Hi-Fi / AV






Ref. No


Price (Inc. UK V.A.T.)


Headphone Amp









  • High Quality Construction
  • Compact Design
  • Alps Rotary Pot
  • Burr Brown Audio Amps
  • Double Sided 1 Oz Copper PCB


Qty : HPA1 Checkout






The HPA 1 headphone amplifier is a derivative of the famous CMoy circuit but with a few modification to improve the use and performance. These improvement that are listed below have not only made this headphone amplifier look and function well but have improved crosstalk and noise reduction to achieve a well balanced, dynamic and transparent amplifier.






The Circuit :-



Audio :- Using the famous CMoy circuit as the basis of the design we immediately decided that we should use the best IC's throughout so as not to compromise the audio signature of the original source, to this end we used the Burr Brown OPA134PA devices that are renowned for their quality and high specification. Using a separate IC for each channel also has the added benefit of keeping the crosstalk between channels to a minimum




Power Supply :- Due to the use of a single 9V supply derived from a PP9 battery some form of power supply splitting is necessary,some designs use simple resistors to split the supplies and can have inherent problems. We have used a Texas Instruments dedicated supply splitter in our design to achieve a true balanced 50/50 split of the 9V supply, also as an improvement we have used the more expensive version of this supply splitter the TLE2426CP which has built in supply noise reduction




Volume Control :- We experimented with a number of volume controls and found the Alps pot to be the best performer all round. We selected a version that has a push button on/off mechanism which is not easily switched off accidentally like a toggle switch.




PCB :- As can be seen by the images the printed circuit board has been designed to be neat and compact, it is manufactured from FRC4 1 oz copper board and incorporates two layers. One layer contains the power and signal tracks, signal tracks are separated and screened. The second layer is a complete copper screen to keep noise and pickup to an absolute minimum. Also worth noting is that our design is completely board mounted and has NO extraneous leads that can induce pick up (except of course the battery lead)




Front Panel :- Keep it simple, 3.5mm jack input and output sockets. Volume control with an easy to use knurled chromed steel knob and a 2mm LED mounted on a brushed stainless steel front panel




Case :- A moulded plastic case that has a detachable battery cover to make changing the battery easy




The HPA1 is a well thought out headphone amplifier and will enhance the sound of most portable equipment such as MP3 players, iPods and MD. It is also excellent for producing higher volume levels for loud environments and drives difficult headphones with ease. The HPA1 is a great all round performer that has qualities that belie it's size and price tag.

(C) B.K.Electronics 2004 E&OE