The table below lists the recommended parts for the ε12 v2
circuit. See the "Parts recommendations and options"
section below for further details. Parts designated with an asterisk (*)
should be omitted for single-supply amplifiers with no virtual ground
(see the Instructions section for
Items shown in
italic are available from the
AMB audio shop.
|-||1||ε12 printed circuit board|
|VR1*||1||3/8" multi-turn cermet trimpot 1KΩ|
|R1, R2*||2||1/8W 1% metal film resistor 3.32KΩ|
|R3*, R4*, R5*, R6*, R7*, R8*, R12||7||1/8W 1% metal film resistor 10KΩ|
|R9*||1||1/8W 1% metal film resistor 100KΩ|
|R10*||1||1/8W 1% metal film resistor 1KΩ|
|R11, R13||2||1/8W 1% metal film resistor 475KΩ|
|C1, C3, C4*||3||low-ESR electrolytic capacitor 100µF 25V|
|C2||1||multilayer ceramic capacitor 0.1µF 50V (X7R)|
|C5*||1||film capacitor 1µF 63V (MKT or MKS)|
|C6*, C7||2||non-polar electrolytic capacitor 100µF 16V or 25V|
|U1||1||Texas Instruments TL082CP dual JFET-input operational amplifier|
|Q1, Q3*, Q4*||3||NPN small signal BJT BC546B|
|Q2*, Q6||2||PNP small signal BJT BC556B|
|Q5||1||N-channel small signal enhancement mode MOSFET 2N7000|
|D1||1||24V 500mW zener diode 1N5252B or BZX55C24|
12V 500mW zener diode 1N5242B or BZX55C12 for single supply, non virtual ground amplifiers
|D2, D3*, D4*, D5||4||small signal diode 1N4148|
|K1||1||24VDC DPDT relay Omron, Fujitsu or Tyco|
12VDC DPDT relay for single supply, non virtual ground amplifier
(see comments below)
|PWR||1||2-circuit Molex KK 254 pin header and crimp housing|
|IN, OUT||2||4-circuit Molex KK 254 pin header and crimp housing|
|-||10||Molex 254 crimp terminals|
|-||-||PCB standoffs, screws and other hardware|
Parts recommendations & options
Most components are non-critical, and you may substitute with
other parts with similar specs. Be sure the parts you choose are
compatible with the footprints, lead spacings and pin-assignments
of the PCB. There is no need to use "boutique-grade"
components in this circuit.
For a standard ε12, the following 24VDC relays are recommended:
For use with non virtual ground, single-supply amplifiers, a 12VDC
relay should be used:
These are "high sensitivity" types with low coil current.
If you use a different relay, use one with the correct coil voltage
specifications, and a coil current lower than 15mA to reduce
Q1 and Q2 transistors' heat dissipation. The relay must fit the
footprint and pinout configuration of the board.
The U1 opamp
may be substituted with others, but only FET-input
dual opamps with low input bias current are recommended.
Do not use opamps with very wide bandwidth and high slew rates because
those characteristics are not necessary in this application, and may
lead to unstable operation. Alternatives are
LF353N or other
low-cost dual FET opamps in a DIP-8 package.
If you use other transistor types than those listed above, be sure to
verify the pin-out compatibility.
- Q1, Q3, Q4:
BC546B (NPN small signal transistor, TO-92)
- Q2, Q6:
BC556B (PNP small signal transistor, TO-92)
2N7000 (N-channel small signal enhancement mode MOSFET, TO-92)
The ε12 PCB has 0.300" lead spacing for the D1 diode,
and 0.200" lead spacing for D2, D3 and D4.
or any 24V 500mW or greater zener diode with a DO-35 or
12V 500mW zener diode for amplifiers with single supply and
no virtual ground)
- All other diodes:
Almost all 1/8W resistors fit nicely.
1% metal film or 5% carbon film types may be used.
The ε12 PCB has 0.300" lead spacings for all resistors.
The VR1 trimpot is a 1KΩ 3/8" multi-turn cermet trimpot.
Any of the following series are recommended:
- C1, C3, C4:
These should be low-ESR electrolytic type rated at least 25V.
The lead spacing is 0.100" (2.5mm);, and the maximum
body diameter is 0.240" (6.3mm).
This should be a multilayer ceramic type (X7R). The lead spacing
is 0.100" (2.5mm).
This should be film-type. A metallized polyester (MKT or MKS) box capacitor
is recommended. The holes on the PCB support a capacitor with
0.200" lead spacing and no larger than 7.5mm x 5.5mm footprint.
- C6, C7:
These should be non-polar (also known as "bi-polar")
aluminum electrolytic type rated 16V or 25V. The lead spacing
is 0.138" (3.5mm), and the maximum body diameter is 0.315" (8mm).
- Molex KK 254
pin headers, friction lock
(choose vertical or right angle, gold or tin plating):
- Molex 22-11-2022 (2P, gold-plated, vertical)
- Molex 22-23-2021 (2P, tin-plated, vertical)
- Molex 22-11-2042 (4P, gold-plated, vertical)
- Molex 22-23-2041 (4P, tin-plated, vertical)
- Molex 22-12-2024 (2P, gold-plated, right angle)
- Molex 22-05-3021 (2P, tin-plated, right angle)
- Molex 22-12-2044 (4P, gold-plated, right angle)
- Molex 22-05-3041 (4P, tin-plated, right angle)
- Molex KK 254
- Molex 22-01-3027 (2P)
- Molex 22-01-3047 (4P)
- Molex KK 254
(choose gold or tin plating):
- Molex 08-55-0102 (gold plated)
- Molex 08-50-0114 (tin plated)
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