in still waiting/searching for the right +-15V toroidal transformer and the right case, i was searching yesterday again at these fabulous diyaudio.com-forum->https://www.diyaudio.com/forums/digital-line-level/314935-es9038q2m-board-347.html and there is still some AK4137-modding „in the work“..
As said in this post before->http://essabre-90xx-rpi.sfb2.com/2018/09/raspi-ak4137-single-hat-for-2-3b-3b-pi-iso2dsd-v7/ the AK4137 is an digital up-sampler/sample-rate-converter (SRC) with such enormous values like: up to 768khz, DR: 186dB !! ● THD+N: -150dB –
„„..The main function of this board is to improve the quality of the Raspberry Pi I2S signal and reduce jitter..“+“And the AK4137 reconstruction clock reduces the Raspberry Pi output signal jitter enhancement.“..
so and as this raspi-hats, „standalone“ boards are meanwhile down to 22€/26$ (Link) respective 23€/27$(Link), u can give it a try..
by that, i have to say that these ES9038Q2M (stock) + some AD797s + raspberry pi (or some xmos-device) already have a superb sound/tune; as posted before i had a Cambridge-Audio-DAC-Magic (150€) here, and it was very well and clean manufactored (Wolfson-chips in it) but it was nevertheless absolutely no comparison to what ESS-chips (ES9038Q2M) are capable of->much better soundstage,3D,positioning,resolution->
„Forget about dual Wolfsons, this new unit shows what the ESS Sabre chip is truly capable of..Just fantastically detailed all along the entire frequency range, wide open, huge soundstage and separation, no noticeable coloration, but slightly warm and ultimately spot on timbre. There’s more than sufficient dynamics and air. A very worthy musical experience..„
so, back to the theme: i havent got understand it at first right, but with the following pictures its more clear..
and so you can select via the K1-K10 jumper/bridges the appropriate sample-rate/DSD-PCM-options, like with with the different filter-settings on the ES9038Q2M par example..
such a „standalone“ PCB with I2S-in and I2S-out is better for a XMOS-usb-bridge for example (or the expensive versions of these have a spdif-input too (to directly connect to a transporter CD/Blu-ray))..
would be very interesting if these AK4137 have such a great impact on the tune (less jitter and so on) also on 44,1khz/16bit (Redbook)..
another thing is that some user, also in the diyaudio-forum, means that these „upsampling“ by the AK4137 in general or in special this „PCM to DSD“ conversion have enormous advantages noise-wise..the noise will be moved in some inaudible frequencies or better completely removed (through this sigma-delta-extra extrapolation/conversion).
anyway, as we have now different possibilities to „pimp-up“ the already very good „sounding“ ES9038Q2Ms->soldering some other voltage regulators on it (keyword „AVCC“ etc.), use another,cleaner power supply (toroidal +-15V), use other OP-Amps (AD797,Muses) + upsample/reduce jitter with the AK4137, we must now see whats the best cost-performance relation..
so, back to the top, these 22€ for some AK4137 could be also a very good alternative but as i had yet not such a hat here, i unfortunately cant say anything to the benefits..
(if anybody has some experiences with the AK4137 and with a ES9038Q2M please share your experiences here in the comment-section !!)
many greets for now !! 😉