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What compelled you to launch a hifi company at this time in general and out of Greece in particular? Did you have a matured circuit on your hands you wanted to commercialise?
The lack of post 2009 job availability in Greece definitely played its role in my decision to launch a company. Because hifi had been my hobby for many years already to where I had gained personal experience with circuits and topologies, I thought why not turn my hobby into a full-time job? I already had a working prototype of a 20-watt class-A single-ended monaural power amp and a class-A single-ended preamp. Even so I wanted to launch with a more 'commercial' product. Hence I decided on an integrated amplifier. I knew from the beginning that my timing was completely off due to the global economic downturn but I also thought that if I tried hard I would gain a small share of the market.

What is your background in audio engineering? Tell us what led up to the formation of Black Pearls Audio and how you arrived at this name.
I have an Msc in controls engineering and the theoretical knowledge required for power circuits and stability. However audio electronics follow their own rules. It takes a lot of trial and error to understand what works and most importantly, why it does. It requires a lot of reading, Internet research and practical implementation of many circuits and topologies. The name of the company was the result of long brainstorming sessions. I didn’t want a Greek name like an ancient god or city. That’s what every Greek company does and I’m pretty sick of it. I’m not the 'proud to be Greek' type. There’s nothing to be proud of in our late history, not to mention our current situation. I would definitely be proud to be Greek in 400 B.C. but alas, we live in 2013. My  generation must deliver something worth talking about so that the following generations will have something to be proud of. So I was seeking a name that denoted something precious, desirable and prestigious—a thing that expensive high-end equipment can sometimes be—and that’s how I came upon Black Pearls.

How did you decide on a 70wpc integrated amplifier as your first product (a CD player is next I assume since your packing box already offers that tick-off option)?
As I said earlier, most of the circuit was already up and working, reliability was looking good so I had the product needed for a quick company launch. The CD player is on its way. A rough estimate would be around May 2013.

You're combining single-ended class A preamplification with a minimalist (2 transistor per side) Mosfet push/pull current buffer. Is this a simple two-stage circuit then or do you run multiple stages of voltage gain? Why did you prefer this output device to a bipolar transistor or power Jfet? What is your view on feedback, either global or local?
The preamplifier is made up of 3 stages, 2 voltage gain stages followed by a buffer that drives the power stage. The two voltage gain stages are capacitor coupled while the buffer stage that follows them couples directly to what precedes it but is again capacitor-coupled to the following and final power stage. Mosfets are well known for their 'tube' sound and in comparison tests sounded better than bipolars. That is, they worked better in my implementation which might not be the case in another design. My experience shows that everything has to be matched correctly. A circuit or component that provides good results in one design might be a total disappointment in another. Jfets were not suitable for my existing circuit but will certainly be evaluated in a new circuit. I’m very skeptical about negative feedback. Although it produces nice numbers for measurements, it affects the sound in a way I don’t like. I don’t mean to say that every design featuring local or global feedback is bad. It's just that I haven’t been able to benefit from negative feedback until now. I’m still experimenting though.

The presence of a headphone output suggests that you're actively listening to headphones. How does this output derive its signal - directly from the main outputs with a voltage divider to diminish its gain plus perhaps some additional buffering for impedance compensation? What is the approximate output power into 25, 50, 100, 300 and 600Ω?
I don’t personally listen to headphones a lot but thought of it as an extra feature that would be welcome. The headphones are driven directly from the speaker output stage through a series power resistor. This has advantages and disadvantages. The advantage is that your headphones get the same quality sound your speakers get but at the expense of some background noise. Headphones have very high sensitivity. If the circuit's noise floor isn't low enough it gets audible. The approximate output power is 0.325Wrms into 25Ω, 0.53 Wrms into 50Ω, 0.77 into 100Ω, 0.88 into 300Ω and 0.7Wrms into 600Ω [the most efficient power transfer thus occurs between 100 and 600 ohms - Ed].