By John Siau
Most people have seen the CE mark on electronic equipment, but few have had the opportunity to witness the tests that are required to conform to the CE specifications. This post takes the reader on a behind-the-scenes photo-tour of the CE tests of Benchmark's new AHB2 power amplifier.
The CE mark is a manufacturer's declaration that the product has passed a comprehensive set of tests to evaluate the ability of the product to operate in close proximity to other electronic products. This means that the product must be immune to interference caused by nearby products, and that it must not emit excessive interference that could cause problems to nearby products.
There are two parts to the CE tests - immunity and emissions.This photo-tour focuses on the immunity tests.
Photo 1 shows the AHB2 being exposed to high levels of Radio Frequency (RF) interference.
The transmitting antenna (which looks like a giant egg beater) is positioned in front of the AHB2. The spherical object on top of the AHB2 is an RF field strength probe. During these tests, the radio interference is swept over a wide range of frequencies while the product is rotated to maximize exposure on each of four sides.
As a professional product, the AHB2 must continue to operate at full performance under these test conditions. In contrast, consumer products are subjected to lower RF levels and are permitted some loss in performance.
These tests are performed in a shielded room. The high-power radio signals used in these tests must not be allowed to escape the room where they could interfere with radio communications systems. RF absorption panels on the walls help minimize reflections of the RF energy to improve the uniformity of the interfering signal.
Photo 2 shows the AHB2 being exposed to a magnetic field.
The coil induces a magnetic field at frequencies between 50 Hz and 15.75 kHz to test for magnetic immunity. The coil is held at a precise distance while scanning all surfaces of the device under test. The AHB2 has two layers of magnetic shielding, and easily passes this series of tests.
This is part of a special series of tests for rack-mounted professional products. Consumer products are subjected to lower magnetic field levels and are only tested at 50 or 60 Hz. This difference underscores the importance of selecting professional products for use in the studio.
Photo 3 show a technician zapping an AHB2 with a high-voltage discharge. All sides of the product must be able to withstand direct and indirect discharges, and the product must continue to function normally. This test is is designed to insure that your speakers do not make a noise if someone walks across the carpet and touches the power amplifier.
Consumer products are subjected to the same tests but are allowed non-permanent malfunctions. A pop or crackle from the speakers would be considered acceptable from a consumer power amplifier. The standards allow a complete shutdown or reboot of consumer-grade products as long as no permanent damage is sustained.
Photo 4 shows some of the equipment used to expose the product to power line surges, dips, and brownouts.These test standards minimize the chances that a product will fail due to power line surges.
Photo 5 shows some of the apparatus used to inject interfering signals onto the input and output cables of the AHB2. This test shows capacitive coupling of an interfering signal. Other tests use direct injection, while others use magnetic coupling. Together, these test are designed to cover all possible means of interference.
CE tests vary by product type, intended application, and intended environment. See The CE Mark - What Does it Mean, and Why Should I Care? for more background on the CE tests.
The Benchmark AHB2 power amplifier and HPA4 headphone amplifier both feature feed-forward error correction. This correction system is an important subset of the patented THX-AAA™ (Achromatic Audio Amplifier) technology. It is one of the systems that keeps these Benchmark amplifiers virtually distortion free when driving heavy loads. It is also the reason that these amplifiers can support 500 kHz bandwidths without risk of instability when driving reactive loads.
This paper explains the differences between feedback and feed-forward systems. As you read this paper, you will discover that you already understand the benefits of feed-forward correction because you use it instinctively to improve a feedback system commonly found in your automobile. If feed-forward correction can improve your driving experience, it may also improve your listening experience!
If you look at the back of any Benchmark product, you will find balanced XLR analog-audio connectors. As a convenience, we also provide unbalanced RCA connectors on many of our products. In all cases, the balanced interfaces will provide better performance.
We build our unbalanced interfaces to the same high standards as our balanced interfaces, but the laws of physics dictate that the balanced interfaces will provide better noise performance.
This application note explains the advantages of balanced interfaces.
Benchmark has introduced a new analog-to-analog volume control circuit that features a 256-step relay-controlled attenuator and a 16-step relay-controlled boost amplifier. The volume control has a +15 dB to -122 dB range in 0.5 dB steps and is a key component in the HPA4 Headphone / Line Amplifier.
Our goal was to produce an analog-to-analog volume control with the highest achievable transparency. We wanted to be able to place this volume control in front of our AHB2 power amplifier or in front of our THX-888 headphone amplifier board without diminishing the performance of either device. Our volume control would need to have lower distortion and lower noise than either of these amplifiers. Given the extraordinary performance of these THX-AAA amplifiers, this would not be an easy task!
This application note discusses the engineering decisions that went into the development of this new analog volume control circuit. The end result is a fully buffered volume control with a signal-to-noise ratio that exceeds 135 dB. THD measures better than the -125 dB (0.00006%) limits of our test equipment.