Parts list
The table below lists the recommended parts for the ε12 rev 1.2
circuit. See also 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
more details).
Items shown in
italic are available from the
AMB audio shop.
| Part | Quantity | Description |
|---|
| Circuit board |
|---|
| - | 1 | ε12 printed circuit board |
| Potentiometers |
|---|
| VR1* | 1 | 3/8" multi-turn cermet trimpot 1KΩ |
| Resistors |
|---|
| R1, R2* | 2 | 1/8W 1% metal film resistor 3.32KΩ |
| R3*, R4*, R5*, R6*, R7*, R8* | 6 | 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 | 1 | 1/8W 1% metal film resistor 475KΩ |
| Capacitors |
|---|
| C1, C3, C4* | 3 | tantalum capacitor 22µF/25V |
| C2 | 1 | multilayer ceramic capacitor 0.1µF/50V (X7R or C0G) |
| C5* | 1 | film capacitor 1µF/63V (MKT or MKS) |
| C6*, C7 | 2 | non-polar electrolytic capacitor 100µF/16V
(Note: C7 does not need to be non-polar, a standard polarized electrolytic will also work) |
| Integrated Circuits |
|---|
| U1* | 1 | TI/Burr-Brown OPA551PA high-current operational amplifier |
| U2* | 1 | Texas Instruments TL081CP JFET-input operational amplifier |
| Transistors |
|---|
| Q1, Q3*, Q4* | 3 | NPN small signal BJT 2N3904 |
| Q2* | 1 | PNP small signal BJT 2N3906 |
| Q5 | 1 | NPN small signal darlington BJT MPSA14 |
| Diodes |
|---|
| D1 | 1 | 24V 500mW zener diode 1N5252B
(12V 500mW zener diode 1N5242B for single supply, non virtual ground amplifiers) |
| D2, D3*, D4* | 3 | small signal diode 1N4148 |
| Miscellaneous |
|---|
| K1 | 1 | 12VDC DPDT relay Omron, Fujitsu or Tyco (see comments below) |
| * | 2 | DIP-8 socket |
| * | 1 | Aavid-Thermalloy 580100B00000 DIP-8 clip-on heatsink (for U1, optional) |
| - | 2 | Aavid-Thermalloy 575200B00000 TO-92 clip-on heatsink (for Q1, Q2 if supply voltage > ±18V) |
| - | 1 | 2-circuit 0.100" pin header and receptacle |
| - | 1 | 8-circuit 0.100" pin header and receptacle |
| - | - | hookup wire |
| - | - | 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.
Relay
The following relays are recommended:
These are "high sensitivity" types with low coil current.
If you use a different relay, use one with a DC 12V coil, and a coil current
lower than 15mA to prevent false triggering and to reduce
Q1 and Q2 transistors' heat dissipation.
The relay must fit the footprint and pinout configuration of the board.
Opamps
Do not substitute the U1 opamp with another type. The
OPA551
is chosen specifically for its high output current and low output impedance,
and low input bias current characteristics, which are essential for this
application.
The U2 opamp (TL081CP) may be substituted with others, but only FET-input
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 to the TL081 are TL071, LF411,
LF351, LF356, LF357, or other low-cost FET opamps in a DIP-8 package.
Transistors
For Q1, Q3 and Q4, virtually any small-signal NPN TO-92 transistor will work.
Alternatives to the 2N3904 are 2N4401 or 2N5088. For Q2, you may use
2N4403 or 2N5087 instead of 2N3906.
For Q5, this should be a darlington NPN TO-92 transistor
with Vce greater than 25V, Hfe greater than 5000
and Ic greater than 100mA. Alternatives to
the MPSA14 are: KSP13, KSP14, KSP25, KSP26, KSP27, MPSA13, MPSA27,
MPSA28, MPSA29, 2N6426, 2N6427, 2N7052, 2N7053, BC372 or BC373.
If you use other transistor types than those listed above, be sure to
verify the pin-out compatibility.
Diodes
The ε12 PCB has 0.300" lead spacing for the D1 and D2 diodes,
and 0.200" lead spacing for D3 and D4.
- D1: 1N5252B, or any 24V 500mW or greater zener diode with a DO-35 or
DO-41 casing
(1N5242B 12V 500mW zener diode for amplifiers with single supply and
no virtual ground)
- All other diodes: 1N4148 or 1N914
Resistors
Almost all 1/8W resistors fit nicely, and some 1/4W
resistors should also fit. The Vishay-Dale RN55 series will barely fit,
but the RN60 won't.
The resistors specified are 1% metal film type, but the budget-minded can
use 5% carbon film type. The ε12 PCB has 0.300" lead spacings
for all resistors.
Trimpot
The VR1 trimpot is a 1KΩ 3/8" multi-turn cermet trimpot.
Any of the following series are recommended:
- Vishay-Sfernice T93YA
- Vishay-Spectrol 64W
- Vishay-BC CT94W
- Vishay-BC CT9W
- Bourns 3296W
- Murata PV36W
Capacitors
- C1, C3, C4:
These should be tantalum type rated at least 25V.
Tantalums are superior to aluminum electrolytic type for this application.
The lead spacing is 0.100" on the ε12 PCB, and the maximum
body diameter is 0.200".
- C2:
This should be a multilayer ceramic type (X7R or C0G/NP0). The lead spacing
is 0.100".
- C5:
This should film-type. A metallized polyester (MKT or MKS) box capacitor
is recommended. You may also use metallized polypropylene (MKP) or
polycarbonate (MKC) types. There are holes on the PCB
for 0.200", 0.300" or 0.400" lead spacings.
- C6:
This should be a non-polar
(also known as "bi-polar")
aluminum electrolytic type rated at 16V or higher. The lead spacing
is 0.2", and the maximum body diameter is 0.400".
- C7:
This does not have to be non-polar,
but it doesn't hurt to use the same specification as C6 to make ordering
easier. The lead spacing
is 0.2", and the maximum body diameter is 0.400".
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