When shopping for a new power amplifier, the biggest concern for most when considering a Class A amplifier for audio/ video installations is heat. Building a Class A amplifier that is capable of driving the majority of today’s loudspeakers correctly, makes excess heat and cooling even more important to a purchasing decision. There are several methods for cooling audio amplifiers, the most common being electric fans and or the addition of heat sinks. Besides being a mechanical device that can clog or fail overtime, fans are not optimal for Class A amplifiers. Usually when an amplifier's temperature increases so does the fan speed allowing for efficient cool down. This works great for a Class B or A/B design as the harder the amplifier is being driven the hotter it becomes while the increased fan speed cools it down more quickly. Because Class A amplifiers are at their very hottest when sitting idle, fans would be on at full speed creating unwanted noise during the very quietest musical passages or when no music is playing at all.
We chose to use oversized internal heat sinks to cool our amplifiers. The more heat sink area the more heat is dispersed overall, keeping the unit cooler. Most output stages are in an open space where heat is openly distributed, in BSC Audio amplifiers they are tightly grouped in the most efficient way to maximize thermal stability and focus heat dissipation. BSC Audio’s unique placement of the heat sinks within the chassis centralizes the thermal area effectively creating a heat tunnel. The heat rises virtually straight up through the top cover openings and quickly to the ceiling. Unlike an externally mounted heatsink where the heat radiates outward, quickly warming up the surrounding area, the heat tunnel approach fills the highest point in the room with heat, where it takes much longer to settle downward to the listening position. Additionally, external heatsinks are typically very sharp and can cause serious injury to adults, children, and or pets in some cases.
The bias control switch on BSC products is not a gimmick, or form of sliding bias scheme, but an elegant solution to a long standing problem. Class A amplifiers draw a lot of power from the wall. Many times music is played in the background or during social interactions where focused listening isn't the main objective. In those cases, a lot of extra power is wasted and unwanted heat is continually generated during Class A operation. Energy usage being of major concern to our collective future at large, facilitated the addition of a bias level control switch. BSC Audio is a strong proponent of fixing the bias at a specified level and leaving it there to minimize the settling time of the output transistors. Even in a Class A/B design leaving the device On as much as possible and leaving it there adds to the performance envelope.
BSC Audio is not the first company to offer a Class A On/Off switch. Since at least the 1970’s there have been components offering this option, but to our recollection none of them was really class A to begin with, as they didn’t have the cooling capacity to actually work correctly, and when switched On or Off the sonic difference was not apparent. Despite the earlier examples having no apparent value we looked more closely into the concept and how it related to the modern audiophile.
We determined that with correct implementation you could indeed boast a full class A amplifier, but also offer a High bias class A/B and even a low bias class A-B variant. Utilizing a mechanical switch to select levels was the first step in maintaining a current. The bias switch allows "on the fly" reduction of class A bias on the output stage by 50% and eventually to approximately 98% or what we call ECO mode. This adjustment effectively makes the amplifier a High Bias Class A/B and Class B amp respectively when the bias level is reduced. The listener can now vary the amount of energy and heat used during a particular listening session without changing the maximum power output capabilities. It is quite handy in home theater installations as well. When critical listening is paramount, switch to 100% bias mode and within minutes the full performance capabilities are restored.
All BSC Audio components begin with a base of thick machined or folded 6061 aluminum. The 5 Series amplifiers employ a dual chassis design, whereas the 1/8” thick internal chassis is used as a skeleton to support and brace the circuit boards, power supply components, and external chassis structure. The internal chassis alone is more than adequate and could be used on its own as a stand-alone chassis. BSC Audio Believes the chassis is a big part of the sonic presentation. Great measures are taken to isolate and or increase the structure in such a way to minimize the mechanical interaction of the circuitry to the outside world. When a circuit vibrates the motion creates an instability in the circuit which translates to additional noise in the signal path. Albeit low level these subtle changes when compounded over the entire chassis affect the global noise floor or the “blackness” in the sonic presentation. Heavy machined aluminum plates are then bolted to the sub chassis to enhance the anti-resonant structure as well as add the cosmetic industrial design elements.
The industrial design of our products is first and foremost determined by the performance criteria. Knowing the heat sink and power supply area will be large, maximum effort is put into the chassis design itself and the placement of various sub-assemblies to minimize external surface area. Precision component placement tolerances along with ergonomic circuit layouts allow us to compress to maximum density and reduce the overall size of our units ready to integrate into most listening environments and commercially available audio furniture without compromising on rigidity or resonance control.