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Is it a Tripath clone? I asked Jason: "The heart of the Icon is a patented NuForce class D IC, the NF12X201."
From the high resolution photos posted on Icon website, I noticed that the NF12X201 looks identical to the Texas TPA3004D2 in every respect. Why the similarity? "Brand switching is intended." That's why the two have exactly the same power output, measurements and number of pins. But that's where similarities end. The Texas IC has a 32-step DC volume control as well as a line output for an external headphone amp and can drive speakers as low as 4 ohms. The NuForce IC is purely dedicated to class D amplification with an external volume pot (a stepless 10K pot in this case) and a discrete headphone amplification circuit to optimize headfi performance. Jason guards their proprietary design with zeal-ed lips but is very proud of their headphone amp. He slipped something though: "This is proprietary to Nuforce. Basically, we convert the incoming DC to +/- 15V to suitably power all the internal circuits to maximize dynamics. The headphone amp is constructed with differential bi-polar drivers with a DC-coupled output."
NuForce vs. TI

Catching on, I tried to pry into the secret with a new question: The two SMPS - the small one is 15VDC/1.6A/24W max, the optional larger one is 12VDC/4.2A/40W max. My understanding of Tripath chips is that the VDD voltage correlates directly with output power vs. THD and noise. "Tripath's IC is not exactly a closed-loop design and hence more susceptible to power supply quality, resulting in many DC power tweaks out there. The NuForce circuit is a closed-loop circuit and the feedback corrects some of the SMPS noise. With our S-1 speakers, there should be enough loudness from the 24-watt SMPS. We will be offering a $45 45-watt SMPS for the Icon in a few weeks. The 45-watter I sent you wasn't final but close enough."

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DC rail integrity is critical to class D amplification and NuForce has been perfecting its know-how from day one. Inside the tiny Icon, a big black NuForce audio-grade NH15 DC-to-DC converter dominates the circuit board, joining forces with other proprietary audio-grade capacitors to optimize the DC current feeding the NF12X201. The Icon powers up with a ceremonial transient pop like all NuForce and Tripath amps. That's understandable. But one of the Icons I received produced right after the pop a very high-pitched noise which gradually lowered in pitch before subsiding after about 20 seconds. (By request, Jason had sent me two loaners to bi-amp.) This wasn't very loud but clearly audible. "This is normal. The performance should be the same after the initial power-up self oscillation has settled down. The SOA (self-oscillating chip) might take longer to lock to the correct oscillating frequency. They don't all behave exactly the same." About three seconds seems to be the norm. Fortunately, the oscillating sound soon disappeared after a few weeks and I never heard of it again. [My loaner never exhibited this behavior at all - Ed.]

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From the Icon forum, I learned more about the ingenious combination of self-oscillation and negative feedback that forms the backbone of the Icon's unique approach to class D amplification. "The principle of NuForce amplifiers is based on self oscillation with the speaker as part of the loop... Unlike traditional class-D amplifiers that utilize a constant PWM to modulate the audio signal, NuForce amplifiers employ a self-oscillating circuit that switches the MOSFET at 500kHz and utilizes an ultra-fast feedback operating at 1MHz to correct for THD almost instantaneously... The feedback network takes the error at the output and inject at the input summing junction to cancel out harmonic distortion. However, when there is no music, a Nuforce amplifier may have a higher background noise. It is adding noise to the system in an attempt to cancel out distortion but when noise is the only signal present, it can't be cancelled out. The result is a higher noise floor when putting the ear next to the speakers."