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Post subject: Re Bassman 50-Can I rewire my 4x10 8ohm cab to 4ohms?
Posted: Fri Sep 17, 2010 10:16 am
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Hi - just managed to pick up a Bassman head. I'm going to use it with Roland Cab, with 4 10" speakers. The Cab is rated 80 watts, 8 ohms, and it's wired in what I think is "parallel-series" configuration. So, going on that, I believe each speaker is also 8ohms. General opinion seems to be that, while running a 4ohm head into an 8ohm cab is safe enough, performance will be compromised, so, my question is; is there a way I can re-wire my cab to draw a 4ohm load?

I've drawn some lines to show clearly how it's wired at the moment.
So, is there anyone out there who can tell a rookie how to manage this in language that's as simple as "connect the red one to spkr 1, positive." etc.

Much appreciated.

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Posted: Fri Sep 17, 2010 6:01 pm
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That's an interesting wiring scenario. Don't see 4ohms from 4X8ohm speakers. Art

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Posted: Fri Sep 17, 2010 11:49 pm
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Have you determined the impedance of these speakers?

Arjay

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Posted: Sun Sep 19, 2010 8:59 am
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No - I know the cab is 80 watts, so I'm guessing they must be 20watts each - no?


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Post subject: Speaker ohms
Posted: Mon Sep 20, 2010 9:57 pm
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Hi simian,

If your 4 speakers are 8 ohms each, the only way to get 4 ohms would be to only use 2 speakers. Remove the green wire and red wire from speaker 1 and 2. Then remove the black wire from speaker 3, connect it to the - terminal of speaker 1. Then remove the white wire from speaker 4 and connect it to the + terminal of speaker 2. You'll have a 4 ohm load, but only 2 speakers. You might like the sound of 2x10s. :)

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Posted: Tue Sep 21, 2010 7:00 am
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Thanks Shimmilou - the only problem there is, that leaves me with 2 speakers adding up to 40 watts, I'm using a 50-watt head. I think I might just have to buy/steal/find a new cab.


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Post subject: 4x10 cab wiring
Posted: Tue Sep 21, 2010 7:24 am
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Yes, you could blow the speakers if you crank up the amp, but limited to half volume you'd be OK. Just remember, if you want 4 ohms, generally you need two speakers (8 ohm each, in parallel), because you can't get 4 ohms from 4 speakers that are 8 ohms. You can use 4 speakers that are 4 or 16 ohms each, and just replace the ones that you have. Using 4 ohm speakers, 2 paralleled pairs, each pair in series with each other, giving 4 ohms. Using 16 ohm speakers, all four in parallel will give 4 ohms. In either case, you can use fairly low wattage speakers (20 watts or more each is plenty), as long as all four are being used with the 50 watt amp. Of course it might be cheaper and easier to just buy a 4 ohm cab, but where's the fun in that? :D

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Post subject: good amp wiring resource
Posted: Thu Sep 23, 2010 12:51 pm
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http://www.svvintageamps.com/speaker.php#question11

this link has a good wiring theory and formulas as well as diagrams.


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Posted: Thu Sep 23, 2010 2:28 pm
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very interesting zoodiscmcc. Thamk's


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