#1
Hi guys,

Got my JCM 900 Hi Gain Dual Reverb head and 1960A cab today, Just a couple of questions really:

1) Impedance - I'm a bit confused as to what to use, the manual is a bit ambiguous. What mode should I run in between mono and stereo and which impedance do I have to run at? I was thinking run the amp at 8ohms and then go in the 4ohms mono side, but I'm not sure if this is correct.

2) The way to switch on and off a vavle amp properly - do you have to turn standby on first before you supply mains power and then vice versa? I don't want to ruin the amp, so would appreciate some advice.

I've only ever played on valve amps, never had any experience of switching them on/off or setting them up correctly.

Thanks for any help/advice!

Steve
#3
i think the 1960A cabs are 16ohm mono. if my memory serves me correct, there should be a socket on the back of the head that is both 4ohm and 16ohm. use that, and make sure the switches match what you've plugged into
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#4
Wait..

I just read in the Amps Q and A that says something about switching to standby first and then power on... am confused now....

Of course, I still haven't touched it yet, I'm scared I'm gonna break it! LOL
#5
You want your amp to be in standby for a minute or two before playing. You will be able to correctly identify 'standby' because your amp will be on and the tubes will glow, but when you strum your guitar no sound comes out of the speakers.

You want to match the impedance on your head and your cab.
...Bleep Bloop...
#6
I got that same halfstack for my brother last week, it's a pretty awesome amp. You'll want to be plugged into 16ohms mono. If there's an impedance selector on the back, which I'm pretty sure there is, make sure that's also set to 16.

Before playing, turn the black switch to standby, then turn the red power switch on. Do this first and let it warm up while you get your guitar out, tune it whatever. Once the tubes are glowing nicely you can plug in and turn the black switch to play. If the police aren't there within half an hour something's wrong.

It won't kill an amp to be just played cold once in a while, so you won't destroy it while you figure out which position "standby" is.
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#7
The Q&A is wrong.. what Serendipity said was right.
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#8
Make sure you're in MONO not STEREO otherwise you will only be using 2 of the 12's and not all 4 . A problem I had when I first got my 900 stack.

Match the ohms, I like the 16 (4) setting best.

Keep in at 100 watts, it sounds better.

Turn it on, let it sit for a few minutes, then flip the standby, don't flip the standby and then the power.

Always do the power first.

Have fun.
High as tits
#9
Thanks for the advice guys. I was gonna run it on 50 watts mode, just so I could keep it quiet....

But I don't suppose there is much chance of that lol.

So I take it to turn off would be the opposite way... i.e. standby off > pwer off?

lol

Steve
#11
sweet nice amp ! how bout some pics ?
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#12
I'll upload some later.... I've gotta move it into the back room... because I'm not too pleased about it being in the living room at the moment, I have a bay window with blinds so it's like having a "Nick me" sign on it, although I had it covered up overnight!

Steve
#13
Quote by Suicidal_Brick
Keep in at 100 watts, it sounds better.


Doesn't having it on 50W allow you to drive the power tubes harder making it sound better?
I'm gonna get to play with mine next week so I have an interest here too
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#14
OK, I wait for the power on to go red.... nothing happens when i switch onto standby, no sound.... I'm set at 16 ohms mono... as is the head..... so can't think why it's not working... I bet it's bust, it'll be just my luck....

God I feel like a noob now. LOL
#15
It depends on the amp. some of them have standby as the setting when the amp won't play. Some of them have standby as ready to play. Stupid labels.

I always set it to standby (won't play) before I shut it off, that way, it starts on standby the next time.
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#16
It's a JCM 900 hi gain dual reverb...

I'm powering on - waiting a couple of minutes to let the tubes warm up and then putting the standby in the "1" position, which I am led to believe is the "ready to play mode".... The manual is no help either.... I am confused (and embrassed actually) lol

Steve
#18
Quote by StevieBaby1981
Hi guys,

Got my JCM 900 Hi Gain Dual Reverb head and 1960A cab today, Just a couple of questions really:

1) Impedance - I'm a bit confused as to what to use, the manual is a bit ambiguous. What mode should I run in between mono and stereo and which impedance do I have to run at? I was thinking run the amp at 8ohms and then go in the 4ohms mono side, but I'm not sure if this is correct.

2) The way to switch on and off a vavle amp properly - do you have to turn standby on first before you supply mains power and then vice versa? I don't want to ruin the amp, so would appreciate some advice.

I've only ever played on valve amps, never had any experience of switching them on/off or setting them up correctly.

Thanks for any help/advice!

Steve



congrats on that score....thats a super sweet amp..........wanna sell it?...lol
#19
OK well it's still not working. (no sound coming from the speakers)

I'm thinking it's broken now. Although I've matched the impedance right 16 ohm on the amp and 16ohm mono on the cabinet, nothing comes out of the speaker when I power on, wait a couple of minutes and then turn standby to the 1 position - nothing comes out!

If I switched the impedance of the amp to 8 and the spaker to 4 ohms mono, would that work?

I hope i haven't blown the valves.
#20
Try flicking the standby switch the other way? Perhaps you are turning it on, then flipping it onto standby and trying to play?

If the valves are buggered they won't glow.
...Bleep Bloop...
#21
Quote by GHJ
Try flicking the standby switch the other way? Perhaps you are turning it on, then flipping it onto standby and trying to play?

If the valves are buggered they won't glow.


I've done that before xD

TS, noone has really been clear so far as to the whole turning it on and off thing so I'll try my best.

1. Make sure head and cab are connected (if you power up a head with no cab you can ruin it)

2. Engage the standby (IE if it was on there would be no noise)

3. Turn the power ON.

4. Wait, a minimum of 5 minutes, if it's before recording or a gig I'd wait around 30 to make sure you get the best tone.

5. Turn the standby to ON so that it will make noise.

6. ROCK OUT.

7. When rocking is done, engage the standby so the amp is silent, unplug your guitar, whatever.

8. Wait, a minimum of ten minutes, longer if you've been pushing it hard for a long time.

9. Turn the standby to ON, so the amp is functioning again.

10. Wait around 60 seconds, then turn the power OFF.

at this point you can put it back on standby so you don't have to do it next time you turn it on.

about 10, not many people do this, but many amp techs have told me about it, and I've read it in a book or two.
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#22
2. Engage the standby (IE if it was on there would be no noise)


5. Turn the standby to ON so that it will make noise.


See this is the thing that's confusing me....

The JCM 900 has a standby you can switch between 0 and 1 obviously, so if both the power AND standby are on, I should get noise, but don't. I get noise when I power on but it's more to do with the fact that there's an electrical current coming through it. When I switch standby to on... nothing.... lol

I think it would have helped if Marshall provided a better manual, but instead it's like two pages of.... nothing really!!!

Thanks for all your replies so far.
#23
Quote by hamish5178
I've done that before xD

TS, noone has really been clear so far as to the whole turning it on and off thing so I'll try my best.

1. Make sure head and cab are connected (if you power up a head with no cab you can ruin it)

2. Engage the standby (IE if it was on there would be no noise)

3. Turn the power ON.

4. Wait, a minimum of 5 minutes, if it's before recording or a gig I'd wait around 30 to make sure you get the best tone.

5. Turn the standby to ON so that it will make noise.

6. ROCK OUT.

7. When rocking is done, engage the standby so the amp is silent, unplug your guitar, whatever.

8. Wait, a minimum of ten minutes, longer if you've been pushing it hard for a long time.

9. Turn the standby to ON, so the amp is functioning again.

10. Wait around 60 seconds, then turn the power OFF.

at this point you can put it back on standby so you don't have to do it next time you turn it on.

about 10, not many people do this, but many amp techs have told me about it, and I've read it in a book or two.

There's a few things I disagree with.

First, you really don't need to wait that long before playing. I would say not longer than 30-60 seconds. Just enough to get the tubes warm. What standby does is allow the tubes to get warm before taking power from the rectifier - since most tube amps have solid state rectifiers, the power is available immediately from the rectifiers but unusable by the tubes until they get warm.

Second, you don't need to let the amp "cool down" in standby before turning it off. You can just kill the power. Putting it in standby first and waiting does absolutely nothing.

The only time you need to let your amp rest is after killing the power completely, you should let it rest until the tubes are cool to the touch before moving it.

As far as your O-1 debacle, it really means O and | - circuit open, circuit closed. You should set the switch to the | setting to play.

By the way, I understand your confusion since amp makers don't realize the wording can be confusing. If standby is on - practically speaking - it means standby is engaged and you shouldn't hear any sound. So every amp should have the standby "off" when you're playing. A lot of amp manufacturers (including Mesa/Boogie, which is what I have) don't understand the concept of "English," per se, so they don't know what words mean. It makes no sense to have to switch standby to "on" to play an amp.
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Last edited by Dirk Gently at Aug 7, 2007,
#24
OK Here are instruction from me a JCM900 4100 OWNER. ONLY follow these SIMPLE directions to set it up as mine is set up:

Put the head on top of the stack. Plug the head into your outlet.

Now, use an amp cable (NOT an instrument cable!) and plug into this setting on the CAB:

Have the switch to the LEFT onto MONO. Plug the cable into the RIGHT plug where it says 16 ohms above the word "input. Below it will say "8 ohms left". Doesn't make sense since its plugged into the right but just leave it! Now take the other end of the cable and plug it into the back of the head here: "POWER LEVEL OUTPUT LOUDPSEAKERS 100WATTS RMS" on the LEFT side. Set the impedence switch to 4(16).

Now you're head and cab are connected correctly. Now to the front of the head. Have both the power and standby so the bottom is sticking out and the top part of the two way swith is pressed in. They are both now OFF.

Press the RED button on the LEFT (power) down so it turns ON. Wait for a minute or two. NOW hit the BLACK standby button next to it DOWN into the "1" position. Your amp should now be ON.

Make sure you don't have a pedal tuner on, and that your guitar volume is all the way up. Also make sure the actually volume of the amp is ABOVE 1/2 or it won't make a lot of noise.

If this doesn't work, it's broken.
High as tits
#25
Why do some of you think that it sounds better when amp and cab are both set on 16 ohms? I have them both on 4 ohms because I understood from this forum that there is no difference in sound as long as the impedance is equal... (and this prevents me from blowing up the speakers when i would connect it wrongly)
#27
Quote by Dirk Gently
The 16 ohm setting allows you to use all 4 speakers in series.


All speakers are in use in 4 ohm mode (mono!), at least in my set up...
#28
It's only the left two or the right two depending on what side you have plugged in. Maybe he meant Stereo? That's what happened to me before going on Mono.
High as tits
#29
I haven't tried it in stereo yet, or 4ohms mono....

I presume to go 4 ohms mono I switch impediance to (4)16ohms on the amp and use the 4ohm mono input?
#30
Just to let you know I got it working....



It sounds great, but obviously at low volumes it's not going to sound as good as it should just yet cause I am unable to drive the tubes etc....

Now onto the next problem, getting it to rehearsal!!! LOL

Thanks guys!
#31
what was wrong ? pics ?
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#32
Just the fact that I needed to have the master above 2 to get anything out the amp....I admit though I was bothered about it being too loud... I have peeps living on tops of me... didn't wanna cause an uproar.

Soundwise I haven't had the time to properly dial in a good sound - but I'm not going to be able to do that properly until I am in a situation which permits louder volumes...

I'll upload some pics later!

Steve