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I'm designing a device using a DAC (TI PCM 2704 like this one to be precise,) and optionally a headphones amplifier.

I noticed that connecting (32 Ohms, closed-back Beyerdynamic) headphones to the line output of this TI PCM 2704 module seems to work with good audio level, even though there is no amplifier chip at all.

Does this mean this DAC has enough line output level to drive most headphones?

In general, which dB attenuation is there for a listener with headphones connected on line output instead of headphones output?

(I know it will vary from device to another, but I'm looking for a general estimation if the devices use the "standard" specifications for line level and headphones level.)

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    \$\begingroup\$ Hmm, the title of the PCM2704's datasheet (ti.com/lit/ds/symlink/pcm2704.pdf ): is "STEREO AUDIO DAC WITH USB INTERFACE, SINGLE-ENDED HEADPHONE OUTPUT AND S/PDIF OUTPUT" so what can we conclude from that? \$\endgroup\$ Nov 20, 2021 at 13:00
  • \$\begingroup\$ Oh sorry @Bimpelrekkie I looked at many different DACs and I think I mixed them up in my mind! Still my second question is valid: which dB attenuation (in comparison to headphones out) will there be with a line-level output DAC + headphones such on this device using PCM5102? Will the sound be audible? \$\endgroup\$
    – Basj
    Nov 20, 2021 at 13:04
  • \$\begingroup\$ 1) it is not called "dB attenuation", You mean to ask: how much attenuation would I need to make line level from a headphone output. An answer could be: a factor 2 or 6 dB attenuation. 2) compare the maximum output voltages of the PCM2704 and the PCM5102. Are these voltaegs hugely different? Have you ever connected a headphone output (of for example a smartphone) to a line-in input of an amplifier? In my experience that usually just works. Especially since there's a volume control on both devices so I can easily decrease or increase the signal level. \$\endgroup\$ Nov 20, 2021 at 18:37
  • \$\begingroup\$ The PCM5102 datasheet specifies a minimum load impedance of 1kOhm. It doesn't say what happens if you violate that requirement. It may give you a very quiet output, a distorted output, or it could even damage the device. General advice: if a datasheet says not to do something, and you want to do that something, look for a different part. \$\endgroup\$ Nov 20, 2021 at 19:27
  • \$\begingroup\$ @Bimpelrekkie "Have you ever connected a headphone output (of for example a smartphone) to a line-in input of an amplifier?" In this direction, it's easier: phones out (high level) -> line input (expecting low level) because it is something loud going to something that expects a low level, so we can just use a volume control to lower the phones out level. In the opposite direction, it's probably more difficult: line out -> headphones. \$\endgroup\$
    – Basj
    Nov 21, 2021 at 9:51

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The first headline of the datasheet says the chip can drive a headphone output. So yes, the chip can and is even intended for driving headphones.

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  • \$\begingroup\$ Oops, my mistake @Justme! I looked at many different DACs and at the end I think I mixed them up in my mind! Still my second question is valid: which dB attenuation will there be with a line-level output DAC such on this device using PCM5102? Will the sound be audible? \$\endgroup\$
    – Basj
    Nov 20, 2021 at 13:06
  • \$\begingroup\$ @Basj that's a completely different question and unanswerable for many reasons. First one being that it depends on components external to the chip so unless you have the schematics for the board you linked it is unknown. The output impedance of DAC is also unknown. And it is rated to operate at load impedances higher than 1 kohm, so even if parameters were listed, they would not be valid any more if part ia used outside specs. \$\endgroup\$
    – Justme
    Nov 20, 2021 at 13:16
  • \$\begingroup\$ Thanks, I think you can add this comment in your answer (for future reference), I accepted it. \$\endgroup\$
    – Basj
    Nov 20, 2021 at 13:16
  • \$\begingroup\$ PS: here is the datasheet for PCM5102a ti.com/lit/gpn/pcm5102a \$\endgroup\$
    – Basj
    Nov 20, 2021 at 13:17

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