Parts list for standard configuration
The table below illustrates a standard configuration σ22 PSU,
for ±30VDC output rails. One σ22 PSU in this configuration
is capable of supplying up to four β22 amplifier boards, if the
amplifier is intended to drive headphones only. Multiple σ22
boards and/or larger offboard heatsinks should be used, if the β22
amplifier is intended to drive speakers. Please refer to the
Board & heatsinks section for heatsink
considerations.
See the sections below for specific parts
recommendations and options. Items shown in
italic are available from the
AMB audio shop.
| Part | Quantity | Description |
|---|
| Circuit board |
|---|
| - | 1 | σ22 printed circuit board |
| Resistors |
|---|
| R1, R2, R8, R9, R11, R16, R17 | 7 | 1/8W 1% metal film resistor 10KΩ |
| R3 | 1 | 1/8W 1% metal film resistor 1KΩ |
| R4, R5, R6, R7 | 4 | 1/8W 1% metal-film resistor 100Ω |
| R10 | 1 | 1/8W 1% metal-film resistor 6.81KΩ (see notes below) |
| R12, R13, R14, R15 | 4 | 2W 5% metal-oxide resistor 0.47Ω |
| Capacitors |
|---|
| C1, C2, C3, C4, C16, C17 | 6 | multilayer ceramic capacitor 220pF |
| C5, C6 | 4 | aluminum electrolytic capacitor 2200µF 50V (see notes below) |
| C7, C8, C18, C19 | 4 | metallized polyester capacitor 1µF
|
| C9, C10, C13 | 3 | aluminum electrolytic capacitor 100µF 63V (see notes below) |
| C11, C12 | 2 | aluminum electrolytic capacitor 470µF 63V (see notes below) |
| C14, C15 | 2 | film capacitor 3900pF |
| Transistors |
|---|
| Q1, Q3, Q4, Q9, Q10, Q12 | 6 | NPN small signal BJT BC546B |
| Q2, Q5, Q6, Q7, Q8, Q11 | 6 | PNP small signal BJT BC556B |
| Q13, Q14 | 2 | International Rectifier N-channel power MOSFET IRFZ24N |
| Q15, Q16 | 2 | International Rectifier P-channel power MOSFET IRF9Z34N |
| Diodes |
|---|
| D1, D2, D3, D4 | 4 | 8A ultrafast recovery rectifier MUR820 |
| D5 | 1 | 12V 500mW zener diode BZX55C12 (see notes below) |
| LED | 1 | Your choice (superbright) |
| CR1, CR2 | 2 | Current regulator diode 2.4mA 1N5307 |
| CR3, CR4 | 2 | Current regulator diode 4.7mA 1N5314 |
| Power transformer |
|---|
| - | 1 | Avel-Lindberg Y236356 2x30V 80VA toroidal (see notes below) |
| Miscellaneous |
|---|
| - | 4 | TO-220 extruded heatsink Aavid-Thermalloy 529802B00000 1.5" |
| - | 4 | TO-220 heatsink mounting kit (if required, see notes below) |
| - | 1 | heatsink thermal compound (if required, see notes below) |
| - | 1 | 0.200" 4-circuit terminal block |
| - | up to 4 | 0.200" 3-circuit terminal block |
| - | 1 | 0.200" 2-circuit terminal block |
| - | 1 | IEC power entry receptacle with fuse |
| - | 1 | power switch (optional) |
| - | 4 | circuit board standoffs or spacers |
| - | - | hookup wire |
| - | - | heat-shrink tubing |
| - | 1 | chassis case (your choice, see below) |
| - | 4 | rubber feet for chassis case |
| - | - | imperial #4-40 or metric M3 machine screws, hex nuts |
| - | - | other hardware as needed |
Parts recommendations & options
To obtain the blank σ22 circuit board and some related parts,
visit the
AMB audio shop.
You can get almost everything else from the vendors listed on the
AMB Audio DIY Page. The
favorite vendors are
Mouser
and
Digi-Key.
The following is a list of recommendations and options. Please read
through this carefully before you order any parts.
Resistors
- All except R12-R15: 1/8W or 1/4W 1% metal film type
Lead spacing 0.400"
- R12-R15: 2W 5% non-inductive metal oxide or metal film type
Lead spacing 0.700"
- Xicon
MO series
(Mouser 282-0.47-RC or Mouser 262-0.47-RC)
- Panasonic
ERG2S series
(Digi-Key P0.47W-2BK-ND)
Notes about R8 and R10
The voltage gain of the positive error amplifier is determined by the ratio of
R8 and R10. This gain, multiplied by the D5 zener diode voltage, determines
the output voltage of the positive regulator.
The gain is computed by the formula:
G = (R8 / R10) + 1
When R8 is 10KΩ and R10 is 6.81KΩ, the gain is 2.5.
With a 12V zener diode as D5, then the positive rail output voltage
is 30V. The negative rail will automatically invert and track the
positive rail so its output is -30V.
Please do not change the value of R8, because it forms a RC time constant
with C16 which shapes the high frequency response of the error amplifier.
These values were carefully tuned to provide extended bandwidth while
maintaining stability.
The following table gives a list of example R10 values and the appropriate
zener diode to use for some common output voltages. Other combinations
of D5 and R10 values may be used to achieve different voltages.
| Output voltage | R10 value | Zener diode (D5) |
|---|
| ±36V | 4.99KΩ | BZX55C12 (12V) |
| ±30V | 6.81KΩ | BZX55C12 (12V) |
| ±27V | 7.87KΩ | BZX55C12 (12V) |
| ±24V | 10KΩ | BZX55C12 (12V) |
| ±15V | 39.2KΩ | BZX55C12 (12V) |
| ±12V | not installed | BZX55C12 (12V) |
| ±9V | not installed | BZX55C9V1 (9.1V) |
| ±5V | not installed | BZX55C5V1 (5.1V) or LM336-5.0 (ADJ pin unused) |
Notes about R16 and R17:
R16 and R17 are the current limit resistors for the LED.
The optimum value of these resistors depends on your choice of LED. Use this
online LED resistor value calculator
to determine what value your R16 and R17 should be.
Depending on the value of the resistor and the voltage drop across it,
you should be mindful to use a resistor rated at high enough power.
The actual power dissipation is computed by:
Watts = V2 / R
where V is the voltage dropped and R is the value of RLED.
For example, if you use a 10KΩ resistor and the voltage dropped
is 29V, then the power dissipation will be about 0.08W. In this case a
1/8W or 1/4W resistor will work fine.
Since there are two current limit resistors, if they are equal in value,
then each will drop half of the voltage.
Note that the voltage supply to the resistors and the LED is taken
across the rails, so on a σ22 configured for ±30V,
the total voltage is 60V.
The type of resistor is not critical as long as it fits well.
Capacitors
- C1-C4: multilayer ceramic capacitor (NP0 or C0G)
220pF
Lead spacing 0.100" or 0.200"
- C7, C8, C18, C19: metallized polyester film capacitor
1µF
Lead spacing 0.200"
- Wima
MKS2 (AMB audio shop; Mouser 505-MKS21/63/10)
- Vishay-BC
MKT370
(Mouser 594-2222-370-11105; Digi-Key BC1622-ND)
- Vishay-Roederstein
MKT1817 (Mouser 75-MKT1817510064)
- AVX BF/BQ series
(Mouser 581-BF074D0105J; Digi-Key 478-3367-ND)
- C5, C6: aluminum electrolytic capacitor low-ESR high-reliability
Lead spacing 0.300", 18mm diameter (2 per rail) or
Lead spacing 0.400", 25mm diameter (1 per rail)
- For ±30V output or below:
2x 2200µF 50V or 1x 4700µF 50V
- Panasonic
FC
(Digi-Key P10335-ND)
- Panasonic
TS-HA
(Digi-Key P6682-ND)
- Nichicon
HE
(Mouser 647-UHE1H222MHD6)
- Nichicon
PW
(Mouser 647-UPW1H222MHD)
- Nichicon
FW
("boutique")
- Vishay-BC
136 RVI series
- Elna
Silmic or Cerafine
("boutique")
- For ±36V output:
2x 1500µF 63V or 1x 2700µF 63V
- C9, C10, C13: aluminum electrolytic capacitor 63V low-ESR high-reliability
100µF
Lead spacing 0.200", 10mm or 13mm diameter
- C11, C12: aluminum electrolytic capacitor 63V low-ESR high-reliability
470µF
Lead spacing 0.200", 13mm diameter or
Lead spacing 0.300", 18mm diameter
- Panasonic
FC
(Digi-Key P10351-ND)
- Nichicon
HE
(Mouser 647-UHE1J471MHD)
- Nichicon
PW
(Mouser 647-UPW1J471MHD6 or 647-UPW1J471MHD3)
- Nichicon
KZ (Muse),
FW or
FG
("boutique")
- Vishay-BC
136 RVI series
- Elna
Silmic or Cerafine
("boutique")
- C14, C15: metallized polyester film capacitor
3900pF
Lead spacing 0.200"
- AVX BF/BQ series
(Mouser 581-BQ014D0392J, Digi-Key 478-3399-ND)
Notes about C5, C6:
For each rail, the circuit board has holes for two 0.300" pitch,
18mm diameter 1500µF 63V or two 2200µF 50V capacitors,
or for one 0.400" pitch, up to 25mm diameter 2700µF 63V or
4700µF 50V capacitor.
Notes about C5, C6, C9-C13:
63V capacitors should be used for ±36V output configuration,
but 50V parts may be substituted for ±30V output or less. Note
that some 50V capacitors may have incorrect lead spacings which lead to
poor board fitment.
Diodes
- D1-D4: TO-220 2-pin rectifier diode (8A 100V minimum)
Lead spacing 0.200"
- MUR820 8A 200V ultrafast recovery rectifier
(Mouser 863-MUR820G, Digi-Key MUR820GOS-ND)
- other similar
- D5: 500mW zener diode, DO-35 or DO-41
Lead spacing 0.300"
- BZX55Cxx series
(AMB audio shop 12V: BZX55C12; Mouser 9.1V: 512-BZX55C9V1, 5.1V: 512-BZX55C5V1)
- 1N52xx series
(Mouser 12V: 512-1N5242B, 9.1V: 512-1N5239B, 5.1V: 512-1N5231B)
- LM336BZ-5.0 or LM336Z-5.0 5V reference diode, ADJ pin unused
(Mouser: 512-LM336BZ50, 512-LM336Z5; Digikey: LM336BZ-5.0-ND, LM336Z-5.0-ND)
This zener diode sets the reference voltage, which, along with the
voltage gain of the error amplifier, sets the output voltage of the
PSU. See notes above for the R10 resistor for details.
Note: The accuracy of σ22's output voltage depends on the accuracy
of the D5 zener voltage. Zener diodes have a fairly wide tolerance, so
your actual output voltage may not be exactly on target. Normally this
is inconsequential, because audio circuit are not usually sensitive to
such voltage tolerances. If your application requires a high level of
voltage accuracy, then you should get a handful of D5 zener diodes to
pick from. You may want to use sockets for D5 on the σ22 board
to allow changing diodes without desoldering.
- CR1, CR2: 2.4mA current regulator diode
DO-35, DO-41, TO-92 or TO-18
(see the Instructions section)
- Central Semiconductor
1N5307
(Mouser 610-1N5307)
- Vishay-Siliconix
CR240
(Mouser 781-CR240)
- Vishay-Siliconix
J508 (not for ±36V configuration)
- Semitec
E-202
- CR3, CR4: 4.7mA current regulator diode
DO-35, DO-41, TO-92 or TO-18
(see the Instructions section)
- Central Semiconductor
1N5314
(Mouser 610-1N5314)
- Vishay-Siliconix
CR470
(Mouser 781-CR470)
- Vishay-Siliconix
J511 (not for ±36V configuration)
- Semitec
E-562
- LED:
Lead spacing 0.100"
Your choice of size and color (affects value of R16, R17, see
notes above for R16 and R17 for details)
Transistors
- Q1, Q3, Q4, Q9, Q10, Q12: NPN small signal BJT
BC546B (TO-92)
(AMB audio shop, Newark)
- Q2, Q5, Q6, Q7, Q8, Q11: PNP small signal BJT
BC556B (TO-92)
(AMB audio shop, Newark)
- Q13, Q14: N-channel power MOSFET International Rectifier
IRFZ24N (TO-220AB)
(AMB audio shop, Digi-Key, Newark)
- Q15, Q16: P-channel power MOSFET International Rectifier
IRF9Z34N (TO-220AB)
(AMB audio shop, Digi-Key, Newark)
Notes about the transistors:
- No special transistor matching is necessary.
- Do not substitute the transistors and MOSFETs with other types.
The compensation capacitors' values were tuned for optimum
performance with the specified devices. Changing to other types
may degrade the performance or cause stability.
- Do not mount the MOSFETs off-board on a remote heatsink. The
added wiring from the board to the MOSFETs may cause oscillations.
Heatsinks
Your choice of heatsink will affect chassis case compatibility due to height
and other mechanical/physical attributes.
Board-mount heatsinks:
- Aavid-Thermalloy
529802B00000 (onboard, 1.5" tall, screw-mount)
(AMB audio shop, Digi-Key)
- Aavid-Thermalloy
529802B02500 (onboard, 1.5" tall, pin-mount)
(Mouser, Digi-Key)
- Aavid-Thermalloy
529902B02500 (onboard, 2" tall, pin-mount)
(Mouser, Digi-Key)
- Aavid-Thermalloy
530002B02500 (onboard, 2.5" tall, pin-mount)
(Digi-Key)
- Wakefield
647-15ABP, 657-15ABP or 657-15ABPN
(onboard, 1.5" tall, pin-mount)
(Mouser, Digi-Key)
- Wakefield
657-20ABP (onboard, 2" tall, pin-mount)
(Mouser, Digi-Key)
Off-board heatsinks:
TO-220 heatsink mounting kit
If the tops of the heatsinks will be in close proximity to the top metal
cover when the board is installed in your chassis case, then you should mount
the MOSFETs to the heatsinks using TO-220 mounting kits, which electrically
isolate the MOSFETs' mounting tabs from the heatsinks. If you are using
offboard heatsinks, then TO-220 mounting kits are also required.
Otherwise, you may mount the MOSFETs to the heatsinks directly.
Heatsink thermal compound
Not needed if using mounting kits with Thermalsil or Sil-Pad isolators.
- Radio Shack
276-1372
- Wakefield 120-SA (Mouser 567-120-SA; Digi-Key 345-1006-ND)
- others
Connectors
PCB terminal blocks
(optional, allows easy wiring connect/disconnect to PCB):
- Phoenix Contact
1729128
0.200" screw terminal block, 2-circuit
(Mouser 651-1729128; Digi-Key 277-1247-ND)
- Phoenix Contact
1729128
0.200" screw terminal block, 3-circuit
(Mouser 651-1729131; Digi-Key 277-1248-ND)
- Phoenix Contact
1729128
0.200" screw terminal block, 4-circuit
(Mouser 651-1729144; Digi-Key 277-1249-ND)
Power transformer
Both dual-secondary and center-tapped secondary transformers are
supported. Toroidal type is recommended for minimum
stray magnetic field. The following table lists the transformer secondary
recommendations for various output DC voltages.
| Output voltage | Transformer secondary |
| ±36VDC | dual 35V or 70VCT |
| ±30VDC | dual 30V or 60VCT |
| ±27VDC | dual 25V or 50VCT |
| ±24VDC | dual 25V or 50VCT |
| ±15VDC | dual 18V or 36VCT |
| ±12VDC | dual 15V or 30VCT |
| ±9VDC | dual 12V or 24VCT |
| ±5VDC | dual 9V or 18VCT |
For other output voltages, a rule of thumb for this PSU is that
approximately 9V-10V drop should be maintained across the pass MOSFETs under
load. This allows for the 4V Vgs of the MOSFETs plus about 5V of headroom
to allow for line voltage fluctuations. Using the ±15V output as an
example, the pre-regulator voltage should be 24V. Accounting for a
couple of volts drop across the rectifier diodes, that figure goes up to 26V.
The transformer voltage should be 0.707 times that of the rectified DC
voltage, so 26V * 0.707 ~= 18V. Thus, a dual 18V or a 36VCT
transformer should work well.
The appropriate VA rating of the transformer depends on the intended load.
For a β22 serving as a headphone-only amplifier, one σ22 PSU
can supply either 2, 3 or 4 β22 boards (corresponding to
passive-ground 2-channel, active-ground 3-channel or fully-balanced
4-channel configurations). The recommended transformer ratings are
as follows:
| Number of β22 channels | Recommended transformer rating |
| 2 | 50VA |
| 3 | 80VA |
| 4 | 100VA |
If the σ22 will be supplying power to a β22 amplifier intended
to drive speakers, it is recommended that one σ22 board be used
per channel, each board supplied by its own 100VA transformer. A
similar recommendation applies for other power amplifiers.
The following are some recommended transformer types:
Chassis / case
Be sure to use a case that provides enough internal clearance for
the heatsinks you choose. If your heatsinks are not external to
the case (exposed fins), then you should cut ventilation slots in the
case (if not already so equipped) to ensure proper cooling.
The following are some examples of case styles that may be used
with the σ22.
Miscellaneous
IEC power entry receptacle with fuse
SPST toggle, paddle or rotary switch for power on/off (if IEC
receptacle doesn't have an integrated switch)
Main: σ22 Main |
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