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| | |-+  Basic clean / OD channel switcher based on Plexi
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Author Topic: Basic clean / OD channel switcher based on Plexi  (Read 3446 times)
LRebo
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« on: July 24, 2012, 01:23:58 PM »

Posting as I am currently asking Nik about something like this but using the AFD amp as a base since it already has the relay.

The principle would be:

Plexi clean channel with a footswitchable modded 2204 OD mode.

Starting with a Plexi 50 amp for instance, one DPDT relay would switch between two volume (gain) controls, one of which would route the signal straight to the mixer (for plexi cleans) and the other would cascade the first gainstage into the second one, and then to the mixer for OD. A second relay would switch a pre PI MV in and out, being only active in OD mode for volume balancing. A post PIMV could be used for overall volume.

It's basically a switchable one wire mod (with tweaks for better tone) but also switching the pre PIMV in and out for volume balancing. The cleans side can be nice as Plexi cleans are or get to medium gain, and the OD mode could be tweaked from anything from a Jose style, to a Bogner Blue channel or whatever.

It works great, I've done it with some sucess but I'm a rookie and my amp looked a mess so I wouldn't trust its reliability ... it would be nice to get it straight from Nik for it to be wired properly! I don't really know why nobody offers and amp like this stock ... they always add too many bells and whistles.

The AFD is already almost there, you just need that the relay also switches the pre PI MV in and out for it to be active only in OD else you have too much of a volume difference especially if you want the cleans to be really clean. Also, instead of both modes sharing the first gain control, the relay should also toggle between two gain controls for proper setup of clean and OD.

If the base amp is a Plexi of course there'd be a stage gain less than on the AFD. With the extra tube the AFD allows more tone shaping ... you could even have a switch to bypass one of the stages in OD mode for a medium gain setting.
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guitar2
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« Reply #1 on: August 15, 2012, 01:26:42 PM »

Hey that's a good idea.  I have been thinking the same thing about my 2550 clone. I have tired of the diode clipping and was thinking of dropping in a valve only preamp board such as the JCM800 2204.  With the relay it should be possible to switch between the two inputs and so effectively create a clean and gain channel.  Volume levels would be very different but the second pole of the relay could be used to switch between two different master volume pots.  There would be a spare pot position as the lead master would not longer be required.

Questions would be around electrical compatibility (2550 power transformer has slightly higher voltages then 2204) and mechanical compatibility (would the board fit, would re-drilling be required).

I have not tried it yet but would be interested to know how your mod turned out?  What circuit did Nik suggest?
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LRebo
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« Reply #2 on: November 05, 2012, 10:30:24 PM »

Hey that's a good idea.  I have been thinking the same thing about my 2550 clone. I have tired of the diode clipping and was thinking of dropping in a valve only preamp board such as the JCM800 2204.  With the relay it should be possible to switch between the two inputs and so effectively create a clean and gain channel.  Volume levels would be very different but the second pole of the relay could be used to switch between two different master volume pots.  There would be a spare pot position as the lead master would not longer be required.

Questions would be around electrical compatibility (2550 power transformer has slightly higher voltages then 2204) and mechanical compatibility (would the board fit, would re-drilling be required).

I have not tried it yet but would be interested to know how your mod turned out?  What circuit did Nik suggest?

Sorry about the late reply ... at the end Nik suggested to wait until the release of his new King Kong amp (basically two Yetis or Chupas in one amp) ... he was too swamped with work to do custom one-offs. It's been a while though.

The idea does work and it really has been mentioned online in a few places including the Metroamp forum where I got most of my info from. No secret really, just seems odd to me that something like that is not commercially available ... always too many extra tone tweaks. You have to use relays for it to work easily and without problems IMO. I had trouble with signal bleeding and oscillation using optos/vactrols and FETs. My amp is pretty much butchered so I'm selling it as is to a local guy who is fully aware and I'll probably will start from scratch modding a new Plexi 50 or 2204 already built kit to have something reliable to play on ... more than reliable "clean" as the amp is perfectly functional but the chassis looks like Swiss cheese and I have too many knobs ans switches on the outside.
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