ES9068AS datasheet, re: Topping G5 un-amp'd 1/8" output's output impedance

[mike7877]

So I have a topping G5 and am wondering what the output impedance of the non-amplified 1/8" jack is.

The 3 page product brief is available for the ES9068AS, but not the ~100 page datasheet which seems to be provided for most if not all of their other DACs...

A while back I looked at the 2 channel version of the ES9068AS, and (to my memory), output impedance was spec'd to be about 400 ohms. Recently I looked again and found a new DAC in their repository - 9069. It looks like an updated 9068AS. Its output impedance is listed to be 390 +-15% ohms.

Is it a pretty safe bet that the 8 channel 9068AS output impedance is about 400 ohms? If the G5 is set up differential/dual differential, how would this affect the 400 ohm output impedance (per channel, I'm assuming). Does anyone know how the G5 makes use of the 8 channels of the 9068AS? In my mind it'd be pretty odd to not use 6 of the 8 available channels to improve performance somehow, because if not, why not just buy the 2 channel version? Unless there was a firesale of the 8 channel versions... unlikely IMO with what happened with AKM


Aside: it's so odd the 9068AS only has a product brief available... what do engineers need to do - guess all the registers? Lmao
If there's some ndaa, why only for the 9068AS?

 

[staticV3]

Fwiw, you can measure the output inpedance yourself with relatively inexpensive equipment.

$20 for an E1DA Cosmos Load board and $15 or so for a Multimeter (in case you don't have one already).

Then just use this calculator with instructions:

Measuring input impedance and calculating output impedance calculation calculate audio amplifier op-amp how to measure impedance voltage gain total loudspeaker speaker microphone resistance resistor bridging matching test load loudspeaker source resi

Calculate input impedance and measure output impedance calculation total audio amplifierr op-amp how to measure impedance voltage gain total loudspeaker speaker microphone resistance resistor bridging matching test load source resistance - Eberhard Sengpiel sengpielaudio

www.sengpielaudio.com

You can even test different frequencies, then plot Zo vs Frequency in Excel, Sheets etc.

 

[mike7877]

Fwiw, you can measure the output inpedance yourself with relatively inexpensive equipment.

$20 for an E1DA Cosmos Load board and $15 or so for a Multimeter (in case you don't have one already).

Then just use this calculator with instructions:

Measuring input impedance and calculating output impedance calculation calculate audio amplifier op-amp how to measure impedance voltage gain total loudspeaker speaker microphone resistance resistor bridging matching test load loudspeaker source resi

Calculate input impedance and measure output impedance calculation total audio amplifierr op-amp how to measure impedance voltage gain total loudspeaker speaker microphone resistance resistor bridging matching test load source resistance - Eberhard Sengpiel sengpielaudio

www.sengpielaudio.com

You can even test different frequencies, then plot Zo vs Frequency in Excel, Sheets etc.

I do have equipment to measure. Would be interesting to see over its whole spectrum. I have an oscilloscope good to measure up to 50MHz (200MHz), so could easily do up through 160kHz accurately.

An interesting task for sure, but if anyone knows the stated output impedance from the probably limited availability datasheet, I'm still interested

 

[KSTR]

Can you show us this strange "non-amplified 1/8" jack?
According to Topping Website there are only regular converted buffered outputs (after I/V stage) with < 0.1Ohm output impedance, and anything else wouldn't make much sense at all. Also, there is no 1/8" jack, only 4.4mm and 3.5mm (1/8" is 3.175mm).

 

[kekotron]

Assuming Mike's talking about the LINE IN/OUT 3.5 port as per this picture (number 3):

Topping lists the output impedance of the Line Out as 50 Ohms:

 

[voodooless]

There is no point to looking at DAC datasheets. The DAC output is never directly connected to the device outputs. There is always at least one opamp in between.

 

[mike7877]

Assuming Mike's talking about the LINE IN/OUT 3.5 port as per this picture (number 3):

Topping lists the output impedance of the Line Out as 50 Ohms:
View attachment 303278

Totally missed that! Thanks

 

[mike7877]

There is no point to looking at DAC datasheets. The DAC output is never directly connected to the device outputs. There is always at least one opamp in between.

In this case the G5's amplified THD+n is nearly identical to the DAC chip specification of -120, output voltage too. If there were 2 (or 3) more stages of amplification between the DAC's output and the headphone output, they'd all have to be good for -130+ to keep the miraculous -120dB in this $400CAD portable headphone amp/DAC combo (which already seems almost impossibly good)

Wouldn't the opamp after the DAC you're referring to usually be the headphone stage amplification after the DAC? I'm wondering why buffer something with an output impedance already so low? The input it drives 99% of the time is 10-20k ohms, with below 5k being rare. I had a difficult amp once that was 1100 ohms (140WPC class A behemoth) and it could be driven just fine by my 300 ohm RME Babyface Pro

 

[Killingbeans]

Most high performance DAC chips have current output, and the op-amp in question is used as an I/V stage, not an amp.

The output impedance in the data sheet is most likely the one of an I/V reference design. The DAC designer is not bound to that.

 

[KSTR]

The DAC chip "output" spec is after the recommended I/V-stage, I/V is integral to the design (also to low-pass filter the output and remove the DC component).

The I/V's output seems to directly feed the Line-Out in one mode. After that there is one(!) gain-selectable output stage for headphones output -- which can also take a Line-In Signal in another mode. No problem to make that stage -120dB or better SINAD, 1kHz full scale.