Project files: The Zen Headphone Amplifier

What is it?
The board files for my Zen Headphone Amplifier “remake” shown here.

How big are the boards?
The board measures 3.575” x 3.75” (app. 91 x 95 mm). This is obviously for a mono-channel.

What is the status of the boards?
The boards are version 1.0. The prototypes seem to work well and there wasn’t really anything that needed changing in my view.

Does it use any special/expensive/hard-to-find parts?
Not really.

Anything else I need to know?
A few things:

  • Heatsinks: The basic type for me here in Europe is the Fischer SK129, but there are many manufacturers of this profile. The board is designed for the heatsinks to be soldered in place with pins, but screw-mounted versions might work as well. You can use 1″/25mm heat sinks, but in that case I recommend to tune the bias a little lower. My prototype measured app. 240 mA of bias and the heat sinks seemed to stabilise at around 55C in free air, which probably is a bit too much when the board is cased. So, either turn the bias down a bit and/or use taller heat sinks if your case allows for it.
  • Adjustments: Space around R10 and R12 is quite tight, especially with heat sinks/output caps taller than 25mm. In order to easily be able to adjust bias and balance of the amp, my suggestion would be that you don’t trim the leads of the two resistors completely flush but leave enough of the resistor legs that you can connect crocodile clips to them on the underside.
  • Output capacitors: The recommended value is 2 x 470uF from the original schematic, but if you’re using low-impedance headphones I think you should consider 2 x 1000uF instead. This is one place where I think “audiophile” capacitors can’t hurt, so look for Nichicon Muse (KZ/KW, FG/FW, ES etc.), Elna Cerafine/Silmic capacitors or similar. Bypassing the electrolytics with small film capacitors is easily done on the underside of the board if you want to.
  • Transistors: The Q3 footprint on the board is for a BC550C, but the original ZTX450 from the schematic can be used as well if it’s turned 180 degrees. Remember also to match at least the two Q2 FETs between channels as described in the build article. If you buy 8-10 of the IRF610 FETs you should be able to get a couple of very tight matches and the leftovers can be used for the current source (Q1).

Download design files here

Related information:
See the original post for some more information and links to the build article for this design. After posting I actually also managed to find the original headwize article cached here – amazingly it seems that most of the headwize library has been kept intact there! 🙂

Note: Always read the “intro post” for additional important information about my designs.



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