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Old 24th June 2013, 11:51 AM   #21
ryuji is offline ryuji  United States
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the tpa6120 consumes a lot more power idle then i please. im going back to o2 style, except i have decided that I am rebuilding it with smd parts at a smaller profile. Focusing on power efficiency.

i think i've decided what to use for smd amp. These seem to be the lowest quiescent current that still compare to original specs of o2

lm7332 will be the output, unity gain and parallel, same output current as stock o2's but 2mA per ic quiescent instead of 8-ish
http://www.ti.com/lit/ds/symlink/lm7332.pdf

RC4680 for the gain stage. cheap, low quiescent. labeled as substitute for 5532. 6 total mA idle
http://www.ti.com/lit/ds/symlink/rc4580.pdf


At a total of 10 mA idle, at 70% switching efficiency(picked worst efficiency off the graph) and +-12v it should consume 342 mW, battery is rated at 7.4 Watt-Hours, so 21 hours baseline, less for regulation/filtering inefficiencies and whatever power is consumed through the headphones obviously.

Goal is going to be to make this as small as possible, and use an appropriate slim/small chassis.
Got quite a bit of free time this week, so progress should be somewhat steady.
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Old 24th June 2013, 04:39 PM   #22
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Quote:
Originally Posted by ryuji View Post
the tpa6120 consumes a lot more power idle then i please. im going back to o2 style, except i have decided that I am rebuilding it with smd parts at a smaller profile. Focusing on power efficiency.

i think i've decided what to use for smd amp. These seem to be the lowest quiescent current that still compare to original specs of o2

lm7332 will be the output, unity gain and parallel, same output current as stock o2's but 2mA per ic quiescent instead of 8-ish
http://www.ti.com/lit/ds/symlink/lm7332.pdf

RC4680 for the gain stage. cheap, low quiescent. labeled as substitute for 5532. 6 total mA idle
http://www.ti.com/lit/ds/symlink/rc4580.pdf


At a total of 10 mA idle, at 70% switching efficiency(picked worst efficiency off the graph) and +-12v it should consume 342 mW, battery is rated at 7.4 Watt-Hours, so 21 hours baseline, less for regulation/filtering inefficiencies and whatever power is consumed through the headphones obviously.

Goal is going to be to make this as small as possible, and use an appropriate slim/small chassis.
Got quite a bit of free time this week, so progress should be somewhat steady.
The output buffer has pretty nice power ratings for the quiescent power draw but a couple things I noticed when I skimmed through the datasheet was the subpar noise rejection and unless I missed something I didn't see any performance data under 1k ohm. is it rated to drive continuous loads of down to 16ohm?
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Old 24th June 2013, 05:01 PM   #23
agdr is offline agdr  United States
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That output chip looks like a motor driver or current loop driver. The THD graphs are done with a 100K load resistance. The extra quiescent current of the NJM4556A may be worth it to get some better distortion numbers. The NJM4556A THD graph is specified into 200 ohms, bottom of pg. 3:

http://semicon.njr.co.jp/eng/PDF/NJM4556A_E.pdf

and that is with 30dB of voltage gain. Should be a lot better at unity. The LM7332 graphs are already at a voltage gain of 2, about as good as they will get.

Last edited by agdr; 24th June 2013 at 05:16 PM.
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Old 24th June 2013, 05:13 PM   #24
ryuji is offline ryuji  United States
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Originally Posted by Amperage View Post
The output buffer has pretty nice power ratings for the quiescent power draw but a couple things I noticed when I skimmed through the datasheet was the subpar noise rejection and unless I missed something I didn't see any performance data under 1k ohm. is it rated to drive continuous loads of down to 16ohm?
That concerned me too, i thought i would try it out but perhaps with some more looking ill find a better suited one
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Old 24th June 2013, 07:26 PM   #25
ryuji is offline ryuji  United States
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doesnt really look like there is anything that is able to put out decent current at +-12v other then the NJM4556. plenty of options if i were to stick to +-6v but i believe that would not work so well with 300~600 ohm headphones.
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