Relays: can I get away with 2 here?

[alfi27]

Hi fellas,

I'm planning my first ever amp build from scratch, and I want it to be an extraordinary amp that I will use a lot. This is just one of the ideas I'm looking into, but it's a fairly serious contender as I have both of these circuits in each of my vintage Marshalls and I love them both! It will be a fairly small, portable amp so that's why I'm thinking about the same circuits as I already have.

I attached the schematic. Please ignore the added text, it's some guy who decided to use this of all schematics to explain an AFD mod... So what I'm thinking is the Crunch and Lead channel, with individual volume and gain for both but shared EQ. As they will have to share the first and final stage invidual gain is probably easier than shared anyway, but it's the individual master volumes I'm struggling to figure out. There needs to be a relay at the output of each master volume pot at least, but if there is no relay at the input there will be a 1M to ground all the time if I'm not mistaken? Also, is it sufficient to wire it exactly like in the schematic up to the 220k grid resistor on V3A, and then put a relay just before that resistor? Or would I need a relay before the 1M/220pf and 1M/1000pf of the gain pots as well?

And finally, I thought it could be awesome to make the crunch channel switchable (no relay, just a DPDT switch) between two and three gain stages, omitting the second stage with a switch. What do you guys think, should that be able to yield at least a decent clean tone?

Cheers!

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[Phil_S]

One can dream...

IMO, the amp you propose to build is neither small nor simple. It is a lot for a 1st time build. I am an amateur builder. I don't know nearly as much as others here, so take what I say with a grain or two of salt.

From the schematic, it looks like about 7 tubes and 10 switches. I'd want a 22"w x 8"w x 3"h chassis for that. I suspect just jumping over the 2nd triode is not the same as the clean channel. My guess is that you'll neuter the tone. Look at the 1st triode in each preamp. Values for Ra, Rk, and Ck are all chosen for a reason. These circuits are about tone shaping as much as they are about gain.

I've built a dozen or so amps. I don't think I'd be willing to try what you describe.

I don't want to burst your bubble. Just think about this more carefully. There is a chance you'll spend quite a bit on parts and end up with an amp that is nothing like you expect.

[bal704]

I second Phil S.....

[alfi27]

Thanks a lot! I probably know even less than you, so I certainly am a bit ambitious! For the record, I didn't mean that bypassing the second stage of the crunch channel would equal the clean channel, but maybe you didn't mean that either.

There's a bunch of tubes in the preamp, because all the channels are totally independent of each other apart from the crunch and lead channel sharing the first stage. And the final stage is identical as well, but it's not shared because of the independent tone stacks (but in my amp they will share the same tone stack).

So let's just forget about the clean option altogether, it's not important. I attached a very rough draft of the preamp section, I'm just starting to learn about relays so they are probably not wired correctly... Pretty sure this should be doable though, the amp would be 14" wide so it's not tiny.

A little update: I have decided to go for it. It won't be overly spacious, that's for sure, but I know for a fact that the chassis can fit a turret board with the Lead channel alone. And the crunch channel won't add much the way I have designed the layout. Worst case scenario I'll turn it into a single channel amp with a switchable master volume or something, so there isn't really anything that can go disastrously wrong!

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