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Review and Measurements of Topping DX7s DAC and Headphone Amp

My pleasure. And welcome to the forum with those good questions! The matrix of testing can be huge in these devices and hence the configurations I choose to test. But if there are specific additional tests you want me to run, feel free to ask. Since I don't have to return this unit, I can continue testing it in the future.
 
Mad_Economist said:
Topping lists the headphone drivers as TPA6120A2 - if that is the case, the 10Ω resistors on the output are there to ensure its stability with load capacitance (see page 11 of spec sheet http://www.ti.com/lit/ds/symlink/tpa6120a2.pdf). Removing them could cause oscillation. Very unfortunate that they chose the TPA6120A2 - it is a good option for cheaper designs when very high current output is required (Monoprice's own budget DAC-amp, for example), but for a "statement" DAC-amp it would have been nice if Topping had used something better, perhaps the 1688 or 1622.
Click to expand...
Some products I've seen use the TPA6120A2 but offer lower output resistance. DACport Slim/HD says 1 ohm and Stoner Acoustics UD125 was measured at less than 1 ohm by a reviewer. Do these products risk damaging headphones by doing this or is it not something to worry about?
 
I would be curious to see if balanced outputs have the same THD/IMD than the unbalanced ones.

Two other things I would be curious about:
  • Does the other antialiasing filter change the passband shape significantly ?
  • How close are the two ES9018q2m synchronized? And does restarting the unit and/or resyncrhonize it to another input sampling rate change that?
That second item would require a specific test mechanism, maybe something like looking at the IR resulting from a sweep recorded with REW from the summed output?
 
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One last thing I would be curious to see: the 1kHz spectrum is probably taken at a level close to 0dBFS (-1dBFS or maybe -3dBFS? difficult to tell as it is removed).
As -30dBFS to -10dBFS is probably closer to real normal use of that unit given its digital volume control functionality, it would be interesting to see how this measurement evolve when fed with a -1dBFS, -10dBFS, -30dBFS (etc.) signal.

Maybe in a synthetic table like this, one row per dBFS level, one column per distortion order, and distortion calculated relative to the level of the 1kHz signal, either in % or in dB (probably better) :

HD vs dBFS.png
 
Standard tests use -1 dBFS IME. A sweep like that could be useful, maybe just once to see if there really is any difference. Normally the DAC itself performs best near FS but the output stages may have higher distortion. I suspect a sweep at -1 and -10 dBFS would tell pretty much all.
 
You're all talking about the D50 from Topping. I can't find any information about it, what exactly is this device? Is it the successor of the D30?
 
SchwarzeWolke said:
You're all talking about the D50 from Topping. I can't find any information about it, what exactly is this device? Is it the successor of the D30?
Click to expand...
No it doesn't replace the D30 as it is double the price. It is in a smaller more compact box than D30 and with a display/menu. It is very solidly built.

I don't know why their web site is behind availability of the unit as I have had one for a couple of weeks.
 
I think the Chinese guys are pretty serious about New Year!!:)
 
amirm said:
No it doesn't replace the D30 as it is double the price. It is in a smaller more compact box than D30 and with a display/menu. It is very solidly built.

I don't know why their web site is behind availability of the unit as I have had one for a couple of weeks.
Click to expand...

They are waiting for your measurements and review before they put it up for sale. No pressure.
 
stunta said:
They are waiting for your measurements and review before they put it up for sale. No pressure.
Click to expand...
Its because they are on chinese new year for the last 8 days. And they will be on new year for the next 3-4 days still.
 
amirm said:
No it doesn't replace the D30 as it is double the price. It is in a smaller more compact box than D30 and with a display/menu. It is very solidly built.

I don't know why their web site is behind availability of the unit as I have had one for a couple of weeks.
Click to expand...

I've been wanting to buy a D30 for awhile now. Is the D50 basically the D10 but wall powered? Can you give any more details about it?
 
dat yeti said:
I've been wanting to buy a D30 for awhile now. Is the D50 basically the D10 but wall powered? Can you give any more details about it?
Click to expand...
No the D50 is a dual 9038 device also I believe.
The D10 is a 9018K2M device like the SMSL M8 but it has no external power supply
 
stalepie said:
Some products I've seen use the TPA6120A2 but offer lower output resistance. DACport Slim/HD says 1 ohm and Stoner Acoustics UD125 was measured at less than 1 ohm by a reviewer. Do these products risk damaging headphones by doing this or is it not something to worry about?
Click to expand...

It would depend. In concept there are alternative ways to stabilize the output, but at that point I would think that it would be simpler to implement a different solution. One could always test the devices in question with a capacitive load and see if they do, in fact, oscillate, or at the least look around the output section of the board to try to figure out what protections (if any) have been implemented.

Practically speaking I'd rather simply avoid TPA6120A2-based amps when driving low-impedance headphones with nonlinear impedance (that is, not planar magnetics) is a priority - there are better options out there that don't break the bank - but if you were really worried and already had the amp, you could use a 10Ω resistor in-line for peace of mind's sake.

Edit: As an example of an alternative solution for output protection with low impedance, NwAvGuy used an inductive ferrite chip to short the output resistors on a DIY amp using the TPA6120A2 - see subheading "Output Impedance Modification" here http://nwavguy.blogspot.com/2011/06/qrv09-diy-headphone-amp.html - and such a scheme might well be employed by the DACport Slim, Stoner, etc (although it would be unsafe to bet on it, in my opinion).
 
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Mad_Economist said:
It would depend. In concept there are alternative ways to stabilize the output, but at that point I would think that it would be simpler to implement a different solution. One could always test the devices in question with a capacitive load and see if they do, in fact, oscillate, or at the least look around the output section of the board to try to figure out what protections (if any) have been implemented.

Practically speaking I'd rather simply avoid TPA6120A2-based amps when driving low-impedance headphones with nonlinear impedance (that is, not planar magnetics) is a priority - there are better options out there that don't break the bank - but if you were really worried and already had the amp, you could use a 10Ω resistor in-line for peace of mind's sake.

Edit: As an example of an alternative solution for output protection with low impedance, NwAvGuy used an inductive ferrite chip to short the output resistors on a DIY amp using the TPA6120A2 - see subheading "Output Impedance Modification" here http://nwavguy.blogspot.com/2011/06/qrv09-diy-headphone-amp.html - and such a scheme might well be employed by the DACport Slim, Stoner, etc (although it would be unsafe to bet on it, in my opinion).
Click to expand...
Yes I have seen this. But which amps that "don't break the bank" are available with 0 ohm output impedance?
I see O2, Magni3... Basically outside of that there aren't many 0 ohm output impedance amps period that are under $500... and even at $500 there aren't many.
What I have found is most are $800 or $1000+ often with no measurements at all....
I really want an Amp that is just like the A30 but with a proper output impedance.

What I have used before is the UE Buffer jack, and I have wondered if that really does "lower" the output impedance or if it doesn't, if its possible to build such a device that is simple and can lower the output impedance by say presenting the amp with a 100 ohm or more load and then having its own output of 1 or less.
 
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