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Helix headphone out to speaker cab: amp unnecessary


aaronlyon
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On a whim I plugged the headphone output from my Helix floor unit into my 4-ohm, 2x12 speaker cabinet. Instant practice amp. The headphone out drives the cabinet perfectly well for low volume practice--no amp required.

 

Interesting to know that works. Wonder if it might do damage eventually though to the Helix's headphone amp by making it work too hard. I know the headphone output expects more than 4 ohms of resistance. Any electrical engineers want to weigh in on this?

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I know the headphone output expects more than 4 ohms of resistance. Any electrical engineers want to weigh in on this?

Don't need one... it's a bad idea. An amp is an amp. If you supply a bigger resistance load than its expecting, you'll lose some power, but you won't blow anything up. A smaller load however, will eventually fry things.

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Don't need one... it's a bad idea. An amp is an amp. If you supply a bigger resistance load than its expecting, you'll lose some power, but you won't blow anything up. A smaller load however, will eventually fry things.

This^

 

4 ohms is much less than headphones (around 20-250 ohms depending on model). That's quite a bit less impedance. I am not an amplification expert by any means, but I would not try it for very long. There are lots of cheap solid state amps out there to drive a cabinet. 

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I don't know the circuit details of the Helix headphone output, but if it is not properly protected against short-circuit conditions, then it may end up driving excess current (beyond the rating of the output amp) into the load. That could eventually cause the amp output stage to fail. Solid state amps don't have a problem with driving higher impedance loads, they just get quieter as they can't usually drive high enough voltages to get the full power across to the speaker.

 

On the other hand, tube amps with output transformers become inefficient outside of their nominal impedance operating range. If you leave the output transformer winding incorrectly terminated (ie. with a short circuit or with an open circuit) then the transformer can be damaged (and/or output tubes due to flyback). It is never advisable to significantly mismatch the impedance on a tube amp, as the amp can be damaged. Some amps protect against catastrophic failures to some degree and will pop a fuse. But, older style amps will just end up with blown tubes, fused circuitry, and melted windings in the output transformer.

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