Pro Audio Design Forum

b1gtuna wrote:Hello everyone, I am back with another question. I appreciate all your guidance!
The short-circuit maximum current of NE5534 is 38mA (as per the datasheet). Can I assume that I can power 2 X NE5534 with an 80mA boost circuit?

Not sure I understand the question. If you are asking can 2x5534 be powered from an 80mA power supply yes. Not sure what you mean by boost circuit?

I have tried calculating the power requirement. So far I got only this far:

A pair of Sennheiser HD449 has 38ohm impedance. The gain of my design is 3.2 ((2.2k + 1k)/1k). So I don't think the output will ever reach the 12V r.m.s as long as I feed a sane input audio signal.

You will never reach 12V rms from +/-12V dc rails. the op amps will run out of PS voltage and clip.

I read somewhere that iPod's have output voltage of 1.1v r.m.s. With the gain of 3.2, the output from the amp is 3.52v (1.1v * 3.2 gain).

Hence the power output from the amp is about 0.1 watt (3.2v * 38mA).

Power is (E^2)/R so (3.5V ^2)/38 ohm= 326mW

Can I assume that an output voltage based on 0.1watt and the impedance of my headphones (38ohm)?

for 100mW into 38 Ohms the voltage needs to be 1.94V

JR

Thanks JR for answering my question.

I guess I wanted to find out if a power supply that can provide 80mA maximum current is enough for my amplifier design. I am looking at a 5v to +/-12v boost converter: http://www.ti.com/tool/lownoisesplitrai ... -boost-ref. It looks like this might do the job!
The RMS voltage of 12v is 8.5v (12v/sqrt(2)), which is much more than the expected output of 3.52v with the gain of 3.2.

And this brings me to another question: is 3.52v at the output too much for a pair of over the year headphones like the Sennheiser HD449? I just don't want to blow stuff up =).

Thank you very much for your help as always!

JR. wrote:

b1gtuna wrote:Hello everyone, I am back with another question. I appreciate all your guidance!
The short-circuit maximum current of NE5534 is 38mA (as per the datasheet). Can I assume that I can power 2 X NE5534 with an 80mA boost circuit?

Not sure I understand the question. If you are asking can 2x5534 be powered from an 80mA power supply yes. Not sure what you mean by boost circuit?

I have tried calculating the power requirement. So far I got only this far:

A pair of Sennheiser HD449 has 38ohm impedance. The gain of my design is 3.2 ((2.2k + 1k)/1k). So I don't think the output will ever reach the 12V r.m.s as long as I feed a sane input audio signal.

You will never reach 12V rms from +/-12V dc rails. the op amps will run out of PS voltage and clip.

I read somewhere that iPod's have output voltage of 1.1v r.m.s. With the gain of 3.2, the output from the amp is 3.52v (1.1v * 3.2 gain).

Hence the power output from the amp is about 0.1 watt (3.2v * 38mA).

Power is (E^2)/R so (3.5V ^2)/38 ohm= 326mW

Can I assume that an output voltage based on 0.1watt and the impedance of my headphones (38ohm)?

for 100mW into 38 Ohms the voltage needs to be 1.94V

JR

b1gtuna wrote: And this brings me to another question: is 3.52v at the output too much for a pair of over the year headphones like the Sennheiser HD449? I just don't want to blow stuff up =).

Thank you very much for your help as always!

I could not find a power handling spec even from the mfr.

Good Luck...

JR