A40 Part Substitutions — Nelson Pass / 2000

After 22 years, it appears that quite a few DIY enthusiasts are still eyeing the A40 Class A amplifier design, but are discovering that not a single transistor from this design is still available. The following information is for those scouting out substitute parts: The Lambda output devices are no longer available, and they weren’t that common to begin with. Lambda appears to still be in business, but not in the business of power transistors. Common everyday complementary power darlington transistors will substitute for these. They need to be rated at 75 watts or higher, 5 amps for higher, and… More...

Son of Zen — Nelson Pass / 1997

The Zen has proven to be a popular and enduring do-it-yourself amplifier. The design addresses the audiophile's enthusiasm for singleended amplification, but is even more interesting for its exploration of the performance available at the extremes of simplicity, having only a single gain device. Judging by the mail, more than a thousand of them have been constructed, not including a couple of commercial rip-offs. Incoming mail is an excellent barometer of interest and taste among the readers. Letters suggesting design improvements provide the direction and the excuse to proceed with the Son of Zen. It responds to the following common… More...