Dual Clean Idea

[Luthierwnc]

Since about my second "D" I've been musing about having two clean channels. The idea started because I really prefer the low-plate cleans but was having a hard time dialing in the OD section. The original notion was that I'd have a dedicated 100k clean-only V1 and a separate two-tube OD with 220k/150k on both.

As my experience and the knowledge base here at AG increased, I really like the low-plate clean into a high-plate OD. That said, the hi/hi RF style has it's own special charms so the plan morphed into a dual clean switching into a single non-HRM high-plate OD. There are several builders here who have dual OD versions but one of those is probably enough for me (or talk me out of it).

The issue is switching. Attached is a rough Paint block-diagram of the current iteration. There is no high-plate clean only option since, to my ears anyway, the low-plate is much more interesting. This doesn't show an additional OD relay that would kill the NFB loop on the low-plate channel when in clean mode on one side and kill the volume bright switch in OD. So four relays; two OD with connected relay ground-outs to the footswitch and two Hi/Lo relays -- also in parallel. Plus a mid and PAB rounds the relay count up to 6. The PAB would be a simple trimmer wired as a VR between the Middle pot lug 1 and ground so the relay could handle a channel on either side. The reason the bottom of the clean master feeds into the OD entrance rather than grounding is so the bright cap (if needed) has more resistance to bleeding highs.

It seems to work on paper but; a) there might be much easier ways to do this and b) there might be fundamental errors that our gentle readers will catch.

Please have a look at this and let me know what you think,

Thanks, Skip

[David Root]

I like the idea of having switchable lo-hi plate clean-OD but a six switch footswitch is a custom deal. I guess you could bolt two three switch cases together though. And if you want footswitched NOR/FET inputs that's seven and you're really screwed!

Then you are also going to run afoul of remembering which switch does what. Especially for us GOOFs like me (that's Genetically Obsolete Old Farts).

Couldn't there be a sequencing alternative to a DPDT relay? I'm certainly not a switching guru. Maybe I should revisit a couple of the TUT books, Kevin O'Connor IS a switching guru.

[Luthierwnc]

Only four buttons on the footswitch; Mid, Hi-Plate OD, PAB, and Lo-Plate OD. The two Hi/Lo relays share a common ground out to the footswitch and the two OD relays do as well. Remember -- the OD relays are normally closed in the clean position and the Hi/Lo relays are normally closed in the Lo position.

The attached diagram shows the two OD relays in parallel going to the footswitches. You'll have to imagine the Hi/Lo relays looking the same. In this case:

a) when the Hi OD and Lo OD footswitches are both off, it is clean,
b) when the Lo OD is on, it shorts the OD relays to ground but the Hi/Lo
relays are still closed and
c) when the Hi OD is on, it dumps both sets of relays to ground and
cuts the juice to the Lo OD switch. That way only one of the LEDs can
be on at a time.

When I was fooling with dual cleans and ODs, I messed with relay switches that tied into the negative side of the 12v pin and routed it to the positive 12v side of another relay so the latter couldn't be activated unless the former was on.

This is the point where I'm hoping someone says, "Why don't you just use a CMOS" or something like that. sh