Two clean channels

[Luthierwnc]

I am casting about for my next winter build and wanted to know if anyone has built (or considered building) an amp with two clean channels. The concensus is that the amps with the best cleans don't lend themselves to the best OD. I was thinking of doing an amp with a dedicated clean channel (possibly using 100k values, no lnfb) and having a dedicated two-tube circuit for the overdrive with CL1 and 2 optimized for feeding the OD. The latter could be divisible but the permutations start using a lot of real estate on the panel. As a one-piece circuit, I can use some presets internally. With an HRM that would be an easier decision to just hardwire the PAB but I already have one of those and want to use an 80's voice on the OD.

The problem is keeping the options managable. If it matters, I play low gain buckers and singles. This could either go over a pair of Thieles or two British 12's and I have a D-lator/G Sharp 2U box to match when the occasion calls for it.

Experience, suggestions, opinions welcome.

Thanks, Skip

[Luthierwnc]

No one has any thoughts on a one-tube dedicated clean and a two-tube dedicated OD set-up?

[briane]

well I supose you wont get too many reply's. You need to do some serious thinking about how this would be implemented, cause it cant be done in my mind and retain exactly the dumble circuit.

You will need an internal mixer to bring the 2 channels together. Cant tie to either end of the PI or you lose NFB.

If you use a resistor mixer, then additional resistors and tone loss (and where do you put it? it should go in front of a gain stage, and theyll be all done at that point, dont want to put it in front of PI). If you use a tube mixer, then you have an additional tube to deal with.

pretty clear its not a dumble as we generally know it. Anyways theres 2 cents for the coffer.

In my mind it seems obvious dumble did it this way for a reason!

[mlp-mx6]

I built a "TDS-style" amp - the first stage is common, then there is a dedicated clean channel, and a switchable ODS side, for 3 selectable channels total. 3 button footswitch - dedicated clean wins, else OD/clean on the OD side, and PAB for the OD side. 5 "tonalities" total. I also built in a Dumbleator. It has 5 preamp tubes, and is a WIDE chassis. Sounds great, though.

The first tube is a cathode follower to drive the 2 tone stacks. The rest is "standard" ODS stuff.

[Luthierwnc]

MLP: My idea is a bit more modest. One DPDT relay at the jack to either grid and grounding the other in an X pattern. One DPDT relay on the same ground line to combine them just before the PI.

Folks here are raving about the 100k clean but that it burns up the OD. So, the 100k would be a dedicated clean with no lnfb. It would get a deep and bright (don't care much for the mid-boost). The OD would be 220k/150k on both tubes with a lnfb. I'd probably use trimmers for the TMB on the OD side. Maybe a bright. No mid, deep or jazz/rock. I was also thinking about using the single switch PAB like the D-lite build so I could use either side of a single DPDT relay for both channels. Three relays total.

Briane: the switching wouldn't get anywhere near the PI. The clean side has a master and the OD has the level and ratio (and its own gain) on the panel so no different than your mill-run front adjustments. It will need a little more real estate than usual but less than putting in a loop or reverb. It also saves a lot of wanking with a switchable lnfb. One side is clean as good as you can make. One is OD, dialed in. No compromises on either side. I already have an HRM so the goal is an 80's voice.

Alright! We got this thing rolling. Come on down ... sh

[mlp-mx6]

Perhaps better to have the input jack go to both grids of the first tube (sharing the grid stopper) and ground the signal at the volume pot for each stage (post tone stack). That way your switching noise is reduced because you're just shorting out the volume pot. (built-in 1M resistor across your switch) I can't help but think that switching in front of the first gain stage would be difficult to keep quiet.

[Luthierwnc]

I've done panel switches like that with no problem but that is a suggestion that might come in handy during the chopstick phase. The relay is right under the input jack so the lead is only about 2". There are two runs of coax to the terminal strips next to the clean and OD sockets so I can run the grid stoppers right up to the pins.

In noodling around with the layout, it looks a lot like an HRM with the trimmers on the board. If it were an HRM I'd just hardwire it to PAB but with the 80's style I want to retain the either/or option. sh

[keithrick]

FWIW - I think Bob-I did a three channel build as well and I am sure it is in the files section. You can use it and read through some of the related threads to get some ideas on how to mix the channels.

Sounds iteresting. Good luck!