AB2204

[Smokebreak]

I've got a dude that wants a BF Bassman and a hotrodded Marshall in the same box and I'm starting from scratch on this one. I'm using a Watts blank chassis, some MC iron, and I haven't worked out the board yet. I'll use something on hand, maybe a pre-made turret board or I have some eyelets.

Just back from office depot and did the big holes :

[Smokebreak]

I've got a couple of questions. I've attached a rough outline. M denotes Marshall stages and F is for Fender.

I'm not sure the best way to go about the dropping string and HT supply for the preamp(s). The first stage will be shared by both channels(I actually like Marshall values on Fender V1...sometimes). What's the best way to do this, to supply the two "F" stages? Run a parallel node off "d"? Run all four of "E"? Leo did! I'd like to use capcan down by the preamp that shares a ground. We all know this can work, but I'm not so sure in this case. By biggest concern is noise, as I usually stick to a strict ground scheme, that will be destroyed if the whole amp up to the PI has minimal separation. The preamp capcan isn't a deal breaker though.

Next, for the Fender tone stack, I drew it up without figuring or calculating, figuring if that first 2n cap is in parallel with the Fender treble cap, the TS cap should be around 320p, to get down to 250p. But when I look at it, well the 2n sees the slope too, so I'm not sure how this will react. I would think that with a larger cap, it wouldn't be an issue, but 2n...I dunno.

Finally, what the hell am I supposed to listen to when I build this ? Van Halen or... SRV?? Shit that was kinda difficult thinking of a famous Fender rockstar.

[Smokebreak]

I had some odd sized blank boards around so I decided to do eyelets.
I also decided I'll just put a .1u cap before the switch, then I don't have to worry about the clean stack, and can use lower voltage caps I may have. I can then just use 2n after the switch on the Marshall side.
I also added a node on my cap board to experiment with how to work the preamp supply and filtering.

[The Ballzz]

Smokebreak,
I am and will be following your build closely/eagerly, as I'm in the planning stage of an amp with similar stuff and issues to work out. Correct me if I'm mistaken, but it kinda looks as though the 2 channels will end up out of phase with each other? Not really an issue if only ever used one at a time, but if they ever want to be combined/blended.........? Of course, two out of phse channels being blended just "MIGHT" create some interesting tonal variabilities, not sure here.
Just Wonderin'
Gene

[Jana]

They won't be out of phase.

[Smokebreak]

Yep, the signal of the cathode follower is in phase with the signal that enters, so blending probably wouldn't be an issue(both channels see the same number of stages/phasing), other than maybe sounding like poo
I'm not gonna give the end user the chance, though. Single input, 2 channels, MV only on dirt channel. Only 1 voicing switch! That will swap out the 10K stage cathode.
I got some chassis and board work done. I'm trying to use up some carbon comps granted they are in all the wrong places in this one.

[The Ballzz]

They won't be out of phase.

Please forgive the relative "newbie" (that be me) and thanks for the comment. I see/understand, upon a closer look, why this is so!
Thanx Again,
Gene

[xtian]

Beautiful work. I see we're competing for anal-retentive detail champion of the world, so I'll have to call you out on your resistor orientation...the tolerance bands are oriented all willy nilly, as if you don't even CARE!

[Smokebreak]

Thanks man. In my defense, I'm just using parts on hand, and some of those resistors were labeled upside-down

[Colossal]

Good looking build dude. Always fun to see what you are cooking up.

[Smokebreak]

Thanks Dave! I'm looking forward to the next Colossal build. That Express is etched in my brain!

I woke up to the realization that my arrangement to parallel switch the 10K cathode stage is wrong. You can see I've got 110Ks under the c/r to be switched in(shorting the 110Ks that keep the caps charged and prevent popping), but of course this only works when switching in caps only. Since I'm switching to get to 10K, 5K/1u, 2K7/.68..... 110Ks will only give me some wacky bias and bypassing. (btw I used 110K just because I have a boatload of that value)

I drew up a couple iterations of a series arrangement for the cathode...5K, 2K7, 2K7 to get to ~10K, and then insert the 110Ks propping up the caps, but this got way to complicated for a simple switching system.

Of course I could just remove the 110Ks from the board and switch in the c/r directly to ground, but it's gonna pop. It used to not bother me but now it does.

Is there a solution to this?