Correct impedance select for Road King & 4x12 Standard Recto cab

Gear
#1

Heya! I have a Mesa Standard Rectifier 4x12 cab which has an 8 ohm input and I want to run a Mesa Road King 2 into it. I know the Road King tolerates some mismatching, but which output should I ideally be using? The “8-16 ohm” one?

This is the output section:

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This is the cab input:

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So, is this correct?

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I understand the purpose of the shorting jack, but the manual doesn’t explain what the 8-16 ohm output itself does exactly. Is that the correct one, and what does it mean to have “from 8 to 16 ohms”?

The cab isn’t modified in any way, so the four speakers are (to my understanding) wired in series parallel, resulting in 8 ohms total.

#2

8-16 is your choice. Actually any amplifier is quite torelant to higher impedance but not to lower one. So, you could use even 32 Ohm or 40 Ohm load. Until you reach kiloohms - nothing bad will happen. Very high impedance (or no load at all) could lead to a transformer short circuit and/or output valves damage (transistors damage in case of solid state amp)

1 Like
#3

Okay, thanks for clearing that! Why does it say 8 to 16 ohms, though? Something to do with the amp’s different A+B speaker configurations?

#4

It has nothing to do with A+B stuff.
8 Ohm and 16 Ohm are typical cab and speaker impedances. Sometimes they do three different transformer taps: for 4,8, and 16 Ohm. Sometimes they don’t. There’s no much difference for an amp between 8 and 16 Ohm load, so manufacturers often use “combined” tap. Difference is that lower impedance cab would sound a bit louder.
On my selfmade valve amps I used only one tap for 4 Ohm, and I connected 8 and 16 Ohm to this output as well without any troubles.

1 Like
#5

Got it. Thank you. :muscle: