Ti Kan's β22 Amplifier and σ22 Power Supply
April 3, 2007
 amb1.jpg 800x600, 68KB |
 amb2.jpg 800x600, 80KB |
 amb3.jpg 800x600, 60KB |
 amb4.jpg 800x600, 32KB |
 amb5.jpg 800x600, 111KB |
 amb6.jpg 800x600, 118KB |
 amb7.jpg 800x600, 146KB |
 amb8.jpg 800x600, 86KB |
 amb9.jpg 800x600, 62KB |
 amb10.jpg 800x600, 116KB |
 amb11.jpg 800x600, 145KB |
 amb12.jpg 800x600, 125KB |
Also see the official
β22 amplifier,
σ22 power supply and
ε22 backplane board websites.
Brawn and finesse taken to a new height
The β22 is a high-end stereo amplifier for headphones and
speakers. I designed this to be a top-tier amplifier,
as a community service project for the DIY audio hobbyist.
It is capable of driving any dynamic headphone and extract
the optimum performance from the best of them. And it's powerful
enough to serve as a superb low-power speaker amplifier in a moderate
sized room.
Featuring an all-discrete, fully complementary topology
with dynamic cascode and pure class A operation in every stage,
the β22 employs low noise JFETs in the input stage,
high-gain wideband BJTs in the VAS stage, and high-current power
MOSFETs in the output stage. Every detail is carefully considered
for the utmost in linearity even before application of global
negative feedback. And only a moderate amount of feedback is
used to reduce output impedance, extend the bandwidth and
maintain overall stability.
The β22 is designed to be flexible, and can be built in
2-channel passive ground, 3-channel active ground and 4-channel
fully balanced configurations. An optional ε22 backplane
board may be used for a 3-channel active ground configuration,
and makes for minimum internal wiring, improved shielding, optimum
grounding, and improved serviceability.
The companion power supply, σ22, is a dual-rail tracking
regulated wideband design, also with an all-discrete complementary
topology. It has very low noise, low output impedance and excellent
line and load regulation characteristics. It also features MOSFETs
for very high current output capability and reliable operation.
I am now offering professionally-manufactured β22 and σ22
printed circuit boards and some related parts for sale at very
reasonable prices. A limited quantity of ε22 boards is
also available.
For full details please visit the official
β22 amplifier,
σ22 power supply and
ε22 backplane board websites.
This unit was my own build. I use it daily and it
serves as the demonstrator/showpiece in meets and gatherings.
Configuration
These units are configured as follows:
- Amplfier output power MOSFETs biased to 160mA per channel
- All active devices are hand-matched pairs or quads.
- Vishay-Dale RN55D mil-spec 1% metal film resistors
- Vishay-Roederstein film capacitors
- Panasonic FC and Nichicon HE low-ESR high reliability
electrolytic capacitors
- Amplifier voltage gain set to 8
- Alps RK40 black-beauty volume control potentiometer
- Two headphone jacks (can be used for two pairs of headphones concurrently)
- Rear panel input and loop-out RCA jacks, speaker output binding posts
- PSU output voltage set to ±30V
- Corcom 10VR1 AC RFI line filter
- Avel-Lindberg 80VA 30V+30V toroidal power transformer
- Ultrafast recovery rectifiers and snubber capacitors
- Heavy-duty Amphenol-Tuchel locking connectors and wiring for the
power supply to amplifier umbilical cable.
- Custom-made enclosures with aluminum base and acrylic front/rear
panels and top cover. The design of the casing and internal layout
puts a strong emphasis on symmetry, reflecting that of the circuit
topology. The transparent top covers display the beauty of the
circuitry in full glory.
RMAA Test Results
RightMark Audio Analyzer
software, running on a Toshiba 2.8GHz Celeron laptop computer via an
M-Audio Firewire Audiophile
mobile interface running in 32-bit, 96KHz mode.
This test provides data and graphs of frequency response, noise, dynamic
range, total harmonic distortion, intermodulation distortion and
stereo crosstalk performance.
Even though the β22's measured results are excellent, it can be seen
from the loopback graphs that the β22 added almost negligible distortion
to the M-Audio Firewire Audiophile's baseline. Hence, the distortion
measured is predominently the sound interface's performance, not that
of the β22 amplifier.
The slight rolloff at the low end in the frequency response graph is due
to the M-Audio's coupling capacitor. The β22's actual frequency response
is flat down to 0Hz. Likewise, the high-end rolloff in the graph is due
to the M-Audio's anti-aliasing filters. β22's actual response extends
to 2.5MHz (-3dB) in the tested configuration.
The β22's RMAA results remain essentially unchanged whether its
outputs are loaded with 330Ω, 33Ω or 8Ω. Many amplifiers' distortion
performance deteriorate significantly with lower impedance loads, and
the stereo crosstalk behavior degrades. There is no such problem here.
These results amply illustrate the benefits of β22's high-current class A
MOSFET output stage, three-channel active ground topology and the use of
dynamic cascoding in every stage. See the Technical highlights section
for details.
Other Test Results
These were measured with a Wavetek 4MHz sweep function generator,
a Tektronix TDS2014B 100MHz digital storage oscilloscope,
a Protek 6510 100MHz analog oscilloscope and
a Fluke 95 50MHz digital ScopeMeter.
- Input impedance
47.6KΩ
- Output impedance
less than 0.01Ω, 20Hz-20KHz
- Maximum output voltage
(at 1KHz, prior to onset of clipping)
43Vp-p (15.2Vrms) unloaded
38Vp-p (13.4Vrms) into 32Ω
- Maximum output power
(prior to onset of clipping)
0.75Wrms into 300Ω
5.6Wrms into 32Ω
18Wrms into 8Ω
- Frequency Response
(at 1Vrms output, sine wave)
0Hz - 2.5MHz, +0, -3dB
- Rise time
(100KHz square wave, at 43Vp-p output, 10% to 90%)
175nS
- Slew rate
(100KHz square wave, at 43Vp-p output)
198V/µS
Oscilloscope waveforms
The oscillogram waveforms of the β22 amplifier are shown below.
All input waveforms are produced by a Wavetek 188 4MHz sweep function
generator.
The following is the 100KHz square wave response as tested with a
Tektronix TDS2014B 100MHz digital storage oscilloscope. The top trace
is the input and the bottom trace is the output. The rise and fall times
as well as the peak-to-peak output amplitude is shown on the right
hand side of the display.
Below are additional waveforms as measured with a Protek 6510 100MHz
analog oscilloscope. In all graphs except the Lissajous waveform, the
top trace is the input and the bottom is the output.
The square wave graphs show that there is minimum slewing and ringing at
the leading and falling edges. The 100KHz sine, triangle, and Lissajous
graphs also show very small amount of phase shift between the input
and output. Within the 20Hz to 20KHz audio band, there is no measurable
phase shift.
 1KHz square wave |
 10KHz square wave |
 100KHz square wave |
 100KHz sine wave |
 100KHz triangle wave |
 100KHz Lissajous |