single channel channel switching

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Fndrfreek69

New member
I own a late eighties marshall jcm800 1x12 combo single channel. it has the low and high sensitivity inputs and i was wondering if there was a way to switch between the two, maybe with an ab switch or something...thanks for any help!
 
Re: single channel channel switching

No. I owned a couple of these back in the day.

IIRC, the jacks are wired so plugging into the clean jack disconnects the high-gain jack. I believe the clean jack actually skips over (disconnects) an entire tube gain stage, though I'm not sure about that because it's been a long time, and Marshall built a couple different versions of this.

The single-channel JCM800's are great amps, though. You can set them up for medium gain and get them to clean up by reducing the guitar level using a compresor or EQ (check the new Paul Gilbert signature clean EQ pedal - don't recall its name but ErikH just posted about it recently).

Of course MORE gain from a JCM800 is easy - any clean boost, EQ, or dirt box will give it to you.

I wish I had my single-channel, 50-watt, 1x12 model 4010 combo back. The perfect amplifier IMHO.
 
Re: single channel channel switching

Crank that baby to get the goods and use an EQ (graphic or Paul Gilbert's Detox EQ) to get a clean-ish tone if you want a quick stomp rather than rolling the guitar volume back. I like the idea of being able to do either/or so having the EQ out front to choke the signal back and re-EQ for a nice clean-ish tone is great. I'll be using a Detox EQ with a single channel JCM 900 MkIII once the thing gets here. Darn UPS for not working on the weekends.
 
Re: single channel channel switching

Fndrfreek69 said:
I own a late eighties marshall jcm800 1x12 combo single channel. it has the low and high sensitivity inputs and i was wondering if there was a way to switch between the two, maybe with an ab switch or something...thanks for any help!
Click to expand...

I don't think that'll work... typically with dual input amps, plugging into both at hte same time gives the same tonal result. What I do with single channel amps is set it up so that when the guitar volume is all the way up, a chord is distorted but single notes generally aren't... then use dirt boxes/boosts/fuzz to push it harder for more grind, and back down the guitar volume & lighten my hands to get clean sounds.

The whole key is finding the point where the amp starts to saturate.
 
Re: single channel channel switching

thanks guys....it just seems that the marshall always has to much gain for me... i mean i am absolutely in love with the amp but im not really a metal or even hard rock style of player so all that gain is not necessary....is there a way to reduce the gain on the high sensitivity channel while keeping the insane amounts of volume....i mean this thing is like a stack in a very small box
 
Re: single channel channel switching

Turn the master volume up - that will give you the insane amount of volume. Then turn the preamp volume up just a little - it should stay fairly clean. It's a Marshall, so don't expect Fender Twin Reverb kinda clean.

It's a balancing act - the master volume shifts your dirt generation to the output stage, while the preamp volume makes dirt in the preamp. YOu have to find a sweet spot that works for you. In my opinion, master-up, preamp-down type of overdrive is easier to control from the guitar, with the volume pot or just picking strength. Of course it's going to be loud.

On second thought, it's hopeless. Just send the amp to me, and I'll dispose of it for you.
 
Re: single channel channel switching

plug into the hi input and put a footswitch into the lo input. could do this to a Peavey VTM, which is supposedly modeled after a jcm800.....
 
Re: single channel channel switching

lastwinj said:
plug into the hi input and put a footswitch into the lo input. could do this to a Peavey VTM, which is supposedly modeled after a jcm800.....
Click to expand...

This won't work on the 800s. Plugging into thlow input disconnects the first stage. An A-B won't work either; you end up with only a clean channel.
 
Re: single channel channel switching

Fndrfreek69 said:
thanks guys....it just seems that the marshall always has to much gain for me... i mean i am absolutely in love with the amp but im not really a metal or even hard rock style of player so all that gain is not necessary....is there a way to reduce the gain on the high sensitivity channel while keeping the insane amounts of volume....i mean this thing is like a stack in a very small box
Click to expand...

There are things you can do increase the clean head room and then you would use a pedel or pedals set to taste for your overdrive/distortions.

Using a lower gain tube like a 12AY7 in V1 will go a long way to keeping it cleaner while getting louder. You could also try a 12AT7 in the phase inverter slot (v3), and you would probably like it better setup for 6550/KT88 rather than for EL34's. You can also fine tune it some with how the tubes are biased.
 
Re: single channel channel switching

i was thinking about getting some of the thd yellow jackets for it to maybe give it a more voxy vibe but i am afraid that with the high gain tendencies of the amp as it is using the el-84's would just make it distort earlier than just providing a more class A sound. thanks for the help!
 
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