Music Man HD-130 amp and B-15 cab - Series wiring question added!

[drbassman]

Both items are coming tomorrow, so I'll hook them up and review here.  

CORRECTION:  The cab is being delivered today.

[drbassman]

Got online and did some searching and found that Mark Knopfler, Johnny Winter, Albert Lee and Eric Clapton used Music Man amps during their hayday.  Even found pics of some of them on stage or in an ad:  http://www.mk-guitar.com/2009/02/15/music-man-guitar-amps/

[drbassman]

Now the fun begins!  The two speaker jacks on the Music Man HD-130 are wired in series with a 4 or 8 ohm switch.  SO, to run two 8 ohm cabs, I can plug one into each jack and flip the switch to 8 ohms?

[Granny Gremlin]

Ampoutput jacks being series is very unusual; are you certain?  Usually parallel.  If series and you use only one cab, only one jack will work (easy way to test if series or parallel, though one should never run a tube power section head with no load for more than a few seconds, which would be thae case if a single speaker is plugged intop the wrong series jack).

2 8 ohm cabs in series = 16 Ohms (use the 8 0hm setting on the amp; you will have half the rated wattage, but approx twice the efficiency of a single 8 Ohm speaker so balances out, kinda).

2 8 ohm cabs in parallel = 4.

The best thing to do (assuming that the amp outputs are series) would be to set the amp to 4 Ohm output and plug one cab into the amp.  Then plug the second cab into the parallel jack on the first cab (as you would if the amp only had 1 output jack.  Another benefit of this method is you don't have to worry about whether the amp jacks are series or parallel.

[drbassman]

Don't know for sure.  Here's what the back of the amp looks like and says:  Speaker jacks are connected in series.  Always observe proper load impedance.  

Class II wiring may be used.

[Chris P.]

I know some Dutch artists playing them and with The Last Waltz of The Band there's a MM combo onstage. Could be Eric's.

[Chris P.]

Robertson: I started with Fender, switched a while, then when we began working with Bob Dylan I went back to Fender. Whatever I used beside Fender just didn't get loud enough. Today I use Music Man amps, and they're all right. They break down a little too much for me, though. They're more powerful than the early Fenders; out of those small Music Man amps you get a bigger sound. They're just powerful, but I have blown out one a couple of times and another one once. I use two amps together--a little Music Man 210 HD, and a bigger 212 HD.

[drbassman]

I saw "Jimbodbassman" talked about having one in an old TB thread.  Is he Eric?

[drbassman]

Got the 15" Ampeg cab today and hooked it up to the Mesa Walkabout amp.  Sounds good, lots of bass and able to handle the amp cranked up and driving it hard with my LP Triumph.  Rattling shelves and the like!  I'm gonna try it with a TB reverse plugged in too.  It might be a cheaper unit, but I'm looking forward to hearing it in tandem with my Mesa 15" cab.  I'm expecting an improvement in my bass output/projection.  It sounds stronger than the old 12" Mesa cab, so I'm very happy with that.

[Psycho Bass Guy]

Music Man amps do indeed have series-wired extension jacks.  Their 70's endorsers were mostly paid spokepeople brought to post-Fender fold. Clapton famously used stacks of them... unloaded with his old Bluesbreaker hidden backstage. The HD-130 makes for an excellent bass amp, but their cabinets were ported and used low-wattage drivers, so lots of them ended up blown.

Now the fun begins!  The two speaker jacks on the Music Man HD-130 are wired in series with a 4 or 8 ohm switch.  SO, to run two 8 ohm cabs, I can plug one into each jack and flip the switch to 8 ohms?

No. You would need to hook the cabinets in parallel to each other, set the switch for 4 ohms, and use a single output jack. What you suggest would be putting a 16 ohm load across the 8 ohm tap, not a good idea.

[drbassman]

Music Man amps do indeed have series-wired extension jacks.  Their 70's endorsers were mostly paid spokepeople brought to post-Fender fold. Clapton famously used stacks of them... unloaded with his old Bluesbreaker hidden backstage. The HD-130 makes for an excellent bass amp, but their cabinets were ported and used low-wattage drivers, so lots of them ended up blown.

No. You would need to hook the cabinets in parallel to each other, set the switch for 4 ohms, and use a single output jack. What you suggest would be putting a 16 ohm load across the 8 ohm tap, not a good idea.

Well now, that figures.  I figured as much on the endorsing stuff.  Athletes have figured that one out, too!  I'll try your suggestion.

So, I'll be running a 4 ohm set up doing as you suggest, maximizing the amp's power.  Sweet!

[Granny Gremlin]

It's like there's an echo up in here.

I kinda wonder though, Psycho, if the jacks really are series, does one of them not work if the first isn't also not in use?  Any idea why they did that?  I have never used MM amps.

[Psycho Bass Guy]

So, I'll be running a 4 ohm set up doing as you suggest, maximizing the amp's power.  Sweet!

Tube amp with output transformer = the same power at every rated output impedance.

[drbassman]

In my glorious ignorance, I have to say, I don't recall ever seeing series jacks on the back of an amp.  They must have had a good reason, which we'll probably never know.

[drbassman]

Tube amp with output transformer = the same power at every rated output impedance.

Oh, I see.  Even better I think.