April 2020

We Ask 10 Questions For High-End Audio Manufacturers
Featuring Nelson Pass Of Pass Labs And First Watt
Enjoy the Music.com's 25th Anniversary brings you a new special feature!

  During Enjoy the Music.com's very special 25th Anniversary we're asking various high-end audio manufacturers to answer the same ten questions. Their answers may surprise you! This month we're featuring Nelson Pass of Pass Labs. Pass Laboratories was founded in 1991 by Nelson Pass. Operating out of his shop at home, Pass developed prototypes of a single-ended Class A amplifier design. At the same time, he and Mike Burley were constructing an in-house machine shop with three home-built CNC milling machines with which to produce the amplifiers when the design was finished. The first product, the Aleph 0, shipped in 1992. In 1994 Pass Labs released a newer Aleph design which simplified the circuit from three gain stages down to only two stages and used a newly patented power current source to bias the single-ended output stage. Also in 1994 Nelson was joined by Wayne Colburn, who began working on improved version of the preamp and on a new phono stage. The company received two patents this year, one of them the design that became the SuperSymmetric circuit in use today.

Fast-forwarding a bit, in 2002 the first XA amplifiers were released, combining the X and Aleph topologies into balanced single-ended Class A amplifiers with many of the characteristics of both the X and Aleph series. The XA200 was rated at 200 Watts mono, the XA160 was 160 Watts. Eventually, In 2007, Pass Labs is applying the '.5' advances to the XA series of amplifiers. These revisions are said to dramatically lower distortion and noise and also dramatically improved the performance of the amplifiers into low impedance loads.

Q. What is your first memory of falling in love with music?

A. My mother had a decent record collection and we had music in the house. When I was quite young I had an AM radio tuned to KGO (SF) all night. Weeknights I fell asleep to Ira Blue (talk radio) and woke up at 3am every night when their Jazz DJ played Jimmy Smith's Walk on the Wild Side. By the arrival of the white album, I was hooked.

Q. How did you first get introduced to high-fidelity audio gear?

A. My father's business partner had a Fairchild turntable and tube gear and one of his friends had gone with Heathkit Electronics, one of which I helped assemble. My first taste of separates: Garrard, Radio Shack amplifier, full-range 8" speakers 8" in homemade boxes, later fitted with tweeters. The Radio Shack amplifier had Germanium output transistors that overheated, so I had to modify it for better heat sinking.

In college, I fell in with the audio crowd - Dynaco, JBL, Shure, and McIntosh. In my second year, I was building things from scratch, and by my third year working for ESS.

Q. What is your favorite piece of vintage hi-fi, and why?

A. I admire many of the classics in speaker and amplifier design from the 1940s and 1950s which achieved such great quality of sound. They are the exemplars of simplicity that inspire my work. We have several pair of Tannoy 15" coaxial drivers from the 1960s, that we still use as references, not because they are particularly the best sounding loudspeakers, but because they are very revealing of amplifier differences.

Q. When did you decide to start a high-end audio company?

A. In 1971, after constructing a giant JBL driven horn speaker (The Claw), I formed a little speaker company with a buddy at UC Davis and did a production run of three-way speakers that somehow all got sold at a profit. In 1973 I took a job at ESS about a month before they met Oskar Heil and participated in their transformation from a little garage operation to the big time over the course of two years. It was physics classes by day and ESS by night, and where I met my future wife Jill. In 1973 I graduated and left ESS to start an amplifier company, Threshold with partner Rene Besne who had also been at ESS.

Q. What, and when, was your company’s first product?

A. We shipped the 800A power amplifier in 1975. It was a 200 Watt Class A amplifier using a newly patented circuit that improved efficiency by about 50%. It put Threshold on the map and was the source of income for the first couple of years. At that time Dan D'Agostino was with Dayton Wright loudspeakers, and he introduced many of their dealers to the 800A, as it was one of the few amplifiers that would drive them. ITALICS Thanks Dan!

Q. What challenges did you face during those early years?

A. The usual — not nearly enough money — the company was started on a shoestring.

Q. How have your products evolved over the years?

A. Well, I guess it's been about 50 years now...

When I first started out, I was looking for the best measurable performance, and that gradually evolved into Bart Locanthi's (JBL) philosophy of making circuits as linear as possible and then applying modest feedback. Initially, that meant Class A operation (still does), and techniques such as cascoding to minimize the distortion of the transistors themselves without recourse to feedback. By 1978 this approach resulted in designs without global feedback, the Stasis amplifiers, still manufactured today.

In 1991 I left Threshold and started Pass Labs, shifting my attention to simpler amplifiers operated single-ended Class A. These designs relied even more on the quality of the gain devices, and I abandoned Bipolar transistors for Field Effect Transistors (FETs) having a square-law character similar to Tubes.

In 1995 Pass Labs developed and patented the "Super-Symmetric" circuit, of which the first was the X1000, a 1000 Watts monoblock, with only two stages and local feedback. This circuit remains the mainstay of our amplifier products, having gone through three evolutionary upgrades over the course of 25 years. Currently, we offer fourteen "X" power amplifiers and six preamplifiers .

Starting in 1978 I published a series of simple little Class A amplifiers for DIYers, starting with the A20, followed by the A40 and A75 (with Norm Thagard) and the Zen amplifier series. This activity ultimately morphed into First Watt in 2000 with commercial production as well as additional DIY designs. The most powerful First Watt amplifier is 25 Watts, and the least powerful is about five Watts. Now numbering fourteen with each having a unique design and very limited production.

The F1 and F2 were groundbreaking current source amplifiers using MOSFETs without feedback, the F3 used a newly minted power JFET in a cascode single-ended amplifier and the F4 was a push-pull power follower with no voltage gain. The F5 used only two JFETs and two power MOSFETs to deliver high performance, the F6 and J2 used the new Silicon Carbide power JFETs and NOS Toshiba JFETs, the M2 achieved voltage gain with an input transformer and current gain with a power follower, and the F7 (pictured above) was a lateral MOSFET design with positive current feedback and a fantastic damping factor.

In 2005 I started working with more exotic and unique parts, starting with the Toshiba small-signal JFETs and Lovoltech power JFETs, and in 2008 with the SemiSouth Silicon Carbide power JFETs. Iin 2008 there was an opportunity to have some SIT (static induction transistors) custom-made by the same SemiSouth, power JFETs with curves that resemble Triode tubes and deliver a similar sonic character. They have some advantages over tubes - no heater, long life, and operation at voltages and currents directly compatible with loudspeakers, so no need for output transformers. The results were very successful SIT-1, 2 (pictured below), and 3 amplifiers.

At present, I have acquired an inventory of new and old transistors, and am focusing on the unique character that each of these can bring to audio amplifiers.

Q. What is your company’s most popular product(s)?

A. Last year the product with the most units shipped was the SIT-3, which is coming to an end as we use up the last of the SemiSouth SIT transistors. The XA25 and the integrated amplifiers have become popular, but overall no product seems to dominate our sales, we are how we like it.

Q. What is your next planned product offering and its’ features?

A. That would be telling. We do have some cool stuff coming, though, so stay tuned!

Q. What advancements do you speculate high-end audio will offer ten years from now?

A. I don't spend any time thinking about it. I'm just an old fart having fun refining simple topologies and playing with new parts. No doubt the industry's propeller-heads will continue to dazzle consumers with digital legerdemain and ever more exotic faceplates.

Manufacturer
Pass Laboratories
13395 Airport Road
Suite G
Auburn, CA 95602

Voice: (530) 878-5350
Fax: (530) 878-5358
Email: info@passlabs.com 
Website: www.PassLabs.com