REVIEW / MEASUREMENTS: Pass Labs / First Watt SIT-2 stereo Class A amplifier. [And Stereophile steps in with MQA yet again...]

 

Greetings all. For this post, as you can see above, I've got something exotic to review / measure here at chez Archimago. It's a Pass Labs / First Watt SIT-2 stereo amplifier which was made in limited quantities back around 2011-2013.

This amplifier comes with a nice backstory; that of the silicon carbide (SiC) "Static Induction Transistor" which you can read about here (aka V-FET). The thought is that these transistors behave in a "triode-like" manner, hence perhaps they will be able to convey a "tube-like" sound. Furthermore, this device follows the general audiophile philosophy of "simplicity and minimalism" (quoted from the manual) as principles that would result in a device sounding "good". As such, this amplifier has only a single SIT gain stage, operates in Class A, built with minimal components, employs no feedback, and as expected, accepts single-ended input only.

Online I found this user manual and Japanese product flier for those wanting a bit more information from the company. The cost of this amplifier when it first came out was around US$5000.

OWNER'S COMMENTS: Pass Amp Camp Amp (ACA) 1.1 by Mitch Barnett

[What follows are comments from Mitch Barnett, the owner of the Pass Amp Camp Amp 1.1s that I listened to and measured. I appreciate Mitch's input on the matter, it's a great example of how owners of the ACA might put them to use in one's system, recognizing one's needs.]

Thanks Arch for the great time with your family for a fun night of good food, wine and of course music and movies. Great job on the objective measurements and subjective listening impressions, “It actually sounds good…” with the caveat of not asking too much from the amp. In my mind, this is the dichotomy between objective measurements versus what sounds good to our ears.

MEASUREMENTS: Pass Amp Camp Amp (ACA) 1.1. The crossroads between objectivism and subjectivism, and reconsidering von Recklinghausen.

Back in 2012, Dana Brock, Nelson Brock, and Mark Cronander (aka Variac) organized an "Amp Camp" in Northern California at the Brock's ranch. Nelson Pass, well known among audiophile circles, contributed with one of his designs and I'm sure they all must have supervised the participants as they went about soldering and building those first kits. The result was a simple, solid-state, Class A amplifier to take home. This amp was of course the Amp Camp Amp (or ACA) which we'll be talking about and measuring here.

You can see Pass' article introducing the amplifier with schematics and measurements. What a great idea! There is no substitute for the value of experience and the memories of building something, especially while sharing with a loved one; regardless of the subjective or objective performance of the final product.

The ACA has developed a healthy following over the years - check out the long-lived discussion thread on diyAudio. Nothing official, but I heard over the grapevine that there have been >2000 kits sold, suggesting conservatively >2500 actual stereo amps out there with no accurate way to estimate non-kit PCBs, unofficial "clones", or just completely DIY builds with the published schematics.