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rdsmith3

Epiphone 1x12 cabinet with Fender VibroChamp XD

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My little VibroChamp XD sounds much better with a 12" speaker. The sound is much fuller and deeper. Even though the impedance of the Epi cabinet is 16 ohms, it works well with the Fender.

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My little VibroChamp XD sounds much better with a 12" speaker. The sound is much fuller and deeper. Even though the impedance of the Epi cabinet is 16 ohms, it works well with the Fender.

Just wonderin'.... what's the Fender putting out??? ... and how big's the original speaker? I know the VJ sounds WAY huger through the 12" than the stock 8" (although my combo speaker is a 4 ohm speaker and my VJ cab is the 16 ohm speaker) - am just assuming more of the sound difference is coming from the difference in amount of air being moved and the speakers themselves, compared to one being run at 4 and the other at 16 ohms...I dunno.. .... every time I think I have my head wrapped around the whole ohms thing, I get confused again, or read something else to confuse me yet more.....so I just stick to matching output to speaker and don't worry about it [biggrin]

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Yes, I think a 12" speaker is moving about twice as much air as the stock 8" speaker in the Fender. That is where the sound is coming from. The Fender has a 4 ohm speaker, and the Epiphone is 16 ohms, so it should be less efficient, but it ends up being louder.

 

I did a blind listening test with my 17 year old son and he could clearly tell the difference.

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Yes, I think a 12" speaker is moving about twice as much air as the stock 8" speaker in the Fender. That is where the sound is coming from. The Fender has a 4 ohm speaker, and the Epiphone is 16 ohms, so it should be less efficient, but it ends up being louder.

 

I did a blind listening test with my 17 year old son and he could clearly tell the difference.

Just wonderin'.... are you running the cab w/ a 4 ohm output from the amp, or does the Fender have 8 and 16 ohm out jacks as well? I like the convenience of the combo/8" speaker, but.... yeah, the 12" cab is definitely better and more sound [thumbup]

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There is only one output from the amp. My understanding, which could be wrong, is that you can safely use a higher resistance load, e.g., 16 ohms instead of 4 ohms, but it is less efficient. If you use less resistance than the amp manufacturer calls for, then you could damage the amp. Someone correct me if that is bad advice.

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Just wonderin'.... are you running the cab w/ a 4 ohm output from the amp, or does the Fender have 8 and 16 ohm out jacks as well? I like the convenience of the combo/8" speaker, but.... yeah, the 12" cab is definitely better and more sound [thumbup]

It is always best to match the impedance of the OT, of course. But if your hand is forced, it is better to mis-match on the low side. It is with too large an impedance that you run the risk of break down and fly-back voltage which in turn can cause catastrophic failure of tubes and transformers. It is all available for reading if you feel like it. What you are proposing, 4 ohm tap into a 16 ohm load is a bad idea. That is the theory behind the shorting jack on the speaker outs. Amp designers prefer a (almost) direct short instead of a much larger impedance should the speaker load be removed from the OT.

Good Luck

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It is always best to match the impedance of the OT, of course. But if your hand is forced, it is better to mis-match on the low side. It is with too large an impedance that you run the risk of break down and fly-back voltage which in turn can cause catastrophic failure of tubes and transformers. It is all available for reading if you feel like it. What you are proposing, 4 ohm tap into a 16 ohm load is a bad idea. That is the theory behind the shorting jack on the speaker outs. Amp designers prefer a (almost) direct short instead of a much larger impedance should the speaker load be removed from the OT.

Good Luck

I wasn't proposing, was just wondering what the op was actually doing. I play by the "rules" because I don't know any better...LOL. My 4 ohm 8" combo speaker gets the 4 ohm out, the cab gets the 16 out.... that way, no worries, other than my marginal talent :)

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Is there some way I can connect, say, a 5.4 ohm resistor in parallel with the 16 ohm load to get a total load of about 4 ohms?

Yeah, there is. But keep this in mind. You will loose about half the power of your amp to the resistor (a resistor does not produce any sound). The resistor will need to be BIG, about double the wattage of your amp. And, not that it really matters, a speaker is a reactive device, its impedance changes with the frequency of the signal. A resistor sits there at is resistive value, regardless of the AC signal it passes.

I think you will be much happier if you get a 4 ohm speaker. It is a good idea to have a few in your arsenal anyway.....

Good Luck

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The 16ohm speaker load will be reflected back onto the primary as an increased load (is this by inverse square of turns ratio?): you will make the amp work harder.

 

This is a speaker mis-match and a "bad thing" especially in a hifi amp.

 

This is not a hifi amp.

 

This is a guitar amp.

 

Will it hurt the amp? - probably not. The transformer may get a bit hotter than before, but consider - the transformer was probably robbed from a 30+watt push-pull amp because s.e. amps need massive transformers. It is almost impossible to blow a good op transformer: you could put the primary across the mains and leave it there all day. The op valve will have to work harder and may shorten its life: nevermind get another valve.

 

Some Fender amps will take a 2ohm load - this is not one of those amps: you do not want to go below 4ohms on this one, but you can reasonably use an increased load: 8ohm would be reasonable; 16ohm is on the edge of the envelope. Probably ok if it sounds good (especially if you don't crank it right up to 11).

 

If the amp has negative feedback (NFB) then it is practically self-matching to load anyway.

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The 16ohm speaker load will be reflected back onto the primary as an increased load (is this by inverse square of turns ratio?): you will make the amp work harder.

 

This is a speaker mis-match and a "bad thing" especially in a hifi amp.

 

This is not a hifi amp.

 

This is a guitar amp.

 

Will it hurt the amp? - probably not. The transformer may get a bit hotter than before, but consider - the transformer was probably robbed from a 30+watt push-pull amp because s.e. amps need massive transformers. It is almost impossible to blow a good op transformer: you could put the primary across the mains and leave it there all day. The op valve will have to work harder and may shorten its life: nevermind get another valve.

 

Some Fender amps will take a 2ohm load - this is not one of those amps: you do not want to go below 4ohms on this one, but you can reasonably use an increased load: 8ohm would be reasonable; 16ohm is on the edge of the envelope. Probably ok if it sounds good (especially if you don't crank it right up to 11).

 

If the amp has negative feedback (NFB) then it is practically self-matching to load anyway.

 

Thanks. That is helpful. I almost always only have the volume at 3 or below because of spouse and sleeping kids.

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