News
- December 2008: the ε22 has now been discontinued from
the AMB audio shop. A group-buy may be a future option if there
is sufficient interest,
- Please read the
ε22 PCB v1.00 notes
before using the board. These notes do not apply to v1.1.
Overview
ε22 ("epsilon 22") is a circuit board designed
to serve as a "backplane" for the
β22 stereo amplifier in
3-channel configuration. The three β22 boards
(left, right and active ground channels) are mounted
on the ε22 as "modules", using standoffs.
The ε22 board contains circuit
traces that takes the place of most physical wires, allowing
the β22 amplifier to be built with minimal wiring clutter
in the enclosure. Not only does this make the amplifier internals
appear tidy, the large ground planes provide very low ground impedance
and interference shielding properties, while the optimized trace routing
reduce stereo crosstalk. ε22 also greatly improves the
serviceability of the amplifier. Each β22 board can
be removed as a module simply by removing the mounting screws and
unplugging the board from the backplane.
The ε22 board provides the following connections:
- Front panel connections
- Connections to two stereo headphone output jacks
(Molex KK .100 3-pin headers)
- Connections to left and right volume control potentiometer
or stepped attenuator
(Molex KK .100 3-pin headers)
- Connection to a power indicator LED, optional
(Molex KK .100 2-pin header)
- Rear panel connections
- Connections to left and right audio inputs
(Molex KK .100 2-pin headers)
- Connections to left and right loop-out, optional
(Molex KK .100 2-pin headers)
- Connections to left and right speaker output, optional
(Molex KK .156 4-pin header)
- Connection to DC power V+, G and V-
(Molex KK .156 3-pin header)
- Internal connections
- Audio/ground input connections to each β22 board
(Molex KK .100 2-pin headers)
- DC power V+, G, V- and amplifier output connections to
each β22 board
(Molex KK .156 4-pin headers)
- Positions for speaker output Zobel network resistors and
capacitors (RzL, RzR, CzL and CzL). These parts are
needed only if the amplifier will be used to drive speakers.
- Positions for Ground loop breaker resistor and
capacitor (Rg and Cg).
- The right-rear mounting screw hole connects to the chassis
via a metal standoff. Input signal ground connects
to the chassis through the Ground loop breaker at this point.
If a direct chassis connection is desired, then do not
populate Rg and Cz, and install a wire jumper across Rg.
Schematic diagram
The following is the schematic diagram of the ε22 board.
Parts list
The following is the parts list to populate the ε22 board.
| Qty | description | Part number |
|---|
| 8 | 2P Molex KK .100 header | Molex 22-23-2021 |
| 8 | 2P Molex KK .100 plug | Molex 22-01-3027 |
| 4 | 3P Molex KK .100 header | Molex 22-23-2031 |
| 4 | 3P Molex KK .100 plug | Molex 22-01-3037 |
| 28 | Molex .100 crimp terminal | Molex 08-50-0114 |
| 1 | 3P Molex KK .156 header | Molex 26-61-4030 |
| 1 | 3P Molex KK .156 plug | Molex 09-50-8033 |
| 4 | 4P Molex KK .156 header | Molex 26-61-4040 |
| 4 | 4P Molex KK .156 plug | Molex 09-50-8043 |
| 19 | Molex .156 crimp terminal | Molex 08-56-0106 |
| 2 | RLED1,RLED2 10KΩ 1/8W or 1/4W resistor | |
| 2 | RzL,RzR 22Ω 2W metal oxide resistor | see β22 parts list |
| 2 | CzL,CzR 0.047µF 100V film or multilayer ceramic capacitor | see β22 parts list |
| 1 | Rg 10Ω 5W wirewound resistor | Vishay-Dale CP series or Xicon CR series, see β22 parts list |
| 1 | Cg 0.1µF 250VAC class X or Y film capacitor | see β22 parts list |
| - | Metal standoffs, machine screws, washers, and other hardware | Imperial 4-40 or Metric M3 |
Notes:
- All the Molex KK .156 headers and crimp terminals listed have
gold contacts. Tin-contact versions are also available
at lower prices.
- For non-speaker use, Rz and Cz are not required, and one less
4P Molex KK .156 connector is needed.
- Rg and Cg are not required if PSU is in separate case (jumper
the Rg position to connect signal ground to the amp chassis).
- If loop-out is not used, two less 2P Molex KK .100
connectors are needed.
- If only one headphone jack is installed, one less 3P Molex KK .100
connector is needed.
- If the extra panel-mount LED is not installed, one less
2P Molex KK .100 connector is needed, and RLED1/RLED2 may be omitted.
- The value of RLED1 and RLED2 may need to be changed depending on
the LED.
- The height of the standoffs for mounting β22 boards on the
ε22 board must be tall enough to clear RzL, RzR, CzL and CzR
if these parts are populated.
The circuit board
The ε22 board is made of high quality FR-4 glass epoxy,
double-layer with plated-through holes as well as silkscreen and
soldermask. The copper layers are 2 ounce heavy duty construction for
low impedance. There is a ground plane on each side of the board for
lowered ground impedance and improved shielding.
The dimensions of the board is 9" x 10" (228.6mm x 254mm).
The thickness of the board is 0.062" (1.58mm).
Additional information
Please see the
β22 amplifier website and the
β22 project thread on headwize.com
for further information.
The ε22 board:
With β22 boards mounted:
Copyright ©
Ti Kan
All rights reserved. Commercial use of this design is prohibited
without prior permission.
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