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Marshall amp building

5/10/2000 1:44 PM
Edward Ross
Marshall amp building
I want to build a marshall JCM 900.  
I have the schematics for the JCM900 preamp, a marshall 100 watt power amp and a master preamp.  
Once I have built these components how do I piece them together to get my JCM900 amp.  
5/10/2000 2:22 PM
Peter S

The JCM900 is a pc board amp.....I don't know if Marshall will sell you the pc board, but that would be ideal because the component layout of these amps is critical to the amps tone and stability. If you cant get the pc boards, then what I would suggest is getting a hold of a JCM 900 so you can copy the layout exactly. Then just wire up the circuit using turret have to be really careful to get the component layout nearly identical to the Marshall layout or the amp probably wont work. This may be very challenging. I've been repairng amps for 30 years and building my own amps for over 20 years and I dont think I would want to tackle the challenge of trying to clone a JCM 900.......good luck!  
Peter S
5/10/2000 3:19 PM
Ray Ivers

Are you going to build the Dual Reverb, the original Master Volume, or the SL-X JCM900 amp? Unless you want a change of packaging (rack-mount, for example), or are planning on making so many circuit modifications that the end result will be extremely different from the stock amp, I would heartily recommend buying a JCM900 head (they seem to be for sale everywhere) and saving yourself a ton of grief. Even if you want a rack-mount package, buying a JCM900 gives you an entire assembled amp to work with, with no last-minute parts-availability bummers. I ordered the 5201 switching op-amps this AM from Korg that the JCM900 and many other Marshalls use - they couldn't even give me a ballpark delivery date.  
I played thru an SL-X at a recent guitar show, and I thought it was the best-sounding JCM900 I had heard. The SL-X design uses all tube distortion stages with a diode bridge, whereas the JCM900 Dual Reverb gets most of it's gain and overdrive from the second 5201 op-amp; both channels share the standard Marshall/tweed Bassman gain stage/cathode follower tube stage.  
Ray Ivers  
R.A.G.E. Electronics
5/10/2000 3:39 PM
Jim S.

As others have said, this is an extremely complex amp to build as a homebrew project, even for experienced homebrewers. For example, even a copyu of a plexi Marshall would be far far easier to manage than a JCM 900.  
The real question is, why do you want to build it? If it's to save money, then forget about it. You would be much better off buying a used JCM 900 in excellent condition. Amp building is expensive - the chassis, cabinet, and transformers will set you back many hundreds of US$.  
If it's to get into amp building, then I strongly recommend you start with something smaller and much simpler. If you've never built an amp before, may I suggest something like a clone of a Fender Tweed Champ or Tweed Deluxe, or the AX84 project?  
Here's a bit of pop philosophy, which you can take or leave:  
The path of learning and doing amp building can be tremendously rewarding (and fun), but it's not worth starting down that path if you're only focused on the destination and not on the journey itself.
5/10/2000 9:50 PM

I have to agree with these guys, you're tackling a big project, especially since this is a high gain head and you'll have to be very careful of how you lay out components and run your signal paths. But, if you were going to attempt it anyway, why not rework an older Marshall like a JCM800? I know it won't have the exact transformers, but it's a starting point.
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