Pass Labs Zen amp


With some schematics from Nelson Pass, and more than a few helpful tips from the diyaudio community, this amp came together fairly painlessly in about 5 days. And, with my choice of quasi-adequate heatsinks, the amp not only drives speakers, but can burn a fingertip off in mere seconds.


my, chris, what a nice protoboard you've got.

 circuit bottom
ah god! the horror!

The amp is powered by two el-cheapo "SIGNAL" transformers (7A at 48V each, I'm running the 230V models at 115, so there's about 24V at the 48 tap. not bad for $7.50 a piece), going into one rectifier and filter section.  So, the amp is almost a dual-mono, except I only have one rectifier and cap filter section.  Actually, only one channel is done, so it's a mono-mono.  Notice the clumped-on nature of the fan, which was put on in an effort to not make the amp so super hot.  It sort of works.  The fan's a bit noisy, and being that my dorm room is, well, a room, I might have to convert my closet into the "amp room."


Before I got the transformers, the amp ran on a separate variac, but now that the two are installed, the whole thing weighs more than anything.  So, it's both impractically heavy, and unreasonably hot.  yeah audio!

Finger-burning aside, the amp is pretty groovy.  I haven't run it on any special speakers, but so far I dig how it sounds.  It's pretty hum-free, and so long as the preamp isn't overdriven, nice and clear.  I don't have any fancy preamps lying around, so it's been running off the "rec out" of an old receiver, sourced from the headphone out of a portable cd. player.  When I get back to school, it can run off the preamp out of a DB-series Sony receiver, but I'm not sure that will change anything.  

My gratitude to Nelson Pass for his plans, and the people on diyaudio for their ready help.  And my dad's shop-owning friend who welded the chassis.  And Apex Jr. Surplus, for the cheapest, biggest transformers ever.


nothing says serious like one of those computer-type power sockets (they have an actual name, probably).  It took me 400 hours and a few drillbits to chew a hole out of the chassis big enough to get the socket in, but that detachable power cord is sure nifty.

mmm, plug