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jd0272 · May 2014

Internet giving a million different suggestions, so I'm still none the flamin wiser.

My cab, a Marshall 1960AX 4x12 states 16ohm on the jack. Bog standard cab. No idea if the speakers are series or parallel.

My amp, 30 watt valve, has a wee switch on the back that gives the options if 4,8, and 16ohm settings.

I've had the amp set at 8. Other guitarist in band 'thinks' it should be set at 16 to match the cab.

Help??? Ta.

bandmaster188 · May 2014

Yep you should set it to the correct impedance. If your cab is 16 ohm then set it at that. You should not go lower or it could damage the amp. i.e. the output transformer.

Misterg · May 2014

jd0272 said:

My cab, a Marshall 1960AX 4x12 states 16ohm on the jack. Bog standard cab. No idea if the speakers are series or parallel.

Probably both (*) - If the cab is 16ohm, then set the amp to 16 ohm, too. I'd be surprised if running it one 'step' off (8 into 16, etc) would cause any damage though. YMMV. <-- Typed that before seeing bandmaster's response - I'm not disagreeing with him.

(*) If you wire 4 speakers by putting pairs of them in series, then running the pairs in parallel, you get a combined impedance the same as that of an individual speaker. I would guess that your cab has 4 x 16 ohm speakers wired that way.

Cirrus · May 2014

Yeah, set it to 16 ohms. I am curious why you thought 8 was the right setting though?

ICBM · May 2014

Cirrus said:

Yeah, set it to 16 ohms. I am curious why you thought 8 was the right setting though?

Exactly… if the cab says 16 ohms, does it not make sense to set the amp to that?

8 ohms (amp) into 16 (cab) won't cause any damage in almost all cases - there may be a very few amps where it would be risky, but they would have to be pretty poorly designed or built. It could potentially damage the power valves though - which in some cases could then damage the amp if they failed badly.

Same with the other way round - contrary to popular belief that won't blow the transformer either, but it will stress the valves and shorten their lives even if they don't fail outright.

The only way you're likely to blow the transformer is running the amp with no load, or worst of all with an intermittent bad connection in the speaker circuit. Although running a 4-ohm amp into a 16-ohm cab is sometimes close enough to 'no load' to be risky. Don't do that, or the other way round.

jd0272 · May 2014

Cirrus;236873" said:
Yeah, set it to 16 ohms. I am curious why you thought 8 was the right setting though?

I didn't fella, that's the way it came to me. I must brush up my knowledge on this shit.

Many thanks lads for all the advice tho, appreciated muchly.

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