Channel switching mod idea, what do you think?

SteadyEddie · Post by **SteadyEddie** » Sun Nov 22, 2015 2:56 pm

I've got a 2204 clone. Sounds killer, gets me right up to some great blues and classic rock sound. I mean AC/DC sound in spaces.

But I'd like a lead boost. A boost in both gain and volume.

So... My amp started out as a plexi, so I have some extra holes. Was gonna get a mojotone relay kit, and switch in a second master volume, AND switch in a .68uf cap across that 10k cathode resistor on V1B. To make it adjustable, put a pot in series with it, so I can dial in the amount of extra gain I want.

Sounds like a good idea? Anyone see any problems with this?

What value pot would you recommend for this?

d95err · Post by **d95err** » Mon Nov 23, 2015 6:03 am

Sounds like a good idea.

Guessing at the pot value, I think a 50-100k pot would make the 0.68uF cap essentially out of the circuit at max resistance. You'd have to experiment with the taper of the pot to make the sweep usable. Reverse log taper might be best.

herbvis · Post by **herbvis** » Mon Nov 23, 2015 6:36 am

A second master is cool. Ive got one so I can balance out the volume between a dirty and clean channel. You can make your amp do just about anything if you plan it out well.

SteadyEddie · Post by **SteadyEddie** » Mon Nov 23, 2015 9:34 am

I just tried a 100k audio pot because it's what I had laying around. I soldered the .68uf cap right to the pot and ran a wire to the 10k.

Taper is all wrong. All the gain comes on right at the end of the pot sweep.

BUT, the gain boost is substantial, as I guessed it would be. You're bypassing a 10k resistor (cold biased stage) and the effect is very noticeable. Notes fly off the fretboard with little effort. A friend heard it and called it the "slash mod" because it takes the amp from AC/DC or ZZ Top territory to GnR and I could also pull off Ozzy stuff. Say goodbye to overdrive pedals. I'm really puzzled as to why some people add extra tubes and so forth, when one cap gives you such a gain boost.

So I'm stoked. When I get this set up with relay switching for a second volume, it will be really really nice. A 2204 is just such a great sounding amp and this kind of expands on it.

Next step will be the effects loop.

herbvis · Post by **herbvis** » Mon Nov 23, 2015 4:27 pm

You can make a 2203 a very versatile amp with some creativity. I turned my 2203 into a 3 channel footswitchable amp. 2 classic Marshalls and the afd mod in one amp. With independent gains for each channel and a seperate mv for the cleaner 1959 type channel. No channel bleed or crosstalk either.

pretty rockin amp.

You will have to post some samples of your amp when you get it situated

giordydiver · Post by **giordydiver** » Wed Dec 02, 2015 6:24 am

i have a question about mojo relay kit, on the jack side I have Fs and Grd, what is the difference?

Am_I_Evil · Post by **Am_I_Evil** » Mon Jan 11, 2016 7:28 am

Hi, I modified my Marshall JCM800 with one more footswitchable volume, and it works great.

http://www.ampspecs.com/marshall-jcm800 ... olo-boost/

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Channel switching mod idea, what do you think?

Channel switching mod idea, what do you think?

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