Sluckey's Dual Marshall

[pompeiisneaks]

I'm about to build an amp Sluckey put together on paper, but has never built himself, BUT I can't use his amazing layout because I have a crap vox chassis with the preamp sockets already done in the middle of the board, so I'm moving things around to fit where I've got the sockets mid board, a la dumble steel string slinger etc. (using what I got)

I tried to be very careful to not break connections until I had to, to just reconnect them to the right spot. I've hopefully kept everything 'right' and can from this layout build the working amp. Attaching schematics and layout. Please let me know if anything seems wonky.

Edit: updated wth a few more fixes, I also have added eyelets next to any specific connection going down, so I can bring the wires up from the sockets to those, so there is a bit more simple connectivity etc.

DualMarshallPhilLayout.PNG

Preamp.PNG

Poweramp.PNG

~Phil

[pompeiisneaks]

Oh and one of the things I'm debating is cutting off the power side after the PI and moving them off a bit, so the blue wires between PI output and the Power input may be on their own board. It's a bit odd having all that extra space, but it is what it is. The measurements of those sockets are lined up with the chassis offsets (2 5/8")

~Phil

[pompeiisneaks]

Welp the design phase is over, here's the first video, intro on the circuit, if anyone has answers for my questions on the circuit, I'd love to know more about the caps that confused me here




~Phil

[xtian]

I like preamp tubes-in-the-middle layouts. Very nice. Carry on.

[M Fowler]

Looks like a fun project.

Martin Manning and Jana S. also built a nice through hole PCB style modded JCM.

Mark

MPM_2204-ISH_Layout.jpg

MPM_2204-ISH_Inside.jpg

[RockinRocket]

Not sure I can help however the plexi 68 and Jcm800 power amps are completely different and contribute a lot to the tone.

Ive never built a dual preamp like this but it is possible to switch that V2 .68 and negative feedback on one switch without any issues except the typical pop from the Negitive feedback DC changing as a parallel resistor is inserted.

[pompeiisneaks]

Not sure I can help however the plexi 68 and Jcm800 power amps are completely different and contribute a lot to the tone.

Ive never built a dual preamp like this but it is possible to switch that V2 .68 and negative feedback on one switch without any issues except the typical pop from the Negitive feedback DC changing as a parallel resistor is inserted.

I understand that there had to be a decision on the power output, the output used is that of the plexi it seems instead of the JMP type, which seems to have used 6550's instead of EL34's.

I don't exactly follow what you mean by the second part, though. Are you meaning to add another switch that lifts the bypass cap and the negative feedback? If so, then yes, a DPDT switch with each on either pole side would work. Is that a common switched mod people do? The pop can sometimes be managed I think by adding a cap across the contacts so the extra charge can be stored in the cap on disconnect and feed back out after if I recall. Not done it before but seen it on some schematics.

~Phil

[RockinRocket]

Its a mod I do and works quite well.

The negative feedback on a plexi is 16 ohm tap 47k. 800 is 4 ohm 100k. Simply, a 31k (or closest common value 33k ) paralleled across the 100k 4ohm will make the feedback equivalent to a plexi. No way getting around the DC pop on this.

A switchable grounded 10k - 47k in series with the .68uf will eliminate any switched noise here. The resistor will have a very small effect on the frequency (based on size traded off for switching noise) but is so small it is not noticeable. When the .68uf is engaged the 10k- 47k ground is lifted.

[pompeiisneaks]

The Dual Marshall Build continues:




Somehow the 'video' link seems to have stopped working. Gotta look into that, using the 'youtube' one instead.

~Phil

[Guy77]

Excited to hear how this sounds when its done!

Cheers

Guy

[pompeiisneaks]

Thanks, I'll keep everyone posted with the videos and a demo at the end of course

[coldengray]

This is extremely interesting, I am following this and looking forward to seeing how it goes.

[pompeiisneaks]

Thanks! I'll have more time to tinker on it this weekend I hope

~Phil

[pompeiisneaks]

Video 3:




~Phil

[pompeiisneaks]

Here's the latest video: