Please explain Marshall impedance settings?

[timdash]

Hi all,

I have just been "tinkering" with my JCM800 combo (4103) & noticed that the 2 speakers are Celestion 16ohm, but the Amp impedance selector is set to 8ohm.

Is this correct?

I have had this amp for 20 yrs & the impedance selector setting has never been changed as far as I know. The amp sounds fantastic as is, but it struck me as odd that the 2 values do not match up

Could someone please explain what the impedance means & how it relates to the settings on my amp?

Many thanks in advance

Cheers!

[Stan Martin]

are probably wired in parallel, 16/2 equals 8. your amp is fine

[64Strat]

You need to understand Ohm's Law and more specifically, series/parallel resistance. Wikipedia works. Follow the wiring of the speakers and then figure it out.

Stan is probably correct but you should verify it.

[johnreardon]

Stan is right, assuming speakers are wired in parallel, however, I would forget checking Wikipedia for stuff as it is often incorrect.

Just google speaker impedance and you'll get lots of hits. This one is not bad.


http://www.merlinpa.com/resources/Im...am%20Allen.pdf

[timdash]

Thanks for all the info, I am sort of understanding & agree that 16/2 = 8
lol

You will love this next story
last night I decided to change the worn control Knobs with new ones I got last week. This ended up with me snapping the shaft of the Master Vol Pot completely off whilst trying to get the old broken knob off. ARRRR !

I forgot that it was glued on by me back in the 90's as it used to fall off all the time.

I took it in to my Guitar shop today for professional treatment. I was going to have it serviced next year anyhow, this simply sped up the process. Hopefully it will come back all sorted & better than ever!

let this be a lesson. never ever force anything that does not want to budge !
(this includes 2-4yr olds!)

Cheers,

Tim

[JPW2105]

I worked in a guitar shop for years that was the district main dealer for Marshall in the 90's, their 'knobs' where always coming off... They were a nightmare. I used to put a little bit of blu-tac on the end of the spindle and then push it on, used to work a treat

If the wiring of the speakers has not been changed since it left the factory then the impedance setting is right. However, with the amp being 20 odd years ago, I would suggest that you check to see how your valves are bearing up, I would thik that they are possibly getting a little tired by now.... maybe worth getting your local friendly guitar shop to look at them also, providing you trust them that is and they won't tell you they need changing when they don't