required wattage of chip resistors in audio opamp circuit?

Question

I have the following DAC output stage in a design I'm working on, which takes the differential outputs of a DAC to create an unbalanced audio signal, 5.7Vpp.

For the R and C I would like to use 0402 chip capacitors and resistors. How do I figure out the required watts for the resistors and if the standard 1/16 watt power rating will be adequate?

The differential inputs to the stage are 2.8Vpp signals centered around 5V.

I'm not an everyday user of opamps, but have used TINA-TI by texas instruments to simulate the stage to make sure it works (i.e. that it has the current gain and frequency response).

The circuit is powered by +14/-14V rails and I did put an amp meter in the simulation software on the rails, which gave me 4mA both for each of the rails, but that doesn't tell me everything?

I also have a second (similar) version of the below circuit in which I want to use the opa1622 headphone amplifier opamp to drive headphones, and there this question will be even more important since that opamp is capable of outputting a lot more power than the ne5532.

Answer 1

Well there is clearly less then 6V in play anywhere, so that is ~2mA into a 3K ohm load, giving 12mW, so 0402 is probably fine from that perspective. There is however something to be said for physically larger parts as they tend to have lower excess noise.

I note you are specifying 0.1% parts, for resistors, but that PC92 & 93 are not so tightly specified (Good luck with that!)? This will hurt CMRR at high frequency.

Also R110 should be 100 ohms or so, to ensure stability when driving long cables.

In the headphone case R110 should be 20 ohms or so, but may dissipate some power if the cans are shorted, or the jack is only partly inserted, calculate this assuming a short to ground and full scale output, a 1206 or so is usually sufficient.

I note the lack of an output coupling cap, usually a good idea, 100uF or so with a 10k bleeder across the socket, particularly for headphones, DC offset matters (But for cans the coupling cap should be much larger to support low impedance units). If you think a phantom power accident is possible then make this cap a 63V part and wire it positive terminal to the socket, with the ESD diode where PC148 is, that way the diode is behind the build out resistor which will limit the surge current.

Answer 2

Tiny chip resistors have very fast thermal response: 1mm size are approximately 11 milliSeconds. The 0102 resistors are thus even faster (scales by 1/size^2).

Problem is: if you use tiny resistors to SET THE GAIN, the low frequency response of the resistors is excellent because the R has adequate time to fully change value during bass music content. This response ----- as gain-settling resistors -------- causes AM-modulation of all the musical content, even the high notes.

Walt Jung warned about this. So use physically-large resistors to set gain.