Boston Audio Society
Amplifier Test Clinic
Saturday November 22, 12:00 Noon to 6:00 PM
The BAS Amplifier Test Clinic
The BAS is known for high-quality test
clinics. During our 42 years, we have set standards at our
clinics for testing amplifiers, preamplifiers, CD players,
recording tape, headphones, microphones, and more. Some
have been adopted industrywide.
On November 22 we will hold another
pace setting series of tests in an effort to help consumers
choose the best amplifier for audio playback or to uncover
a reference amplifier with standards that lead the industry.
Our primary test tool will be the AudioGraph,
a Swedish company, home of the PowerCube. The PowerCube
is a unique piece of test equipment that measures an amplifier's
output voltage across 20 loads. The loads have impedance
magnitudes of 8, 4, 2, and 1 ohm, and phase angles, capacitive
to inductive, of -60°, -30°, 0°, +30°, and
+60°. The PowerCube adheres strictly to IHF 202 signal
standard to create informative three-dimensional (3D) graphs
of voltage versus impedance and phase at a single frequency,
typically 1 kHz.
Critic (opens a PDF
in a new page) was the first magazine to use the
new method for assessing dynamic power output. The PowerCube,
a software-driven automated instrument with a PC front end,
measures the maximum voltage the amplifier can deliver into
the load at 1% distortion for a duration of 20 ms at 1 kHz.
The graphic output of the instrument shows the 20 data points
connected to form a more or less cubelike polyhedron, which
illustrates at a glance the true dynamic performance of
the amplifier. The test takes only a few minutes per channel.
Under ideal conditions the voltage sourced by the amplifier
should be a constant. Amplifiers, in PowerCube, will look
like the Figures below.
Our literature search revealed that
amplifier testing is spotty, some consider it a black art,
and some manufacturers are reluctant to give you all the
known specifications for their amplifier into real
world loads/conditions. There are numerous standards
but wide disagreement on how and what measurements correlate
to a quality playback experience in a listening room.
In addition to the PowerCube results,
our tests will include: (1) frequency response into an IHF
load, and (2) distortion at a moderate playback level.
How Do I Signup / Participate?
The clinic will be held in Wayland,
MA. At the clinic, you will be charged $5.00 for each amplifier.
After completing the form below, email it or snail mail
it to the Boston Audio Society, POB 260211, Boston, MA,
02126. You will be notified of the exact time to arrive
with your amplifier.
Please bring your amplifiers accessories
if it is unique and required to test your unit. We will
have on hand standard XLRs, phone, and phono input/output
connectors. You will receive a printed copy of your tests
results. We will notify you in advance of the actual time
to arrive at the Clinic and the address. If you do not have
an amplifier to test, you are invited to attend the clinic
to observe. However, you must return this form including
only your name and e-mail address. We will forward the address
of the clinics location.
for the form. (opens into a new page)