Cheap headphone amplifier integrated with DAC
Goal
+ good quality headphone amplifeier;
+ good quality DAC;
+ integrated device for cost reduction (one power supplly and one housing);
+ headphone amp. and DAC board must have common voltage of power supply;
Key elements:
+ A-class headphone amplifier board, chinese clone on Lehmann topology with some improvements (rectifying diodes, caps, heat radiators);
+ dual single DAC board, chinese board with dual AK4490EQ chips;
+ toroidal mains transformer;
+ power supply section separated with grounded board;
+ volume potentiometer by ALPS version with SMD resistor ladder (attenuator);
+ DAC output and headphone input selectors made by ELMA (low resistance connectors);
+ DIP8 socket for operational amplifiers chips (possible changeover);
Project realisation
* On following pictures has been shown some major assembly steps.
* I have choosen Mini ITX housing MODECOM FEEL 302 because of low price and compact size. Before buiding I have check dimesions of boards and other main elements but without cables. With all cables it was reaaly difficult to fit into this case. Some larger case would better solution for this kind integrated device;
* Front and rear panels of mini-itx housing do not fit for DAC and Amp device, so new ones has been made (CNC - wood, laser cut - wood and plexi).
* All mechanical elements for assembly has been made by laser cutting of plexi or by printing 3D of PLA;
* Aluminium knobs comes from old devices (refreshed by polishing);
* ELMA selectors let to use DAC and head phone amp. as a separate devices (RCA inputs and outputs on rear plate);
* Small fan 70mm size power supplied with only 7 vdc is almost noiseless but seems to be necessary due to A-class head phone amp. board (around 40*C on heat radiators of transistors);
* On second hand market was an opportunity to buy used discrete op-amps SPARKOS LAB;
* Because power transformers are oversized (both are 50W) that is why 5vdc output has been placed on rear plate for additional device (like USB or BLUETOOTH audio receivers);
Summary
Device is quite big and heavy in comparison to other headphone amps. But it has integrated DAC and it is powerfull. There is no problem to drive poor efficiency headphones. Tested with planar around 90dB headphones (TAKSTAR HF580). Enjoy has been reached in less than 50% of volume setup. For future developing stays I2S connection into DAC via ETH port (not connected yet).
