need some suggestions on JCM 800 mods

[WhoFan]

OK i for years have been wanting a JCM 800, since i was teen in the 80's. In fact i used to go to a Toronto store every Saturday and dream about an 800 and a 4x12 cab.. When i got older Marshall had changed to 900 series and i ended up buying other companies amps. I hear the 800's can be extremely great sounding when set up right.

I bought a beat up used 800 last winter. It's an early 80's 50 watt head. Some one had stripped the vinyl off the head and it has an extra Pre Tube gain mod of some sort. Sad part is it is also noisey. The more you turn the gain up the buzz and hum get louder. I have a good tech, one of the best around i will take it to soon but before i do does anyone have any tips as to what i should have done?

Some questions i have are
1-Can an 800 be gain modded but be dead quiet? I've heard of many pro players having such mods in their Marshalls..... The extra noise in my 800 is there even if the guitar cord is unplugged from the amp. As long as the standby is on and the preamp gain is up the amp has much louder hum then any of my other higain amps.

2-The tech has suggest removing the gain mod but says an EQ mod he has done before greatly improves the sound of the amp. Is there any mods i should know about and ask about before i take the amp to him.

I heard Eddie Van Halen used JCM 800's live on stage from 1982-1990.... i know his whole systems were a complete custom job but his 800's sounded great! I'd like to get close to that. The 5150 is a great amp and i own one of those but i'd like to try and get his 80's tone... and oneday maybe try the VH1 sound.

WhoFan

 

[WhoFan]

Re: need some suggestions on JCM 800 mods

PS-Can anyone give me detailed info on how i should cut and glue new vinyl back on the amp.....

WhoFan

 

[STRATDELUXER97]

Re: need some suggestions on JCM 800 mods

The best mods you can do right off the bat,is to remove the extra gain stage..That adds alot of extra wiring,antenna effects,and hissy,noisey crap all around the preamp..If you need more gain from an 800,either use a pedal with it,or sell it! LOL....


After that,replace all of the 50/50 standing can caps,put some fresh tubes into both the preamp and output section and have the tubes biased...Sit back and listen to what a stock 800 sounds like,and then decide what you'd like your amp to have? More bass,more mids,less highs,etc....

John

 

[Lewguitar]

Re: need some suggestions on JCM 800 mods

The best mods you can do right off the bat,is to remove the extra gain stage..That adds alot of extra wiring,antenna effects,and hissy,noisey crap all around the preamp..If you need more gain from an 800,either use a pedal with it,or sell it! LOL....


After that,replace all of the 50/50 standing can caps,put some fresh tubes into both the preamp and output section and have the tubes biased...Sit back and listen to what a stock 800 sounds like,and then decide what you'd like your amp to have? More bass,more mids,less highs,etc....

John

Right On! :laugh2: The best mod for a modded early 80's JCM 800 is to return it to stock, recap it and put some great tubes in it, because those are some of the best sounding rock amps ever created. Put it back to stock and then if you need more overdrive get a nice Boss DS-1 or Duncan Pickup Booster or something similar to goose the front end.

 

[STRATDELUXER97]

Re: need some suggestions on JCM 800 mods

Right On! :laugh2: The best mod for a modded early 80's JCM 800 is to return it to stock, recap it and put some great tubes in it, because those are some of the best sounding rock amps ever created. Put it back to stock and then if you need more overdrive get a nice Boss DS-1 or Duncan Pickup Booster or something similar to goose the front end.

Right on brother Lew! The extra gain stage in the 800s is just a bad thing...Added gain,but added noise,hiss,hum,and and an overall crappy compressed tone...Yucky and not for the 800 series...I say buy the DSL or the TSL Marshall stuff if you need all that gain...

John

 

[Pandemonium]

Re: need some suggestions on JCM 800 mods

If you need more gain from an 800,either use a pedal with it,or sell it! LOL....

Gets my vote.

 

[Boleslaw Gers 666]

Re: need some suggestions on JCM 800 mods

What works about Marshalls for me is you get them out of the box (be it from Guitar Centre or from eBay), wire it up, plug in, turn on, and you've got the best tone around. Sorry yours isn't working for you. JCM800's I've seen didn't have an overdrive channel.... or am I crazy?

 

[WhoFan]

Re: need some suggestions on JCM 800 mods

Thanks for the imput.... my gut has been telling me to return it to stock. That extra noise/gain mod is bugging me..... before i would buy the head the store i bought it from sent it to a tech for retubing.... He just put in power tubes and cleaned up a few pots and replaced a speaker jack. Once i bought the head i took it back as it had tons of noise and was picking up radio stations. They replaced a few caps and a bad pre tube plus sheilded some parts from noise which made it better but not the best with no futher charge to myself. So they tried a lot and grabbed the head for a steal of a price so i'm just happy i got it.

I should return it to stock i guess. The one mod i think i will go for is to replace the jacks to metal ones. The plastic Marshall speaker and imput jacks are brand new and they do not hold the cables pin well enough for me....... I worry the speaker cable could come out....

WhoFan

 

[STRATDELUXER97]

Re: need some suggestions on JCM 800 mods

Thanks for the imput.... my gut has been telling me to return it to stock. That extra noise/gain mod is bugging me..... before i would buy the head the store i bought it from sent it to a tech for retubing.... He just put in power tubes and cleaned up a few pots and replaced a speaker jack. Once i bought the head i took it back as it had tons of noise and was picking up radio stations. They replaced a few caps and a bad pre tube plus sheilded some parts from noise which made it better but not the best with no futher charge to myself. So they tried a lot and grabbed the head for a steal of a price so i'm just happy i got it.

I should return it to stock i guess. The one mod i think i will go for is to replace the jacks to metal ones. The plastic Marshall speaker and imput jacks are brand new and they do not hold the cables pin well enough for me....... I worry the speaker cable could come out....

WhoFan

The plastic jacks are still in my 73 head and they aren't a problem..I'd leave those alone,but have them take that silly preamp gain stage outta your amp! You also don't know anything about the mods or whether the guy that did the mod even was good at it? Picking up radio stations isn't a sign that the mods were done right...Anytime you add gain stages or do anything to the preamp,you have to shield the wiring to the input jacks,use very short lead runs,and correctly lift and reposition certain wires that create noise...These types of mods make a Marshall very unstable,cause for more overall noise,and it can create a host of oscillation problems and ghosts and goblins as you start turning up your volumes... :smack:

This high stuff is better left to an amp that has it built in from the factory correctly....I.E. The DSL and TSL series or a boutique high gain amp such as the Soldano SLO 100 etc..

 

[WhoFan]

Re: need some suggestions on JCM 800 mods

Ya i have no idea what the mod was..... all i knew is it had been gain modded as it had an extra tube, but i also knew that this amp was a real fixer upper when i bought it...... so i knew it needs work to be a great amp. The plastic jack's seem to let the cords fall out way too easy.... the first tech that the store uses says that is the way Marshall makes them. It worries me that the speaker cable could fall out..... The imput HIGH jack allows my cord to fall out all the time and it is a new jack and the speaker jacks are the same as far as their holding power! The tech i wish to take this amp to works for some huge sound companies working in the big Canadian arenas.... He gets called into help the pros out when needed. He said he could change the Plastic Marshall imput/output jacks with the same ones most touring bands add and they are made of metal and will not break that easy. Not sure what brand of jack it is he is talking about but he also said the original ones can be replaced if i ever wanted to return them... He says anytime you mod an amp it is important to be able to return it to stock....

WhoFan