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Mountred's picture

two 115RH-65 for a HD-130 head: which impedance setting?

Nice place here!
I own a HD-130 head (no reverb/tremolo, SS preamp, all stock) and two 115RH-65 cabinets (all originals).
Since the cabinets are 8 Ohm each (as the specifications on the MM 1977 Amp Catalog), which output impedance setting may I choose from the head?
On the back of the amp there are two speaker outputs linked in series and a switch that says 4 or 8 ohms.
Now, two 8 ohms cabinets in series are 16 ohms total...obviously there is a impedance mismatch with the amp!
Is it safer to put the switch on 4 or 8 ohms position?
On page 17 of the MM1977 amp catalog there is a nice picture of a full stack with a HD-130 and two 115RH-65 cabinets...so Music Man knew that this combination was ok; however, I can't find any information on how to set the impedance in the amp!
Please, help me! :D I don't want to ruin my beautiful amp and cabinets!
Thank you!


Trick question

Hi there,

to get full utilization of the 130 head + 2 x 115RH you need to run them in parallel and set the impedance switch to 4 ohms. I forget if the cabs have one or two jacks on the back? If they only have one, you need to do the paralleling in the wiring. Make sure to phase them correctly or you'll get very little bass.

Running the cabs in series (16 ohms) and setting the switch to 8 ohms won't hurt anything - you're just not getting all that much power out of your rig.


Mountred's picture

It makes sense

Thank you, Lars!
A parallel wiring is the way to go (the cabs have only one jack on the back).
However, Music Man didn't mention this solution on their instruction manual; it says only "when both speaker jacks are used, place the impedance switch in the 8 ohm position (for best average performance)".
"For best average performance" sounds a little insufficient to me...Lars explaines better when says "you're just not getting all that much power out of your rig" :D
I can understand that could be a little tricky to make a parallel wiring (solder jacks, check the phase, etc.)...anyway, I wonder why Music Man, back in the days, didn't say nothing to make the most from the amplifier;
perhaps the "best average performance" was loud and powerful enough! and believe me...still is! :D
Again, thanks a lot!



Check page 7 of that catalog. There is a 212RH-130 ext spkr cab that has 4 ohm impedance. Set the switch to 4 ohms if using one of these. -mgriffin

mm210's picture

Personally, I'd add the

Personally, I'd add the parallel jacks to the cabs you have and use the 4 ohm setting. Why they didn't add the jacks at the factory is beyond me, especially considering the fact that they always used 8 ohm speakers so it was consistent. Then, you could use one cab on 8 ohms and two on four. JMHO. Mike.

Mountred's picture

cab modification

Nice idea, Mike! thank you!
But I don't think I want to modify the cab making another hole for the speaker jack...at least not now.
I'm currently playing in small clubs and in my rehearsal room and there is enough power with only one cabinet (of course with impedance set at 8 ohm) and it's easy to carry around...
I could even think to sell the second cab in the future...and I would like to sell it without any modification...

mm210's picture

YOu can always just make a

YOu can always just make a little parallel box with three 1/4" jack, all ganged together. Cord from amp to box and cord from each cab to box. Just tie all the +'s together and all the -'s together and you're jake. Mike.

Mountred's picture

Yes, I'm jake!

Hi there!
Mike, look at this little box from Palmer.
This solves my problem!
Besides, I also play guitar...I played a gig a week ago with my HD-130 connected to a Marshall 4 x 12" cab (4 ohm): terrific!
Again: thanks!


Thank you for posting

That's a great product. Obviously simple as a concept, but would take most of us hours to make ourselves. The Cab Merger can also be used to add a single 8ohm 12" (for example) to a 112-65/75 two channel MM. You need two short patch cords (one really short) in this particular setting. With the two cabs to one head you need the aforementioned really short (jumper) cord and two slightly longer ones.

PS - nice sunburst

Lars Verholt

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