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August 2020
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Orchard Audio BOSC / Starkrimson Monoblock Amplifier
Learning just how far digital (switching) technology has evolved.
Review By Ron Nagle


Orchard Audio BOSC / Starkrimson  Class D Monoblock Amplifier Review


  I could give you four reasons to like a Class D switching amplifier and four reasons to prefer a classic tube amplifier. It seems to me its always been like that. But as the years have passed the lines have blurred. These distinctive qualities have inevitably merged and become more and more a moot subject. Remaining are two camps, neither one right neither one wrong.


I recently attended an online Zoom Meeting of the New York Audiophile Society. The meeting featured a relatively new company called Orchard Audio. At that meeting, several members who had auditioned their prototype switching amplifier gave it very high praise. So ever curious I called Orchard Audio and tossed my hat into that discussion.

Warp forward and here I sit looking into a cardboard box. Inside the box there are two black aluminum boxes. I see that the top cover of the box has a very stylized logo of a tree silk-screened in white paint This pair of black boxes are the 150 Watt per channel (BOSC /Starkrimson, same amplifier two different names) switching amplifiers. They are only 2" high and 4.5" wide and 4" deep. Digging a little deeper I unwrap two large black power supplies. They are rated at 56 Volts DC and 4.5 Amps. At one end they have a socket for an IEC power cord and at the opposite end, the cord is terminated in a four-pin Molex plug.


Orchard Audio BOSC / Starkrimson  Class D Monoblock Amplifier Review


That Molex plug Locks into and powers the amplifiers. Along with the supplied connecting cords I asked for and received a set of 1.5-meter speaker cables. One of the advantages of these small box amplifiers is the ability to place them directly behind your speakers. You can order the amplifiers in two configurations. The first version places all the connections on one side of the amplifier, so the speaker connections and the XLR jack and the 4 pin Molex connector from the power supply are grouped together. The other option is to order the amplifier with the speaker binding posts on one side and the XLR and Molex connection on the opposite side. Either version of the Orchard Amplifiers is priced at $1499.99.

Instead of the word BOSC printed on my two amplifiers they have the word Starkrimson silk screened on the cover. I had to ask the designer and founder Leonid (Leo) Ayzenshtat what that meant. He replied that they are the names of two types of pears. "Well I guess there is logic in that since they are manufactured by Orchard Audio."


Salient Features
What this refers too is the stuff inside the box. This Orchard amplifier is referred to as a Class D amplifier most people believe that means Digital. Class D indicates that this is a switching amplifier. There is a lot to commend the amplifier.But by far the single most salient design aspect is the effort to keep the Class D circuit as simple as possible. The amplifier is DC coupled and completely balanced from input to output. The fact that the amplifier is DC coupled means that there is no phase shift and that bass can be more tightly controlled. Added to that is the implementation of Gallium Nitride (GaN) transistors. Gallium Nitride transistors have many listed advantages but basically, they have lower internal resistance and are much faster than more common types.

Since GaN devices can switch faster the dead time is far less than their Silicon counterparts. The GaN transistor allows the Bosc amplifier to switch at frequencies up to 800 kHz. The higher switching frequencies allows a standard LC (Inductive and Capacitor) filter network to work extremely well. The direct result is that the switching artifacts of the Orchard Amplifier are reduced by a factor of 40dB.


Orchard Audio BOSC / Starkrimson  Class D Monoblock Amplifier Review


This is a functional diagram of the dual feedback system (Patent Application) or PWM (Pulse Width Modulator) controller. The DC Modulator works with the feedback network both pre and post to essentially eliminate DC offset at the output. The design enjoys the benefits of the highest quality and larger than necessary board-mounted  components, inductors, and filter capacitors. All of these are placed on a four-layer circuit board. It uses a custom stack-up on a high-end dielectric material and ENIG (Gold) finish. Note: Additional information will be appended at the end of this narrative.


Placing the Orchard components was unusually direct. I used my homemade one-meter XLR cables from my preamplifier to feed the Starkrimson monoblocks. One adaptation was necessary for me to install the individual parts into my system. Since there was no more room on my equipment rack I placed a low table up front between my speakers. That allowed me to use the supplied custom made 1.5-meter speaker cables from the monoblock amplifiers that were now placed on the table. Not necessary, but I Isolated the 56 Volt power supplies by placing them on the floor under the table.


Music From The GaN
Power on and my very first impression was clean and clear music overlapping what was a very dead black background. Let me focus on that reference. Black Background refers to the absence of non-musical electronic/system noise introduced into the sound by circuit components. It is fundamentally important because it allows the music to breathe and to rise and swell naturally. It seems to me at this point that what I am hearing is just about the blackest background I have experienced. First, let me say that the more I sit and listen and to these monoblocks in my system the more the sound seems to improve. And yes, my pessimistic supposedly super hearing Golden Eared friends will tell me that this is a psycho-acoustic effect and I am simply acclimating to the sound. However, I never heard that any digital amplifier would change or need time to break in.

But let me be cautious and not jump to conclusions, I need to put some more hours on these black boxes. After thirty or forty more hours they do seem to have become slightly quieter. My reference and preference is and has been the sound of a human voice. If anything would be the antithesis of digital sound then it would have to be an analog vinyl disk. It very well may be able to highlight some digital artifacts, that's if any are present. Of course, you need to select a very good recording to hear any of these minute details.


Orchard Audio BOSC / Starkrimson  Class D Monoblock Amplifier Review


Let's try one of my favorite go-to albums, Christopher Cross' Another Page [Warner Bros 9-23757-1].The liner notes list additional guest vocals by Micheal McDonald, Carl Wilson, Art Garfunkel, J. D. Souther, Don Henley, Karla Bonoff, and a long list of great guest musicians. This is a studio album but done in such a way that you can look into the mix and pick out some of the people backing the lead vocal along with layers of accompanying instrumentation. On track two, "Baby Says No", when we get to the line: "I really think I've got it bad this time". You can hear a plaintive baritone voice that echoes deep in the background and repeats the words "So Bad".

There's enough clarity and pitch definition that I can hear through the mix to the source, the voice belongs to Micheal McDonald. Cut to the chase, from the beginning till the end the album has, detail, clarity, and focus. At this point, I can't find anything wrong to hang a verb on. Moving right along let me try one of my reference albums, Diana Krall CD that I bought for $4 at my local flea market. This is Ms. Krall's very first debut album:  Stepping Out [Justin Time, Just 50-2]. This is a record label based in Montreal Canada. My favorite track is, "Do nothing till you hear from me". She forms the third part of a trio. And accompanying Ms. Krall on the piano is Jeff Hamilton on Drums and John Clayton on String Bass.

With the Orchard Audio's BOSC / Starkrimson monoblocks pushing notes, there is an unexpected reality that moves forward and sits in my lap. Clayton's bass conveys a crystal clear bass line. That gets resolved to the sound of his finger friction stroking those fiddle strings. Clayton's bass is the sound of a wooden chamber that projects and propels the music into my room. When the lights in my room are turned down low, Ms. Krall's words and phrasing are intimate and real as she seems to sing just for me.


Orchard Audio BOSC / Starkrimson  Class D Monoblock Amplifier Review


The Wrap
During this review, I have learned just how far digital (switching) technology has evolved. A long time back switching amplifiers were used primarily in industrial and military equipment and nothing back then was sophisticated or refined enough to power audio. When the very first CD players came out some writers cautioned Audiophiles to keep their equipment free from the radiated noise generated by the CD players switching oscillators. Let's just say for a long time I was not impressed by CD sound.

Even now I still have my Sony SACD deck plugged into and powered by an isolation transformer. The Orchard amplifiers have two separate dedicated 56 Volt DC power supplies and therefore are essentially isolated from the rest of the systems AC power source. Today none of that seems necessary. The parts quality and simplicity of this Class D solid-state design impressed me as near foolproof and extremely quiet and durable.

I said it previously, yet it is worth repeating. I can find no obvious faults to the way Orchard Audio's BOSC / Starkrimson amplifier reproduces music. At the same time, it is not a SET (single-ended triode) amplifier lovers cup of tea. There is no harmonic halo around any element of the music. Within the useful frequency capabilities (45Hz to 43kHz) of my Aurum Cantus two driver monitor speakers. Additionally, they are constrained by practical small room limitations. The Orchard amplifiers at $1499.99 set a new benchmark for value, laser-like clarity, and inner detail at this price range. Highly recommended.

Remember to Enjoy The Music and from me Semper Hi-Fi.




Sub–bass (10Hz – 60Hz)

Mid–bass (80Hz – 200Hz)

Midrange (200Hz – 3,000Hz)

High Frequencies (3,000Hz On Up)



Inner Resolution

Soundscape Width Front

Soundscape Width Rear
Soundscape Depth

Soundscape Extension Into Room


Fit And Finish

Self Noise

Value For The Money



Type: Class D monoblock solid-state amplifier
Frequency Response: DC to 60 kHz
Sensitivity: 5V in for 150 Watts
Gain: 16.8dB or 6.92
Signal to Noise Ratio (SNR): 121dB (A-weighted)
Residual Noise: 32uV (A-weighted)
THD @ 0.25W: <0.0030% for 20Hz to 20kHz into 8 Ohm
THD @ 150W: <0.015% for 20Hz to 20kHz into 8 Ohm
THD @ 0.25W: <0.0030% for 20Hz to 20kHz into 4 Ohm
THD @ 150W: <0.015% for 20Hz to 20kHz into 4 Ohm
Input Impedance: 5kOhm fully balanced for 16.8dB gain amp
Output Power: 150 Watts RMS
Damping Factor: >550 @ 1kHz
Dimensions: 5.5" x 4.8" x 1.9" (WxDxH not including binding posts)
Power Supply Dimensions: 8" x 3.7" x 1.72" (WxDxH not including cables)
Price: $1499.99



Company Information
Orchard Audio
Voice: (504) 233-3444
Website: www.OrchardAudio.com
















































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