The New Jersey-based Orchard Audio has a compact class D monoblock amplifier that outputs 500 watts continuous and 1,000 watts peak into 4 ohms, costs $2,499 each, and it is an analog switching amplifier. The Starkrimson Mono Ultra Premium monoblock, the subject of this review, employs the latest Gallium Nitride field-effect transistors (GaNFET), with inherent superiority in signal response time and thermal performance over MOSFETs, with lower resistance and noise.
Company owner and chief engineer Leonid Ayzenshtat holds a BS and MS in Electrical and Computer Engineering from the New York Institute of Technology. He created four primary sections and stages inside the Starkrimson series of amplifiers, beginning with the input stage, from which the signal flows to the modulator/feedback section, which feeds the dual GaNFET bridged output stages and finally the output filter section. Per Leo:
“The input stage has a 44kOhm input impedance and drives the modulator. The design uses Orchard Audio’s proprietary DC-coupled, fully balanced (differential) dual feedback modulator. This creates the pulse depth modulation (PDM) waveform. The feedback is taken both pre and post filtered. This enables the amplifier to have a very high damping factor as well as have a load independent frequency response. The PDM waveform is amplified by the two GaNFET half bridges. The filter is a very important part of a class-D amplifier. Orchard’s amp uses oversized very high-quality, oxygen-free copper (OFC) inductors and a very high-grade film capacitor. This ensures low distortion across the amplifiers whole power band.”
Traditional MOSFET based switching amplifiers, including ones that utilize FPGA circuits and DSP chips operate in the 300 to 400kHz range of switching frequency, producing a phase shift of 50 degrees or more at 20kHz due to the filter design. The SMUP uses a switching frequency of 800kHz, producing only 7 degrees of phase shift at 20kHz, allowing for the use of a minimalist LC filter and thus producing higher quality in sound. The importance of a precision in phase manifestation cannot be overstated; some companies take such pride in their commitment in maintaining the highest integrity in phase as to name themselves as such.
Per Leo, “With GaNFET devices the open loop performance is much better than with MOSFETS, this eliminates the needs for high-gain negative feedback loops.”
A high level depiction of the SMUP
The Orchard Audio analog class D design’s vanishingly low noise floor piqued my interest in its suitability versus amplifiers using directly-heated triode tubes, such as 211, 833, 300B, etc. in driving extremely sensitive horns. An unflinching Leo:
“I would recommend my 150W monoblocks amplifers vs the 500W that you have. This is because they have an even lower noise floor. These 3 items are where I see the Starkrimson amplifier has an advantage over DHT.
- Noise – Starkrimson Mono Premium amplifiers have an SNR of 121dB at 150W which equates to 98.9dB at 1W or a total noise of just 32uV. Assuming an 8 ohm speaker with 100dB sensitivity from which you sit 6 feet away this equates to a sound pressure level of -1.9dB, completely inaudible. Even with a good DHT amplifier, you are likely to get around 80dB SNR at 1W. For the same scenario above you get a sound pressure level of 17dB of noise.
- Distortion – the distortion of my Starkrimson amplifiers is lower at -94dB with THD+N at 1W, which is already much better than just the noise floor from a DHT amp.
- Damping factor – The damping factor of my amps will be very high compared to a DHT amplifier. This determines how well the amplifier can control the speaker. Even though a speaker is highly efficient it can still be reactive and have varying impedances over its frequency range. This is where an amplifier with a high damping factor will show its advantages more clearly. In my experience, high-sensitivity speakers usually also have a large woofer(s); the high damping factor of my amps will allow for precise control here whereas the bass performance of DHT will not be as good.”
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