dam1021 R2R DAC and Headphone Amplifier 0.02% tolerance resistors. BUILT IN USA!

dam1021-12 R2R DAC and Headphone Amplifier 
You can buy on ebay too if you like: 

https://www.ebay.com/itm/dam1021-R2R-DAC-and-Headphone-Amplifier-0-02-tolerance-resistors-BUILT-IN-USA/123530785351  

This is a realization of the Soekris dam1021-12 R2R DAC board that is known for its world-class R2R pure analog sound. Never listen to the shrill voice of delta sigma dacs again! 
This unit uses an extremely high quality LINEAR regulated power supply, rather than the cheap switching power supplies used by other DIYers. 
There are two versions of the dam1021 R2R DAC board.  This uses the the higher quality model with the 0.01-0.02% tolerance resistors. 
HAND MADE IN THE USA! SHIPS FROM THE US!
There are two outputs:   - the buffered 4 pin XLR headphone jack  - the unbuffered pair of 3-pin XLR balanced line outputs. These go to your high-quality balanced amplifier. 
There are three inputs:   - a USB digital input (this unit uses the Combo384 USB to I2S Digital Interface which uses the Amanero USB IIS module. Supports DSD512 32bit 384kHz)  - an optical TOSLINK digital audio input.  - a digital RCA Coaxial input. 
AC Power cord is included! 
Short (shorter is better) 3 pin XLR interconnects are included for connecting the unit to an amplifier!
I even soldered the cables you need for firmware update. Just connect your RS232 adapter to the cables and you can update the firmware whenever you want. 
Having said all that, there are THREE major caveats:
1) There is no input selection switch. It automatically searches for the first active input it finds. 
2) If you want to listen with headphones, you need to unplug the line out connections. I would recommend using it either with headphones without any line out connection or exclusively with line out to an amplifier. 
3) Even though the line out is unbuffered, its level is still controlled by the volume knob (Don't ask me why, I didn't design the board). Set it to be near the highest level at which you don't hear clipping. This is more or less with the knob pointing straight to the right. 
Unit weight: 4 lb 12 oz (2.14 kg)  Unit dimensions: 8" x 5.5" x 3" 
The dam1021 is a DAC module based on a discrete R-2R sign magnitude DAC design, with FPGA based FIFO buffering/reclocking and custom digital filters, < 1 ps jitter clock generator, with 28 bit resolution so there is headroom, oversampling up to 3.072 MHz. Up to 24 bit / 384 kHz input from SPDIF, I2S and USB (via USB to I2S interface board), with isolation on the I2S interface. The board is very flexible, with digital volume control and filter parameters that can be downloaded. The board is fully firmware upgradable over a simple serial connection, which enable new features later on. Now full support for DSD when using firmware version 1.05 or newer.

The basis R-2R network has an output voltage of 1.4V RMS and output impedance of 640 ohm and can therefore drive a lot of things directly. There is also onboard balanced output drivers that also can drive high impedance (e.g. 300 ohm) headphones directly. 

The harmonic distortion gets better with more precise resistors. The more precise resistors have smaller temperature drift and better long term stability, and therefore will be better in the long term.
Please don't hesitate to ask questions. 
I accept payment only via PayPal.