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Post subject: Matching an extension cab to my Bassman 50
Posted: Tue Apr 12, 2011 2:01 pm
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Hi - hoping someone can help with a question - I have a Bassman 50 (Silverface, no M.V.) and use it with a 4ohm cab (ie. 2 x 8ohm speakers wired in parallel.) . So, I'm thinking about adding another cab to the "Extension Cab" jack on the back panel of the amp - my question is, what ohms rating should my cab/cabs have? Can I connect two 4 ohm cabs to this? Bearing in mind that the label on the amp reads "Total load 4 ohms" - does this mean I need 2 8ohm cabs? I have 4 x 8 ohm speakers in total, so is there a wiring configuration I can use to give me a total load of 4 ohms spread over the two speaker outputs?

Thanks in advance.


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Post subject: Re: Matching an extension cab to my Bassman 50
Posted: Tue Apr 12, 2011 2:22 pm
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If you're already useing 4 ohms you can't add more becase that would be a 2 ohm load on a 4 ohm amp.

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Post subject: Re: Matching an extension cab to my Bassman 50
Posted: Tue Apr 12, 2011 8:59 pm
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Hi simian,

The "Total load 4 ohms" simply means that your amp will be the most efficient with a 4 ohm speaker load. You can run a 2 ohm or 8 ohm speaker load just fine, but simply will not get full power from the amp with anything other than 4 ohms. So you can use an additional cabinet of 4 ohms or 8 ohms with no problem. If you use an 8 ohm cab with your existing 4 ohm, you will have a total of 2.6 ohms, and of course two 4 ohm cabs will give you 2 ohms. :idea:

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Post subject: Re: Matching an extension cab to my Bassman 50
Posted: Wed Apr 13, 2011 2:09 am
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:?: Confused ?? 2 different answers, who to listen to? Aarrgh!!


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Post subject: Re: Matching an extension cab to my Bassman 50
Posted: Wed Apr 13, 2011 6:56 am
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:lol: Many know that impedance matching of an amplifier and speaker load is important, but not many know why. Here is some good info about tube amplifiers, including impedance matching (link below). Under the heading "Transformer Questions", look at questions 14, 15 and 16 about impedance matching.

Super kid seems like a great person, and no offense meant as he obviously is knowledgeable about amps/speakers/guitars, but I have been using tube amps with mismatched amp/speaker impedance's for longer than he has been alive. I know that there are other forum members that use their amps with a mismatched impedance of amp and speaker on a regular basis, some even do so professionally. On a tube amp, too low a speaker impedance is not a problem, but too high a speaker impedance can be. Generally speaking, you may not even be able to hear much difference in sound with a 2 to 1 impedance mismatch vs matched impedance, and there will not be a lot of difference in performance either as the impedance of the speaker varies with frequency variation from the amp. :idea:

http://www.geofex.com/tubeampfaq/tubefaq.htm#transformers

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Post subject: Re: Matching an extension cab to my Bassman 50
Posted: Wed Apr 13, 2011 7:37 am
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Thanks for the replies - unfortunately, I don't really understand much of what's on that page - I'm gonna try a few different setups to see what sounds best, hopefully at the very least I won't fry my amp/self


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Post subject: Re: Matching an extension cab to my Bassman 50
Posted: Wed Apr 13, 2011 8:38 am
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Sorry about that, maybe information overload. Just be assured that an impedance mismatch of 2 to 1 will not harm the amp or you in any way, and in fact your amp will run fine even at a zero ohm load on the output (think shorting output jack for protection). Letting your ears decide is a great idea. Let us know what you do and how it sounds. :idea:

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Post subject: Re: Matching an extension cab to my Bassman 50
Posted: Wed Apr 13, 2011 11:09 am
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What it means in other words is that you will be safe with 2 ohm load or a 8 ohm load. One up or down in impedance is safe. One will be harder on the tubes while the other harder on the transformer. Some mismatch on purpose because they like the sound better. However I wouldnt do a 4 ohm amp on a 16 ohms cab.


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