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Audio DAC with AD1865




Circuit AD1865 is considered like best 18bit stereo audio DAC ever. It is not recommended for new constructions and probably is not manufactured now. However it is still available on EBay. Circuit has SNR 110dB and THD+N 0.003%. It requires symmetrical voltage +/-5V and it has current and voltage output.

Circuit description

Supplying need two separated windings on power transformer, because I used positive voltage regulator for negative supply branch. After rectifiers B1 and B2 are filter capacitors C1 and C2 and behind them group of block capacitors. I used available low-drop voltage regulators LE50. One is for supplying of digital part and two are for positive and negative analog part of dac. Closely to regulators and integrated circuits are small filter and blocking capacitors.

DAC doesn't have I2S input, which is usual. It has individual data inputs for left and right channel and individual "latch" inputs which rewrites data from internal register to DAC. Circuit is in two variants, because DAC has 18bit data format input and some SPDIF decoders knows only 16 or 24 right justified output. For connecting with DIR9001 I have to connect additional shift register IC6 which delays data for 6 bits. With this modification DAC works with 24bit right justified format. SPDIF decoder CS8414 knows 18 bit output, but I didn't have them.

Data are in sequence shifted in to the internal shift register of dac first for one channel and after switch of LRCK for second channel. For changing of channels we must latch signal negate for right channel. This connection introduce effect, that left and right channels are not played simultaneously and they are time shifted. It usually doesn't matter, because it is not hearable. It can be theoretically hearable on headphones. it can be solved with 32 bit shift register which delays data for one channel, registers in a dac will be fulled simultaneously and rewriting to dacs will be at one time. Unconnected inputs of IC5 must be connected to ground, because there can be parasitic oscillations.

For analog output I used current output and passive I/V converter with resistors R1 and R2. This output should be highest quality specially with high quality resistors but it must not be very loaded. It should be connected to preamplifier with short cable.

18bit version schematics diagram

Schematics of AD1865 dac - 18bit version schematics of 18 bit version in Eagle 5 format

24bit version schematics diagram

Schematics of AD1865 dac - 24bit version schematics of 24 bit version in Eagle 5 format


We assemble PCB from smaller parts to bigger. We begins with SMD parts and next with parts with wires. First I installed IC5, eventually IC6 and after them SMD capacitors. Circuits we can solder with small soldering iron and small 0.5mm tube tin. In case of emergency we can use transformer soldering iron and bigger tin. When some of pads will be connected together, we can exhaust overflowing tin with solder wick. Next I installed resistors and small capacitors from top side and next voltage regulators, connectors, dac and big capacitors.

18bit version component view

Component view of dac with AD1865 - 18bit

24bit version component view

Component view of dac with AD1865 - 24bit

18bit version PCB

PCB is single sided without wire junctions. It help as to make them in amateur conditions. SMD parts are from a bottom side and parts with wires and connectors are from a top side. Supply wires are designed with accent on right ground wiring and junction of analog and digital ground in a one point. Block capacitors are very close to circuits. PCB has four assembling holes for mounting with screws.

PCB of DAC with AD1865 - 18bit version PDF format Eagle5 format

24bit version PCB

Board is almost identical to 18bit version. In addition includes circuit IC6 and blocking capacitor C21. This board is suitable for connecting with DIR9001 SPDIF decoder.

PCB of DAC with AD1865 - 24bit version PDF format Eagle5 format


Top view Bottom view - 18bit version Bottom view - 24bit version


SMD capacitor have 1206 size which help with soldering. Integrated circuits in SO14 package we can solder too. Except AD1865 circuits, which I bought on EBay are all components commonly available.

Part list
name value and type quantity
R1, R2 200R 0.5W 2x
C1, C2 4700uF/25V elektrolytic 2x
C3-C8 47uF/10V low ESR elektrolytic RM2.5 6x
C9-C20 100nF SMD1206 ceramic 12x
C22, C23 4n7 SMD1206 ceramic 2x
IC1 AD1865 1x
IC2-IC4 LE50 3x
IC5 74HC04 SMD SO14 1x
J1 Molex 3pin 1x
B1, B2 Bridge rectifier 1.5A/100V 2x
SV1 Jumper ribbon 6 pins 1x
X1, X2 Frame terminal AK300/2 2x
Additional parts for 24bit version
C21 100nF SMD1206 ceramic 1x
IC6 74HC164 SMD SO14 1x



First I built 18bit version. When I had only noise from output that I got across that with 24 bits right justified data will be 6 bits shifted out from a shift register of dac and they must be delayed. I easily solve these troubles with 74HC164 circuit. Analog output sounds great and looks very nice on oscilloscope. I must only built DAC in a box and finish preamplifier.