Marshall question

[jgcable]

I have a JCM800 #2210. It has 2 speaker outputs. The impedance switch in the back can be set 4,8,16 ohms. If I am plugging 2 4 ohm cabinets into it do I use the 8 ohm setting? Actually, my Altec Lansings are rated 6 ohm but I always treated them as 4 ohm.

[cobhc]

Re: Marshall question

i think generally 8 ohms, splits down to 4 ohms if your running it in stereo, tho i'd let someone back me up before you try as i wouldn't want you to damage anything [img]/images/graemlins/smile.gif[/img]

[Dreamland_Rebel]

Re: Marshall question

i'd use it set to 4ohms since you're really drawing 3ohms with those 2 cabs at the same time.

remember 2 cabs = half their rating draw on the amp.

[jgcable]

Re: Marshall question

So, if I use both speaker outputs on the Marshall and each cabinet is drawing 4-6 ohms I should set the amp to 4 ohms?

What if I use both speaker outputs on the Marshall and each cabinet is drawing 8 ohms? How about if each cabinet is drawing 16 ohms?

[adrenaline junkie]

Re: Marshall question

No, I'm afraid you're in danger of blowing a transformer. To use two 4 ohm cabs, you'd need a 2 ohm setting.

If you've got two 16 ohm cabs, you use the 8 ohm setting. Two 8 ohm cabs, you use the 4 ohm setting. For two 4 ohm cabs, you'd need to use a 2 ohm setting and Marshall doesn't go that low.

[StukaJU87]

Re: Marshall question

2 cabs @ 8ohms each= 4 ohm setting
2 cabs @16ohms each= 8ohm setting

[Shawn Lutz]

Re: Marshall question

right its rule of 2. If tou run 2 16 ohm 4x12's with one head, you set the amp at 8 ohms.

[Dreamland_Rebel]

Re: Marshall question

ok:

1, 16 ohm cab = 16 ohm draw on head (set output selector to 16) same as 1, 8 = 8 1, 4 = 4 etc.

2, 16 ohm cabs = 8ohm draw on head

2, 8ohm cabs = 4ohm draw on head

2, 4 ohm cabs = 2ohm draw on head (thats why speaker cabs with more than 1 speakers almost always are 8 or 16 ohms. (even if each speakers inside are 4 ohms each they can wire it series to add instead of divide)

single speakers will sometimes be 4 ohms and some 8 ohm cabs will split to 4 ohms stereo and 16mono will split to 8ohm stereo. marshalls are not a stereo amp. with stereo amps you treat each side (right and left) as an independant head. so if you had a stereo head you'd run matching impendence i.e. if the cab is 8ohms mono and 4 ohms stereo you'd run each side at 4 ohms.

this trick of halving the impedence is the same with daisy chaining as it is with seperate speaker outs. (and again with stereo heads treat right and left as 2 seperate heads and apply same rules)

[parntz145]

Re: Marshall question

If your running 2 cabs in mono the rule of thumb is to split the ohms in half. If you are running stereo you run at wahtever ohms you plug the jack into. If you are running 2 4 ohm speakers at 4 ohms im pretty sure you will have problems with the head. You should be running them at 2 ohms. I would just run one cab at the 4 ohm setting.