Pass headphone amp

"My headphone amp, which I have dubbed the Aleph H, is simply a scaled-down version of Nelson Pass' Aleph amplifier series. Nelson Pass has made the unbelievably generous donation to the DIY world of making public the service manuals to all of his designs once they are out of production - and he actively participates online on the Pass Labs Forum at DIY Audio helping hobbyists like myself with our creations. Nelson's single requirement is that we restrict the use of his intellectual property to the creation of products for our own personal use. If you want to contact me looking to buy an Aleph H, go ahead but be aware that I'll have to make some sort of licensing arrangement with Mr. Pass first, assuming of course that he's amenable to the idea.

The Aleph H circuit topology is identical to a Pass Aleph 3 with the exception of substituting a pair of lower power IRF610 MOSFET transistors for the 4 larger IRF244s and adjusting several resistor values to set the proper operating parameters of voltage and bias within the circuit. The Aleph H swings a maximum output of 14V and 0.5A compared to the Aleph 3's stats of 23V and 8A.

I must also point out that like most DIYers, I had some help along the way of creating this amplifier. First, Marcello Pellerano modified the Pass Zen amplifier to create a Zen headphone amp, which he documented at headwize.com and diyaudio.com. Also, 'Grey' Rollins from diyaudio.com created a scaled-down version of the Aleph amplifier, which he called the mini-A intended as a low-wattage speaker amplifier. Next, jwb from diyaudio.com modified the Aleph circuit to produce a headphone amplifier that substituted JFETs for the MOSFETs in the input stage. I studied these design extensively in preparing for my amplifier.

Click to expand...