[kookaudio]

I have both the ak4490 and ak4497 versions, the ak4490 version works great with all my kz iems and low impedance gear and the ak4497 for my high impedance gear

That’s exactly what I was thinking.

 

[Themilkman46290]

But the schematic on them is very different, in the 4490 version the lpf is replaceable and feeds the line out, in the 4497 version the opamp is replaceable and the 2 op275 (lpf) feed a 2.5 balanced out, so they are fairly different and it's easier to get modification directions and help on the ak4495 and 4497 versions, it seems no one likes the 4490 version. In the beginning I was also disappointed with it but then I tried my more sensitive gear and realized it had far better synergy, now I am happy I have both

 

[kookaudio]

Btw, where did you get your leather cover, if I can ask?

 

[Themilkman46290]

I work with leather wood and metal, made it

 

[kookaudio]

I work with leather wood and metal, made it

Really nice!

 

[Themilkman46290]

Really nice!

Thank you

 

[hakuzen]

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.

 

[kookaudio]

Do you call this the “upgraded version”?
And you say out R is 10ohm, right?

 

[abartels]

Man oh man, how many times do i have to upload and post pictures of Standard version (the above is STANDARD) and Upgraded version..... Upgraded version has NO 4 electrolytics but 4 SMD caps, and i suppose these are bypass caps for psu and not coupling caps. In schematics it shows balanced output is direct from opamps without caps. Dont think there are output resistors either, i will measure this to be sure.

 

[kookaudio]

Ok, so we can assume upgraded version is the one with the 4 SMD caps instead of the 4 Nichicons. But if they are not coupling caps I guess there must be some output resistors, no?

 

[ThanosD]

Guys, if I remove the output resistors, what are the possible downsides? Does the output impedance turn to 0? I think I read somewhere that they are for protection, but protection for what?

 

[abartels]

You could damage the opamps, but I really think they aren't necessary. Be sure to connect your hp's before powering on Zishan.

Don't remove the resistors, just solder 4 short pieces of wire on their top to bridge them, or, solder second smd resistor's on top of them (parallel)

 

[Draknodd]

Guys, if I remove the output resistors, what are the possible downsides? Does the output impedance turn to 0? I think I read somewhere that they are for protection, but protection for what?

I guess they are there to protect the fake opamp, usally originals opamp do have short circuit protection and thermal protection so, in theory, the resistors are not so necessary, in particular if you change the opamp. Correct me if I' m wrong

 

[Merlin-PT]

From @abartels photos of his _upgraded_ version:
https://www.head-fi.org/threads/the-zishan-dsds-corner.826185/page-79#post-14632154

We can see 100 in the SMD resistors just before the audio outputs, so it has 10 ohm output resistors in 2.5 and 3.5 output.

The 4 caps (near the DAC) are in the audio path between the DAC output and the 2 opamps inputs.

The other "2 caps" (each made of 2 parallel caps) are also in the audio path after the transistors.
After those caps there are the 10 ohm resistors and then the 3.5 output.

In the _standard_ version, those resistors are marked 220, so they are 22ohm.

 

[abartels]

Does differential output of 4497 need coupling caps??? Very strange, will have a look at the whitepapers