Building a JCM900.

[cibonato]

Hello everybody, I'm here again with a another problem. Probabily it's kind of "conceptual". I'm planning build a JCM900 amplifier and did not have problem in finding schemathics around the net. I think I have in my computer 3 schemathics of this model. But, and here is indeed the issue, on all of them I see at the bottom a label that says "Pre Amp" (the schematics I have ares copy of the originals, made using a scanner, I guess so.) and searching on the net I could see that there are "pre amplifiers" and "amplifiers". I went to some stores where I live trying to solve this problem and looking for help.

Everyone told me the something:

1) "pre amps" are the "box" that amplifies the signal but DOES NOT have the speakers just the head (I've already seen one this head in a store).

2) "amplifier" could be the "complete" combo with speakers and all.

A point that caught my attention was the fact that all the schematics have the wiring to the speakers, I mean: I can see the lines I'm suppose to connect the speakers.

That's all. I hope I've done a good explanation of the problem. Thank again to everyone that have the patience to answer and read some messages.

Miguel D.

[AL]

You need to get a better "primer" in tube amps. There are very high voltages in amps that CAN KILL YOU !!! So, if you're going in you really need to know what you're doing.

Go to the GEO FX link and check out the tube amp information there.

A tube amp, like the JCM 900, has a pre-amp and a power amp section within the same "box".  The amplifier with the speaker in the same "box" is generally called a "combo".

There are plenty of sights around the net with schematics and info on DIY tube amps. You should read up on these before you attempt to build your own. Whatever you decide be safe.

AL

[Pedro Freitas]

Is it a dual reverb one your after??? if so, it is a monster to replicate!!! :shock:

Anyway, the preamp and amp are both inside a normal JCM head. They
just have diferent names because they do different things.
The preamp amplifies your tinny guitar signal (then it will be big but not strong ), finnaly the output amp makes that amplified signal strong enough to push speakers.

Pedro

[cd]

Out of curiosity, WHY WHY WHY are you planning on building a JCM900?  They're some of the worst sounding Marshalls ever, and can be found dirt cheap, certainly for the cost of parts it would require to build.  Even if you have to import one you'd save yourself tons of time, $$, and headache.

[vanhansen]

Out of curiosity, WHY WHY WHY are you planning on building a JCM900?  They're some of the worst sounding Marshalls ever, and can be found dirt cheap, certainly for the cost of parts it would require to build.  Even if you have to import one you'd save yourself tons of time, $$, and headache.

Not all the JCM 900's sound bad.  I do agree that the dual reverbs are horrible.  However, the 2100 Mk III is great.  One channel (with boost volume), great gain, no reverb.  I own one and love it.  I wouldn't touch a dual reverb.

cibonato, if you going to make your own Marshall style amp, look at the Super Lead (with Master Volume) or the JCM 800 2203 or 2204 (100 or 50 Watts).  The 2203 and 2204 use the exact same preamp design.  The only difference is in the poweramp section, 2 or 4 tubes.  And by all means, be careful.

[geertjacobs]

If you still have to learn about tube amplifiers, it may not be such a good idea to go and build a JCM900.
There are a lot of simpler (and even better sounding) projects for beginners.
If you really want to get into amp building, visit  http://www.ax.84.com and read for a few days.
The P1 is probably one of the best beginner amps around. That can be converted into a Hi-Octane. That is a 5 Watt amp that is too loud for your bedroom and it comes very close to the Marshall sound.
Then the Marshall 18 Watt or the November may be closer to what you want.
If later on you really insist on having 50 Watts , which is REALLY loud, you can find an example of a good layout for a Marshall Plexi (THE Marshall) on Hoffmanamps.
http://www.hoffmanamps.com/images/Plexi50.gif

So IMO there's still quite a way to go...

G.

[GreenEye]

If you're not an electrical engineer, just buy one on Ebay and make some stompboxes to satisfy your thirst for electrical knowledge.  If this is your first amp build, for god's sake buy a simple Doberman kit or something.

[vfr800fiman]

Then the Marshall 18 Watt or the November may be closer to what you want.

I agree, I built the November, and it's very good sounding at reasonable volume levels. That was my first amp build, and even that was a little bit of a challange (I'm an ME, not an EE).
Glenn

[Jim Jones]

You can buy a JCM900 for a lot less than you can build one.

Jim

[ED]

Jim is exactly right. Much cheaper 2nd hand than to buy individual parts from scratch.

This is the case with ALOT of amps EXCEPT the say 60s early 70s amps,
where prices are just CRAZY for these vintage amps.

I'm currently struggling through building a marshall 1987 plexi clone(late 60s). STILL, i could buy a reissue used for around the same price of the money ive spent on my project so far. Tube amps are not easy to build either! If i had thought a bit more about it first I wouldve just bought secondhand, and theres

NO TURNING BACK AFTER YOUVE BOUGHT THE PARTS!!!

Best of luck if you choose to build,
ED