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Sythrix
302
Aug 31, 2018
In case anyone is wondering, this is yet another TPA6120 design, which means the output impedance (of course missing from the specs lists) is roughly 10 ohms.
This would not be a good choice for most IEMs.
Check the impedance of your gear before buying. Non-planar drivers below ~80 ohms may suffer impaired frequency response due to the high output impedance. Most IEMs are below 80 ohms, which is why they are mentioned, but many common dynamic driver over-ears and on-ears are as well.
drmedpepper
0
Sep 2, 2018
SythrixWill I be fine with this Dac/amp combo if I buy the HD58X?
Sythrix
302
Sep 2, 2018
drmedpepperYes, it should be fine.
The HD58X is 150 ohms. It won't be significantly affected by the high output impedance of the DAC-X7.
L3ar
2
Sep 3, 2018
SythrixSo it won't be fine with a philips Fidelio X2HR/00 am I right ?
Sythrix
302
Sep 3, 2018
L3arIt's certainly not a very good match, no. The X2HR have only 30 ohms of impedance and dynamic drivers. No matter how you look at it, there's probably going to be some audible changes to the frequency response.
L3ar
2
Sep 3, 2018
SythrixDo you know an equivalent that would fit a philips Fidelio X2HR/00 ?
Sythrix
302
Sep 3, 2018
L3arWhat input ports to you need? What will you be using it with? There's a lot of different options out there.
L3ar
2
Sep 3, 2018
SythrixOptical to plug it to my pc, and the ability to switch between aux for the headphone and another aux for my 2.1 kit (I just looked on my 2.1 kit and it's not a coaxial it has an aux and RCA )
Sythrix
302
Sep 3, 2018
L3arYou'd have to do some searching. This one I think meets your requirements: https://audioengineusa.com/shop/components/d1-24-bit-dacheadphone-amp/
but there's no switch. the headphones output when plugged in, otherwise the RCAs for your 2.1 speakers. Output impedance is 2 ohms. Output voltage isn't very high (2 volts), but your headphones are incredibly easy to drive, getting to over 120 dB with that voltage.
EDIT: What's unfortunate, is that many of these all-in-one designs that take account of these various connections and configurations, while still be relatively cheap, are cookie cutter Chinese designs which require the TPA6120. Which of course leads to the 10 ohm output impedance. Finding something that does all the same things, but doesn't use the TPA6120 and is still cheap can be a challenge depending on what you need.
Ben4Cans
21
Oct 16, 2018
SythrixHow do you know that the implemented architecture, on this device, of the TPA6120 is set to 10 Ohms? Are there measurements that provide this?
If you plugged in a low impedance IEM or headphone that does not meet the rule of eighths, then wouldn't you be able to tell right away if impedance had an issue based on the sound? Of course you would have to know what the IEM/headphone should sound like beforehand.
Other manufacturers like Stoner Acoustics use the same TPA6120 but have a claimed output impedance of ~0.1 Ohms. Below is quoted from their FB page. So would it be possible that this or other TPA6120 devices don't automatically have an output impedance of 10 Ohms?
*** Output Impedance
The TPA6120 is traditionally designed with 10 Ohms of Output Impedance, however, this is not the case with the TPA6120 used in the UD125 and UDXA! The UD125 and UDXA has a ~0.1 Ohms of Output Impedance, due to a different design architecture used. This ensures consistent and best performance across different earphones and headphones with different load impedances!
https://stoneracoustics.com/ud125/
https://stoneracoustics.com/udxa/
Sythrix
302
Oct 16, 2018
Ben4CansIf they had an output impedance that was lower, they would advertise it. These companies are not oblivious to the fact that customers want to know. They've made many models and been asked many times what it is.
Yes, it is possible to get around this output impedance, as you show. However, most companies don't and most circuit designs don't. Since the overwhelming amount of examples point to the output impedance being ~10 ohms, we can only imagine (for lack of any competing evidence to suggest otherwise) that they have not done the necessary work, as they have made absolutely no indication of such.
An anecdotal account of one company taking this into account and accommodating, does not invalidate that FX Audio has used a chip with 10 ohm output impedance. If they at some point indicate that they have designed the circuit to get around this limitation, then I will welcome it... but they have not.
Ben4Cans
21
Oct 17, 2018
SythrixThanks for your analysis. It is unfortunate as this seemed like an awesome product... I guess its going to be more of a high impedance HP Amp and/or just a DAC for those lower than 80 Ohm IEM/HP. I guess my search continues.
Any chance it is possible to swap out or roll this part?
Sythrix
302
Oct 17, 2018
Ben4Cans" Any chance it is possible to swap out or roll this part? "
Unfortunately no, at least not that I'm aware of. I have never seen anyone attempt it and I don't know of a suitable replacement. The entire circuit is usually designed around it.
NvAwguy had a method he used on another amp, which involved soldering ferrites onto some of the output resistors, but you would need to do a technical analysis of this amp and find out which resistors were appropriate in kind. That would be no simple task (although you could try asking FX-Audio, but even they may not have really designed their own circuit. Such is the way of Chi-Fi audio), and NvAwguy mentions that this mod doubles the distortion of the amp he used. I would note that FX-Audio does not even list the THD of this amp...
Here is NwAvguy's page where he details the process: http://nwavguy.blogspot.com/2011/06/qrv09-diy-headphone-amp.html
Scroll down to "Output Impedance Modification" and continue reading from there to see what I'm talking about.
Note again, this is for a different DIY amplifier that used the same output buffer (the TPA6120).
Another unfortunate reality is that NwAvguy went missing or incognito, so contacting him to ask him is not possible.
Ben4Cans
21
Oct 17, 2018
SythrixAre there other chips apart from TPA6120 that has this issue or is it going to be a thing with all Chi-Fi desktop gear?
I suppose for now people can refer to the audiosciencereview site for a listing of some of these devices and their headphone output impedance.
Sythrix
302
Oct 17, 2018
Ben4CansNot all Chi-Fi gear uses it, no. However, many of the cheaper Chi-Fi offerings default to using it, so you may be looking at spending more to obtain something without it. As far as I know, this is the most infamous mainstream chip with high output impedance.
As you mentioned, audiosciencereview.com has many listings of similar products, so I would peruse there for alternatives, or at the very least stick to manufacturers that advertise their specs in full detail.
Sythrix
302
Oct 17, 2018
Ben4CansOne other thing, are you not interested in the O2 + Grace combo DAC/Amp as an alternative? It's on Massdrop right now for the next 20 hours, here: https://www.massdrop.com/buy/massdrop-o2-sdac-dac-amp
At 149.99, I think it would be a worthy competitor... and one that isn't afraid to post their specs either (0.54 ohm output impedance). ; )
Ben4Cans
21
Oct 18, 2018
SythrixYes, it is something I am strongly considering though the USB and RCA inputs is a bit limiting.
I am also considering going another route and just getting the Cayin N5ii or some other portable player that can double as portable and desktop... I dont think i'll be getting into cans over 300 Ohm anytime soon so it could be worth it.
The portable DAC/AMPs are like Xduoo XD 05 look great but the shipping time, then the iFi iDSD Micro BL cost my kidneys, iFi Nano has no aux in and finicky USB port from what im reading....so yeah i got lots of problems... :)
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