adapting 'headphone out' to 'line out' with voltage divider?

Archived from groups: rec.audio.pro (More info?)

Sorry if this is FAQ; a search only readily turned up arguments over "what
is the difference between 'line out' and 'headphone out'?" I know the
basic difference -- power driving ability and output impedance --- but what
I'd like to know is whether one can, if no alternative exists, *optimize*
the use of a headphone out to drive a larger (consumer) amplifier? By
optimize, I mean minimize overall noise and distortion at reasonable
overall level?

I ask, because I've got a reasonably good flash memory-based MP3/WAV with
no line out, and I'd like to use it occasionally to drive a stereo amp in
place of a CD player.

My naive hypothesis is that if I put a voltager divider with the right pair
of resistors R1 + R2 = ??? ohms (8?, 16? more?) on the output, I can
present an optimal load to the headphone out, while presenting a signal of
the right peak voltage to the input of the amplifier. This assumes of
course that the headphone output voltage at a non-distorting volume is
greater than the typical signal amplitude present on a line out. Not sure
whether this is true.

Also, I'm wondering whether the EQ on signal from headphone out is
different than a line level signal in order to account for differing power
driving requirements of bass vs. treble frequencies. If so, would adding a
cap of the right size to the voltage divider compensate for the difference?

It's probably apparent that I'm not well-versed in audio electronics, so
any informed advice is welcome.

Thanks,
Grant

Archived from groups: rec.audio.pro (More info?)

"Grant W. Petty" wrote:

> Sorry if this is FAQ; a search only readily turned up arguments over "what
> is the difference between 'line out' and 'headphone out'?" I know the
> basic difference -- power driving ability and output impedance --- but what
> I'd like to know is whether one can, if no alternative exists, *optimize*
> the use of a headphone out to drive a larger (consumer) amplifier? By
> optimize, I mean minimize overall noise and distortion at reasonable
> overall level?

First consider that pro and consumer concepts of 'line level' are different (
or *may* be ).

An mp3 player type device will produce 'pro' line level like signal voltages
without any fiddling. Loading the headphone output with a typical 10k ohm load
will reduce output stage distortion too.

Consumer gear levels aren't so well defined. Your headphone out would work just
fine into a CD input but may benefit from attenuating otherwise.

Your idea of a voltage divider is fine but you don't need to use low value
resistors. The headphone out will perform with less distortion in a higher
impedance load. Make the resistors hundreds of ohms at least.

Have you tried it without an attenuator yet though ?

Sometimes headphone outs do have daft EQ applied. You ought to be able to
cancel it hopefully.


Graham

Archived from groups: rec.audio.pro (More info?)

Richard Crowley wrote:

> "Grant W. Petty" wrote...
>
> > Also, I'm wondering whether the EQ on signal from headphone
> > out is different than a line level signal
>
> Huh? You have a separate output for EQ? Try that one
> again, and fully explain what you are talking about?

Many of those devices have gazillions of dB bass bost applied to the earphone
out to cope with the horrible characteristics of those earbuds and to suit
'modern listening taste'. ;-)

Graham

Archived from groups: rec.audio.pro (More info?)

In article <Pine.LNX.4.60.0412022300240.22933@cloud.aos.wisc.edu> gpetty@aos.wisc.edu writes:

> I ask, because I've got a reasonably good flash memory-based MP3/WAV with
> no line out, and I'd like to use it occasionally to drive a stereo amp in
> place of a CD player.

No problem. Start out with the playback volume control set low and the
volume control on your stereo amp set to its normal position for CD
listening. Then turn up the volume on the MP3 player until you get
normal listening volume. It may be distored. If that's the case, back
off the volume on the player and raise the volume control on the
stereo amplifier. That's what it's there for.

> Also, I'm wondering whether the EQ on signal from headphone out is
> different than a line level signal in order to account for differing power
> driving requirements of bass vs. treble frequencies.

Some players have a "bass enhancement" equalization built in, but on
most, it's switchable. You probalby want it off.


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