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Old 01-05-2013, 07:41 AM   #1
Viban
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Small book of JCM 900 Questions

So my JCM 900 MKIII (2100) came in today, and I haven't a clue as to how to work the thing. It appears to have stereo output, and I'm rather confused as to how that works. There is an impedance selector that says "(4)16" and the other "8", My question with this one is, what does the "(4)" in front of the 16 mean? Also is that the total impedance between the two cabs or is that per cab? How does having two cabs plugged into the amp work? Does it work as if they are in series or parallel (impedance halved or doubled?)?

Also, it looks like it looks like it uses EL-34's in the power section and 12AX7's in the pre-amp. I already plan on using an ECC-803 in V1 and ECC-83's in V2 and V3. I might just get some more EL-34's for the power section but I was wondering if anyone else had any good alternatives to use on this amp before I go and spend $60 on power tubes. It came with a set of Groove-tubes in, I'm not sure where those stand in terms of quality, but I'll probably let them stay until I buy a cab.

Thanks in advance
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Old 01-05-2013, 08:29 AM   #2
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First off. It's not a stereo amp.

The speaker outputs:
The (4)16 ohm output means that you can plug either a 4ohm or 16ohm cab in there.
As for the 2 cab set up. You want to run them in series where the impedance is halved. Ie. 2x 16ohm cabs in series will have an impedance of 8ohms. And 2x 8s will be 4

As for your pre amp tubes. I would recommend either a JAN 5751 in v1 or a JJ ecc803. And JJ ecc803s for the rest.

Power tubes.
This is where people argue a lot. The most recommended would have to be the Winged C's if not go for JJs. Also if you want a tighter low end and a little more punch, try e34l's. I put some in my JVM410h and loved them
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Old 01-05-2013, 08:42 AM   #3
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Quote:
Originally Posted by loki_lulamen
First off. It's not a stereo amp.

The speaker outputs:
The (4)16 ohm output means that you can plug either a 4ohm or 16ohm cab in there.
As for the 2 cab set up. You want to run them in series where the impedance is halved. Ie. 2x 16ohm cabs in series will have an impedance of 8ohms. And 2x 8s will be 4

As for your pre amp tubes. I would recommend either a JAN 5751 in v1 or a JJ ecc803. And JJ ecc803s for the rest.

Power tubes.
This is where people argue a lot. The most recommended would have to be the Winged C's if not go for JJs. Also if you want a tighter low end and a little more punch, try e34l's. I put some in my JVM410h and loved them

so then it is safe to use a 4ohm cab into one of the outputs when it is in 16 ohm mode?
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Old 01-05-2013, 08:54 AM   #4
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Directly from the manual.

6. Impedance Selector Switch
Two-way switch for matching the amplifier to
speaker impedance. Amp heads feature 8 or 16
Ohm operation. Combo versions feature 4 or 8
Ohm options
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Old 01-05-2013, 08:56 AM   #5
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Actually scratch what I said on the impedance.

Combo JCM900s will run 4 or 8 ohm
Heads will run either 16 or 8.

Your amp can run 2 cabs in parallel. Which means that you set the switch to 8 and run two 8ohm cabs or 16 and two 16ohm cabs

So to answer you question.
Head: no
Combo: yes

However depending on your cab you might be able to rewire it to 8 or 16

Tis amazing what you find when you RTFM

Edit: good catch Cath!
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Old 01-05-2013, 08:59 AM   #6
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Quote:
Originally Posted by Cathbard
Directly from the manual.

6. Impedance Selector Switch
Two-way switch for matching the amplifier to
speaker impedance. Amp heads feature 8 or 16
Ohm operation. Combo versions feature 4 or 8
Ohm options

Where might I find one of these manuals? I'd like to give it a readthrough.
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Old 01-05-2013, 09:00 AM   #7
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http://www.drtube.com/schematics/marshall/jcm900.pdf


You can get away with just about any EL34 in those. However, as always, SED =C= if you can afford them, JJ if you can't.
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Old 01-05-2013, 12:39 PM   #8
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Quote:
Originally Posted by Cathbard
http://www.drtube.com/schematics/marshall/jcm900.pdf


You can get away with just about any EL34 in those. However, as always, SED =C= if you can afford them, JJ if you can't.

I was gonna buy all JJ's for it anyway, I figure might as well buy the best product I can.
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Old 01-05-2013, 12:44 PM   #9
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Quote:
Originally Posted by Viban
I was gonna buy all JJ's for it anyway, I figure might as well buy the best value I can.


Fixed.
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Old 01-05-2013, 12:53 PM   #10
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Quote:
Originally Posted by Viban
I was gonna buy all JJ's for it anyway, I figure might as well buy the best product I can.

Nice amp
I highly recomend the SED=C=EL34 I run them in my JCM2000 DSL100 and they are a great tube.

But JJ E34l not the EL34 if you go JJ the E34l have more bass than the standard EL34
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Old 01-05-2013, 01:01 PM   #11
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I'd love to use the winged C's, but that'd nearly triple the price of the tube change, I might just stick with JJ's and pay like $90 or so for the whole retubing. I planned on using the regular EL34's because I don't really like having too much bass, I'd hate to buy a whole new set of tubes just to sound muddy.
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Old 01-05-2013, 01:17 PM   #12
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Quote:
Originally Posted by Viban
I'd love to use the winged C's, but that'd nearly triple the price of the tube change, I might just stick with JJ's and pay like $90 or so for the whole retubing. I planned on using the regular EL34's because I don't really like having too much bass, I'd hate to buy a whole new set of tubes just to sound muddy.

The E34L won't make you sound muddy that would be your EQ. And they also help in the Lower-mids also which I think the JCM 800/900mkII are lacking in

Now get a cab and crank that amp. You can get used Marshall 1960 cabs for <$300 on GC also. And I prefer the Celestion G12H30 or clone with those amps I think they sound better than V30 or G12T75 speakers. I use Eminence V12 with my DSL and I really like them also so you may want to check out the used Krank Rev 4x12 cabs on GC also (<$400 used)
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Old 01-05-2013, 09:28 PM   #13
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Quote:
Originally Posted by Robbgnarly
The E34L won't make you sound muddy that would be your EQ. And they also help in the Lower-mids also which I think the JCM 800/900mkII are lacking in

Now get a cab and crank that amp. You can get used Marshall 1960 cabs for <$300 on GC also. And I prefer the Celestion G12H30 or clone with those amps I think they sound better than V30 or G12T75 speakers. I use Eminence V12 with my DSL and I really like them also so you may want to check out the used Krank Rev 4x12 cabs on GC also (<$400 used)

That was the plan, a used 1960 and some form of bass cab since I play teh br00tz dethcore now and I'll need something to make that 97 Hz low note a little more, pronounced.
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Old 01-06-2013, 10:01 AM   #14
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Quote:
Originally Posted by Viban
That was the plan, a used 1960 and some form of bass cab since I play teh br00tz dethcore now and I'll need something to make that 97 Hz low note a little more, pronounced.

instead of a bass cab, I would sugest looking into a cab that has K-100 speakers. They are good for bass or guitar. Or get a 2x12 cab and put 2 K-100's in it.(and have a 6x12 rig). The EV12L is also goo, but at $200 a speaker it is very pricey
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Old 01-06-2013, 01:04 PM   #15
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Sounds like what you need is a Marshall MF400.
JJ EL34L also sound like the right tubes, given what you're saying you want.
With those two things your low notes will make the glass shake out of your windows.

The mod I explained to you will also help in that regard because it will remove the fizz and make the whole thing just growl.
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Old 01-06-2013, 03:51 PM   #16
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Quote:
Originally Posted by loki_lulamen
Your amp can run 2 cabs in parallel. Which means that you set the switch to 8 and run two 8ohm cabs or 16 and two 16ohm cabs




if you connect two 8 ohm cabs in parallel then that would be a 4 ohm load (so you wouldn't want to run two 8 ohm cabs with that amp).

same thing with two 16 ohm cabs, it'd be an 8 ohm load total and you plug one 16 ohm speaker into each speaker out with the head set to 8 ohms.

so to recap

-(1) 16 ohm cab - amp set to 16 ohms
-(2) 16 ohm cabs - amp set to 8 ohms
-(1) 8 ohm cab - amp set to 8 ohms
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Old 01-07-2013, 04:39 AM   #17
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Quote:
Originally Posted by gumbilicious


if you connect two 8 ohm cabs in parallel then that would be a 4 ohm load (so you wouldn't want to run two 8 ohm cabs with that amp).

same thing with two 16 ohm cabs, it'd be an 8 ohm load total and you plug one 16 ohm speaker into each speaker out with the head set to 8 ohms.

so to recap

-(1) 16 ohm cab - amp set to 16 ohms
-(2) 16 ohm cabs - amp set to 8 ohms
-(1) 8 ohm cab - amp set to 8 ohms

That's what I thought, I just wasn't sure.
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Old 01-07-2013, 09:43 AM   #18
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Quote:
Originally Posted by Viban
That was the plan, a used 1960 and some form of bass cab since I play teh br00tz dethcore now and I'll need something to make that 97 Hz low note a little more, pronounced.

...why a bass cab? You play guitar, not bass.

If I was your live sound engineer, I wouldn't even mic your bass cab, because its going to cause so much unnecessary lowend issues. Metal guitarists crack me up sometimes, leave the bass to the bass player. An engineer who knows what he's doing is just going to chop out all the frequencies that low in your tone, otherwise the mix is going to sound like crap.
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Old 01-07-2013, 05:08 PM   #19
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Quote:
Originally Posted by MatrixClaw
...why a bass cab? You play guitar, not bass.

If I was your live sound engineer, I wouldn't even mic your bass cab, because its going to cause so much unnecessary lowend issues. Metal guitarists crack me up sometimes, leave the bass to the bass player. An engineer who knows what he's doing is just going to chop out all the frequencies that low in your tone, otherwise the mix is going to sound like crap.

Well for some reason the lead guitar player decided we should now be in Drop G, I went to G standard because I don't like drop tunings. Plus I'd run it in tandem with the guitar cab to make it balance out a tad. It's really more of just an idea, but I don't know the lowest frequency guitar speakers can handle so I just wanted to be safe as my lowest note is now at around 97Hz.

Personally I prefer neoclassical/power metal, which usually involves E standard, the regular one, not the octave down one, But I joined a deathcore band (Go ahead and say it) because I need money, but me and the other guitarist both hate this tuning so we're gonna try to get them up to a more appropriate guitar tuning.
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Old 01-07-2013, 05:14 PM   #20
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Viban
I think Cathbard is right you need a Cab with the K-100 speakers. The MF400 4x12 cab can be had for <$400 another option is the Orange PPC 4x12 HP it has the K-100.
www.avatarspeakers.com has just about any opyion as far as speakers and color combos.
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