[ThanosD]

So, I can remove (or bridge the 2 ends) of these resistors

(Photo from abartels' player)
I eliminate the output resistance. But in case of a sort (for example: First I boot the player, and then I connect the IEMs) I might burn something. If I replace these resistors with ones of a lower value (let's say 0.3 ohms), do I lower to almost 0 the output impedance AND keep the "protection" that these resistors offer, or with such low values, it's the same as I didn't have any resistors at all?

 

[Merlin-PT]

There are several amplification schematics in the DAC datasheet:
https://www.akm.com/akm/en/file/datasheet/AK4497EQ.pdf

The ak4497 evaluation board also has the amplification circuit diagram in the last pages:
https://www.akm.com/akm/en/file/ev-board-manual/AK4497EQ.pdf

 

[abartels]

Those 100uF caps are part of it's low pass filter

Also VERY important, caps used for Vref, between VREFHL-VREFLL and VREFHR-VREFLR, they must preferably be 2200uF or higher value.
I know there's not sufficiant room for high values, but must try as high as possible.

In my previously build AK4495 dac I used 6800uF for vref cap values, very good!

 

[Merlin-PT]

I can see the PCB traces going from some of the 4x 22 ohm resistors (marked 220 in my standard version) to the 2.5 connector.
I'll try to post a photo of mine:
(I see you next post, but had the photo here , others can also see what we looking at)

 

[abartels]

You are right! Also strange standard version has 22ohm resistors, just checked AD8620A datasheet, it has indefinite shorting protection, will short my 10 ohm resistors and try how it sounds with my HE400i and KZ-ZS10.

Btw, have my HE400i balanced connected, sounds great! KZ-ZS10 sounds great too, very good value for money.

OFFTOPIC:

If someone uses HE400i, try Defean Lambskin Leather Angled pads, cost about USD45 on AE, but they are worth EVERY penny, much more open sounding, and they also do help with providing a
little more sub-bass output! They also are very comfortable

 

[Merlin-PT]

Interesting that the "ak4497 evaluation board" circuit uses 10uF caps in those areas, but the rest of the circuit could have different values I didn't check.
Also interesting, that circuit output has the output resistor marked as short, looks like they removed the resistor and shorted the PCB pads, but they use decoupling caps. We don't know what connector they use and didn't look at the rest of of the circuit.
This is a hobby for me, so my understanding is limited, but I always want to learn more.

I'm using high impedance earbuds here, so I'm not removing the resistors.

I'm also curious to know if removing those small value resistors, you can hear any change or if it sounds better ?

I remember when I had players with noise in output, using earbuds with volume sliders would attenuate that noise.
Beside that, I only remember the volume changing when I used those volume sliders at output.

 

[abartels]

I removed 4x10 ohm resistors, sq is definitely better, especially bass output is much better

About the 10uF value for vrefh to vrefl (both channels), this was also in whitepapers of 4490 and 4495,
values of 10uF, as well in whitepapers of evaluationboard of 4495, BUT in whitepapers of evaluationboard
of 4490 it was noted that higher values resulted in better bass response etc. If I remember correctly they
opted for 1000uF, but in graphics you definitely could see that it kept improving with higher values....

Not sure but I think our Zishan has 10uF per channel for vrefh. I definitely will increase those values,
it will improve A LOT.

 

[Merlin-PT]

I was talking about the 10uF coupling caps in the eval board circuit.
I see what you mean about the vrefh to vrefl caps, it's a good idea to use high value there.
Also glad to know removing the resistors improved the bass, try to see if you can hear the noise from the LCD light on (medium brightness) without the resistors or increased background hiss (with very low impedance phones).

 

[abartels]

the other cap values are correct, except for VrefH(L/R) to VrefL(L/R)
Unit is deadquiet, no background noise.

 

[Merlin-PT]

Our player uses 100uF and 220uF coupling, the eval board circuit uses 10uf coupling.

EDIT: I'm not talking about the VREF H/L caps, I know we should increase those.

 

[abartels]

Graph about Vref from Arduino site, taken from AKM whitepapers:

 

[kookaudio]

I removed 4x10 ohm resistors, sq is definitely better, especially bass output is much better.

Removed or shorted?

 

[abartels]

i removed them and soldered wire on the pads

 

[PapaHet]

ak4495 stock version output impedance was under 1 ohm (ok for balanced armatures iems), but had output coupling capacitors (noticeable bass roll-off for very low impedance iems of any type).



upgraded ak4495 used symmetrical voltage, so they removed the coupling capacitors (no longer needed, no bass roll-off). but they added output serial resistors of 10 ohms, output impedance (wrong decision to protect the opamps: tonal alteration, specially at highs, of balanced armature iems). guess these resistors could be bridged, always you take care of lowering the volume before plugging low impedance iems; however, i've not tested if the opamps start to oscillate after bridging the resistors..

ak4497 has output coupling capacitors (noticeable bass roll-off for very low impedance iems of any type), and output serial SMD resistors labeled "100" (this means 10 ohms). i.e., the worst source design for modern low impedance multi-BA iems. it seems to be designed aiming to over 80ohms headphones.
upgraded ak4497 uses symmetrical voltage, but i still see the coupling capacitors (?, upgraded, though), and the output resistors (correct me if i'm wrong). and bridging SMD resistors is more difficult.

maybe you don't notice bass roll-off and mids-highs alteration when using low impedance BA iems, because they are a few dBs difference, or maybe you like the result of that alteration with specific iems, but you are not listening to those iems like they were intended. if you are not critical perfectionist, guess you can live with it, but it's not a good design for modern iems.

What headphones would you recommend to deal with the powerful output of the 4497 stock version if the bass rolloff is to be avoided? I'll certainly try with my Dm6 and my boss hifi br8 and see if I will actually notice the roll off but I am thinking about a high impedance alternative on a budget. Approx 100 € max, the less expensive the better. Chi-fi very welcome but no must. I was thinking eventually the beyerdynamics dt 770 pro in the 80ohm version. Any other recommendations are very welcome. Happy new year, all.

 

[Themilkman46290]

What headphones would you recommend to deal with the powerful output of the 4497 stock version if the bass rolloff is to be avoided? I'll certainly try with my Dm6 and my boss hifi br8 and see if I will actually notice the roll off but I am thinking about a high impedance alternative on a budget. Approx 100 € max, the less expensive the better. Chi-fi very welcome but no must. I was thinking eventually the beyerdynamics dt 770 pro in the 80ohm version. Any other recommendations are very welcome. Happy new year, all.

Well these are my favorites, in order from most favorite to least, k's samsara, seahf f400s , ty hi-z hp150ts
Beyerdynamic DT 770 PRO, 250 Ohm are also great and I recently tried hd650's and the are amazing, saving money for them allreay