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PCM2704 + TDA1308 Questions

post #1 of 4
Thread Starter 

Hello everyone,

I was examining the PCM2704 datasheet to compare their suggested circuit to what was included in a simple DAC I have when I noticed some differences. Specifically, on my DAC there are no pull-down resistors on the output (in front and behind the caps). Are these something that I should add?

 

 

Also, I was wondering about series resistors on the headphone output. I noticed that some people add 120 ohm guys in series at that location. What are the benefits/uses of this? It's gonna increase the total output impedance, and I would guess it will cut down on volume and lower the noise level.

 

Thanks!

post #2 of 4

Wont affect the audio. Look like they're there to discharge the cap when open so no fast discharges when closing the circuit. Wont hurt to use them but probably don't need them.

post #3 of 4
Thread Starter 

Ahh, that makes sense.

 

Now what about adding series resistors? Will that cut down on the noise level? There is definitely some hiss, not as bad as straight out of the headphone jack on my laptop, but it is there nonetheless.

 

Also, this thing is loud - I have to set windows volume at 2 in order to not blow my ears out. Is there anyway to decrease the volume? The op amp gain on the tda1308 if I remember correctly (-R2/R1) is at around 1.5. I don't feel like I can lower that anymore with the risk of destabilizing the amp. With that said, is there anyway to decrease the overall gain so that I can set windows volume at around 50 for a comfortable listening volume. I don't think there is anyway to decrease the output on the USB receiver (PCM2704) so I'm not sure what my options are...

 

Thanks

post #4 of 4
Thread Starter 

Anyone have any input on the series resistors at the output of the amp?

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