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Reviewer: Srajan Ebaen
Financial Interests: click here
Source: Source: Ancient Audio Lektor Prime, Apple iMac 1TB with AIFF files up to 24/192, Pure Music 1.71 in memory play mode, Weiss DAC2, Burson Audio HA160D as DAC, iPod Classic 160GB, Onkyo ND-S1 digital-direct iPod transport
 Preamplifier: Bent Audio Tap-X (AVC passive), Esoteric C-03 (transistor), ModWrigh tLS100 (tube)
Amplifier: FirstWatt F5 and J2, Linnenberg Audio amp3E [on review]
Loudspeakers: ASI Tango R, Zu Audio Essence
Cables: ASI Liveline
Stands: 2 x ASI HeartSong 3-tier, 2 x ASI HeartSong amp stand
Powerline conditioning: 2 x Walker Audio Velocitor S, 1 x Furutech RTP6
Sundry accessories: Furutech RD-2 CD demagnetizer; Nanotech Nespa Pro; extensive use of Acoustic System Resonators, noise filters and phase inverters, Advanced Acoustics Orbis Wall & Corner units
Room size: 5m x 11.5m W x D, 2.6m ceiling with exposed wooden cross beams every 60cm, plaster over brick walls, suspended wood floor with Tatami-type throw rugs. The listening space opens into the second storey via a staircase and the kitchen/dining room are behind the main listening chair. The latter is thus positioned in the middle of this open floor plan without the usual nearby back wall.
Review Component Retail: €1.948 or $3.000
Unlike many of my reviews which answer manufacturer solicitations, today's occurred in reverse. I was doing the asking.

It all started with Steve Marsh's RMAF 2010 show report mention in these pages of a $3.000 transistor amp from Germany he'd spotted in US importer Jeffrey Catalano's HighWater Sound exhibit [above]. Having been to Jeff's many years ago to appreciate his tastes in exotic hifi—he's primarily a tube man as the next photo shows—the bells tolled for whom but moi. Perusing the maker's home page clinched it. I had déjà vu all over again. This was so very first watt, here by way of a 3-stage 4-transistor class A design pulling an honest 150 watts from the wall to make all of 10 watts into 8 ohms (8 into 4Ω).


Lucky for me—and perhaps you reading this—Ralph Beerschwenger was amenable to my review inquiry. Then he explained his background. "As you suspected, the roots of Audioprojekte are DIY. But it goes farther than that. I'm a 47-year old electronics technician. Audio electronics were my hobby since I was ten. During my professional career I worked in the pro sector mainly in sound reinforcement, recording studios and broadcasting. During this time I gained a lot of insight into how all of the classical and modern instruments, classically trained or Rock/Jazz voices and full orchestras sound in real life.


"I started Audioprojekte as a source for high-end DIY modules and as a repair and upgrade shop. The two latter functions were specifically geared toward more exotic components where solid know-how and voicing skills are required to maintain or even improve sonic performance. Custom commissions on preamp and power amps is another specialty [next two photos]. Audioprojekte itself is very small. I have two helpers and my wife Stefanie runs the front office. By the spring of 2009 we ceased offering parts to concentrate on customer service and production. As you might imagine, during my many years of selling premium parts by Mundorf, Mills, Jensen & Co., I amassed great experience on how to best use them. It was very easy to experiment with different parts in key locations of various amps or line stages regardless of whether those were tube or transistor. All of this was education which would eventually inform my own designs.

"Over the past 20 years I've heard many components of course. To me the best-sounding amplifiers were almost invariably the small ones that made just a few watts. They had simple circuits cleverly finessed to overcome the typical problems of linear amplifiers. Our CA10 is based on the so-called 4-transistor topology. All transistors are operated in pure class A. The amp uses current feedback into a single-ended input stage. It was hard work to find the proper semiconductors for their respective junctions and determine their appropriate operating parameters. For certain technical reasons this kind of topology is very sensitive to the quality of the power supply. Hence it took time to develop a proper supply with very low noise, ripple and good transient response.

"The CA10—that's only my personal opinion of course—sounds warm and full like an Uchida 2A3 tube amp with good musicality but crossed with a quality solid-state amplifier like perhaps an A3 yet without any sonic artefacts that would become objectionable over the long haul. The more and longer you listen to this amp, the more you love it. I lived for months with CA10 prototype boards in my personal setup while developing and fine-tuning the circuit and sound. I've optimized each and every detail to my personal satisfaction about how an amp should sound."


The arc from studio and broadcasting work to repairing then modifying and finally designing electronics has many successful precedents (I'm thinking Roger Modjeski and Dan Wright for just two). It seems to be a far more practical education than any formal university degree could provide. The craftsmanship of Ralph's work also looked impeccable while the pricing was competitive with other low-power transistor precedents by FirstWatt and Linnenberg Audio for just two again. On paper, this had all the makings of a SET outing where 't' stands for transistor and 'SE' are my initials.


The CA10's input stage with current feedback is formed by a resistively loaded single bipolar transistor (the current driving the input transitor varies with the output signal and is used for the feedback loop). The voltage gain stage runs another bipolar part with a constant current source fixed to a low-noise voltage reference. The single-ended output stage runs two bipolars, one for gain, one as load. Circuit gain is a high 24dB, input sensitivity a concomitant very high 0.55V. Bandwidth at -3dB is 5Hz to 150kHz. Input impedance is 100k, internal resistance below 200mΩ. Output noise is below 1mV unweighted from DC to 100kHz, DC offset less than 5mV. Dimensions are 17.7 x 13.4 x 5.5" WxDxH, weight is 32lb. There are no sound-degrading output relays but the power supply deliberately scales up the voltage over 20 seconds to prevent turn-on transients. Fragile high-efficiency drivers are thus deliberately protected. The absence of relays of course also means no hard shut-down. Turning the amp off means music will continue for a few seconds, fade, then progressively distort before evaporating to mute.
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