Speaker hack,, sort of, with questions

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Offline
Joined: Dec 20 2003
Posts: 455

Okay, what i am doing *is* a hack but it doesn't really involve an apple but I would like someone's advice.

Bascially, I am sick and tired of the low volume outputs from the headphone jacks on laptops.

So what I did was to tear apart a crappy set of computer speakers that were self-amplified.

I then desoldered the speakers that connected to the amp board.

I then mounted the amp board and volume and headphone jack into a little plastic box.

It works fine but it gets quite warm. Seems to be warmer than when it was mounted in the orginal speaker boxes.

Also there is now a low constant hum that wasn't there before (this hum is not volume dependent, its the same volume no matter what the volume is set at.)

Any ideas?

Do i need to keep a resistor across the speaker terminals? and if so, what size resisitor?

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doug-doug the mighty's picture
Joined: Apr 14 2004
Posts: 1355
well...

It sounds like the larger case allowed for more room to buffer the heat. I assume from the description that there was no heatsink of some form. It may just be that you notice the heat more due to the smaller casing.

The hum comes from the fact that there is interference getting into the circuit, most likely on the input side. It could be that the impedence is off slightly between the output from the laptop in question and the input of your new toy. You can play around with some resistors on your input in order to attenuate the noise ratio. do a google on 'input impedence' and 'noise filtering with resistors'. You will also find good info on high pass filters and low pass filters out there. A clean sound out is best with a clean sound in.

Adding resistors to the output will only serve to adjust the impedence of your output (i.e. if you need to hook 8ohm speakers to a 16ohm output).

HTH

--DDTM

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--DDTM ('Fritter Critter' since Apr 26 2004 - 18:16)

'If it ain't broke, take it apart anyways. If you can't take it apart, break it so that you can fix it.'

Dr. Webster's picture
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Joined: Dec 19 2003
Posts: 1687
I think the reason your circu

I think the reason your circuit is getting warm is because of impedance issues, which you somewhat allude to. Headphones run at a very high impedance, whereas normal drivers run at something much lower. If the amp has to work harder than it's used to, it'll warm up...it's the same as if you wired 30 pairs of bookshelf speakers in parallel to a home receiver.

My advice? Skip the resistors part, go to a Best Buy-type store and drop $20 on a Boostaroo...they're specifically designed to drive headphones.

The hum is likely a ground loop, but that could also be noise from the amp overworking.

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