Omicron is:
- A compact, ultra-low distortion headphone amplifier that we developed jointly with @Rus2000 from the RCL-electro.ru forum
- Designed to work with 32 to 600 ohm headphones and tested with a range of over-the-ear and on-the-ear cans from AKG, Beyerdynamic, Grado, Klipsch, and Sennheiser but proved to be equally at ease with lower impedance 16 and 8 ohm headphones, such as AKG's K3003 3-way in-ear monitors; the ubiquitous white Apple EarPods (tethered ones, both 1st and 2nd generation) sound great with Omicron, too!
- Very musical, with pure, clean, liquid sound and perfect clarity even in the most harmonically complex pieces.
The sound immediately fascinated me so much that I began listening without adjusting the quiescent current. You want to turn up the volume, no mess, even the quietest sounds are clearly heard, but at the same time the sound is very comfortable, not harsh, a beautiful three-dimensional scene. Very nice bass. In short, top notch!
... sounds flawless and works equally well. [...] The claimed <140db probably holds true because this design sounds cleaner and smoother than anything ive built and that includes single opamp setups and well known discretes.
This amp is fantastic, I've been listening away and taking notes for a better review, spent a few hours last night playing games with it, worked wonderfully. It really blows all of my other headphone amps and line amps out of the water. The clarity is surreal.
Last night compared Omicron with my composite LT1210 based headamp. At first, it seemed that the LT1210 sounds softer and more beautiful, but after listening to Omicron for about an hour, I switched back and realized that now I want an Omicron for myself! With the same tonal balance, it gives an accurate, fast, assertive bass and better conveys space. Sounds great on good recordings.
Features:...the sound really is fantastic. [...] It's a huge step up from [...] bottlehead crack with the speedball upgrade.
The soundstage is really amazing with my hifiman cans and there's a wonderful amount of detail. Very liquid sounding and the amp just seems to do everything right. The amp runs very cold too, the case never even gets warm.
- Vanishingly low distortion: with THD and IMD better than -140dB (0.000 01% - that's only 100 parts-per-billion), Omicron is an order of magnitude more linear than other "high-performance" and "ultra-high performance" amplifiers
- Compact: Just one IC and two transistors per channel
- Inexpensive, commonly available parts (NE5532, BD139, BD140; just $42 at Mouser for the whole BOM)
- Easy through-hole construction (NEW: a smaller board with easy-to-hand-solder SMT parts has been developed, see its photo above)
- Functionally complete: One 80×110mm (60×90mm for the SMT version) board carries two amplifier channels, a sensitive DC protection for your headphones and an optional (switchable in the SMT version) cross-feed circuit, which helps create a realistic soundstage in headphones
IMD 19+20kHz, 5Vpp @32ohm (see post #11 for more measurements):
Theory of operation:
- Schematic design: post #2
- Mod: increasing input impedance: post #67 (this mod is now the stock version and part of the BOMs linked below)
- Loop gain (simulated): post #27
- Crossfeed schematic and frequency response: post #33
- DC protection: post #34
- Power supply: post #35
- Distortion, clip, frequency response: post #11
- Distortion and clip for the SMT version with no heatsinks and half the quiescent current: post #109
- Through hole Omicron board
- Schematic: post #295
- Board outline: post #142 - includes a discussion of how to fit Omicron into 1U enclosure
- Part list: post #155
- Winding the output inductor: post #71
- Mod: crossfeed switch board by @gajira: post #334
- SMT Omicron board
- Power supply board
- Assembly guide: post #225
- Choosing volume control: post #170
- Mod: running Omicron from +/-12V rails
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