Does Volume Control on DAP Mean My External DAC isnt Working?

[neptune134]

Hello all. I hope I worded my question coherently enough, but I have a few examples which should help mitigate things.

I have a basic AGPTEK T06S touchscreen chinese digital audio player with a USB type C connection for synching and charging. It is a touch screen running on Android Oreo. The advertisement for it states it has "OTG" but to not use the USB C as a "audio out" source, and to instead use the female 3.5mm buiit into the device.

My goal was to make it work with my Fiio Q5s with a digital connection (usb type c to micro usb cable) and it seems to work perfectly, aside from the battery running out on the DAP within 1 hour when its proported to have a 8 hr life. Then I noticed that that I was able to adjust the volume not just on the Q5s as should be expected, but the volume control also works on the AGPTEK DAP at the same time, almost like a pre-amp. If the DAP is tethered to my Q5s with a cable, shouldnt that mean that its using digitial and not analog?

My confusion comes from being previoulsy obsessed with the whole ipod video > Fiio L9 Cable > Fiio Amp/DAC (ie Andes, Alpen, or whatever from the early 2010's) and it was there I learned that the Fiio L9 cable was only a conduit, and not actually allowing for the external DAC to take over, only to amplify the DAC already built into the ipod. THis was proven by being able to use the click wheel to volume up and down as well as the external amp, meaning that it was only a analog signal being amplified.

Now let me see if I can summaraize this in a nut shell with my limited knowledge of this stuff; if a Android DAP is connected "digitally" via a USB type C to Micro USB, but yet Im still able to affect the volume with the either the Q5s or the DAP independently, does that truly mean Im using the Q5s's DAC, or just as an amplifier?

Example, I have a Vamp Versa DAC AMP made in 2012 made particularly to override the Ipod Classic DAC completely, by plugging the 30 pin to to USB A inout on the Versa itself, and this makes using the volume ability on the ipod to no longer work, and depends completely on the Versa as the volume control.

If Im able to use the volume on both the master and slave device basically at the same time in a preamp/amp type scenerio, does that mean the sources DAC is still being used?

 

[phofman]

Digital volume control is just dividing all sample values by a fixed number. It can be performed at any part of the chain, multiple times. I.e. both in your player and in the DAC, independently. Also your USB DAC can offer its internal volume control as a usb-audio volume feature and the player can use this volume control instead of dividing the samples internally. Typically this feature is called HW (vs. SW) volume control in software players (e.g. MPD). But my 2 cents in your case the volume control occurs at two points of the chain, independently.

 

[AnalogSteph]

My goal was to make it work with my Fiio Q5s with a digital connection (usb type c to micro usb cable) and it seems to work perfectly, aside from the battery running out on the DAP within 1 hour when its proported to have a 8 hr life.

Presumably the Q5s is also charging via USB and sucking the DAP's battery dry like that. (9 hours of runtime from a 3800 mAh battery when using USB input is not exactly what you would call a power miser. The DAP only has 1200 mAh to offer while powering itself to boot.) Perhaps that's why using the USB for audio is discouraged.

In theory, you could insert a powered hub and power that from a portable power bank, but that's getting awfully complicated for my tastes. I would rethink the whole setup.

 

[staticV3]

Then I noticed that that I was able to adjust the volume not just on the Q5s as should be expected, but the volume control also works on the AGPTEK DAP at the same time, almost like a pre-amp. If the DAP is tethered to my Q5s with a cable, shouldnt that mean that its using digitial and not analog?

Your DAP is doing digital volume attenuation, then sending the digital signal to your Q5s, which is also doing digital volume attenuation then decoding the signal with its AKM DACs.

The signal between your DAP and Q5s cannot be analog because the Q5s is not capable of analog audio input via Micro USB.

 

[neptune134]

Digital volume control is just dividing all sample values by a fixed number. It can be performed at any part of the chain, multiple times. I.e. both in your player and in the DAC, independently. Also your USB DAC can offer its internal volume control as a usb-audio volume feature and the player can use this volume control instead of dividing the samples internally. Typically this feature is called HW (vs. SW) volume control in software players (e.g. MPD). But my 2 cents in your case the volume control occurs at two points of the chain, independently.

Okay that makes sense thank you so much for replying! Love this forum, everyone is so knowledgable.

 

[neptune134]

Presumably the Q5s is also charging via USB and sucking the DAP's battery dry like that. (9 hours of runtime from a 3800 mAh battery when using USB input is not exactly what you would call a power miser. The DAP only has 1200 mAh to offer while powering itself to boot.) Perhaps that's why using the USB for audio is discouraged.

In theory, you could insert a powered hub and power that from a portable power bank, but that's getting awfully complicated for my tastes. I would rethink the whole setup.

This is very helpful information, thank you so much for replying. I was thinking that since the AGPTEK T06S DAP is an Android, I would enable the developer mode to see if there was a customization to prevent the DAP from feeding power out to the Q5s; I found an option that asks what type of functionality the usb type C should have, and it had choices like MTP transfer, and i picked the choice that said Audio Out only. But that didnt seem to work as its still feeding power to the Q5s; is it even possible to use the dev options settings in the DAP to customize that particular setting I wonder?

Coincidentally, the Vamp Versa V-Moda AMP/AKM DAC DOES have this functionality! Who would have thought a device over a decade old would solve an issue with a relatively new TOTL amp/dac from Fiio! LOL

 

[neptune134]

Your DAP is doing digital volume attenuation, then sending the digital signal to your Q5s, which is also doing digital volume attenuation then decoding the signal with its AKM DACs.

The signal between your DAP and Q5s cannot be analog because the Q5s is not capable of analog audio input via Micro USB.

THank you very much for this. I wonder why the volume then on the Vamp Versa V Moda then makes the DAP lose all volume functionality and leave the volume duties solely to the V-Moda device?

 

[staticV3]

THank you very much for this. I wonder why the volume then on the Vamp Versa V Moda then makes the DAP lose all volume functionality and leave the volume duties solely to the V-Moda device?

most likely because the DAP, similar to Macs and iOS devices, only supports UAC2 hardware volume control.
If you plug in a DAC without UAC2 volume support, then the DAP can only send audio at 100% volume.
If you plug in a DAC that supports this feature, then the DAP will recognize it and control the DAC's digital hardware volume via UAC2 USB commands.

 

[neptune134]

Wow static! Youre the man!! Do you know if its possible to prevent the DAP from feeding power to the Q5s using the developer options feature on the Android 8.1 DAP?

 

[staticV3]

It's unlikely there's a setting to disable the power supply to OTG accessories.
You could try making a cut along the insulation of the USB cable that you use to connect DAP and DAC and cutting the red +5V wire underneath.
That way no power power can flow between DAP and DAC, though I can't guarantee that the OTG connection will still work afterwards.
Might be worth a try if you can get that cable for cheap.

 

[neptune134]

It's unlikely there's a setting to disable the power supply to OTG accessories.
You could try making a cut along the insulation of the USB cable that you use to connect DAP and DAC and cutting the red +5V wire underneath.
That way no power power can flow between DAP and DAC, though I can't guarantee that the OTG connection will still work afterwards.
Might be worth a try if you can get that cable for cheap.

I will give that a shot! I have a bunch of cheap cables like that! I will post the results here. THANK YOU!!!

 

[neptune134]

Ahhh man, it didnt work. I just cut the red wire like you said, but now it wont work OTG at all. Luckily I have a few of these so no big deal, but with that great solution idea I had to try it. Thnak you Static, well worth it just to make sure I knew.

 

[neptune134]

Well, I found the fix, and its 100% accurate, and i just field tested it myself.

I did some more Googling and surprisingly only found 2 results abou this topic (god, I miss the old internet before it became a money grabbing algorythim, but I digress)...

You need to connect the DAP to the Q5s via Bluetooth mode first, and on the DAP you need to have the Fiio Bluetooth app AND the Fiio Music Player App. While in bluetooth mode, you connect the usb c to micro USB on the Q5s, and open the Bluetooth app. In the settings, the option "Charging" will automatically be on, you just need to turn it off, and close that app. Next, you need to go to the Fiio Music Player app, settings, and under the Settings, disable "Exclusive USB Mode" and disable "USB Volume Control". The just turn off Bluetooth on both Apps, and the music keeps playing and switches to non-charging mode seemlessly. Both review I read said the same thing; the older Q5 had 2 separate micro usb inputs for charging and for audio, and the new Q5s was supposed to eliminate that and auto detect the situation, which it clearly failed at, and not even the newest firmware fixes this.

Each time you turn off the Q5s and turn it back on, you have to go through the ritual of doing the above each and every single time.