BorderPatrol DAC SE USB + SPDIF Review

Publisher’s note: Doug Schroeder, in conversing with Gary Dews, owner of BorderPatrol, found him “perfectly polite and technically succinct,” which inspired him to write this review in the style of notation form of the Owner’s Manual. This review is separated into two parts, namely a Q&A section, followed by the review observations. Per Doug: “Do not mistake brevity for lack of enthusiasm. Enjoy!”

Since Doug has given us a break this time by writing a sub-8,000 word Review, we’ll let him off.

The Q&A

Doug Schroeder: The DAC SE uses copper for chassis. Why?

Gary Dews: The use of copper for the casework was a spin-off from the BorderPatrol amplifier designs. Early BorderPatrol amps were made with steel and aluminum chassis. There was a noticeable difference in sound between the two. Steel imparted a glare and grainy character to the sound. Aluminum by comparison sounded lighter, more free and more airy but was also somewhat frenetic and unruly by comparison. I was lucky enough to hear amplifiers made by Audio Note Japan and to meet the legendary late Mr. Kondo several times. We discussed amplifier design and I asked him why he used copper for the chassis of his amplifiers. He told me it was not for looks and that copper sounded better than steel and aluminum. He spoke about calmness, tone color, quietness of background, noise floor (audible, not measurable) and freedom from grain. I had copper chassis made for my amplifiers and the difference was clear. When I realized I could use copper casework for the DAC and still make it relatively affordable it seemed like an obvious think to do. Anyone that thinks the chassis material does not play a part in the sound of a product hasn’t done the work.

DS: The DAC SE uses a ladder DAC in a tube circuit. Why?

GD: I was aiming to make an affordable DAC that sounds refined, clean, relaxed, fluid, colorful and human and free from the artificial ‘hi-fi’ sound that characterizes so many budget designs. Lots of DAC’s have dazzling specs but sound machine-like and obviously digital. Information is one thing, but it needs to be presented naturally with recognizable timbre and tone. Not many DAC’s achieve that. In my experience R-2R NOS DAC designs usually sound refreshingly open and natural rather than processed and synthetic. They usually have cleaner, sweeter treble than DAC’s with over-sampling. I thought a NOS design was a good place to start.

I have been designing high-end 300B tube amplifiers for over 25years. The amplifiers are notable for their elaborate power supplies, component quality, casework materials and for not using negative feedback (NFB). Much of the knowledge I have accumulated designing SET amps went into designing the BorderPatrol DAC. In many ways the DAC resembles a BorderPatrol 300B power amp in that it uses a minimalist audio circuit surrounded by high quality passive components and fed from a very high quality linear power supply. Also, unusually for a product of this price, it is encased in copper casework. There is no over-sampling (NOS) or digital filtering so, much like a triode tube amplifier that does not use negative feedback (NFB), what goes in at one end comes out at the other with minimal manipulation of the signal.

DS: The DAC SE uses a linear choke input filter in its power supply. Please explain.

GD: The power supply is a linear choke input filter design, not a switch mode. It uses twin power transformers in a novel distortion cancelling arrangement. Rectification is a hybrid tube/solid state hybrid design that uses a EZ80 tube rectifier in parallel with low noise high speed diodes snubbed by resistors and capacitors. The DAC will work with the tube turned ON or OFF. The supply topology is choke input filter in which the rectifiers feed directly into a high inductance choke.  An ELNA Cerafine reservoir capacitor is used and each of the digital chips has its own voltage regulator. The chassis tray, cover and tube holder are made from copper. Only the faceplate is made from aluminum.

The sound of any product is a sum of the circuitry, parts, materials and the power supply.  Everything has a sonic signature. There are many notable features in the DAC: the NOS R-2R DAC circuit, the high quality output and power supply capacitors, the copper chassis, but if there is such a thing as the ‘star of the show’ it’s the power supply which is significantly more sophisticated than the supplies usually found in DAC’s, regardless of price. During development the power supply began as a solid-state diode, choke input filter design. It sounded very good from day one but it gradually evolved over time with the addition of snubbing techniques, the development of the twin power transformer system and finally the addition of the tube rectifier. Each step made the DAC sound more refined, less edgy, less ‘digital’ and more natural and musical.

BorderPatrol is still the only company to my knowledge that applies tube rectified, choke input filter power supplies to digital circuits and before anyone shouts ‘Lampizator’ there are two crucial differences. One: Lampizator use chokes in the power supplies to the output tubes, which is an analogue application, not digital. Two: Lampizator supplies are capacitor input filter designs, not choke input filter.

Audiophiles know that the quality of the power supply matters: The market for power chords and power conditioners is large yet lots of equipment is equipped with low quality power supplies like switch mode or low cost linear types because the designers would rather spend the money somewhere else. That’s a mistake in my book.

The DAC works with or without the tube turned on. There are some that prefer the DAC with the tube turned OFF arguing that it has subjectively wider bandwidth that way. Most prefer it with the tube turned ON preferring the extra body, depth, warmth and listenability. Some use the DAC with the tube turned OFF when listening at low levels and turned on when playing louder. Whatever works! I turn OFF the tube from time to time. I like the DAC either way but almost subconsciously I usually end up turning it back on.

DS: The DAC SE does not support DSD. Why?

GD: I am not opposed to hi-res: I think my desert island DAC (that’s the DAC you want with you when marooned on a desert island with no chance of rescue) would be a high-res NOS R-2R design with a great power supply etc. but that would probably be very expensive.

Designing affordable products in many ways is much more challenging than designing statement products. Choices have to be made. Given the choice between a good NOS Redbook R-2R DAC with a great power supply etc. and a hi-res delta-sigma design with all singing, all dancing specs and a ‘just enough to make it work’ power supply I’d go with the NOS Redbook DAC every time. Interestingly, the lack of Hi-res hasn’t really been an issue. Some people (like me) never threw away their CD’s and even if they copied them to hard drive, the files are still Redbook quality. Only a tiny fraction of the music available is in hi-res and it is likely to stay that way for a long time.