Cheap MP3 Player as Signal Source - Output Current

I would like to use one of these iPod knock-offs as a portable signal source. For example, I could produce a complex waveform in software and play it as an mp3 via the device's SD card slot.

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My question relates to how much current could be reliably supplied by the player without damaging its output stage, given the same repetitive full volume signal on both channels.

If I plug in a 3.5mm cord (instead of headphones) and solder left and right channel leads together to produce a "mono" signal, how much current could the output stage be expected to deliver on a constant basis?

For example, would it drive an 8R air core coil at frequencies below 200Hz?

Robert Miller

Reply to
Robert Miller
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ISTR most earphones/buds are 32ohm devices.

You also have to ask yourself how *faithfully* you want the signal to be reproduced -- and, over what frequency range(s). E.g., there may be a small time skew between the left and right outputs. Summing them with a mono source that has been encoded in stereo may leave you with distortions in the "waveform" you are trying to synthesize.

Likewise, PMP's are designed with human ears as the intended "load". So, no guarantee that they make *any* effort to have a flat response, no artifacts, distortions, etc.

Why don't you try measuring the output into a high impedance source and see how much cruft comes along for the ride?

Reply to
Don Y

Why not put the antiphase signal on the other channel and take the output as a bridge across left and right channels with 2x the voltage across the transducer you will get 4x the power into a given load.

(assuming the output drivers can cope)

Seems like a crude way to do it. I expect the output stage is designed to survive shorted to ground faults so it might work. I suspect it will only deliver a few mW of output power though.

Only way to find out is to give it a try and see how loud it is. You might be better off with a 64R speaker.

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Regards, 
Martin Brown
Reply to
Martin Brown

On a sunny day (Thu, 4 May 2017 17:08:15 +1000) it happened Robert Miller wrote in :

I have one like this, much cheaper:

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it is powered by a single lipo 3.7 V. I do not think that would drive an eight Ohm woofer. For that you need to add an external audio amp.

Reply to
Jan Panteltje

I don't think an MP3 file will reproduce your complex waveform. If your device can play a .wav (or some uncompressed format) you'd be in with a chance.

Cheers

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Clive
Reply to
Clive Arthur

And if there's such a thing as an mp3 player that'll play wav files (or an uncompressed format that fits in mp3 -- I _think_ mp3 is just a wrapper), then use that.

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www.wescottdesign.com
Reply to
Tim Wescott

I use an old Sansa M240, one AAA, with single-tone mp3's and some music, for a portable speaker tester at yard sale or thrift store. With 4 or 8 ohm speakers its clearly listenable above background, no damage to player.

Reply to
Wond

I did _NOT_ connect the channels together!

Reply to
Wond

SNIP

The owner at a local bar uses a portable MP3 player all the time. He connects it to the sound system in the building and it sounds just fine. He has one of them "Internet Juke Boxes" and he knows that not too many people are gonna feed $5 bills into that thing to play 5 or 6 songs. If someone wants to hear a certain song, the jukebox is there, but if it was not for him MP3 player, it would be silent most of the time in there. He said that having music keeps people in the bar, He also said that the few cents per song he gets from the jukebox company is not worth losing customers over.

Anyhow, he has been doing this for years and has never had any problems with the MP3 player. I dont know what he is running for an amp-preamp, but it has good sound and can get quite loud. He just patches the MP3 player into the AUX input. If someone wants to play the jukebox, he has a switch behind the bar to change to the Juke.

Reply to
oldschool

On a sunny day (Sat, 06 May 2017 13:14:01 -0400) it happened Neon John wrote in :

mm, that 99 cents MP3 player I have from China is just as good or better than the Create Labs Muvo 30$ I have. But, at my age I cannot hear much above 6 to 10 kHz, so... I tried to play a 44.1 kHz mono sweep .wav on it, but it could not find it (there are hundreds of mp3 on it, and finding one means listening to the start of each one in turn).

What I know is that the chip in it is marked as some voltage regulator (type number). Perhaps to avoid mp3 licensing. It is a single chip for everything. I looked up that chip at the manufacturer's website and got promptly blacklisted when I entered the type number... It is China you know (posted about that long ago).

But hey, 90 cents... I have 3, 2 without LCD, and one with LCD. All accept 16 GB micro SD. As to those micro-sd cards, note this:

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Same story with my 'Transcend' 16 GB micro SDcards, now permanently read only. There is crap, crap, and crap, and a lot of crap being sold. The days you need a lucky shot to get something that works. That puts the price back to normal. My Samsung 32 G micro SDcards still work.

Reply to
Jan Panteltje

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