Topping e30 dac - connecting 2 phones

[Megaken]

Hi, I'm using a topping e30 dac with a phone connected via USB. How do I add another phone? The USB port is taken by the first phone. There are toslink and coaxial inputs, but how do I connect a phone to those?
Thanks

 

[AnalogSteph]

Try looking for a USB to SPDIF converter. If you only need 44/48 kHz, you may be able to find a cheap USB soundcard with either coaxial or optical (Toslink) SPDIF output.

 

[Megaken]

Try looking for a USB to SPDIF converter. If you only need 44/48 kHz, you may be able to find a cheap USB soundcard with either coaxial or optical (Toslink) SPDIF output.

But looks like they already have a DAC in them
like this https://www.amazon.com/Signstek-Coaxial-Converter-Convert-Analogue/dp/B00FEDHHKE
And the whole point is for me to use my existing DAC.
Is USB signal digital? And so is SPDIF, right? So what's being converted?

 

[AnalogSteph]

But looks like they already have a DAC in them
like this https://www.amazon.com/Signstek-Coaxial-Converter-Convert-Analogue/dp/B00FEDHHKE
And the whole point is for me to use my existing DAC.

You don't have to use the built-in DAC though. That said, it doesn't look like the PCM2704 supports more than 16-bit samples, so you may have to go with a more expensive XMOS-based solution after all if that is important to you (and the phone supports it).

As a plan B, you can buy USB switches as well, which are normally used to share peripherals between several computers.

Is USB signal digital? And so is SPDIF, right? So what's being converted?

You still have to sync the sample clock to isochronous USB transfers, unpack the data packets and buffer the sample data. From the datasheet:

The more modern XMOS-based solutions are a bit different in that they are using asynchronous USB transfers instead, which means that they dictate the pace at which data is delivered to them. Obviously they still need clock generation and a master clock for that to work.

Isochronous USB is a bit like SPDIF, where the receiver has to reconstruct the clocking from the incoming signal entirely with a PLL. Fancy DACs will be going to great lengths in the PLL department in order to keep jitter at bay, which can easily degrade the measured performance otherwise.

 

[Megaken]

You don't have to use the built-in DAC though. That said, it doesn't look like the PCM2704 supports more than 16-bit samples, so you may have to go with a more expensive XMOS-based solution after all if that is important to you (and the phone supports it).

As a plan B, you can buy USB switches as well, which are normally used to share peripherals between several computers.

You still have to sync the sample clock to isochronous USB transfers, unpack the data packets and buffer the sample data. From the datasheet:
View attachment 155029
The more modern XMOS-based solutions are a bit different in that they are using asynchronous USB transfers instead, which means that they dictate the pace at which data is delivered to them. Obviously they still need clock generation and a master clock for that to work.

Isochronous USB is a bit like SPDIF, where the receiver has to reconstruct the clocking from the incoming signal entirely with a PLL. Fancy DACs will be going to great lengths in the PLL department in order to keep jitter at bay, which can easily degrade the measured performance otherwise.

Appreciate the explanation.
Looks like a decent xmos box would cost me more than my 'decent' DAC, so plan B seems like the way to go.
Thank you sir!

 

[Megaken]

@AnalogSteph so if I connect my 2 phones to a powered USB Hub like this, and then connect the hub to my DAC via USB - you think it won't degrade quality? (compared to phone to dac directly)

 

[AnalogSteph]

This guy is not what you want, it's a powered USB hub with individual power on/off. Multiple peripherals, one computer. You need exactly the opposite - one DAC, multiple hosts. Like this one. Plus matching USB OTG cables for each phone.

 

[Megaken]

This guy is not what you want, it's a powered USB hub with individual power on/off. Multiple peripherals, one computer. You need exactly the opposite - one DAC, multiple hosts. Like this one. Plus matching USB OTG cables for each phone.

Exactly. Learned that the hard way. Thank you.