JCM 800 - second footswitchable volume

Am_I_Evil · Post by **Am_I_Evil** » Sat Mar 07, 2015 7:16 am

Hi,

I "accidentally" got the Marshall JCM 800 2203 (1983), and find out, that this is a great amp. So I decided to kept it. But it has one problem, I can't boost volume for solos, because I use gain knob on max, and boosterst only adds more distortion, and not more volume. This amp does not have effect loop so I cant boost signal there.

I would like to do one mod, without changing the sound of the amp, and it could be reversed any time.
This is what I'm thinking:

- Replace lower input with one 1M pot for second volume
- and use one of the speaker outputs for footswitch
- and use one relay to switch from original Master volume to secondary Master volume

With this mod I could use second volume for solos. Is anybody done something similar to this? Is this good idea?

Thanks,
Uros

Thiez · Post by **Thiez** » Sat Mar 07, 2015 1:41 pm

Never done it myself, but i think its verry well possible.

What comes to my mind is to put only the footswitch input on the back, but the relay close to you MV. This way your signalchain won't have to go from front, to back, back to front again. I think this will reduce the noise.

You can also put a resistor in series with your existing mastervolume (like the famous 220k Mod5 resistor). For standard playing it's in there and with relay bypassing it you'll get a solo boost. This way you can keep your both inputs.

Carbia · Post by **Carbia** » Sat Mar 07, 2015 3:21 pm

I did that mod many times. Works great.

I use the Silver Jubilee circuit to relay's power supply.

herbvis · Post by **herbvis** » Sat Mar 07, 2015 9:13 pm

I have a solution for you. PM sent

Am_I_Evil · Post by **Am_I_Evil** » Sun Mar 08, 2015 7:35 am

What about "dual pot", some mixers have them. In this case, only master volume and output jack are changed and I keep booth inputs.

ivan H · Post by **ivan H** » Sun Mar 08, 2015 8:34 pm

Hi, the dual type pot that u refer to is called a "concentric" pot. Pretty readily available. Hope this helps. Cheers

Am_I_Evil · Post by **Am_I_Evil** » Mon Mar 09, 2015 7:48 am

Thanks Ivan, I didn't know what is the "name" of this type of pots. And I also noticed that is almost impossible to get 1M/1M concentric pot in EU...

If anybody knows, where can I get them, please let me know...

Haze13 · Post by **Haze13** » Mon Mar 09, 2015 2:37 pm

small bear electronics - Not in UK but I trust this man... Bought from him number of times. Not cheap, but it works.

Am_I_Evil · Post by **Am_I_Evil** » Thu Mar 26, 2015 2:27 am

Yesterday I add second volume to my P1Extreme. I switch between volumes with rele, and it works great. Now I have to do it on my JCM. I will attached pictures when I done this mod.

Vegard · Post by **Vegard** » Fri Apr 10, 2015 5:19 pm

You can also install the ZeroLoss FX loop, and put ex. MXR Microamp pedal as boost. Works very well...

wdelaney72 · Post by **wdelaney72** » Tue Jul 07, 2015 11:16 am

Carbia wrote:I did that mod many times. Works great.

I use the Silver Jubilee circuit to relay's power supply.

I just used this relay channel switching circuit in a new build....it's dead silent and perfect.

Carbia · Post by **Carbia** » Tue Jul 07, 2015 8:21 pm

Glad to hear it!

I did it many times and runs perfect.

Am_I_Evil · Post by **Am_I_Evil** » Wed Jul 15, 2015 1:28 am

I agree

it works so great, and it doesn't change the tone. I think this is the best simple option to get "second" channel in one channel amp.

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JCM 800 - second footswitchable volume

JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume

Re: JCM 800 - second footswitchable volume