MojoFilter
Active member
- Joined
- Sep 22, 2006
- Messages
- 37
- Reaction score
- 0
Hey, folks-
I remember there being some confusion about using the "A+B" cabinet configuration, and I called Mesa to inquire about how to do this without damaging either the power tubes or the transformer by inadvertently putting a 2 Ohm load on the amp.
The Road King manual states, on page 12:
"Note: Do not use the SPKR A+B selection when 2 8 ohm cabinets are each connected to the two 4 Ohm OUTPUTS of each Speaker Output Bank. A 2 Ohm load puts an excessive strain on the power tubes causing them to wear unusually fast"
According to Mesa Customer Service, this is saying that you do not want to hook up TWO 8 ohm loads to the "A" side 4 ohm outputs, and TWO 8 Ohm loads to the "B" side 4 ohm outputs, and then run them in "A+B" configuration.
However, according to Mesa Customer Service, it is perfectly safe to hook up ONE 8 Ohm cabinet (or speaker) to the "A" side 4 ohm output, and ONE 8 Ohm cabinet (or speaker) to the "B" side 4 ohm output, and then to use the cabinet switching in any combination, including the "A+B" setting. When just the "A" or "B" side is selected by itself, you'll have a safe mismatch: a 4 Ohm output into an 8 Ohm Speaker load, and the amp will be a little darker and spongier as a result. When you run this configuration in "A+B", you'll be running the correct match.
Apparently, the cautionary note on page 12 is to alert you not to use multiple 8 Ohm cabinets ON THE SAME SIDE (A or B) using the 4 Ohm outputs.
I hope this clears things up a bit...I had some questions about this myself, and stopped using the cabinet switching for a while as a result.
I remember there being some confusion about using the "A+B" cabinet configuration, and I called Mesa to inquire about how to do this without damaging either the power tubes or the transformer by inadvertently putting a 2 Ohm load on the amp.
The Road King manual states, on page 12:
"Note: Do not use the SPKR A+B selection when 2 8 ohm cabinets are each connected to the two 4 Ohm OUTPUTS of each Speaker Output Bank. A 2 Ohm load puts an excessive strain on the power tubes causing them to wear unusually fast"
According to Mesa Customer Service, this is saying that you do not want to hook up TWO 8 ohm loads to the "A" side 4 ohm outputs, and TWO 8 Ohm loads to the "B" side 4 ohm outputs, and then run them in "A+B" configuration.
However, according to Mesa Customer Service, it is perfectly safe to hook up ONE 8 Ohm cabinet (or speaker) to the "A" side 4 ohm output, and ONE 8 Ohm cabinet (or speaker) to the "B" side 4 ohm output, and then to use the cabinet switching in any combination, including the "A+B" setting. When just the "A" or "B" side is selected by itself, you'll have a safe mismatch: a 4 Ohm output into an 8 Ohm Speaker load, and the amp will be a little darker and spongier as a result. When you run this configuration in "A+B", you'll be running the correct match.
Apparently, the cautionary note on page 12 is to alert you not to use multiple 8 Ohm cabinets ON THE SAME SIDE (A or B) using the 4 Ohm outputs.
I hope this clears things up a bit...I had some questions about this myself, and stopped using the cabinet switching for a while as a result.
