adding headphone amp...

[lo]

I am going to add an internal headphone output to an electronic instrument of mine. It seems pretty easy but I have only done a few projects so far and want to make sure I have the best info possible. Any links or input would be great.

[Newz2000]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by lo:
Any links or input would be great.<hr></blockquote><p>One of my first electronics kits was a little amplifier based on the lm386 chip. There are a number of kits available (check ebay for some nice cheap ones) that use this or similar chips. They come with a circuit board and all the parts. All you do is solder it together. If you need stereo, make sure to get that... many amp kits are mono.<p>Here's an interesting site with a lot of amp schematics. Kit 24 is a headphone amp.
http://sound.westhost.com/p-list.htm<p>I'd look for a kit before trying the #24 mentioned above though. The kits really are a good way to start and amp kits are very popular for a first-time kit.<p>If you like ebay, NightFire Electronic Kits has some interesting ones. I've never purchased their stuff, but I like what I've seen. Some kits have PCBs, some don't, but here's one that might suit your needs for $10.50 (shipping included).<p>**NOTE:
I wasn't 100% on the ball when I posted this. My amp kit and the one's I linked to are not technically head-phone amps. I *think* the original lm386 amp will do perfectly... it's about 1/8th watt amplifier, but I didn't try it with headphones, so I'm not sure how it will work.<p>Sorry for the confusion if I caused any.<p>[ September 21, 2005: Message edited by: Matt Nuzum ]</p>

[dacflyer]

hi, speaking of headphone amps..
i have a question to add with this..
i'd like to use my headphones when flying commercial airlines.. they ones they provide are whimpy sounding as a old telephone..
i'd like to use mine..hi quality sound with them rare earth maganets , but i know the impeadence is not a match..is there a amp like the lm386 that will adapt to most any impeadence and then run it into my headphones? i have a home made signal tracer using a lm386 and it can usually work fine with out overloading the signal i am sampling.. so i was thinking to make me a small stereo version to use on flights.. any advice?
and please don;t get crazy , thinking it will short out the engines :p

[Chris Smith]

Here are some numbers from the National Semiconductor Handbook [google them for a diagram]
LM:####7
377 dual 2 watt,
378 Dual 4 watt,
379 Dual 6 watt,
380 Audio power amp,
383- 7 watt power amp
386 low power amp
388-1.5 watt power amp
390 1 watt battery operated amp
391 power amp<p>Also these days they often have FET replacements for the older amps which has low noise [distortion] and less power consumption.

[Robert Reed]

Dacflyer
The last time I flew was on Continental. After an hour in the air and being the tinkerer that I am (also a phenomena with engineers to dissasemble things to see whats inside) , my curiosity got the best of me and I started sneakily prying into there plug in head set. To my amazement, there were no wires at all inside of it. As a matter of fact, it was not even an electrical device. Just a hollow tube that conveyed sound, but from all exterior appearances it looked like a typical head set. I concluded the reason for this might have been a high theft rate from people thinking they were of use at home. These probably cost the airlines 25 cents each-so no big loss if they were stolen. I don't know if these are standard practice throghout the industry, but if it is you will be in for a big surprise when you plug in your 'homebrew' headphones.

[Chris Smith]

I stole my first pair of stethoscope ear phones on a BOAC transatlantic flight. <p>Great for cracking a safe! <p>BOAC, how long ago was British Airways called that? <p>The Same year of the moon landing!

[lo]

Thanks for the links Matt thats just what I was looking for.

[dacflyer]

robert reed >> the headphones you had must have neemon a old airline..the last few i been on were in deed real electric type head phones.. some had dual mono plugs.. others had a 1/8 mini stereo plug....

[philba]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by dacflyer:
robert reed >> the headphones you had must have neemon a old airline..the last few i been on were in deed real electric type head phones.. some had dual mono plugs.. others had a 1/8 mini stereo plug....<hr></blockquote><p>I watched this evolution from the "stethoscope" headphones to the oddball jack electronic ones to the standard (and way cheap) ones. A cousin that is an airline pilot told me that they were worried about people stealing the headphones so they made them so custom that there was no incentive to steal. <p>The problem was that the custom ones cost more per unit that the cheapo standard ones. It also turns out that everyone has dozens of the cheap ones lying around home so few people actually take them. A recent flight I was on they said "yours to keep" but most people just left them. <p>I have a pair of noise cancelling headphones that I use on planes - they totally rock. If i forget them, I don't bother listening with the crappy cheapos.

[jollyrgr]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by dacflyer:
<SNIP>
i have a question to add with this..
i'd like to use my headphones when flying commercial airlines.. they ones they provide are whimpy sounding as a old telephone..
i'd like to use mine..hi quality sound with them rare earth maganets , but i know the impeadence is not a match..is there a amp like the lm386 that will adapt to most any impeadence and then run it into my headphones?
<SNIP>
and please don;t get crazy , thinking it will short out the engines :p <hr></blockquote><p>
I'd not worry about the engines or even causing problems with the plane's entertainment system. My worry would be bringing anything on a plane that is electronic and "home made". I wouldn't want to mess with the TSA. Sorry if this is over gerneralized but these guys don't seem to be the brightest bulbs on the string. <p>Case in point is my brother's experience. He is a high school teacher and used to teach auto shop. He forgot a tire guauge in his coat pocket as he used this quite often in the shop. When he put the coat through the scanner the screeners got real concerned about this object in his pocket. About four of five screeners got together and started investigating the coat and the strange device within the pocket. They finally called over a supervisor and handed it to him unsure of what to do. He takes one look at it and hands it back to my brother saying that "This is just a tire guage." I don't know what concerns me more; the lack of knowledge of what a tire guage is or the fact that these people all probably drive cars and don't know how to check their tire pressure.<p>I brought a "Aircraft" radio on board one time so I could listen to the pilots. (This is the AM/FM radio that had been factory modified by Radio Shack to receive the aircraft band.) I wanted to make sure that it was okay to have the radio on during flight. They became concerned about this causing interference and made me take the battery out and put it away.<p>I would NEVER think of trying to bring in an electronic item that had been home made onboard an aircraft; not any more. Sad comment on things, isn't it?<p>[ September 26, 2005: Message edited by: Jolly Roger ]</p>

[philba]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Jolly Roger:

...
I brought a "Aircraft" radio on board one time so I could listen to the pilots. (This is the AM/FM radio that had been factory modified by Radio Shack to receive the aircraft band.) I wanted to make sure that it was okay to have the radio on during flight. They became concerned about this causing interference and made me take the battery out and put it away.
...
[ September 26, 2005: Message edited by: Jolly Roger ]<hr></blockquote><p>unlike so many other restrictions on planes these days, that one actually has a basis in reality. Many, if not most, inexpensive receivers have an IF that is poorly shielded and can cause interference.

[Mike]

The LM386 isn't well suited for headphone amplifier use, due to its rather high gain. It's designed for driving loudspeakers. <p>Rather than that, I'd suggest using a chip such as the LM4881. It's a dual 200mW headphone amplifier. The best part about this chip is all gain circuitry is inside the chip, and the worst part is since its a single supply chip, it needs some hefty output caps (in the range of 1000uf, a problem for miniature amps). It's perfect if space is not an issue.<p>National also offers a pin-compatable chip with 250mW x 2 output, but I can't recall the name of it off of memory.<p>All you need is a few caps, an LM7805 regulator, and nothing else. when I build these, I build them into a small case with a diode and Ni-Cad 3.6V battery, and use just a 50ma or so wall wart to charge it (make sure if the wall wart is over 5V to use the 7805 before the diode and battery, because 5.5 is the max of this chip). also be careful using much more than 25-50ma, or the battery will charge too quick and get overcharged.