Just for the hell of it, and because I am too cheap to buy one, I have decided to make a headphone amplifier for my ATH-M50's, as my zune doesn't output quite enough power to drive them the best possible. I requested some samples of the LME49710's as those seem to be good little op-amps, (i also requested some MAX4434's and MAX9722's just to play with), and I want to power this thing with lithium cell's, probably 1Ah or 2Ah lithium polymers if i can, but since i need +/- V, I'm having trouble figuring out how to provide a good amount of power. How much power will i likely need to drive a 40ish Ohm source, and possible an 80ish for some Sony MDR7605's. If I split the 3.7v from the battery, thats a puny 1.85v, and not nearly enough for the LME's. I was also considering getting a 5v boost converter, but thats still only +/- 2.5v, which is right on the very edge of the LME's range. My last option was to get two lithium cell's, put them in series, and make the middle the ground point. How well would that work? The issue then, also, is charging. If i want to charge the batteries without removing them, the only way i can think of is to get two chargers, or a charger designed for 2 cells in series.
Anyway, the power has turned out to be the most complicated part, if i want to use the lithiums. Any suggestions as to how i should do it?
Anyway, the power has turned out to be the most complicated part, if i want to use the lithiums. Any suggestions as to how i should do it?
What about an inverting charge pump powered by one lithium cell? Something like the MAX889 will mirror the input volt and provide up to 200mA of current.
Also, you might want to look into the current-feedback LME49713 instead. It is capable of 100mA output current. I've built a headphone amp using two of these and it turned out great. It does take some special considerations since it's a current-feedback op-amp.
Also, you might want to look into the current-feedback LME49713 instead. It is capable of 100mA output current. I've built a headphone amp using two of these and it turned out great. It does take some special considerations since it's a current-feedback op-amp.
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Ahh, I am glad I posted. Was not even aware such a thing existed. I will see if STMicro makes an identical counterpart, as I already have 2 sample requests with Maxim, and I don't want to overuse my free part access. I love maxim, and i would hate it if they cut me off due to abusing the service.
On the subject of the different Op-Amp, for now I think I will stay with the LME49710, and maybe play around with others. This is my first time really playing with op-amps, and I have very little knowledge as to how to use them. If you had a schematic for the amplifier you built, that would definitely help motivate me to look into other designs =P. I plan on trying to build as many different designs with as many different op-amps as I can, just to pick which one is the best, or which is the best for the battery life, as this will be a portable amp, and not just for home usage.
I also wanted to try the OPA series from TI, but they won't sample those, so I cannot get them for free. I suppose I could always actually buy some, but, the reason I am doing this this way in the first place is due to extremely limited budget at the moment.
On the subject of the different Op-Amp, for now I think I will stay with the LME49710, and maybe play around with others. This is my first time really playing with op-amps, and I have very little knowledge as to how to use them. If you had a schematic for the amplifier you built, that would definitely help motivate me to look into other designs =P. I plan on trying to build as many different designs with as many different op-amps as I can, just to pick which one is the best, or which is the best for the battery life, as this will be a portable amp, and not just for home usage.
I also wanted to try the OPA series from TI, but they won't sample those, so I cannot get them for free. I suppose I could always actually buy some, but, the reason I am doing this this way in the first place is due to extremely limited budget at the moment.
Just thought I would mention, I plan on basically following the CMoy schematic, with the substitution of op-amp and power source of course. How much will the rest of the schematic likely have to differ? In terms of the values of the resistors and such?
If that's the case, just use the OPA2132 or OPA2134 op-amp.
I still have my c-moy (which I built about 4 years ago) and I often use it with my ATH M-50's. You will be pleasantly surprised @ how well it performs with those cans!
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You could sample an LM2611 and an LM2735 from National to make a + and - power supply, +/-9v like the CMOY might be about right. See the datasheets for implementation. Plus it would give you a better ground implementation than the CMOY, which was always its biggest weakness.
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