So, it's like an iPod Shuffle, that doesn't shuffle?

What's the best opamps for the F2?

Hi I am using the Muses8920D just now and it has a nice rounded sound. Bass is not as prevelant as in the NJM5532D. I am still experimenting. I have not tried the Burson yet.

The 5532 family of op-amps do tend to have a strong upper-Bass / lower-Midbass sound, but not quite as much "air" and open Sound Stage, as some of the other op-amps (mostly more expensive models...).
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If you can still find any of the discontinued LME-49720-HA (Dual Op-Amp in TO-99 round metal case), give one of them a try.

Thanks for the report, D. Now I just need to figure how to open the F2...

I purchased some small Philips Screws (I think they're 2.5mm x 8mm), and installed them on the top four corners, to make it easier to remove the top of the case.

I own those screws already and the opamp you recommended, but I'll figure out how to take out the existing allan screws eventually? If I remember correctly I read somewhere that you use the OPA604 with yours, or? I also heard the Muses02 works great with the F2?

Not the OPA604, but I do have a few other OPA op-amps that I've used in the F2.
The MUSES02 does sound good in the F2, but mine is already fairly warm sounding, due to installing 4x MUSES8920E to drive the 3.5mm output.
Probably my overall favorite is the Dual OPA627AU on a DIP-8 header (but that's ~$62 ).
Currently, I've got Dual LME49710HA (TO-99 round metal case) on a DIP-8 header - but since it's so wide, I had to swing the upgraded C21 up out of the way, and the top of the case won't go on.

What do you prefer about the OPA627 in the F2? I just installed the AD825 and even though it sounds dark, it's very forward sounding and is "perfect". Have you tried it?

As you mentioned with the LME49710 you can't close the metal case, is there an adapter we can buy so the opamp can lay sideways inside?

I've got some of these BrownDog 111001 dual 1-channel TO-99 -> 2-channel DIP-8 adapters - and they're pretty wide.
https://www.cimarrontechnology.com/product/browndog-111001-single-to-dual-op-amp-adapter

The LME49710HA op-amps might not sit quite as low on a BrownDog 021001 dual 1-channel DIP-8 -> 2-channel DIP-8 adapter (due to the pins having to be bent to fit) - but it is narrower, which may allow the C21 capacitor to remain in place, so the top will fit on the case.
https://www.cimarrontechnology.com/product/browndog-021001-single-to-dual-op-amp-adapter

Those don't look newbie friendly. I'll just enjoy regular opamps then...

Aside from having to solder in the narrow space between the DIP-8 pins, it's not very hard to install the op-amps on those adapters.

I just put the OPA627 in my F2. I quite like the sound as it's bright and sparkly vs the dark AD825 (but I think it may sound better). I look forward to hearing your favorite combo soon. I'm curious, do you know any portable music players/cell phones with the same sound as the DIY Walnut F2?

I didn't really listen to the F2 very much, before modifying it.
The F2, and the previous F1, both use TI DRV134 single-ended to differential line driver chips, for the Balanced 2.5mm output - so they may sound a bit different than devices that use regular op-amp.

The F1 slipped through my grasp and I never bought one...

Have been looking for this info but haven't found it yet--does the F2 let you rewind or fast forward within a track?

Wisco, no.

Thank you, LaughMoreDaily--I appreciate it. Do you know if there are any Zishan or Walnut DAPs that do? My Z1 stopped working and I thought I'd see if any have that ability as I choose a replacement.