[vector84]

I picked those based on previously read reviews and until recently never wondered what is the output impedance of them. I would like to know that to anticipate how will they play with future sets.
Can one tell just by looking at the linked specs what would the output impedance be @1 KHz (how most manufacturers are reporting it)?
For instance, I would think that for Bravo where it says "Output Impedance" one in fact should read "Supported headphone impedance" and seeing a minimum of 20 Ohm I would think that output impedance ~1 KHz would be ~2.5 ohm (x8 rule)?
Similarly for xDuoo TA-01 that would be ~2 Ohm?

Are these assumptions correct or I've got it all wrong?
Maybe the more knowledgeable of you would have a clue.

Nope, that's not going to work. Manufacturers don't play by the 1/8th rule (or even understand what "output impedance" means, most of the time). You can find tons of cheap headphone amps (ex most TPA6120 implementations) that have 10+ ohms output impedance and rated for 8-200 ohm headphones, etc - not even close.

Components can give you a better idea of what might be going on (TPA6120 for example can be very low, but for heat and stability concerns, recommended implementation has a 10 ohm series resistor on the output, so >10 ohms output impedance) but that still only works if the amp maker followed the suggested implementation.


If your amp works in open loop, and you have an AC capable multimeter (DC won't work, need to measure Vrms) a simple way to get a ballpark figure is playing a 1kHz sine wave and measuring open loop voltage and voltage across a sense resistor of known value (in the general range of a headphone... where lower will give you a more accurate result iirc), then calculate:
Z = Rs * (Vo - Vs) / Vs

If it doesn't function in open loop, well then you need multiple load conditions and a slightly more complex formula to calculate it that I don't remember off the top of my head, but the idea is the same, you're intentionally constructing a voltage divider out of the unknown element and some known elements and recording the difference to use to calculate the unknown element given that a voltage divider was created and its outputs measured.


To get a complete curve instead of just a nominal value the same process can be done at many different values, but usually an automated tool connected to a setup with a known sense resistor is the way to go for that.


PS: a quick Google search: Xduoo TA-01: output impedance 7 ohms
Can't find an exact value on the Bravo Ocean, but probably in the 10 ohm range too, since what I did turn up was a lot of comments about it's "very high output impedance" being unsuitable for headphones under 300 ohms.
(that's with stock tubes though. I have no idea how tube rolling might effect things, I think it depends a lot on the actual implementation? but opamps can range from like 0.01 ohms to 10 ohms or so? )

PPS: If you can live with 1-2 ohms output impedance and don't need it vanishingly low, voltage dividers are your friend and can sort out linearity and noise issues on a whole variety of setups as long as you have the volume headroom to use them.

 

[maxxevv]

Ok, took delivery of my Breeze ( Weiliang Audio) E19 DAC amplifier yesterday. Its based on the ES9028Q2M chip, with a SA9226 USB decoder, NJM5534DD Op-Amp chips.

Edit: Added pictures.

The volume controls and phone jack

Rear access to power and USB port. No, it doesn't charge the battery, needs the 12V DC adaptor.

The things that came with the set.

Great Stuff :
Very good rendition of details. Very smooth sounding as its a little bit warmer when compared using the same songs to my LG G6 Quad DAC. Very comparable in soundstage between the 2, can't honestly say that I can differentiate between them for these details. That was based on quick A/B comparisons using both my CI880 and ZS6 earphones.

Tracks used:
i) Tchaikovsky and Sibelius Violin Concertos : David Ostrakh with Eugene Ormandy. - FLAC
ii) Fallen (Album ): Sarah Mclachlan - FLAC
iii) Somebody for Someone : The Corrs - MP3 320kbps
iv) Yoshique (Album): Deep Dish - FLAC
v) Santorini - Live ! Yanni - FLAC
vi) Rachmaninov Piano Concerto : Askenazy - FLAC

I have not tested it directly with my handphone for connection yet ( don't have correct cables)

Will have to compare again using harder to drive headphones to see if there are greater differences at higher power output levels. Also, not sure if the circuit needs some burn in period.

Not-that-great stuff:

i) Drivers : Will not work out of the box without the correct drivers for Windows 7. Had to get the download link from seller ( which was wonderfully responsive and helpful, full marks for that ! ) Without the seller's help, it would be virtually impossible to find it on my own.
ii) No instruction sheets of any sort. Put it to charge on with supplied 12V DC adaptor but there were no clear signs of anything (such as LED switching off or changing colour) even after 3~4 hours on the plug. The charger and the unit didn't register any heating up at all. So no idea if the charging was working or not.
iii) Minimal package. Came with USB -> Micro USB charging data cable, Micro USB to Micro USB connector cable, allen keys, 2 silicon bands and that was it.
I would need a USB C to Micro USB cable to plug it into my phone (to test at least).

iv) Its a pure digital DAC. You cannot use it with a line-in as an auxiliary amplifier.

v) It doesn't seem to have iOS support.


Shall post back with pictures when I have some time to do that. Also, I have placed orders for some Op-amps with higher slew rates and bandwidths to test out how much they will influence the overall sound signature.

Preliminary impression:

It totally transformed the sound output quality from my laptop. I would say its really good now, compared to the pretty bland sound previously. But need more time to pin down what's the specific qualities as circuitry has not had any burn-in. And also, if op-amps used are optimal for its purpose.

 

[Adide]

PS: a quick Google search: Xduoo TA-01: output impedance 7 ohms
Can't find an exact value on the Bravo Ocean, but probably in the 10 ohm range too, since what I did turn up was a lot of comments about it's "very high output impedance" being unsuitable for headphones under 300 ohms.
(that's with stock tubes though. I have no idea how tube rolling might effect things, I think it depends a lot on the actual implementation? but opamps can range from like 0.01 ohms to 10 ohms or so? )

PPS: If you can live with 1-2 ohms output impedance and don't need it vanishingly low, voltage dividers are your friend and can sort out linearity and noise issues on a whole variety of setups as long as you have the volume headroom to use them.

Thanks @vector84 , helpful and informative as always.

I'm a bit skeptical of these having an impedance of 7-10 Ohm - I think something like that would crapify most common impedance phones in the 16-32 Ohm range.
Instead, reviews (of Bravo at least which are plenty, not many for xDuoo on the other hand) are very good and I've seen a good deal of people using it with IEM's (so ~16 Ohm phones or even less). And personally although my BDT 880/600 Ohm should mask such high output impedance, I still had good results with 16-32 Ohm cans (such as ISK HP2011 and Bosshifi B8). So... puzzled.

People commenting on very "high output impedance" for Bravo I believe are taking specifications of "Output Impedance 20-600 Ohm" ad literam but that part is wrongly labeled - those are the officially supported loads, so phone impedance to be driven and not equipment's output impedance.
Yes, 1-3 Ohm output would be nice and I'm not striving for less; and afaik that's the definition of a good amplifier. If it's above 5 Ohm (I'm being generous here, one should read 2 Ohm to be conservative) it will crapify sound for most phones, wouldn't it?

If you can still find it please post the URL to the 7 Ohm info for xDuoo please.

I just came to realize there are dedicated threads for these equipments so I'll try asking there, maybe someone has actually measured these because it's beyond me doing it alone.

Regards.

 

[vector84]

If it's above 5 Ohm (I'm being generous here, one should read 2 Ohm to be conservative) it will crapify sound for most phones, wouldn't it?

Generally speaking, >0 output impedance will EQ phones in the direction of their impedance curves. So if a set of phones has dead flat impedance, output impedance doesn't change the tonality at all, but BAs and hybrids especially can have wildly variant impedance curves, and that's where'll you get tons of coloration.

You're probably thinking of damping effects, but realistically speaking there's usually plenty enough mechanical damping in IEMs already, so the bigger effect is usually coloration.
Also higher output impedance will usually reduce the effects of coupling cap induced subbass rolloff - so if a set of phones does have a dead flat impedance curve... it can actually be beneficial.

If you can still find it please post the URL to the 7 Ohm info for xDuoo please.

http://reference-audio-analyzer.pro/en/report/amp/xduoo-ta-01.php
Pretty sure that one's right

 

[maxxevv]

From your link, looks like the near perfect output impedance values of the Chord Hugo, the Centrance Mini M8 would be excellent for the ZS5v1. The Fiio X5-III comes close behind.

 

[vector84]

A weird damping related side track: some very low impedance phones can also need non-zero output impedance to hit critical damping (typical sweet spot values for things that suffer from this that I've seen are in the 2-7 ohm range) - usually not something people can actually hear, but a funny damping related aside

 

[Adide]

You're probably thinking of damping effects, but realistically speaking there's usually plenty enough mechanical damping in IEMs already, so the bigger effect is usually coloration.
Also higher output impedance will usually reduce the effects of coupling cap induced subbass rolloff - so if a set of phones does have a dead flat impedance curve... it can actually be beneficial.

I see your point.
I get your are not a proponent of the x8 rule as a must but more as a guideline with amendments depending on case.
Thanks for the link.

 

[Adide]

PPS: If you can live with 1-2 ohms output impedance and don't need it vanishingly low, voltage dividers are your friend and can sort out linearity and noise issues on a whole variety of setups as long as you have the volume headroom to use them.

Followed your advice and ordered an iFi EarBuddy for the Bravo amp just for the peace of mind. I've been eyeing the Buddy for a longtime but made up my mind during our recent talk.
This amplifier has no gain switch and powers an ISK 32 Ohm headphone.

The Buddy takes whatever amplifier output impedance is and turn it into <1.5 Ohm output while also reducing gain and allowing for more room with the volume pot, all of this without coloring sound.
I think it will only do good.

The xDuoo DAC/AMP on the other hand only powers my BDT 880 (600 Ohm) home setup so 7 Ohm output it's not an issue.

 

[easily_amused]

Hi guys, just wanted to jump into this thread. I've been living in Beijing for 7 years now and only recently got into the audiophile scene. Over the last year I started buying up obscure and odd Chinese headphone DAC/Amps and Amps. I'm mostly focused on the cheaper stuff, so less than 2000rmb ( <$300). I like to buy things that I can find no info on online because it's a little more fun that way. I have about 18 individual units right now on top of 4-5 more well known products. I actually haven't listened to all of them yet, I think I enjoy the process of buying and unpacking them a little too much so I kinda can't stop ...

Quite a few of the products I own are actually DIY kits that I've just asked the suppliers to assemble - they sometimes offer this if you contact them, my personal assistant has gotten used to my strange requests. As a result I've got a bunch of weird metal and clear plastic boxes around that look like they perform some industrial power plant function. Some of them come signed or with home printed pamphlets all in Chinese. Most are just wrapped in copious amounts of bubble tape and shoved in a box too. Haven't had a faulty one yet, although I have almost blown my head off a few times Oh, and the size is usually a surprise. It's amusing how little sense of scale you get from the pictures on taobao.

Recently I've started expanding into cables and am thinking of getting some DAPs newxt, although that's a little harder because I can't read Chinese.

Most of these aren't great products but it's a lot of fun to test out a product with no expectation attached and just explore some new sounds.

If anyone sees anything online in China which they'd love to find out more about, and it's not too expensive, then I am pretty down with the idea of buying one and giving it a go.

 

[NymPHONOmaniac]

Hi all, I receive my DIY Xmos U8 AK4490 DAC-AMP and this time have been UNLUCKY and really did not suggest to buy this if your not an electrician. All compenents are legit as seen in pictures but the fact we have to use AC power that is very problematic and cause poping noise and heat etc. This make the device unusable....after a hard time finding a xmos driver for window 10, I finally get to make it work correctly for 10 minutes....sound was incredible, wich make this even more frustrating!!!!!!!!!! The seller never answer the question about proper power supply to use....when I use power suplly it make the device litteraly burn so I use 9V battery like I seen somme dudes use in ali feedback section, but it do not work perfectly so this is just a pain in they ass. DO-NOT-BUY-THIS. Find a AK4490 DAC that fully work on its own, cause this chip look to sound mesmerizing for real!!!
To NOT BUY:
https://www.aliexpress.com/item/NEW...phone-Output-Support-for-PCM/32788755737.html

To BUY (still work perfectly after 8 months):https://www.ebay.com/itm/252298238894?ul_noapp=true

 

[NymPHONOmaniac]

Hi guys, just wanted to jump into this thread. I've been living in Beijing for 7 years now and only recently got into the audiophile scene. Over the last year I started buying up obscure and odd Chinese headphone DAC/Amps and Amps. I'm mostly focused on the cheaper stuff, so less than 2000rmb ( <$300). I like to buy things that I can find no info on online because it's a little more fun that way. I have about 18 individual units right now on top of 4-5 more well known products. I actually haven't listened to all of them yet, I think I enjoy the process of buying and unpacking them a little too much so I kinda can't stop ...

Quite a few of the products I own are actually DIY kits that I've just asked the suppliers to assemble - they sometimes offer this if you contact them, my personal assistant has gotten used to my strange requests. As a result I've got a bunch of weird metal and clear plastic boxes around that look like they perform some industrial power plant function. Some of them come signed or with home printed pamphlets all in Chinese. Most are just wrapped in copious amounts of bubble tape and shoved in a box too. Haven't had a faulty one yet, although I have almost blown my head off a few times Oh, and the size is usually a surprise. It's amusing how little sense of scale you get from the pictures on taobao.

Recently I've started expanding into cables and am thinking of getting some DAPs newxt, although that's a little harder because I can't read Chinese.

Most of these aren't great products but it's a lot of fun to test out a product with no expectation attached and just explore some new sounds.

If anyone sees anything online in China which they'd love to find out more about, and it's not too expensive, then I am pretty down with the idea of buying one and giving it a go.

Hi man, you have a very interesting passion that I understand fully, its such a joy to have different sound source for our ears! Can you share your favorite DAC-AMP and did any of them are findable on Aliexpress???

I'm very poor so my last buy depress me alot....but my goal is to test DIY DAC-AMP that are easy to use, I mean, plug and play (with or without driver), we do not need case for them to work, its more about protection here...DAC chips are very important, whats your favorite and more affordable one???

Thanks to share here, your some kind of wizard here now

 

[maxxevv]

Hi all, I receive my DIY Xmos U8 AK4490 DAC-AMP and this time have been UNLUCKY and really did not suggest to buy this if your not an electrician. All compenents are legit as seen in pictures but the fact we have to use AC power that is very problematic and cause poping noise and heat etc. This make the device unusable....after a hard time finding a xmos driver for window 10, I finally get to make it work correctly for 10 minutes....sound was incredible, wich make this even more frustrating!!!!!!!!!! The seller never answer the question about proper power supply to use....when I use power suplly it make the device litteraly burn so I use 9V battery like I seen somme dudes use in ali feedback section, but it do not work perfectly so this is just a pain in they ass. DO-NOT-BUY-THIS. Find a AK4490 DAC that fully work on its own, cause this chip look to sound mesmerizing for real!!!
To NOT BUY:
https://www.aliexpress.com/item/NEW...phone-Output-Support-for-PCM/32788755737.html

To BUY (still work perfectly after 8 months):https://www.ebay.com/itm/252298238894?ul_noapp=true

Think your 9v DC power supply had too much current supply. How much power was your 9V adaptor pushing into the circuit ?

It states in the specs that it consumes 2W power only.

Also, compact opamp circuits do get pretty warm. Hence, heat sinks will help in most cases.

A suggestion would be a USB cabled 9v step-up as these only go up to 2W.

https://www.aliexpress.com/item/DC-...-e94f-4115-b088-618ae17b8eaa&rmStoreLevelAB=1

 

[NymPHONOmaniac]

Think your 9v DC power supply had too much current supply. How much power was your 9V adaptor pushing into the circuit ?

It states in the specs that it consumes 2W power only.

Also, compact opamp circuits do get pretty warm. Hence, heat sinks will help in most cases.

A suggestion would be a USB cabled 9v step-up as these only go up to 2W.

https://www.aliexpress.com/item/DC-...-e94f-4115-b088-618ae17b8eaa&rmStoreLevelAB=1

Hi, thanks for the feedback, i'm quite dumb about this power consumption....

I just use a 9V battery.....as seen used with other happy users. For AC power, the seller never answer exact power adaptor is needed but I finally find it included with the finish AK DAC-AMP device:

it's 8.4V. Don't know were to find this....
Did the USB power adaptor can really work you think?
Seller suggest to put a heat sink on the XMOS chip (as seen below)....what became extra hot are the 2 metal piece at the right side.

 

[maxxevv]

There are plenty of those DC adaptors to be found on Aliexpress.

https://www.aliexpress.com/af/8.4V-...SB_20171204210015&origin=n&catId=0&isViewCP=y

 

[vector84]

9V batteries don't really like to source that much current - also a slightly lower voltage (it says rated for 7-9V?) would probably run cooler (but probably lower the output voltage too?).

Also the things that got hot look like voltage regulators - they could probably do for a heatsink more than the XMOS chip, and there's some comments in the aliexpress page that show someone strapping a nice big heat sink to them - you can use thermal glue, or just whatever heat transfer paste or tape or w/e and bolt directly through the metal tabs to a heat sink, that's what they're there for.

Also there's another aliexpress comment that seems to be suggesting they're running it successfully at 7V / 150mA - which is only around 1W.