JCM 900 4500 Dual Reverb

The Scarecrow · Post by **The Scarecrow** » Mon Aug 02, 2004 10:35 am

So, I've got the 50w version of this head (circa '93) which has been rebiased to EL34's from dirty 5881's. I'm running it through a Crate 4x12 with Celestion G12T-75's.

My effects, which I use in the effects loop are a Boss Ch-1 Chorus and an Ibanez PT909 Phase Tone. Between the amp and the guitar I run a Boss BD-2 and TU-2 Chromatic Tuner.

My guitar is a '61 reissue Gibson SG, with '57 classics in the neck and and bridge, completely unmodified.

My problem, has been getting a good tone that isn't too harsh with the stupid shared EQ (which the bane of the majority of the current Marshall range.)

Does anyone here use this amp/or a similar one and can offer some settings that work well for diry and clean. I tend to play overdriven most of the time, so the B-channel is mostly favored, for a hard rock/emo gainy type of distortion a-la Foo Fighters/Queens of The Stone Age/Jimmy Eat world.

Any help appreciated!

Zakk Wylde · Post by **Zakk Wylde** » Mon Aug 02, 2004 6:36 pm

Firstly, Ditch the CH1 for a CE-5

Sorry, had to say it

The Scarecrow · Post by **The Scarecrow** » Tue Aug 03, 2004 8:18 am

Zakk Wylde wrote:Firstly, Ditch the CH1 for a CE-5

Sorry, had to say it

it's not mine, on loan from bandmate. i'd rather have a flanger or delay, but it makes my clean sound (an oxymoron when referring to the 900 series of JCM's in most cases) better.

makes a weird humming noise when on, think it's a bit poked.

Rog · Post by **Rog** » Tue Aug 03, 2004 8:37 am

> makes a weird humming noise when on

Does it make the noise when using a battery?

The Scarecrow · Post by **The Scarecrow** » Tue Aug 03, 2004 9:28 am

DrRog wrote:> makes a weird humming noise when on

Does it make the noise when using a battery?

haven't tried, but i think my bandmate who loaned it to me said it was a bit of screwball. it's quite possibly like that because I daisy-chain the power off my TU-2 and the PSA i'm using is a bit naff.

i'll be using batteries for my gig this Friday.

Rog · Post by **Rog** » Tue Aug 03, 2004 10:02 am

Sometimes, if using pedals from PS you get hum, it can be helped by a smoothing cap in circuit.

Power supplies can be very basic indeed and smoothing is often not given due consideration.
This results in a significant ac ripple on the dc level, which can be heard as humming.

philipnz · Post by **philipnz** » Tue Aug 03, 2004 10:07 am

Although they are expensive I've fouind it best to use the Boss adapters into a TU-2 if you are driving other effects from it. I've noticed hum on other suppliers.

I bought two vintage CE-2 black label MIJ chorus pedals. I have had one Keeley Modded and i'm going to onsell the other (depending which one i like the most.)

angry_young_poet · Post by **angry_young_poet** » Tue Aug 03, 2004 11:03 am

Yup invest in a Boss PSA and a Boss daisy chain and the hum will probably disappear...

gregtarr · Post by **gregtarr** » Tue Aug 03, 2004 5:23 pm

Ok, I have the exact same amp (except with the dirty 5881's). I have the bass set around 4, mids 7, treble either 6 or 7 and prescence around 6. I just leave that, and I have a GE 10 which I have infront of everything, and a GE 7 as a boost, in the loop. I just fiddle with the GE 10 till I like what I hear. At the moment the mids are swept slightly and it sounds great, clean and dirty. Although, I am using a Mexican strat, so single coils usually, but also it sounds pretty good with the SD Hotrails in the bridge.

The Scarecrow · Post by **The Scarecrow** » Wed Aug 04, 2004 8:25 am

gregtarr wrote:Ok, I have the exact same amp (except with the dirty 5881's). I have the bass set around 4, mids 7, treble either 6 or 7 and prescence around 6. I just leave that, and I have a GE 10 which I have infront of everything, and a GE 7 as a boost, in the loop. I just fiddle with the GE 10 till I like what I hear. At the moment the mids are swept slightly and it sounds great, clean and dirty. Although, I am using a Mexican strat, so single coils usually, but also it sounds pretty good with the SD Hotrails in the bridge.

Mate, seriously, shell out the dollars and get rid of those 5881's. I noticed the EL34 difference right away when I rebiased mine about three months ago. It cost a couple of hundred as a had a full service done and my reverb unit replaced, but SO WORTH IT. Automatically sounds warmer, more vintage-Marshall. To me, 5881's sound fairly akin to a lot of the Valvestates out there, but when I think about it, your EQ's probably make up for that.

Hit a sweet spot last night, which works on both channels:

Presence - 4.5
Bass - 5
Mids - 6
Treble - 7
B-Channel Gain - 8
A-Channel Gain - 2

I get a very nice low-end crunch from that, the sound I've been after. The B-channel gain may sound low, but is actually a lot beefier due to the '57 classics on my SG. Sounds gut-renchingly powerful on the neck and wails like 70's lead on the bridge.

I added my BD-2 with the gain set at 7 o'clock (i.e none), tone at 11 o'clock and level at 2 o'clock, and bang, my amp goes all Mesa! Couldn't believe it - the gain level when using on the B-channel was pure Boogie and it gave me a nice vintage Fender-crunch on the A.

Just in time for my gig this week!

gregtarr · Post by **gregtarr** » Wed Aug 04, 2004 10:03 am

The funny thing is that I tried to get rid of the 5881's, and had even ordered some, and then the amp tech here said that he wouldn't "butcher" my amp!
But no, I'd say that it doesn't sound like a Valvestate.
I'll look into in at the end of the year (when I have a chance to make some $) as well as some new preamp tubes (for the hell of it). Just here in Dunedin, I'm a bit limited when it comes to choosing some one to do this stuff. One music shop has no amp technician (at all), and then theres the Rockshop guy who said that he wouldn't. And actually, now that I remember, he said that he had never heard of anyone wanting to change 5881's for EL34's. Who/what/where/when/why did you get to do it to your's?

The Scarecrow · Post by **The Scarecrow** » Wed Aug 04, 2004 11:32 am

gregtarr wrote:The funny thing is that I tried to get rid of the 5881's, and had even ordered some, and then the amp tech here said that he wouldn't "butcher" my amp!
But no, I'd say that it doesn't sound like a Valvestate.
I'll look into in at the end of the year (when I have a chance to make some $) as well as some new preamp tubes (for the hell of it). Just here in Dunedin, I'm a bit limited when it comes to choosing some one to do this stuff. One music shop has no amp technician (at all), and then theres the Rockshop guy who said that he wouldn't. And actually, now that I remember, he said that he had never heard of anyone wanting to change 5881's for EL34's. Who/what/where/when/why did you get to do it to your's?

I had mine done by a place up here in Aucks, through a mate who knew the tech. Apparently it's the place where all the Rock Shops send Marshall's to be repaired. It's costly, but as I said before, so worthwhile. The problem is that they don't deal directly with the public and I had a special favor done, which was expensive even then (but justified considering I only paid around $400 for my JCM900 and $400 for my quad) but if you have it done through a music shop, I wager they'll add their cut. Can't recall the name of the place, Music Factory or something.

I got it done because I did some research online, and the JCM 900's with EL34's are considered to be closer the 800/2000 sound, which I wanted. That and the 5881 versions just don't seem to be rated as much, and IMO, I can kinda see why. The sound is just a lot harsher, less rounded and the EL34's just sound more vintage.

Sound like your local RS guy is a bit behind the times? The rebiasing of tubes is fairly basic if you know what you're doing and don't rush into it, i wager even I could pull it off, though i prefer to leave stuff like that to the techs. A lot of 5881 tube users go to EL34's and wonder why they didn't do it sooner. I do think though, that in this case, proximity is going to make getting the tubes altered a bit of an issue.

The biggest difference is on the clean channel, I found. Jus a lot more warm sounding, less brittle. The gain channel is better to, less fuzzy and harsh, just a creamier tone. One thing I did learn from the tech who fixed my amp, is to leave the half-power option alone, i.e play on full power the whole time, or half-power all the time. Changing can mess with the bias and screw the tubes....

gregtarr · Post by **gregtarr** » Wed Aug 04, 2004 1:32 pm

Ok, well, I'll look into it later anyway. It's still the most awesome amp I've ever heard, by quite a bit. It's a lot better than 30W EL34 Marshall combo, and from what experience that I have had, it sounds better (to me) than (the single) Mesa combo that I've played.
I have read all over Harmony Central about the 5881/EL34 stuff.
$800 for both! I paid nearly twice that (including courier though) and it's been commented that the seller got ripped off...

gregtarr · Post by **gregtarr** » Wed Aug 04, 2004 5:43 pm

I was just thinking, and wondered if the difference you noticed between when you had 5881's and EL34's was perhaps (at least in part) due to the 5881's being old and the EL34's being brand new? I mean, Dr Rog posted a while ago about a whole bunch of guitarists not always even being able to tell the difference between a Marshall stack and a Fender Twin purely on the basis of sound (well, that is kind of what he said, it was more that no one could tell the difference between the guitars.
I myself have heard a Mesa (on tv, it was Incubus) and thought "That sounds exactly like my amp" (honestly), only to find out that it was in fact a Mesa.
I'm just wondering whether the differences (slight differences? they look pretty similar to me, but that's just a guess) are actually significant enough to be audible. I mean, it's still the exact same amp, only different tubes and a different transformer (I think, I'm pretty sure that they run at different voltages).
What does every one reckon?

Tsuken · Post by **Tsuken** » Thu Aug 05, 2004 8:02 am

The Scarecrow wrote:
Zakk Wylde wrote:Firstly, Ditch the CH1 for a CE-5

Sorry, had to say it
it's not mine, on loan from bandmate. i'd rather have a flanger or delay, but it makes my clean sound (an oxymoron when referring to the 900 series of JCM's in most cases) better.

makes a weird humming noise when on, think it's a bit poked.

If I use my CE-5 with a lot of gain on the amp I get a big constant hum. If the gain is only around 8 or less, no problem, but that last little twist of the dial does result in big hummage.

Of course, I'm thinking that I won't need quite so much gain when playing at decent volume (rather than basement-solo-practice levels), I probably won't feel the need for so much gain.

.....yeah, right