running an amp into a cab via headphone jack

[mig50]

i blew my only amp a few months ago, but today my friend loaned me a fender combo.

it doesn't have an extension speaker jack, but it does have a headphone jack.

i can run a cable out of the headphone jack to the cab, but it seems like i've read somewhere that this is a bad idea.

if anyone can tell me any reason i should/shouldn't do this, and/or anything to look out for, please do so.

thanks.

 

[Animal]

Re: running an amp into a cab via headphone jack

I want to know also.

 

[aleclee]

Re: running an amp into a cab via headphone jack

other than the fact that a headphone jack's output is barely enough to be audible through a regular speaker, the impedance mismatch is liable to fry the circuit that drives the headphone output

 

[The Golden Boy]

Re: running an amp into a cab via headphone jack

I was always of the impression that the headphone out is still a powered signal, in other words it's not just a preamp signal. So the input is going to be "slamming" into the second amp's preamp.

OK, I didn't read the question... :duh:

The headphone out signal is powered, but it's not powered a lot. You can try running speakers off it, but it's meant to push two small speakers.

 

[Kent S.]

Re: running an amp into a cab via headphone jack

other than the fact that a headphone jack's output is barely enough to be audible through a regular speaker, the impedance mismatch is liable to fry the circuit that drives the headphone output

+1 ... Generally, this is correct, there are some tube designs that allow for headphones rated down to 8ohms (according to the schematics at least {Fender champ 15 for example, IIRC}, in accordance with the amp still being loaded with it's own speaker). Most headphone outputs specify a minimum impedance ( and most of todays headphones are still much higher impedance than speakers) , going lower than that will try to draw to much current, and that generally leads to something burning up. Headphone outputs also drop the voltage/current of the speaker level, as well as incorporate some simple filtering to accomadate the increased upper frequency response of headphones (compared to the roll-off of guitar speakers).

 

[tone4days]

Re: running an amp into a cab via headphone jack

arent most headphones ~8 ohms? .... i agree that they dont blow much power out those jacks, but i figured the impedance would match an 8 ohm cabinet

or am i all wrong?

 

[Pandemonium]

Re: running an amp into a cab via headphone jack

if anyone can tell me any reason i should/shouldn't do this, and/or anything to look out for, please do so.

The #1 reason would be that's it's a borrowed amp. If there's any question at all what kind of friend would risk another friend's amp? [shaking head in disbelief]

 

[Kent S.]

Re: running an amp into a cab via headphone jack

arent most headphones ~8 ohms? .... i agree that they dont blow much power out those jacks, but i figured the impedance would match an 8 ohm cabinet

or am i all wrong?

Headphones can range anywhere from around 300 ohms for older studio grade phones (from what I've read ... made for connecting across the speaker outputs without disturbing the load hardly at all, and being high enough impedance to draw very little current ... read not blow your head off), to around 48 to 32 ohms for home stereo/sound card phones, to even lower (their are some 8ohm phones around). It really runs the gamut.
The load seen by the amp on the HP jack gets kinda complicated as part of it is due to the voltage/current divider that is set up to drop the level for the phones.

 

[Kent S.]

Re: running an amp into a cab via headphone jack

The #1 reason would be that's it's a borrowed amp. If there's any question at all what kind of friend would risk another friend's amp? [shaking head in disbelief]

Duh, ... Yeah that's an important consideration there ... I totally 100% missed that ... :smack: