Marshall JCM800 FOR BASS

[Dave]

Has anyone ever played through/owned one of these. I saw a band using a Marshall amp and decided I wanted to give one a try to see if I could reproduce the bassist's slightly distorted/overdriven Marshall tube tone (it sounded AWESOME). Must admit I wasn't totally sure this was the head he was using (couldn't get close enough to find out) but I was convinced I could read JCM on the amp, so unless he was using a guitar amp, I don't think it could have been anything else.

Long story short, I picked one up on ebay, but can't for the life of me get it to distort. I wonder if this is because it's the BASS version. There's very little info on this amp on t'internet, but the majority of things I read about older valve amps is you can't really turn the volume past 4 without getting distortion, and yet when I hooked this beast up to my MarkBass traveller 151 I could crank it up to 10 and it still sounded clean (AND LOUD).

While this would normally be a good thing, I was actually after the distorted tone, so it isn't really what I'm looking for. Any suggestions? And before you ask I did have a super-brief chat with the bass player using said amp, and he said he didn't use any effects and the tone was all about the Marshall.

[Wil]

As far as I know John Paul Jones used to use those amps in Zepplin.

I'd suggest increasing your input signal. A volume boost before the input stage should push the valves into soft clipping (nice overdrive). Something like an overdrive pedal with the gain down and volume up should do it.

[cheddatom]

Yeh, you want to try turning up the input, not the output, surely? I didn't know they did a JCM 800 for bass? Weird. I do use a JCM 800 modelling plug-in in the studio on bass quite a lot, and I have no problem getting it to distort, but, that's a plug-in. Sorry, that's not helpful!

[joegarcia]

I had one of these ages ago, think it was my first amp. Great head, Wil has the right idea, just need to drive the front end harder. Something like a Tubescreamer or DOD 250 should do it.

[ped]

Good suggestions RE the input. The power valves could be under-biased too, running 'cold' - you could crank them up and get more grit from it. I wouldn't recommend this until you get desperate though.

[Dave]

Cheers for all the suggestions. I did think about increasing the input as a possibility, but must admit I haven't tried that yet. The guy I saw playing through the Marshall head did have some pedals (and possibly a SansAmp) in his chain, but definitely no distortion/overdrive effects. And he was using a P Deluxe, whereas I was just using my passive P. Was going to try the Stingray to see if it helped, but I do have some overdrive pedals I can try to increase pre-volume without adding distortion. I was a little surprised the amp didn't have a GAIN control knob, and only a master volume after the EQ settings.

By the way Cheddatom, what's the JCM800 plug-in you're talking about? I would assume it's some kind of effect you use, but what equipment is it running on to get the sound. Just curious.

It's my first dive into the world of valve-dom, so not really sure what to expect. I did all the internet research I could, but must admit I'm surprised at how loud it is. I've not tried it in a band setting yet, and I understand (though possibly incorrrectly) that 100W tube power does not equate to the same perceived volume as 100W solid state, but this thing sounds pretty impressive. Most would probably say I'm nuts buying this beast when I've got a super-light 500W LMII amp, but I guess I'm still in search of "the sound in my head", and weight isn't a big consideration... yet.

[cheddatom]

Sorry, the plug-in is a VST plug in for use with DAWs on the computer. I can't remember the name of the programmers.

I would love to try the JCM800, and I don't think you're nuts at all. I am interested to know, what made you say it was bass specific in your first post?

If you have an overdrive pedal, try that. Just set it to boost, rather than distort, and it should make the marshall dirty!

[Wil]

I wish I had one to go with my Little Mark, that's for sure! Portability is one thing, but that's a classic amp right there!

Edit - Oh, by the way, as far as I know, the Bass version is the same as the guitar version, but the EQ is voiced more for bass. So, just a different EQ board, but the same power section. I think.

Edited October 12, 2007 by Wil

[Dave]

[quote name='Wil' post='73283' date='Oct 12 2007, 12:21 PM']I wish I had one to go with my Little Mark, that's for sure! Portability is one thing, but that's a classic amp right there!

Edit - Oh, by the way, as far as I know, the Bass version is the same as the guitar version, but the EQ is voiced more for bass. So, just a different EQ board, but the same power section. I think.[/quote]

You're right from what I've heard/read after enquiring on the Marshall website. I know it's specifically "for bass" because there is a JCM 800 "For Lead" and a JCM 800 "For Bass" (and it's actually printed that way on the front of the amplifier). It's apparently all in the EQ section.

So I tried running my Fender P through three of my overdrive/distortion pedals, increasing only the VOLUME and NOT the gain/distortion knobs to see if I could make the amp sound dirty, but no luck. I've got a Marshall Guv'nor, EH Pi (Russian version) and EBS Multi-Drive and could not get the amp to overdrive with any of these cranked to 11. I must admit I didn't turn up the master volume of the amp very high (to stay in the neighbours good books) but then you said this should not be necessary to get the dirty tube sound as it was all about turning up the input signal.

So if you have any other suggestions to help filthify this squeaky clean sounding amp I'd really appreciate it. Don't get me wrong, it is a great sounding amp, but it's just not behaving in the dirty manner I require, ha-ha.

Edited October 15, 2007 by Dave

[cheddatom]

Well, you should have the master volume down so as not to deafen yourself. Do you have a pre-amp volume knob?

I haven't had much experience with valve amps, but I think you can either have pre-amp distortion, or power-amp distortion, or both. Maybe try the Guv'nor with no much gain, plenty of level, in the effects loop? (if there is one). I don't know, it shouldn't be that hard to get it to distort if you just put a load of level into the amp. Maybe it has the wrong valves in or something like that.

[Musky]

[quote name='Dave' post='74487' date='Oct 15 2007, 10:57 AM']You're right from what I've heard/read after enquiring on the Marshall website. I know it's specifically "for bass" because there is a JCM 800 "For Lead" and a JCM 800 "For Bass" (and it's actually printed that way on the front of the amplifier). It's apparently all in the EQ section.

So I tried running my Fender P through three of my overdrive/distortion pedals, increasing only the VOLUME and NOT the gain/distortion knobs to see if I could make the amp sound dirty, but no luck. I've got a Marshall Guv'nor, EH Pi (Russian version) and EBS Multi-Drive and could not get the amp to overdrive with any of these cranked to 11. I must admit I didn't turn up the master volume of the amp very high (to stay in the neighbours good books) but then you said this should not be necessary to get the dirty tube sound as it was all about turning up the input signal.

So if you have any other suggestions to help filthify this squeaky clean sounding amp I'd really appreciate it. Don't get me wrong, it is a great sounding amp, but it's just not behaving in the dirty manner I require, ha-ha.[/quote]

What pre amp valves have you got in there? It might be that fitting some higher output valves might sort you out. Take a look at the Preamp valve comparison sticky - judging by brycebites comments, maybe Groove Tubes 12AX7M's might do the trick.

[Dave]

[quote name='Musky' post='74563' date='Oct 15 2007, 01:02 PM']What pre amp valves have you got in there? It might be that fitting some higher output valves might sort you out. Take a look at the Preamp valve comparison sticky - judging by brycebites comments, maybe Groove Tubes 12AX7M's might do the trick.[/quote]

I don't think it has ANY pre-amp valves, only power amp valves. It's got 4x EL34 power amp valves, but as far as I'm aware no pre-amp valves. If it did have pre-amp valves, would these glow like the power amp ones? I must admit I don't know very much about valves (apart from the size differences and lifespans of pre/power amp valves), and there's very little info on this model on the internet, but from what I can tell there are no pre-amp valves (and no gain knob) so is it possible I won't be able to get it to distort?

[cheddatom]

Do it have an effects loop? You could use this to drive the power amp, creating power amp distortion, which is apparently better, but, like I say, not much experience.

[Dave]

Well I've just found a schematic for the sweet sweet innards of this amp, and it suggests there should be 3x ECC83's inside, so maybe I need to look into this further. I did open up the back of the amp when I purchased it, but obviously I don't really know what I'm looking at, as the EL34's were obvious and clearly marked (and appeared easy to remove as there were held in place by spring-loaded plates) so I can only assume the ECC83's are well covered/hidden because I didn't see any other glass-valve-looking components within the amp when I removed the backplate.

I guess I was hoping for instant Marshall valve-tone goodness when I plugged in my bass and it simply wasn't there, so am looking for any suggestions what I can do to get it. Maybe this is simply the wrong amp for the job or maybe I need to get it looked at by a professional who may be able to help. A couple of places in the Birmingham area have been suggested to have valve amps serviced, so maybe I need to give someone a call and book her in for a checkup.

But if you DO have any other suggestions of things I can try, then please let me know. Would the use of an active bass make that much of a difference in comparison to a passive one playing through an overdrive pedal with the volume set to 11?

[Dave]

[quote name='cheddatom' post='74620' date='Oct 15 2007, 03:13 PM']Do it have an effects loop? You could use this to drive the power amp, creating power amp distortion, which is apparently better, but, like I say, not much experience.[/quote]

By this do you mean insert a volume/power boost (eg. one of my overdrive pedals) into the effects loop to better drive the power amp?

[cheddatom]

Yep. Apparently it's what Tom Morello does. Maybe i'm just confused. I think I should stop posting before someone who knows about valve amps embarasses me.

[Dave]

[quote name='cheddatom' post='74632' date='Oct 15 2007, 03:33 PM']Yep. Apparently it's what Tom Morello does. Maybe i'm just confused. I think I should stop posting before someone who knows about valve amps embarasses me.[/quote]

Don't stop posting, I need all the help/suggestions I can get! And never be embarassed if you're wrong, it's only a suggestion and can never hurt to try different things I may not have thought of (which is quite likely knowing me). I really appreciate your input.

AND this thread has helped increase my status to "no longer a newbie". Though I don't actually FEEL any less newbie-ish.

[Musky]

[quote name='Dave' post='74621' date='Oct 15 2007, 03:13 PM']Well I've just found a schematic for the sweet sweet innards of this amp, and it suggests there should be 3x ECC83's inside, so maybe I need to look into this further. I did open up the back of the amp when I purchased it, but obviously I don't really know what I'm looking at, as the EL34's were obvious and clearly marked (and appeared easy to remove as there were held in place by spring-loaded plates) so I can only assume the ECC83's are well covered/hidden because I didn't see any other glass-valve-looking components within the amp when I removed the backplate.

I guess I was hoping for instant Marshall valve-tone goodness when I plugged in my bass and it simply wasn't there, so am looking for any suggestions what I can do to get it. Maybe this is simply the wrong amp for the job or maybe I need to get it looked at by a professional who may be able to help. A couple of places in the Birmingham area have been suggested to have valve amps serviced, so maybe I need to give someone a call and book her in for a checkup.

But if you DO have any other suggestions of things I can try, then please let me know. Would the use of an active bass make that much of a difference in comparison to a passive one playing through an overdrive pedal with the volume set to 11?[/quote]

The ECC83's may well be hidden inside metal cans, but they are there. They are interchangeable with 12AX7's which are basically the same valve. If you look at that sticky you'll soon spot that they all have different characteristics, which may get you some way to the sound you're looking for.

I'm a little surprised you can't drive the front end hard enough to get some overdrive with your pedals, and I would have thought that they should be able to match the output of even the Precision Deluxe's 18V electronics. What kind of volume was the guy you saw playing at? It might be that what you heard was power amp distortion.

[cheddatom]

Are you plugging into a low or high gain input? (I think there's two?) try plugging into the low gain input, and just feed it the hottest signal possible.

[Dave]

Once again cheers for all the suggestions. I DID have another look inside the amp and found the 3x ECC83 valves underneath protective metal cans in there, so at least that much has become clear. It's got 2x u Micron valves and 1x Mazda "foreign" valve so I guess I may need to look into swapping these out for something else which may better approximate the sound I'm looking for. Man, this "sound in my head" search is NEVER ending!

As for the amp inputs, there are indeed 2 of them, but none of them are marked as being either high or low gain for active/passive basses, so not sure if they are different or not, but I could try plugging them into each and see if there is a difference. I would assume they must be different otherwise why would there be two of them? Marshall have said this amp is MONO and NOT stereo.

And with a rating of 100W, when I heard the other bassists amp it could well have been turned all the way up and therefore maybe it WAS power tube distortion that I was hearing. I'll have to give that a go at my next rehearsal when I can actually crank the amp up.

The power amp valves are ITT Lorenz EL34's, but I THINK from my readings the brand of power valves should not make much of a difference with respect to tonal quality? The Mazda preamp valve sits between the two u Micron valves and have tried to do some research (there's always something!) on preamp valves to see what I can do to change the tone of the amp, and from what I can tell it looks like I simply have to try a bunch of different valves/combinations until I chance on the right ones. Apparently the first one or two pre-amp valves add most to the tonal quality of the amp so for more distortion I assume I would need some "higher gain" pre-amp valves?

I sure wish there was an easier way, but I guess it's all part of the "fun".

[Dave]

[quote name='brycebites' post='74986' date='Oct 16 2007, 11:15 AM']The Mazda valve [i]could[/i] be a rebadged Mullard. Possibly. Micron are a rebranded valve as well, possibly Chinese. Can you post a pic of them?
V1 is the all important valve where much of the preamp sound is crafted. Change this to a decent valve and you'll be onto a good start.

The EL34's could be East German RFT's (rather good I believe) or some Japenese valves. Watford Valves have done a very useful comparison on EL34/6CA7 valves.

The valves will make a lot off difference in the overdriven sound so this would be the best place to start. If there were pedals being used they would have an impact - especially the Sansamp! Also playing technique can play a big part in the sound.[/quote]

Cheers Brycebites, I was hoping you might chime in! I did take some photos of the valves while the amp cover was off (for future reference) so I will try to upload them tonight.

As for the valve located in V1, I must admit I've no idea which position this would be. I've downloaded a couple of circuit diagrams for this amp, and have located the valve positions, but must admit I really don't know how to read these circuit diagrams. I was actually thinking of looking for a book on this to edumacate myself. The pre-amp valves are all in a row, as are the power-amp valves, so would it be correct to assume V1 is at the far left of the pre-amp valve section, or is it quite possible that this will not be the case?

I actually used to have a Sansamp, but found with the set-up I had at the time it didn't do much to add anything to my sound, so I sold it on. I'm kind of wishing I'd kept it now, as I've changed amps/guitars/speakers quite a bit since then, so perhaps now it WOULD make a difference.

I wish there was some kind of "valve-trading club", so valve amp users could try a number of different ones in the quest for "the sound".

[Dave]

Your link didn't work. I have two different looking diagrams, one shown at:

[url="http://www.drtube.com/schematics/marshall/1992.gif"]http://www.drtube.com/schematics/marshall/1992.gif[/url]

And the other looks like this:



I don't know how to interpret either of them. I tried to see if I could remove the main part of the amplifier from the outer casing, but not sure how this is accomplished, so I guess I'll have to take a better look at the attachment screws.

This photo doesn't show the types of valves I have, but it appear to be the same amp as the one I bought (and it was made in the same year). It is the one on the right here (if this helps at all):

[url="http://www.amparchives.com/album/Marshall/JCM%20800%20Series/1992%20JCM%20800%20Super%20Bass%20100W/index.html"]http://www.amparchives.com/album/Marshall/...100W/index.html[/url]

Cheers for your input!

[Dave]

[quote name='brycebites' post='75148' date='Oct 16 2007, 05:01 PM']I have just corrected my link and it is the same diagram as your link.

To remove the chassis you probably have some bolts underneath that hold it to the case.
Looking at those pics it looks like the preamp is on a PCB which doesn't make things so easy to trace. I would make an educated guess and say V1 is the valve furthest away from the EL34's.[/quote]

Unless the previous owner sorted this out which might explain why the only Mazda valve is in the centre surrounded on both sides by the Micron valves? But from what I understand, one should be able to swap the valves around and see if there is a significant difference in sound with the use of a different valve in either V1 or V2 compared with how it sounds before the interchange?

Cheers for all your help everyone, I'm enjoying this gradual education in the ways of valves.

[cheddatom]

Keep us posted, I want to know how this sounds!

[Amokoma]

Are you guys talking about the Model 2001? Here, I almost bought one on eviilBay.
[url="http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=170162539064&ssPageName=STRK:MEWA:IT&ih=007"]http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...A:IT&ih=007[/url]