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Author Topic: Help me understand tube guitar amplifiers and acceptable speaker impedance  (Read 1307 times)

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Offline tcell

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The Tode has a 4 ohm speaker, but some have used it with 4x12 cabs which probably are 8 or 16 ohms total resistance.  Does that unduly stress the output transformer of the Tode?  I get confused because with solid state amps running an amp designed for say 8 ohms into a 4 ohm speaker risks damaging the amp, but running it into a 16 ohm speaker would reduce loudness, but wouldn't stress the transistors.  Some sources seem to say that it is the opposite with tube guitar amps.  What is the real deal here, at least practically speaking?  Does a safe impedance mismatch at least alter the frequency response?  Thanks
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Offline Doc B.

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Re: Help me understand tube guitar amplifiers and acceptable speaker impedance
« Reply #1 on: September 16, 2016, 04:19:43 PM »
There will be no harm to the amp running 8 or 16 ohm speakers. Guitar amps and speakers are designed for tonal coloration. Whether the amp gives the coloration you want has to be determined by trial and error. I think the sound of the speaker will dominate what you hear from the combination, and any impedance differences will only have a minor influence in the deep bass - which there isn't that much of in a guitar.
Dan "Doc B." Schmalle
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Offline tcell

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Re: Help me understand tube guitar amplifiers and acceptable speaker impedance
« Reply #2 on: September 17, 2016, 03:35:02 AM »
Thanks Doc.  So what would happen if the Tode were plugged into a speaker with 1 or 2 ohm resistance (thought experiment).  Would there be excessive current flow and damage to the amp? Thanks, Jeff
Bottlehead Gear: Foreplay 2&3, Extended S.E.X., Paramours I w/ iron upgrade, Straight 8's, Tode, Bottlehead DAC.  Guitar gear: Les Paul Standard 1981, Ernie Ball John Petrucci BFR, POD HD500x, Marshall JCM1, TC Electronic G-Force.

Offline Paul Birkeland

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Re: Help me understand tube guitar amplifiers and acceptable speaker impedance
« Reply #3 on: September 17, 2016, 06:20:13 AM »
You'll get more distortion from the output stage under those conditions.

Do note that a 4x12 with 16 Ohm drivers will present a 4 Ohm load to the amp with all drivers wired in parallel, which works nicely.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline tcell

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Re: Help me understand tube guitar amplifiers and acceptable speaker impedance
« Reply #4 on: September 17, 2016, 09:54:32 AM »
So no fire and brimstone, eh?  Guitar people seem to think impedance mismatches are liable to cause damage to their amps.  Thanks for your help guys.
Bottlehead Gear: Foreplay 2&3, Extended S.E.X., Paramours I w/ iron upgrade, Straight 8's, Tode, Bottlehead DAC.  Guitar gear: Les Paul Standard 1981, Ernie Ball John Petrucci BFR, POD HD500x, Marshall JCM1, TC Electronic G-Force.