Comments on: Ohm my god

Question: Ohm my god

anazgnos — Sun, 13 Mar 2011 12:52:34 -0800

The bass player in my band has this combo amp. It has 2 internal speakers, and an external speaker jack rated for a minimum impedance of 4 ohms. If he wants to hook up an additional cabinet, what does the impedance of the extra cab need to be?

He bought a Mark Bass 2x12 extension cab rated at 8 ohms. We plugged it in, everything sounded fine, but then we got...a smell.

He has a regular amp tech who assured him this setup would be fine but as this was the first run it made us a little squeamish.

I guess it's not clear whether that 4 ohm impedance includes the existing, internal speakers, or is just a standalone value. If his existing speakers already resist at 4 ohms, then the additional cab needs to be...what? I understand there's a formula to this, but if the info I found here is correct (under 'Calculating Total Impedence of Different Impedance Cabinets')...then there is nothing you can add to an existing 4 ohm load that will result in anything but a fraction of 4 ohms. If anyone's familiar with hooking up a cab to this particular amp and not frying any of the components involved, that'd be great.

By: zephyr_words

zephyr_words — Sun, 13 Mar 2011 13:38:05 -0800

A lot of times when you smell something after using new amplifier equipment it's just dust burning off.

I'll take a look at the stats on all the gear but on quick review it looks fine.

By: zephyr_words

zephyr_words — Sun, 13 Mar 2011 13:52:58 -0800

Yup your setup is fine. The speakers internally run at 8ohms so you can use an 8ohm extension cab.

I found someone with a similar question on talkbass. A direct response from ashdown:
"To answer your questions enclosed. full power is realized into 4 ohms, the internal speakers are wired to 8 ohms therefore giving the opportunity to use an 8ohm extension. the amp puts out approx 300 watts into the internal speakers. The unit has the 1/4" jack socket on the rear for the internal speaker, but it also has a speakon connector for an extension cabinet."