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Old 23rd February 2007, 06:18 PM   #1
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Question question about output power of CMOY

hi.

I was just playing with manual of OPA2134 and read maximum current output of it per channel is 35mA. doing little math, maximum power it can generate in CMOY amp for headphone with impedance R is equal to


W=I^2 * R.

for Koss portapro (60 ohms) W= 73mW
for Sennheiser HD580 (300ohms) W = 367mW

if I go this correct then lower the impedence of headphones, lower is maximum power output of the amp?

according to this table:
http://headwize.com/tech/dbohn1_table.htm

maximum power required by portapros is 400mW.
it means CMOY will distort quite easyly?
so CMOY is really insufficient for normal and low impedance headphones?

please tell me that I'm wrong and that I have messed it all.
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Old 23rd February 2007, 06:42 PM   #2
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I'd have thought it would still work fine for most "normal" people, but I could be wrong. The sensitivity is 101dB for 1mW (presumably). I find this to be loud. The max is 127dB....

Quote:
Hearing damage (due to short-term exposure) 20 Pa approx. 120 dB
I like my hearing
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Old 23rd February 2007, 11:32 PM   #3
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I've been dealing with this same issue....

DIY headphone amp not loud enough

Go with the OPA551 powered by two 9v batteries and you will be very pleased. It should be able to drive any pair of headphones loud enough.
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Old 16th April 2007, 01:28 AM   #4
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Default wrong?

I've posted elsewhere about this but my cmoy with an OPA2134 and a single 9v battery is way too loud at full volume and I'm using a set of 60 ohm Behringers.
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Old 23rd April 2007, 08:44 PM   #5
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Indeed, CMOY is an introductory circuit on how to take an opamp and pass an audio signal through it. Using typical opamps like OPA2134, it is best seen as a voltage gain stage with infinitely low current output, not a load driver. The beauty, and popularity as an entry level amp is due to simplicity and low cost, not the result driving many real headphones.
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