I think an audio output signal usually has a series Capacitor to reject DC and allow the output to be operation +/- around GND. I'm not seeing this on the DAC outputs on the Giga R1 board schematics. Also, the DAC outputs from the processor have an output range of 0 to 3.3V. I'm not sure you can actually plug this into a speaker or headphones directly. I would be concerned with damage. 3.3V/8Ohm=~400mA. That seems like enough to cause damage depending on the speaker or headphones.
Does anyone know if this is true? Can you plug the 3.5mm jack output directly to a speaker or headphones?
You should not expect to see it, because DC voltages are required for many DAC applications.
You cannot plug a speaker or headphones into any MCU output, unless it specifically includes a power amplifier designed for that purpose. The data sheet describes the current limits for all pins, so check and heed those.
To connect the Giga DAC audio output to your audio amplifier/speaker setup, you could include a 1 uF series capacitor to block the DC. However, most audio amplifiers already have such a capacitor on the input.
And, of course, the DAC audio output must be programmed to vary about a reasonable DC offset, or the negative audio excursions will be clipped.
Thanks for the confirmation. I also found this note in the documentation for Giga:
Important note: the GIGA R1 does NOT have an amplifying circuit onboard. Connecting speakers that does not have an amplifier can damage the DAC and the board itself.
So, I definitely do NOT want to just plug this into a speaker or headphones directly unless I know how those devices are built.
Though I do see why there it doesn't matter too much, I think having a cap on the microphone line would be far better tbh, as you may try to connect one. Overall you may use the dac lines for input, where again lack of capacitors may damage the chip. I really wish there were capacitors.
The 0 ohm resistors suggest to me Arduino was thinking about including caps instead, but sadly for some reason decided not to
I agree with your point. I think, however, they were trying NOT to limit the audio solutions. By placing CAP you are also affecting the audio response of the output or input (perhaps shifting the roll-off frequency). I'm guessing they did not want to compromise any audio performance.
It IS a little un-nerving that I have to chose my headphones very carefully before plugging them in (or the microphone as you pointed out) to avoid permanently damaging the board or my headphones. Personally, I would have preferred a series CAP with a high-impedance unity-gain amp on the output and input with a frequency cutoff well above 20MHz only on the 3.5mm jack. Leave the DAC outputs on the header unprotected. That would have been perfect.
