Amp Impedance

[tlingen]

I have a Randall RM100 2x12 combo and I have also been using a Marshall 1960 cabinet at the same time. The Randall combo has two 16ohm speakers and the impedence switch on the amp at 8ohms. The Marshall 1960 cabinet can either do 4 or 16ohms. I've been plugging in the Marshall using it's 16ohm jack and not changing the Randall from it's 8ohm setting. I am wondering if I'm hurting my amp by adding the second cabinet at a improper load. I just don't know how else to set it. Thanks for any help.

[Chad]

The 2 speakers in the combo are wired in parallel, which results in an impedance of 8 ohms. The extension speaker jack on the RM100 parallels with the main speaker input. So go to this calculator...

http://www.1728.com/resistrs.htm

and enter 8 ohms and 16 ohms. This results in an impedance of 5.333 ohms. You don't want to go with an impedance below the ohm setting on the amp, but it's okay to go above. So you should be running it with the 4 ohm setting.

I don't know the electrical specifics (I'd leave it for the amp techs to chime in), but, I'd say that you have been straining some of the components in that amp by running it at 8 ohms.

[tlingen]

Thanks Chad. 4ohms looks closer to what I should be running. I'll try it today.

If anyone has any other thoughts, please let me know.

[Dave L]

This is way out of my league, but I believe solidstate amps might cope better with mismatched loads than tube amps. It´s not like you should be doing it anyway, but there´s a better chance of it not dying if you accidentally do it.

I could be waaay off the mark here, so I´ll be quiet now.