Author Topic: Plexi AND JCM 800 (Read 13966 times)

Bainzy · « **on:** November 09, 2005, 08:42:04 PM »

Would anybody be interested in a mod to those Marshall reissue plexis that adds a switch on them that tonally transforms the amp 100% into a JCM 800? The only cosmetic downside to the mod would be the addition of a 4th preamp tube, and wherever you'd want the switch mounted. The normal channels' pot would act as the preamp gain pot when the JCM 800 mode was engaged.

Just thought I'd ask as I've been working on mods like this for a fair bit of time now, and I'm still working out ways in which to pay myself through university - if there's demand there this would be a cool thing to do.

I can imagine people may be worried that 2 amps in one would be a 'jack of all trades - master of none' affair, but in this mod the circuits would be EXACTLY the same as each amp in question when the respective mode is selected, and should sound EXACTLY the same as a JCM 800 or Plexi that was configured to that circuit.

Ratrod · « **Reply #1 on:** November 09, 2005, 08:54:34 PM »

If I had one, I would be interested. Seems like a great mod.

Bainzy · « **Reply #2 on:** November 09, 2005, 08:57:14 PM »

it'd probably be possible on the JCM 800 reissue, yet it'd require drilling holes for the 2 extra inputs on the front, so you'd lose the amp's stock appearance. I'd object to cutting up any vintage amps like this, unless they were already cannibalised by mods in the first place.

indysmith · « **Reply #3 on:** November 09, 2005, 11:20:36 PM »

i really wouldn't mind you cutting up my 1984 JCM800 if yu could make it a plexi ASWELL! I'd love you forever! Sounds like a great idea. Surely it can only increase the value - who doesn't want the two best marshalls in one package!?

willo · « **Reply #4 on:** November 09, 2005, 11:32:18 PM »

Quote from: indysmith

i really wouldn't mind you cutting up my 1984 JCM800 if yu could make it a plexi ASWELL! I'd love you forever! Sounds like a great idea. Surely it can only increase the value - who doesn't want the two best marshalls in one package!?

well, I reckon it would probably decrease the value actually. You know what some people are like, they really hate mods and treat them with suspicion. Of course, the irony is that most mods are made with the intention of improving the guitar/amp, but sometimes some people are just purists stuck back in the 60's somewhere. My personal opinion is that mods like Bainzy's are all good though; I don't buy something and think of the resale value. So I'd be interested!

How would it work? Like a second gain channel engages the JCM800 circuit?

big steve · « **Reply #5 on:** November 09, 2005, 11:33:48 PM »

if you're worried about the realse value of your amp, then you don't really own the amp, do you? the future owns the amp. you're just leasing it.

willo · « **Reply #6 on:** November 09, 2005, 11:37:10 PM »

Quote from: big steve

if you're worried about the realse value of your amp, then you don't really own the amp, do you? the future owns the amp. you're just leasing it.

exactly! well said, steve!

I would think though, by virtue of us all being here on a retro-fit pickup website that we all have at least some interest in modding! :)

big steve · « **Reply #7 on:** November 09, 2005, 11:40:21 PM »

good point well made, but it's easy to put the old pickups back in if you feel like selling a guitar on...

Bogner · « **Reply #8 on:** November 10, 2005, 01:09:38 AM »

If you could mod my Zakk Wylde 2203 head to have a better gain, I would go for it. To me, it is lacking gain big time. Great amp for some things but pales in comparison to my other heads for straight out of amp gain....

indysmith · « **Reply #9 on:** November 10, 2005, 02:20:08 AM »

i think we need a simple, easy mod to boost a JCM800. The most common complaint about the 800 is that it doesnt have enough gain! I never heard of anyone using a jcm800 without a booster pedal of some sort! I'd love a gain mod, and a built-in attenuator, to make the amp truly my own :lol: 8)

big steve · « **Reply #10 on:** November 10, 2005, 04:43:41 PM »

the classic gain mod is to add an extra gain stage to the preamp. there is an old story about a handwired marshall combo which had tube tremolo which had broken, and a tech modded it to an extra gain stage. the amp went on to be used on numerous seminal recordings, gnr for example.

Bainzy · « **Reply #11 on:** November 10, 2005, 05:40:49 PM »

Quote from: big steve

the classic gain mod is to add an extra gain stage to the preamp. there is an old story about a handwired marshall combo which had tube tremolo which had broken, and a tech modded it to an extra gain stage. the amp went on to be used on numerous seminal recordings, gnr for example.

i can do that mod on a Marshall like a JCM800 or Plexi etc. it'd be more gain than a stock jcm800, you can hear it on Appetite For Destruction. I'll wire that mod up on my plexi in the next few days and record some clips so you can hear it if you like.

The JCM800 probably has room for adding a switchable extra gain stage without adding an extra tube, I'd have to see the specific model to work that out though.

Gain doesn't need to be added through an extra preamp tube, it can be added by changing components or the structure of the circuit. Having said that, I think the extra preamp tube mod is the coolest as it's easily switchable and sounds 'the dogs nads'.

I think the reason there's a lot of people against modded marshalls partly because they are either collectors (who understandably would want a stock amp), or are against mods where the modder has done something irreversible to the amp like throwing away (or pocketing for themselves :x ) components that are no longer in production.

Someone that's purely a player would not be bothered about the mods provided they could be returned to stock if necessary, which is what I'd aim to do. There's no point cutting out holes in the amp however if it's for something that might be taken out later, so if I was in a situation where that had to be done I'd wire it up first and let the owner hear the mod so they could decide whether they're definately wanting the hole made beforehand.

Quote

How would it work? Like a second gain channel engages the JCM800 circuit?

basically the high treble channel has an extra gain stage wired to it that can be cut in and out with the switch. the extra gain stage has the same structure as the jcm 800's additional gain stage over the plexi.

it would be also possible to replace the 4 inputs with 2 inputs, so a switch could select between plexi and JCM 800 on channel 1, then flick a switch so they're on channel 2 that's the same as a plexi's 'normal channel'. that normal channel could be configured to be a fender-like clean channel.

Ratrod · « **Reply #12 on:** November 10, 2005, 06:09:21 PM »

Here in Holland the value of an amp increases when it's modded by a 'legendary' name.

It's probably mostly the Vox and Fender collectors who don't want mods, overhere.

Bainzy · « **Reply #13 on:** November 10, 2005, 06:15:51 PM »

It's a shame to think that some mods that were put in Marshalls in the 80's that actually made the amps sound geniunely better will have been taken out by people wanting to return it to stock for resale value - imagine if that amp slash used for AFD turned out like that.

HJM · « **Reply #14 on:** November 10, 2005, 06:22:50 PM »

All sounds good to me your mod....not seen one like that but I did toy with a channel switching idea like this, one JCM800 channel, one plexi with a power soak and a variac on the preamp valves, but it got shelved no cash.....!