Tone2 Pro - hybrid volume control

[khadas22022]

Hi @Eric68, @Gouwa

On ASR Gouwa wrote: “in preamp mode the ESS DAC volume works for both Line out and headphones”

The product page says hybrid analogue volume control:
"hybrid digital/analog volume control knob, allowing you to rely entirely on analog signal attenuation"

Can you explain how I can have analogue volume control (not ESS chip digital volume) for headphone output?

Or not possible with headphone output ?

And can you explain what the ‘hybrid’ part is ?

Thanks!

[khadas22022]

@Eric68

You can see the relationship from the table below.

	DAC Volume	Analog Volume(NJU72315)	Balanced RCA Output①	Single End RCA Output①	4.4 Headphone Output①	3.5 Headphone Output①
Low Gain	Fix to Maximum	Adjust from -12dB to -62dB	4Vrms	2Vrms	0-5Vrms	0-2.3Vrms
High Gain	Fix to Maximum	Adjust from 0dB to -62dB	4Vrms	2Vrms	0-2.5Vrms	0-1.15Vrms
Pre-AMP	Adjust from 0dB to -127dB	Fix to Maximum	0-4Vrms	0-2Vrms	0-5Vrms②	0-2.3Vrms②

①Note: The results are built on the condition that the digital volume is fixed to maximum and the audio signal souce is 0dB.
②Note: The headphones’ outputs are varying from the RCA outputs.

In summary,if you want to use headphone Jack,I suggest you to choose the low or high gain mode according to the impedance of the headphone.If you want to connect to power amplifiter or active speaker,and the volume of the speaker can not be easy to adjusted,you can choose Pre-Amp mode.

Hi @Eric68 - I saw this table in a different thread. This is very helpful! I wish it was in the user manual !

When you say “choose the low or high gain mode according to the impedance of the headphone”

What impedances is low gain for and what impedances is for high gain ?

[Eric68]

Hi
Our headphone amplifiter maximum output current is about 100mA, according to the Ohm theorem R=V/I,you can calculate the headphone’s minimum or maximum impedance in different gain mode.You can see the impedance matching sheet below.

①Note：This minimum impedance value is built on that the digital volume is maximum.It does not mean that it can not apply to the lower impedance.You can also use the lower impedance headphone by reducing the digital volume.In summary,you should not allow the output current exceeds the limited value-100mA,otherwise you may hear the shock-wave noise.
②Note：This does not mean you cannot use the higher impedance headphone to listen to music.The problem is that the loudness may not reach the headphone’s rated.