[ChrioN]

I've built a cmoy, and the chip was oscillating pretty bad, so I putted a 20ohm resistor at the output. This solved the problem.
What I wonder is, if I connect a 32 ohm headphone to the cmoy, wouldn't the 20ohm output resistor be handling a lot of wattage?

 

[peterpan188]

What chip were you using?

From my little knowledge, the way I understand it is that putting R5 will increase the output resistance of the amp. The wattage that R5 takes isn't a big deal, since the voltage swing isn't great anyway from a standard cmoy.

Peter

 

[ChrioN]

jrc4556, 70mA.

If the opamp amplifies a signal to 10volts, the 20ohm resistor will have roughly a 4v drop. 4*70mA is 280mW.

 

[nikongod]

10v into a 32 ohm headphone creates smoke, and fire, and melted drivers. at the very least the last one.

anther part to consider is that that 10v is likely a spike in the sound, and not a continous signal.

what gain did you use? will the chip even ampl;ify to 10v with your input signals?

if it still concerns you, buy a resistor rated for more wattage and replace the old one. chances are good that it is not a problem.

 

[ozshadow]

Can't find a datasheet on that, but that is the RA-1 opamp correct ? I doubt its 10v output, but what are you using to power it ?

 

[peterpan188]

I am looking at the datasheet of you opamp, NJM4556A, and it seems like it uses a bipolar input. It tends to be cranky as stated in tangent's doc, http://tangentsoft.net/audio/hs-opamp.html.

Take a look and see if it helps you.

Also, a opamp can only output voltage as large as what it is supplied with at V+/V-, in DC form, so what really controls the voltage amplitude across R5 is your input amplitude and your gain, usually small enough.

Peter