Can you do a Slash MOD on a JCM900??

[JCMRobbo]

Hello all! this is my first post.

I have a 96 JCM900 and I was wondering if it was possible to Slash Mod it to get that AFD/UYI attacky sort of tone.. you know the one. I love my JCM 900 sound already but I've found turning down the gain and really attacking the strings it gives me ALMOST that sound but its a bit weak.

How do you do the MOD, how taxing is it to do? and are there any other alternatives to getting that sound? Excuse my naivety but is it a boost through the signal or is it an extra valve or tube giving it the saturation?

MY RIG:
2005 Gibson Les Paul Classic
JCM 900/5881s (thinking of going back to EL34s)
Vintage modern 4x12 (The Purpley blue one)
-------------------------
92 JCM 800 Combo.
Vintage Modern 100watt.

 

[neikeel]

There is no specific mod.
The amp started off as an early 70s super trem. Using the extra Trem tube as an additional gain stage (4th). There is the UYI amp (heated up JCM800 era 2203) which does not have an additional tube. Most of the work is tone and response shaping of the additional gain.
your 900 has extra gain in spades.

 

[Crikey]

Hello all! this is my first post.

I have a 96 JCM900 and I was wondering if it was possible to Slash Mod it to get that AFD/UYI attacky sort of tone.. you know the one. I love my JCM 900 sound already but I've found turning down the gain and really attacking the strings it gives me ALMOST that sound but its a bit weak.

How do you do the MOD, how taxing is it to do? and are there any other alternatives to getting that sound? Excuse my naivety but is it a boost through the signal or is it an extra valve or tube giving it the saturation?

MY RIG:
2005 Gibson Les Paul Classic
JCM 900/5881s (thinking of going back to EL34s)
Vintage modern 4x12 (The Purpley blue one)
-------------------------
92 JCM 800 Combo.
Vintage Modern 100watt.

Use eq in effect loop, season to taste

 

[MarshallDog]

Just want to say welcome to the Forum new MF’r and good luck with your mod!!

 

[JCMRobbo]

Thank you all for your comments! I’ll give it a go!

 

[ampmadscientist]

Hello all! this is my first post.

I have a 96 JCM900 and I was wondering if it was possible to Slash Mod it to get that AFD/UYI attacky sort of tone.. you know the one. I love my JCM 900 sound already but I've found turning down the gain and really attacking the strings it gives me ALMOST that sound but its a bit weak.

How do you do the MOD, how taxing is it to do? and are there any other alternatives to getting that sound? Excuse my naivety but is it a boost through the signal or is it an extra valve or tube giving it the saturation?

MY RIG:
2005 Gibson Les Paul Classic
JCM 900/5881s (thinking of going back to EL34s)
Vintage modern 4x12 (The Purpley blue one)
-------------------------
92 JCM 800 Combo.
Vintage Modern 100watt.

JCM900........what model?

 

[tschrama]

AFD and UYI and very different sounds and amps.

But if you use a GE-7 in front (!) of ur amp, you can fine tune it to both ryoes of sounds.

Modding a jcm900 to AFD or UYI specs would difficult. You might as well reomve the PCB and put in a new turret board.

 

[JCMRobbo]

JCM900........what model?

4100

 

[RobS]

use channel A, gain about 8 and clean boost with a TS9, turn up the master vol

 

[JCMRobbo]

Hey everyone so I’ve bought a Boss GE7 I have mixed reviews about wether to put it in the FX loop or I front of the amp? I like my tone of my amp I did put it through the front adjusted the GE7 settings and it sounded great!... but it was at low volume (bedroom volume) and I know my JCM900 when it’s cranked at Rehearsal it sounds a lot different.

I’ve just re configured the Boss GE7 onto my pedal board to be going through the FX loop but before my Echo pedal.

It won’t let me upload a photo unfortunately. Is this going to be a case of just trying it out to see what’s better sounding OR is there some specific method to the madness having it through the fx loop? I want to keep my amps tone as the foundations but I just want the GE7 to boost it to sound a bit like AFD.. basically in a nutshell!

cheers fellow marshalheads

 

[MickeyJ]

get

* 480-490v on the plates ( new power transformer), 0- 185 or 375-0-375 should do the trick. both of these at around 150 quiescent or 290ma full draw.

* a plexi or metalface output transformer.

you will get what you're after.
be mindful that the jcm900 is bright sounding, don't use an output transformer that has a rep. for being bright sounding.

i'm surprised this isn't a common mod, these amps have the right componentry, and , the wrong choice of transformers for dynamic punch.

 

[ampmadscientist]

4100

A. Adjust preamp feedback loop.
B. Remove local feedback from cathode follower stage, add bypass cap for bass compensations.
C. Remove clipping LEDs from clean channel.
D. Re-adjust effects loop levels.
E. Move reverb cables away from input jack to stop ringing oscillations.
F. You will not need any boost or distortion pedals, these probably will not work very well with this amp. (and don't expect them to work well)
G. Tweak master volume section for clean channel.
H. Check bias etc...

Result: Roaring monstrosity, you will need a permit.
1. This mod is only for experienced guitar players who know how to control extremely high gain amps.
2. Noisy effects pedals: The noise will be greatly amplified. You should probably start with lowest noise effects (such as Eventide DSP).
Any noisy effects pedals should be removed from the chain.
Noise which occurs from pedals is not caused by the amplifier (I'm alerting you in advance)
3. Effects Power:
2 Separate power supplies, one for input jack effects, another for loop effects. This eliminates a ground loop which will occur when running input and loop effects from the same power supply.
4. Single coil pickups are not recommended because any noise will be boosted greatly.

OK
do you think you can do all that yourself?

So the thing is:
If you plan to use boost pedals or distortion pedals, this mod is probably not ideal.
The idea is to get the sound / boost from the amp itself.
This mod makes the clean channel much cleaner and louder (more Fender-like)
It makes the boost channel into a chainsaw etc....

Click on the image to expand the schematic.