Name: Marc Donaldson
Email: mdonaldson@in-tch.com
Subject: speaker settings 4 or 8 ohms
Thread: 121
Time: Fri, 3 Aug 2001 14:41:04 UTC
Steve is correct that most amps have the speaker output jacks wired in parallel, however, this is not the case for all MM amps -- some have series connections. If you look at some of the schematics available on this site (http://www.pacair.com/mmamps/schematics/index.html), you'll notice that even the same numbered chassis (for example 2475-65 & 2275-65) will have either parallel or series connected jacks depending on vintage.
My HD130 has a printed statement under the output jacks that says "Speaker jacks are connected in series. Observe proper load impedance." I would hope MM carried this through on all models set up this way.
If the jacks on your amp are in series, then you'll want the selector on 8 ohms with a single 8 ohm cabinet.
To run two 8 ohm cabinets, you'll need to set the selector to 4 ohms, run a cable from one output jack to the first cabinet, and then connect the second cabinet to the second jack on the first cabinet. The two jacks on the speaker cabinet are connected in parallel, so this places the two 8 ohm cabinets in parallel, resulting in a 4 ohm load, matching the selector setting.