X-Altra HPA-1 Class A Headphone Amplifier
The HPA-1 is a compact high performance class A headphone amplifier that will deliver up to 1.75W into a 32 Ohm pair of headphones. The amplifier features ultra-low distortion, very wide bandwidth and class A operation up to 13 V pk-pk into 32 Ohms. Beyond 13V pk-pk into 32 Ohms, the OPS transitions to class AB operation.
The circuit combines a dual ultra-low distortion opamp, the LM4562, with a discrete power output stage. The complete amplifier, including the opamps, runs in class A.
The document below discusses the design and presents the measurements:-
The Excel spreadsheet below contains the BOM with Mouser Part Numbers (updated 21st March 2021):-
The price of the HPA-1 PCB is $15.99 excluding shipping which is $9.50 to the USA, Canada, Europe, Israel and South Africa and $15 to the rest of the world. Shipping takes 3-5 working days for Europe, USA and Canada, and 5-7 working days for all other destinations. Kindly note prices do not include any taxes or duties applicable in your jurisdiction.
Here are a new set of measurements I did where I replaced the LM4562 opamps with FET input OPA1642 devices. The measurements are very good, and the capacitive load driving ability also excellent.
Hi Nick, thanks for your question. Its basically the same amplifier but slightly tweaked. The original design did not run the 2nd stage opamp properly in class A – the X-Altra HPA-1 does.
Hi Andrew.
Is X-Altra Mini II HPA-1 a replacement of Hifisonix HPA-1 ?
And what’s wrong with the old version ?
Regards
Nickson
Hi Nickson,
I’m working with a guy from diyAudio who is designing one. Will take a few more weeks.
Cheers
Andrew
Hi Andrew
How about PCB for this project?
Regards
Nickson