Confused by Ohms

Agave_Blue

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Ran across a statement regards an amp external speaker output: "Minimum total impedance is 16 ohms".

So can it run, for example, a 2 x 12 cabinet with 8 ohm speakers (total impedance 4 ohms)?

You'd think it would, but that's less than the minimum impedance. Is it just a poorly worded instruction?


It's from the Owners Manual for a Peavey Classic 30, btw. This is exactly what it says:

EXTERNAL SPEAKER JACK (13)

This is provided for connection of an external speaker cabinet. Minimum total impedance is 16 ohms.
 

hipofutura

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No, it cannot drive the 4 ohm 2x12. But, the 2x12 could be re-wired for 16 ohms. Don't run a tube amp with a speaker load that is less than the manufacturer requires.
 

Agave_Blue

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No problem, I understand that.

I'm just having a hard time understanding if this poorly worded or if it really means 16 Ohm MINIMUM load.

It's odd because a lot of external speakers/cabinets are LESS than 16 ohms to start with. So why make an external out that's not very usable with what is commonly available?
 

Indyclone

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Some amps are designed for 4 ohms...


and you can get 4 ohms or 16 ohms out of a 2x12 with two 8 ohm speakers...
0
 

Agave_Blue

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So, for example, a 32 or 64 ohm load would be OK?

(I think that'd be 4 or 8, 8-ohm speakers in series).


It's the use of "minimum" that is confusing me. The other handful of amps I've looked at are not open ended like that. They have a SPECIFIC impedance rating.

Marshall Haze, for example 8 Ohm or 16 Ohm (2 different output jacks) : "The safe combinations are 1x16 Ohm or 1x8 Ohm only."

Fender Blues Jr: "any quality 8–ohm external speaker cabinet that you choose."

Vox VT Series: "Don't use an external speaker whose impedance is other than 8 ohms."
 

dwagar

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It is quite confusing. The spec I see on the amp is
30 watts (RMS) into 16 or 8 ohms

so I assume the speaker in there is a 16ohm, I'd guess the ext speaker needs to be 16ohm, in parallel that'd give you 8ohm then.

I think they mean minimum impedance to the ext jack then.
 

Big John

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...I think they mean minimum impedance to the ext jack then.
Bingo. When you plug into the ext. jack (which is a switching jack), the 8 ohm tap on the output transformer comes into play for running two 16 ohm speakers (onboard & external).
 

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