Speaker question

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I'm installing a new Gigabyte motherboard and have a question about
the speaker connector (for the internal PC speaker). If I wanted to
use this connector as an audio output (going to my powered speakers),
will it require a resistor or something to reduce the signal?

Re: Speaker question

On Tue, 12 Feb 2008 14:02:32 -0800 (PST), Totalrod2@aol.com

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To clarify, you do mean the beeper circuit not the sound
card audio output, yes?

If it were the sound card output, no resistor.
If it's the beeper output, wiring in a log, audio,
potentiometer instead of a resistor would give much better
control over the signal level, maybe choosing a 10K log POT
as it's a fairly common value, I think 50K or more may be
too high especially if these speakers would also have
another audio feed that would tend to be at a higher level.

However, in many powered speakers you already have this, a
log pot at the signal input as the volume knob, so you could
go ahead and try without an additional resistor or POT, with
the volume knob turned down as low as it will go then
progressively increasing volume to find whether it gives you
an acceptible level of volume control or not.  I would guess
that ideally you will also need about 1K resistor in series
but I may be wrong and don't know what volume level you need
for this unknown project, nor how powerful your powered
speakers are.

The volume is the issue, it's not a situation where you
could put too much current through the beeper circuit
connecting it to amp'd speakers, as that would cause less
current through the circuit than if directly driving an
un-amp'd beeper speaker.

Re: Speaker question

Thanks for the info. Very informative. I think my main concern is
"overdrive" (or distortion) from the audio signal being too much. I
suppose the only way to really know for sure would be to wire it up
and see what happens. By the way, this isn't the "beep" speaker, it's
the actual speaker connector for sound.

Re: Speaker question

On Tue, 12 Feb 2008 22:00:24 -0800 (PST), Totalrod2@aol.com

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What do you mean by actual speaker connection for sound?  We
need to know exactly how it's hooked up, typically a
motherboard speaker output does nothing but beep, unless you
have a special driver installed.  If this board is one of
those rarer OEM boards with an integral amp chip to drive
speakers, that is not of much importance to drive an amp'd
speaker set except that the amp stage on the board degrades
sound slightly compared to taking an un-amp'd output if one
is available from the sound card or chip.

The matter of overdrive is whether the amp-integral speakers
are set at a gain too high for their acceptible output based
on the chip and input voltage level.  We just don't have
enough info to make a conclusion so the easier way is just
to try it as-is and then try a multi-KOhm POT if that is too
high a signal level.

Re: Speaker question

You're right about the "PC" speaker connector. I scrutinized my
installation manual and it appears it's just for the buzzer, not
audio. Sorry, I'm fairly new at this. However ,there is another
connector on my motherboard which will probably be more suitable as an
output. "F-AUDIO (Front Audio Connector), which is described as
supporting AC97 front panel audio module. "If you wish to use the
front audio function, connect the front panel audio module to this
connector". Will this work as a "line out" to powered speakers? There
are 3 pins: Line Out (R), Line Out (L), and GND. I just want to make
sure. Please let me know.

Re: Speaker question

On Wed, 13 Feb 2008 13:20:15 -0800 (PST), Totalrod2@aol.com

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It would but it is an unconventional way to do it as I
mention below.

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Assuming the amp'd speakers you have are meant for computer
use, don't they have the typical 1/8" or 3.5mm mini phone
jack cord to plug into the back of the motherboard, in a
sound out or headphone jack?  That is what would typically
be used.

If your speakers have some other input jacks you would
typically buy an adapter cable that converts from their
input, to the male 1/8" minijack which plugs into the socket
on the motherboard's rear audio plugs.  Some boards now have
several channels of output and an input and mic socket as
well.  The left and right channel output jack is typically
green colored for the past 8 years or so.

The front panel audio is just to give a convenient jack on
the case front instead of rear - usually not where someone
wants speakers permanently plugged in. The front panel jack
is handy when the case has switching jacks up front meaning
you can leave your amp'd speakers plugged into the back and
disable the speaker output by plugging headphones (for
example) into the front.

Re: Speaker question

Thanks for your help. The reason for my unconventional way of hooking
up the speakers, is because the they're are internal (I installed the
speakers along with the amplifier circuit inside my tower). The volume
control and headphone jack are mounted on the front. Here's a picture
of what it looks like:
The tower is an old Dell Precision 420 workstation. So there was
plenty of room in there for this modification. And this is by no means
my main audio source. It's just for those late nights when I don't
want to wake anyone else up. In which case I'll probably be using the

Re: Speaker question

Totalrod2@aol.com wrote:
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You can pick up a line level audio signal from the FP_AUDIO
header. And connect that to your amplified internal speakers.
You can run connections directly, if you had no plans to
use headphones.

If you also want to connect headphones to the front of the
computer case, you could connect the return lines from the
front audio wiring, to the internal amplifier. The wiring
would look similar to this.

F_AUDIO               |<-- front_panel_wires -->|         Amplifier

Lineout_Left  --------> left         return_left  ------> amplifier_left
Lineout_Right --------> right        return_right ------> amplifier_right
GND           --+-----> GND
                 +----------------------------------------> amplifier_GND

What that wiring is attempting to do, is include the muting function
of the headphone jack, if it is available. If the computer case wiring
assembly has left, left_return, right, right_return type wires, then
when headphones are plugged in, the return wires are disabled. That
gives you a way to mute the internal speakers, whenever headphones are
plugged into the front of the computer.

Whether that will work right, depends on the kind of wiring available
on the front panel assembly. Computer cases vary, in whether they support
the mute feature, or even have return_left and return_right. Listing the
available wire names, on the front panel assembly, makes it easier to guess
what functions are supported.


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