Simple Marshall amp question
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Posted on Jun 05, 2007 12:35 am
jtrooster
Member Since: Jun 05, 2007
Hey everyone,
I have what is probably a super simple question, but at the risk of being laughed at, I will ask it anyway.
I just got a Marshall JCM2000 dual superlead amp and a 1960BV cabinet. Without knowing the first thing about Ohms, impedance or electrical in even the most simple form, can someone tell me how exactly how I should connect the amp to the cabinet?
For instance, on the back of the head, there are 3 speaker jacks, one 16 ohm, then it looks like two 4 and 8 Ohm, then off to the side a selector switch reading 4 to one side and 8 to the other (I'm sure most of you know all of this but too much info is better than too little I suppose.) So with all that spelled out, I will once again present my question, which jack should I use going out of the head (as well as to what side the selector switch should be set to) and which jack should I use going into the cabinet?
Sorry for the ignorance... can you tell I've always used a combo amp?
Thanks.
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TadpuiI am not a crook's headMember
Since: Mar 14, 2003
Jun 05, 2007 09:56 am It looks like that cabinet has an impedence switch on it that will switch between 4 and 16 ohms. Take note of the switch's position and use the corresponding output on the back of the head, with the head's switch in the same position.
I'm not sure if there's any advantage to one resistance over another on the head/cabinet. So pick one and stick with it I guess.
Example, switch the head to 4 ohms, send a single speaker cable from the head's 4 ohm output to the cabinet's 4 ohm input. Switch the cabinet to 4 ohm mode and wail away.
That's cool that they make both the heads and cabs flexible like that. It opens up your possibilities for different head/cabinet combinations.
Have fun!
Jun 05, 2007 10:07 am find out what ohm load your cabinet takes and use it.
cruxTypo SzarMember
Since: Jul 04, 2002
Jun 05, 2007 11:19 am I get confused between the words Ohms and Impedance, so check out their meanings if ur gonna take my suggestion, but i remember reading that basically you can have too much resistance and match differently if your not sure. So basically if your not sure how much ur cab can handle, just set the head to least feed, whichever that is, coz chances r the cab can handle that lowest number.
Is that even helpful? Just thought id throw that in.
TadpuiI am not a crook's headMember
Since: Mar 14, 2003
Jun 05, 2007 12:05 pm Ohms are a unit of measurement for resistance or impedance. Like grams is a unit of measurement for weight.
As far as I understand it, if you put too heavy of a load on your head (too much resistance) then you limit its output power. If you put too light of a load on it, then you can fry it because the current is so high.
At least that's my laymans perspective...
Jun 05, 2007 12:15 pm you can overheat your amp with too much or too little resistance as I understand it...if you can match 'em...do so...
Jun 05, 2007 12:22 pm Quote:
As far as I understand it, if you put too heavy of a load on your head (too much resistance) then you limit its output power. If you put too light of a load on it, then you can fry it because the current is so high.
Beware! Not sure of the construction of your Marshall, but it is the opposite for tube amps with transformer outputs. Too much impedance can damage or ruin these amps. Here's a useful article:
colomar.com/Shavano/speaker.html
pjkPrince CZAR-mingMember
Since: Apr 08, 2004
Jun 05, 2007 12:25 pm i was kinda fuzzy about the two as well, as I know there's a difference.
This here: www.teamrocs.com/technica...e_impedance.htm explains it quite nicely.
And yes, like Tadpui says, better to be higher load than under. If your speaker output (on the head) says 8 ohms, then you can go over by double, and still be basically safe, just eating some of the amps output wattage.
But, if you under-rate the expected load, like plugging a 4 ohm cabinet into a 8 ohm output, then you're letting the output transformer 'free-wheel' more than it's supposed to. This can be bad. It can overheat the transformer, which is not good.
So, you can go under a little, but not much. You can go over more than under, if need be.
It's been said, that old fender xformers can go double either way, but I'd rather not try it if I can help it =).
Back to JTRooster's ?, it seems that marshalls are 16ohm cabs a lot, so you can plug one cab into your head, set at 16. If you plug 2 cabs into the head, then you'd use the two jacks (2 4ohm, or 2 8ohm). This being, that 2 16ohm cabs plugged into the head will equate to an 8 ohm load, so you'd set the setting to 8 ohm (this is parallel).
There's quite a few speaker wiring diagrams on the net, explaining how speaker combinations work (parallel, serial, etc).
Jun 05, 2007 01:14 pm Thanks everyone, think I got my answer.
Normally I just go by trial and error, but this time with the amount I have invested, I thought the "error" part might have been a little too costly.
Glad I found this forum.
JT-
TadpuiI am not a crook's headMember
Since: Mar 14, 2003
Jun 05, 2007 02:46 pm Hell yeah, I wouldn't take any chances with a amp/cab combo like that! Man what a setup, we're all a little envious :)
Jun 07, 2007 01:16 am Tadpui - thanks for the props. Yeah I must admit, it is awesome. Although I waited 15 years to finally take the plunge. Speaking of envious, the other guitarist in my band is not speaking to me now. It's all in good fun but I can't help but to feel just a a little bit guilty ;)
pjkPrince CZAR-mingMember
Since: Apr 08, 2004
Jun 07, 2007 08:04 am I know a guy that saved up and bought a US strat, then a DSL50, and 2x12 cab. He didn't have much (lived in a little thin half-apartment), but he sure could play =).
Enjoy it.
