DIY audio interface idea - is this possible?

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Hello :)

I have this plan of a diy audio interface. The goals are as follows:
  1. USB connection
  2. at least 1 instrument input (for guitar)
  3. at least 1 output (for headphones)
  4. 16bit/48K minimum
  5. integrated preamp/headphone amp
  6. preferably usb powered, but I might have a 9v transformer that I can use for a linear supply.

Initially I planned on taking a cm108 board and just hooking up an opamp buffer with a level control but while researching on some alternatives to that board because mine had a noise floor of like -60dB, I fell into the DIY audio hole. oops. The analog part should be fine, it's the digital part that I need some help with.

Now, my plan is to take a CM108 and wire in a PCM1802 ADC and PCM5102 DAC via I2S. I chose the combo as I feel like it has some potential to sound good. Is this a bad idea? I don't have much experience with digital audio. I tried researching for other DIY audio interfaces, but I'm a bit lost. I'm open to other options. budget would be approx $30 max.

I'm also looking at modding this, as it apparently sounds good and it also has an I2S input.
SA9023A + ES9018K2M USB portable DAC HIFI fever external amplifier audio card (i'm not buying from this site, only put here for reference)

The reason I'm doing this is because I don't have much money to get other boards or complete units as international shipping is way too expensive in my country (Philippines) and also because I want to get my feet wet in audio more. I'm not really interested in making full speaker setups.

Thank you so much, and apologies if there's something wrong as this is my first post.
 
Once upon a time, there was this little gem of a USB audio interface called Roland UA1G, it does everything you have listed, and more:

- Stereo input and output at 24-bit/96kHz audio quality
- High-end A/D and D/A converters for accurate recording and playback
- Large Input Level knob for easy control while recording
- 1/4" jack with Hi-Z option for recording electric guitar or bass
- Electret condenser mic input
- RCA phono-type and optical-digital audio I/O
- Headphone output
- USB powered – no AC adapter required
- SONAR LE for music recording, editing, and publishing on PC
- Low-latency ASIO 2.0 (PC); WDM (Windows Vista, Windows XP) and Core
- Audio (Mac OS X) support

I built a dedicated +5V power supply for it and was blown away by what AU$100 (brand new) sound card can do, feature-wise and sound-wise. I used it to digitize all my cassette tapes as full resolution WAV files with great results.

I still use it because it also has an optical digital input (24/96!!!; did I say that it is a crazy stupid great value for money???) as an interface between my TV and my audio system.

You can still find them on eBay. Just make sure you also get the SONAR LE CD, which you will definitely need if you want to use it as an analog-to-digital converter to record the WAV files. This application is a striped-down, fully functional version of their professional SONAR software.

I was so impressed by what I was able to buy for AU$100 that I also bought the Super UA-S10 later on... which I exclusively use as a headphone amplifier - stunning - it was on sale for AU$399. Of course, I built a very high-quality external power supply for it.

My suggestions are not DIY, but you can still do a bit of DIY in a way of building a high-quality power supplies / very low noise voltage regs.
 
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Focusrite Scarlett 2i2 has become the defacto standard for the Voice Over Acting industry since COVID hit. Much more VO content is being recorded in VO Actor's home studios rather than having them go into professional studios for recording.

If SPDIF capability were wanted, and IIRC, it might be necessary to go up to a model Scarlett 6i6 to get that.


My comment: Of course they always use very clear sounding condenser mics (e.g. Rode NT1) with 2i2 since it is not SOA clear itself. Still, its a fairly low cost combination that works for the intended purpose.
 
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