Marshall JCM900 SLX selector is confusing, is says (4)16 or 8 ohms ?

[Iplayloud]

So the ohm selector is a 2 way switch and one position says exactly (4) 16 and the other position says 8. I think it desn't make any sense. If the amp only has 8 and 16 ohms taps, then using a 4 ohm load on the 16 ohm tap yould be a greater mismatch than using it with the 8 ohm tap ?

[Darth Balls]

Combos are 4 or 8 ohms, heads are 8 or 16 ohms.

 

 

Possibilities for the head version:

 

1. switch on 8 ohms, one 8 ohm cab

2. switch on 16 ohms, one 16 ohm cab

3. switch on 8 ohms, two 4 ohm cabs

4. switch on 16 ohms, two 8 ohm cabs

 

 

Possibilities for the combo version:

 

1. switch on 4 ohms, one 4 ohm speaker

2. switch on 8 ohms, one 8 ohm speaker

2. switch on 8 ohms, two 4 ohm speakers

 

JCM 900 manual

[JerryP]

 

Originally posted by Darth Balls Combos are 4 or 8 ohms, heads are 8 or 16 ohms. Possibilities for the head version: 1. switch on 8 ohms, one 8 ohm cab 2. switch on 16 ohms, one 16 ohm cab 3. switch on 8 ohms, two 4 ohm cabs 4. switch on 16 ohms, two 8 ohm cabs Possibilities for the combo version: 1. switch on 4 ohms, one 4 ohm speaker 2. switch on 8 ohms, one 8 ohm speaker 2. switch on 8 ohms, two 4 ohm speakers JCM 900 manual

 

 

This is wrong. When you have the amp set to 8 ohms you can run one 8 ohm cab or two 16 ohms cabs. When it's set to 4 you run one 4 ohm cab or two 8 ohm cabs. Running two 4 ohms cabs gives you a load of 2 ohms, two 8's = 4 ohm load. The head is set to run at either 8 or 16 from the factory but it can be wired to run at 4 if you need that.

Jerry

[Jack Bob]

Hi, I just got my JCM900 SLX restored and need clarification. I got a line 6 4X 12“ cabinet, that say 4 ohm (mono) or 8 ohm stereo (2 inputs into same cabinet).

If I utliise 2 speaker out from JCM900 SLX to connect to this cabinet with 2 speaker cable, shall I set the ohm setting in JCM900 SLX amp head to 16 ohm or 8 ohm?

Manual say:

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.

7. Loudspeaker Output Jack Sockets
Parallel wired jacks for linking speaker cabinets.
Ensure that the speaker system is easily capable of
handling the full amplifier power and that the
impedance (item 6) is correctly selected. If in doubt
consult your dealer

  My local tech advice me to set to 8 ohm, but it doesn't seem to be right. Please help.