Impedance/voltage matching: Portable device headphone to line in.

[rich77777]

Want advice for: Portable device headphone to line in impedance/voltage matching

Using a y-cable, it's a cinch to connect cheapo portable devices (cellphone headphone output, dedicated mp3 player headphone output, etc.) to my stereo receiver's aux input. The fidelity sounds good to my ears, no clipping. However, the volume is not there. Even with the device's volume turned to max, the volume coming out of the speakers is about 1/2 what's expected with a proper line-in.

My audio equipment is not high-power, so I really miss the volume. Can I buy a pre-amp gadget, or impedance matching gadget, that boosts the voltage but doesn't cost too much?

I've found (and lost) a few references to gadgets I can buy to remedy this. I recall seeing one that was simple & cheap, but I haven't been able to find it again. Not long ago visited a site called beavis hifi (but it seems to be gone today) where a simple jfet project was modeled. I don't really have the materials at hand to do this, don't really have the time. Something like this, maybe utilizing op-amps, shouldn't be too expensive. Heck, phono pre-amps can be had for under $30, why not a 'cheap mp3 headphone to line-in' preamp also?

Any suggestions?

 

[whoaru99]

On some portable devices they have a setting that limits the output. Have you checked the portable device settings to be sure it doesn't have volume limit setting turned on?

Barring that, if here is adjustment range left on the receiver's volume then I suggest simply turning that more to achieve desired volume. Turning the volume knob higher doesn't make the receiver work harder or have more stress, unless it's actually putting out more power. Since the volume is lower with that source, turning up the receiver to actual volume similar to other sources means the receiver will work about the same, despite a higher setting of the knob. So, just turn it (the receiver volume knob) up more when using the portable player, and you're good to go.

BTW, what do you mean by a "Y" cable, a miniplug to RCA adapter cable?

 

[rich77777]

On some portable devices they have a setting that limits the output. Have you checked the portable device settings to be sure it doesn't have volume limit setting turned on?.

Hmm. Didn't know that. As for my cell phone, I'm sure I've been over every setting. Have ordered a simple cheap mp3 player to augment. I doubt there will be a secondary setting on it either, but I sure will look hard.

Barring that, if here is adjustment range left on the receiver's volume then I suggest simply turning that more to achieve desired volume. Turning the volume knob higher doesn't make the receiver work harder or have more stress, unless it's actually putting out more power. Putting out more power would be indicated by higher volume, not lower. So, just turn it up more when using the portable player.

I am not fully schooled in electronics and yes, a bit afraid to 'turn it up to 11'. You're saying, 'Don't worry,' right? On the other hand, I am building something halfway decent that will blow away docking stations, to leave at work. It will necessarily be turned up loud to overcome the noise of the machinery there. Want to avoid the scenario where someone selects 'TUNER' after running the mp3 player, and blows out the speakers.

BTW, what do you mean by a "Y" cable, a miniplug to RCA adapter cable?

Yes.

 

[johnr66]

Most headphone devices can put out only 500mv rms which is too low for line level inputs. A high quality transformer could work for passive or an op amp booster circuit for an active booster.

 

[markn2wae]

Headphone boosters.

I never used one, but here is what I know- :scratch2:

There is a device that boosts your headphone out, mainly for two reasons,

A) Despite obvious cautions, your a die-hard "head-banger" and your "stock" device doesn't provide the volume you so crave (no personal criticism here, I just know this happens).

B) You want to share your tunes, but your device has only one headphone output and the simple passive "splitter" drops the volume too low.

These are usually battery powered, small (about the size of a lipstick tube) and have one input and usually TWO outputs, they may or may not have a volume control on them.

With the "light load" of a line input (verses a 8-32 Ohm headphone) there should be plenty of reserve to drive a line input nicely. :yes:

Mark T.

 

[rich77777]

By golly, found something through the comments for an Amazon listing. http://electric-avenues.com/audio/ . Not cheap as in 'Chinese mass-made' cheap, but as good as a Canadian engineer-hobbyist making quality stuff would ever be able to charge.