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Post subject: How To Wire Frontman 65R for External Cabs
Posted: Wed Mar 31, 2010 5:04 pm
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I'm picking up a Frontman 65R in a matter of hours, no bout a doubt it.
I'd like to connect some additional speakers to it. I know it has no external cab connection (right?) so I'm faced with wiring one (or more) myself.

The externals I have are a pair of Realistic PA95 mini-towers, 2x10" woofs + one 2"x6" tweety horn in each, each designed and rated to carry 100 W. They're presently serving satisfactorily as secondary stereo speakers and sound good. The wiring is 16g lamp cord into standard snap-down stereo speaker connections, but any or all of that can be changed right up to the cross-over if need be.

Foremost I need some advice on how to wire these two 8 ohm cabs to the one 8 ohm 12" in the Frontman so that none get overloaded due to low resistance. I'm plenty handy with a soldering gun (I grew up fixing things in my dad's TV shop) but not so confident in my theoretical and technical knowledge (I never became a technician, only a neuroscientist*). A simple description would suffice for me, but others who come later might benefit from a schematic. If someone will throw me a wiring bone, I'll be glad to do the schematic myself after testing it. Suggestions as to connectors and cabling would also be appreciated as would making those connector suggestions applicable to better cabs later. I did try to find something on this in the info archives here, but didn't see anything. If it's there and I missed it, my apologies and please point me at it. I'm aware of what it'll do to my warranty. I'm also aware the result may have less volume as a resistance higher than 8 would be preferable to less than 8, but I'm more interested in full and even sound, not volume, because I'm old. Er. Older.
Thanks is advance, or in retrospect prior to answers from those of you with a time machine.

[* I can find the tonotopic map (different places = different notes) on the auditory cortex of a living brain with an EEG and a pair of handheld probes, but I can't juggle Ohm's Law to get these speakers wired. I mean, what happens to E = I*R if the numbers on left and right don't balance out? The leftover turns into smoke, right? Then you have to get a smoke refill and reload the smoke into the parts it leaked out of. See my problem?]


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Posted: Wed Mar 31, 2010 8:59 pm
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Hi Dyna and welcome to the forum. The only reasonable set-up that I can come up with is the two towers in series for a 16ohm load. Then going to the internal speaker for a combined load of 12ohms. The 8ohm speaker will be getting the lion's share of the output, but with a tower on each side, it should sound pretty neat. Art

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Posted: Wed Mar 31, 2010 10:29 pm
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I believe if the two 8 ohm towers were placed in series, then connected parallel with the combo speaker, the overall impedance seen by the amp would be 5.3 ohms, not 12 ohms.

1/T=1/r1 + 1/r2
1/T=1/16 + 1/8
1/T=3/16
T=16/3=5.3

Running a solid state amp with less than the designed impedance can lead to overheating (increased current flow) if 'pushed'.

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Posted: Thu Apr 01, 2010 5:19 am
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Yep, you're absolutely right RVM. It ocurred to me this moning my math was wrong. Thanks for catching that. My bad! Art

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Posted: Thu Apr 01, 2010 7:39 am
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Quote:
Yep, you're absolutely right RVM. It ocurred to me this moning my math was wrong. Thanks for catching that. My bad! Art


No problem, easy thing to do. The good thing about a forum is that there are 100's watching to help each of us catch our errors.

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Post subject: repliedeediedeedo
Posted: Thu Apr 01, 2010 8:13 pm
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Thanks for the responses guys. I'd done those two calculations myself with the help of some web apps. 12 (8 series with (8 parallel 8 =) 4)does seem the safer way to go vs. 5.33. You guys figure it's safe enough to run that way? Don't worry, I won't hold you to repairs, I'm voiding the warranty just by hooking things up like this.

Two questions then: 1. running at a higher impedance will change the frequency charactertistics, but how? High end roll off, yes? And 2. what's the power equivalent that the 65 W will 'look like' coming through 12 ohms? I'm thinking there's a rule of thumb calculation for this.

The one down item to the whole marvelous first day with my new Frontman: the pre-out doesn't serve as a headphone jack. I suppose that'll be the next project.

BTW, I'm using it to drive a Johnson Telecaster copy. First thing, I cranked the volume, drive and reverb, and banged out Trower's 'Bridge Of Sighs'. Suddenly it was 1975 again.

BTW2, this isn't the first Fender in the family. It's less than 3 years from being half a century since my uncle (a Nashville session man for a while) handed me his gaudy turquoise sparkle, 3 split pickup brand unknown solid body, plugged it into his blonde Tremolux, and taught me G, C and D chords.


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Posted: Sat Apr 03, 2010 11:30 pm
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Dyna -

Another way to do this without messing with the internal speaker would be to take the Pre out into a power amp and then power the 2 PA cabinets with that. The power amp may be something you already have (or a powered mixer), but that way you could vary the volume of your Frontman 65R and the Realistic PA-95s to taste.

If you don't have a power amp, ebay or Craigslist would have something; being 100 watts a side, there should be lots of low cost options.

Good luck!

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Post subject: Re: How To Wire Frontman 65R for External Cabs
Posted: Tue Dec 17, 2013 2:29 pm
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Bump

Just wanted to say that I solved the problem. I liked the 65R so much (man is it LOUD for such a small box) that I got a second one. Since my multi-f/x pedal has stereo output I needed a second matching amp to get balance in the effects. Now I've got some high quality LOUD*2.


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