to the relays.

There are many J-FETs throughout the amp. If you look for the others, you might get additional clues on how different parts of the amp are muted. Sadly, there's no logic table saying when these various J-FETs are activated. You'll just have to guess.

What is really interesting to me is that there are no vactrols or LDRs anymore. It's all relays and J-FETs. I'm surprised that Randall has said goodbye to his long-time favorite switching components.

Chip

[Enzo]

He has discovered that he can use a 2 cent JFET in many places where a $2 vactrol would have been.

[Don Moose]

Mucho appreciado, Steve!

[GainFreak]

Anyone has the switching and footswitch part which is missing from that schematic?

[Jazz P Bass]

Ooops!
Maybe it's a secret.

[tedmich]

nice post! An interesting design, switched anode resistor on V1A (!) and a lot of switched cath bypass caps too! I guess the jfets switching is "POP" free??

I wonder what they "left out" to screw with cloning....

[GainFreak]

I wonder what they "left out" to screw with cloning....

The schematic looks OK. I guess the switching part is similar to their other designs.
If someone has it let please post it here or send me a PM.

[raiken]

What is really interesting to me is that there are no vactrols or LDRs anymore. It's all relays and J-FETs. I'm surprised that Randall has said goodbye to his long-time favorite switching components.

I don't know if this is the case or not, but Vactrols contain cadmium (in the cadmium-sulfide photocell), which is banned under RoHS, so they can't be used in any CE/RoHS-compliant equipment.

Randall Aiken

[Gregg]

They are not using vactrols from a long time. I guess they realized that a relay is much cheaper than a vactrol and maybe because of those regulations as well.

[Gtr_tech]

He has discovered that he can use a 2 cent JFET in many places where a $2 vactrol would have been.

And Jfets don't tend to get flaky/fail over time. They're easy to work with and do the job well.

[Gregg]

I have full Mark IV schematics from a forum member with the parts missing from those found in the net. Maybe someone has the full Mark V schematics as well?

[GainFreak]

Hi,

I spent some time studying the Mark V schematic thoroughly and I have couple of questions I hope someone can clarify for me:

1/ Because the switching part is missing it's not clear when J175A (V1a), J175B and C (V3a) are activated? Maybe they have something to do with the Ch2 Mark I Thick switch?
2/ The FB relay RY-FB (page 8) switches between 4 and 8 Ohm taps. I assume the 4 Ohm tap is used in Mark I mode. In Mark II and IV are using the 8 Ohm tap by default.
3/ It look like the RYSM relay (page 8) shortens the OT secondaries which should be a protection against switching the amp on without speaker/s connected to it. I assume it is activated by the output jacks' switches which are connected to ground when there's no speaker/s plugged in?