The M³ Stereo Headphone Amplifier

Parts list for standard configuration

The table below illustrates a standard configuration M³ amplifier. This configuration has a voltage gain of 11 (20.8dB), and has a variable bass boost control. See the sections below for specific parts recommendations and options. Items shown in italic are available from the AMB audio shop. This list does not include the regulated DC power supply.

PartQuantityDescription
Circuit board
-1M³ printed circuit board
Potentiometers
Volume, Bass Boost2Alps RK27112A 50KΩ dual log taper, panel-mount
BIAS33/8" multi-turn cermet trimpot 5KΩ
BIASOP33/8" multi-turn cermet trimpot 1KΩ
Resistors
R121/8W 1% metal film resistor 1MΩ
R2, R3, R4G, R691/8W 1% metal film resistor 1KΩ
R4L, R4R, RLED31/8W 1% metal-film resistor 10KΩ
R5, R891/8W 1% metal-film resistor 100Ω
R731/8W 1% metal-film resistor 7.5KΩ
R962W 5% metal-film resistor 1Ω
Capacitors
C13multilayer ceramic capacitor 33pF
C2, C87metallized polyester capacitor 1µF
(or metallized polypropylene capacitor 0.1µF)
C33multilayer ceramic capacitor 220pF
C4, C57aluminum electrolytic capacitor 100µF 50V
C66metallized polyester capacitor 1µF
(or metallized polypropylene capacitor 0.1µF)
C79aluminum electrolytic capacitor 330µF 50V
Cbb2metallized polypropylene capacitor 0.22µF
Integrated Circuits
OPAMP3Analog Devices AD8610AR operational amplifier
TLE1Texas Instruments precision rail-splitter TLE2426CLP
Transistors
Q1+3International Rectifier N-channel power MOSFET IRFZ24N
Q1-3International Rectifier P-channel power MOSFET IRF9Z34N
Q2, Q5+4NPN small signal BJT 2N3904
Q3, Q46Fairchild N-channel JFET 2N5486
Q5-1PNP small signal BJT 2N3906
Q62Fairchild N-channel JFET 2N5484
Diodes
D111A rectifier 1N4001
LED1Your choice
Miscellaneous
-6TO-220 extruded heatsink Aavid-Thermalloy 531102B0xxxx 1.5"
-6TO-220 heatsink mounting kit (if required, see notes below)
-1heatsink thermal compound (if required, see notes below)
-3SOIC-8 to DIP-8 adapter Browndog 970601
-3DIP-8 socket
-2RCA phono jack, panel mount
-11/4" stereo headphone jack, panel mount, isolated
-1DC power input jack, panel mount, isolated
-40.100" 2-circuit pin header, plug and crimp terminals (for audio inputs, DC power, LED connection)
-1SPST power switch (optional)
-1knob for Volume
-1knob for Bass Boost
-4circuit board standoffs or spacers
--hookup wire
--heat-shrink tubing
-1chassis case (your choice, see below)
-4rubber 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 M³ 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


Notes about R1

The default value of 1MΩ should work well in all cases, but you may choose a lower resistance for a small improvement in noise performance. The minimum resistance should be at least ten times that of the volume control potentiometer.

Notes about R3 and R4

The voltage gain of the amplifier is determined by the ratio of R4L and R3L (as well as R4R and R3R). The default values of these are 10KΩ and 1KΩ, respectively, for a gain of 11. This is usable with most headphones, although it might be a little high for the most sensitive low-impedance types.

The gain may be reduced to suit such headphones. Further, the gain may also need changing depending on whether the amplifier is to be used with computer/portable devices or home stereo. The latter typically have a higher "line out", requiring less gain in the headphone amplifier.

The gain is computed by the formula: 
        G = (R4 / R3) + 1
In terms of decibels: 
        dB = 20 * log(G)
It is prudent to keep the values of R4 and R3 low (i.e., not exceeding 50KΩ) for lowest noise, however the value of R4 should also not be lower than 300Ω to prevent excessive power dissipation at maximum output.

If the optional bass boost feature is not desired, you may optionally use the front panel "bass boost" potentiometer as a variable gain control. To do this, install the bass boost potentiometer, but do not install CbbL, CbbR, RbbL, RbbR, and do not shunt the SbbL and SbbR pads. It effectively puts a variable resistor inline with R4.

This allows the amplifier to be adaptable to a variety of different headphone and input source types, providing a satisfactory range of volume control as well as optimized signal-to-noise ratio performance. The R4 and R3 values should be chosen for a low gain (such as 2). For example, if R4 and R3 are both 3.32KΩ and the potentiometer is 50KΩ, then the gain control range is between 2 and 17.

If you intend to build the bass boost option, the choice of R3 and R4 values also influence the bass boost characteristics. Use this online bass boost calculator to check the effect. This calculator can be used to compute the amplifier gain, even if the bass boost feature is omitted (just set the Rbb value to 0).

The value of R4G (ground channel) should always be 1KΩ. There is no R3 in the ground channel, because it is unity-gain.

Notes about RLED:

The optimum value of this resistor depends on your choice of LED. Use this online LED resistor value calculator to determine what value your RLED 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 24V, then the power dissipation will be about 0.06W. In this case a 1/8W or 1/4W resistor will work fine.

The type of resistor is not critical as long as it fits well.

Alternatively, you may use a 1N5283 through 1N5314 series CRD (current regulating diode) in place of the RLED resistor. The appropriate CRD depends on how much current should flow through the LED for the desired brightness. The use of a CRD has the benefit that the brightness of the LED will not change when you change the power supply voltage, but it is much more costly than a resistor.

Trimpots

BIAS and BIASOP, 3/8" multi-turn cermet
Lead spacing 0.100" inline
  • Vishay-Sfernice T93YA (Mouser 72-T93YA-1K, 72-T93YA-5K)
  • Vishay-Spectrol 64W (Mouser 594-64W102, 594-64W502)
  • Vishay-BC CT94W (Digi-key CT94EW102-ND, CT94EW502-ND)
  • Vishay-BC CT9W (Digi-key CT9EW102-ND, CT9EW502-ND)
  • Bourns 3296W (Mouser 652-3296W-1-102, 652-3296W-1-502; Digi-Key 3296W-102LF-ND, 3296W-502-LFND)
  • Bourns 3299W (Mouser 652-3299W-1-102, 652-3299W-1-502; Digi-Key 3299W-102LF-ND, 3299W-502LF-ND)
  • Murata PV36W (Digi-Key 490-2874-ND, 490-2888-ND)

Panel-mount potentiometers

Volume: 50KΩ or 10KΩ dual log taper
  • Alps RK27112A (perfect fit on circuit board) (AMB audio shop)
  • Noble AP25 (perfect fit on circuit board, however the panel mounting surface is further toward the front panel. This means the board must be mounted rearward by about 0.35" compared to the Alps). (Michael Percy Audio)
  • TKD 2P2511 (hand-wire)
  • Stepped attenuator (your choice, hand-wire): DACT, Goldpoint, Elma, Grayhill, etc.

Bass Boost: 50KΩ dual log taper (optional)
  • Alps RK27112A (perfect fit on circuit board) (AMB audio shop)
  • Noble AP25 (perfect fit on circuit board, same comment as the volume control) (Michael Percy Audio)
  • TKD 2P2511 (hand-wire)
  • Stepped attenuator (your choice, hand-wire): DACT, Goldpoint, Elma, Grayhill, etc.

Capacitors

  • C1, C3: multilayer ceramic capacitor (NP0 or C0G)
    Lead spacing 0.100"
    • Kemet Golden-max C315 series
      (Mouser 33pF: 80-C315C330J1G, 220pF: 80-C315C221J1G; Digi-Key 33pF: 399-4172-ND, 220pF: 399-4163-ND)
    • Vishay Mono-Kap series (Digi-Key 33pF: BC1007CT-ND, 220pF: BC1065CT-ND)
    • others

  • C2, C6, C8: metallized polyester capacitor (or metallized polypropylene capacitor)
    Lead spacing 0.200"
    • Wima MKS2 (AMB audio shop 1µF/63V; Mouser 1µF/63V 505-MKS21/63/10)
    • Vishay-BC MKT370 (Mouser 1µF/63V 594-2222-370-11105; Digi-Key 1µF/63V BC1622-ND)
    • AVX BF/BQ series (Mouser 1µF/63V 581-BF074D0105J)
    • Vishay-Roederstein MKT1817 (Mouser 1µF/63V 75-MKT1817510064)
    • Wima MKP2 (Mouser 0.1µF/100V: 505-MKP20.1/100/5)
    • Vishay-BC MKP416 (Digi-Key 0.1µF/63V: BC2054-ND)

  • C4, C5, C7: aluminum electrolytic capacitor 50V low-ESR high-reliability
    Lead spacing C4, C5: 0.200"; C7: 0.200" or 0.300"
    • Panasonic FC (Digi-Key 100µF/50V: P10323-ND, 330µF/50V: P11258-ND)
    • Panasonic FM (Digi-Key 100µF/50V: P12392-ND, 330µF/50V: P12399-ND)
    • Nichicon HE (Mouser 100µF/50V: 647-UHE1H101MPD, 330µF/50V: 647-UHE1H331MPD)
    • Nichicon PW (Mouser 100µF/50V 647-UPW1H101MPD, 330µF/50V: 647-UPW1H331MPD)
    • Nichicon KZ (Muse), FW or FG ("boutique")
    • Vishay-BC 136 RVI series
    • Elna Silmic or Cerafine ("boutique")

  • Cbb: metallized polypropylene capacitor
    Lead spacing 0.200", 0.300", 0.400", 0.500" or 0.600"
    • Wima MKP2 (Mouser 0.1µF/100V: 505-MKP20.1/100/5, 0.22µF/100V: 505-MKP20.22/100/5)
    • Vishay-BC MKP416 (Digi-Key 0.1µF/63V: BC2054-ND, 0.22µF/63V: BC2062-ND)
    • Vishay-Roederstein MKP1841 (Mouser 0.22µF/250V: 75-MKP1841422255)

Notes about C1:

By default the C1L and C1R capacitors are specified to be 33pF for voltage gain settings of 5 and above. This works well with all the recommended opamps.

If the amplifier is to be subjected to "opamp rolling" (use of different opamps at different times), C1L, C1R should be kept at the default of 33pF.

The following table lists further optimizations of the C1L and C1R values for each opamp type at the specified gain settings. These values have been tested and tuned to provide the fastest slew rate and widest bandwidth possible (given the performance constraints of the opamp), yet provide a square wave response free of ringing or overshoot at the leading and trailing edges.

Note that these optimizations are optional, and are tuned with the IRFZ24N and IRF9Z34N output MOSFETs.

If your voltage gain is 4 or lower, increase C1L and C1R to 47pF. For voltage gains between 5 and 11, you may interpolate an intermediate value based on the table below. If your gain is higher than 11, use the same value as that for gain of 11.

The value of C1G should be kept at 33pF in all cases.

OpampGain C1L, C1R Frequency response -3dBNotes
AD8610AR522pF1.5MHz-
1110pF1.2MHz-
AD8065AR527pF1.8MHz-
1110pF1.7MHz-
AD744JN522pF1.6MHz-
11None1.5MHz-
AD825AR527pF1.6MHz-
1110pF1.2MHz-
AD843JN522pF2.0MHz-
116pF1.5MHz-
AD845JN522pF1.8MHz-
116pF1.5MHz-
OPA627AP527pF1.5MHz-
1110pF1.2MHz-
OPA637AP5--Not recommended
1115pF1.2MHz-
OPA132PA527pF1.2MHz-
1110pF700KHz-
OPA134PA527pF1.2MHz-
1110pF700KHz-
OPA227PA515pF450KHzSlow, limited bandwidth
11None430KHz
OPA228PA5--Not recommended
1115pF1.0MHz-
OPA604AP533pF1.3MHz-
1115pF870KHz-
THS4631D533pF1.8MHzHigh heat dissipation, possibly high DC offset
1115pF1.7MHz
LT1122CCN8533pF1.4MHz-
116pF1.4MHz

Notes about C2, C6 and C8:

The schematic specifies 1µF for C2 and C8, but you could use any film capacitor down to 0.1µF. For C6, the schematic specifies 0.1µF, but you could go up to 1µF if it fits the board. Do not use ceramic disc, electrolytic or tantalum capacitors for these positions.

Notes about C3:

For each channel, if you use 100Ω resistors for R8+ and R8-, then you should also install the 220pF capacitor C3. The N-channel MOSFET's gate capacitance is less than that of the P-channel, and this capacitor equalizes them. An alternative to this approach would be to omit C3, but change the values of R8+ and R8- to 121Ω and 75Ω, respectively. This will assure symmetrical slew rates for positive going and negative going square wave pulses.

Notes about C7:

The circuit board has holes for up to six 18mm C7 capacitors or nine 12.5mm capacitors. They are not intended to be all filled with large value capacitors. The total capacitance should not exceed around 3000µF. If you use only three capacitors, install one adjacent to each amplifier block.

There is no benefit in using more capacitance than recommended. The reason for providing so many capacitor positions is to accommodate different physical capacitor sizes, and allow for paralleling many smaller-value capacitors to achieve the desired total capacitance. Some "boutique-grade" capacitors have large body dimensions for the amount of capacitance in each unit.

If you install too much capacitance for C7, the turn-on inrush current will be large and may cause damage to your power supply. It may also degrade the power connectors' contacts over time. Too much capacitance will also cause the amplifier DC rail voltage to discharge slowly after the amplifier is turned off, and this may cause undesirable noise at the output.

If you will be driving speakers with the M³, you can increase the total C7 capacitance to 6000µF, but only if your power supply is rated for 3A or more. See the Options section for more information.

Notes about Bass Boost, Cbb and other related parts:

This amplifier contains a provision for an optional on/off bass boost switch or a continuously-variable bass boost control. It implements a "shelving" filter.

If the bass boost feature is not desired, the CbbL, CbbR, RbbL, RbbR and and front panel bass boost panel-mount potentiometer should be omitted. Further, a jumper wire should be installed across the SbbL and SbbR pads on the circuit board.

To implement a fixed bass boost switch, install CbbL, CbbR, RbbL and RbbR. Do not install the bass boost panel-mount potentiometer. Connect a DPST switch to either the PbbL/PbbR or the SbbL/SbbR pads. These two are equivalent; the Pbb pads are close to the front panel to reduce wiring length, but the Sbb pads are spaced 0.100" apart to allow the use of a standard pin header for a Molex-type plug. The bass boost function is "off" when the Pbb or Sbb pads are bridged by the switch.

To implement a variable bass boost control, install CbbL, CbbR and the bass boost panel-mount potentiometer. Do not install RbbL and RbbR, and do not install anything at SbbL and SbbR.

The values of Cbb, Rbb (or the bass boost potentiometer resistance) interact with the values of R4 and R3. To arrive at the desired frequency range and amount of boost, please use this online bass boost calculator

Diodes

  • D1: 1A rectifier diode
    Lead spacing 0.300"
    1N4001 to 1N4007 series (DO-41) (Mouser 512-1N4001GP, Digi-Key 1N4001DICT-ND)

  • LED:
    Lead spacing 0.100"
    Your choice of size and color (affects value of RLED)

Notes about D1:

This diode protects the amplifier from damage if the DC power supply polarity is reversed by accident. The 1N400x series diode causes approximately 0.8V drop across it. You may place a jumper wire across this position to defeat the protection and eliminate the voltage drop, but this is not recommended. If you are planning to drive speakers with this amplifier, you should upgrade D1 to a 1N5401 series diode (rated 3A), or use a TO-220 2-lead diode such as the MUR805. You will need to form the leads of these to make it fit the board. See the Options section for more information.

Transistors

  • Q1+: N-channel power MOSFET International Rectifier IRFZ24N (TO-220AB)
    (AMB audio shop, Digi-Key, Newark)

  • Q1-: P-channel power MOSFET International Rectifier IRF9Z34N (TO-220AB)
    (AMB audio shop, Digi-Key, Newark)

  • Q2, Q5+: NPN small signal BJT (Mouser, Digi-Key)
    • 2N3904 (TO-92 inline leads)
    • 2N4401 (TO-92 inline leads)
    • 2N5088 (TO-92 inline leads)
    • MPS8099 (TO-92 inline leads)
    • BC550C (TO-92 inline leads, note reversed pinout)

  • Q5-: PNP small signal BJT (Mouser, Digi-Key)
    • 2N3906 (TO-92 inline leads)
    • 2N4403 (TO-92 inline leads)
    • 2N5087 (TO-92 inline leads)
    • MPS8599 (TO-92 inline leads)
    • BC560C (TO-92 inline leads, note reversed pinout)

  • Q3, Q4: N-channel JFET (8mA < Idss < 20mA) (AMB audio shop, Mouser, Digi-Key)
    • 2N5486 (TO-92 inline leads)
    • 2N5459 (TO-92 inline leads)
    • PN4393 (TO-92 inline leads)
    • J111 (TO-92 inline leads)
    • BF245C (TO-92 inline leads, note reversed pinout)

  • Q6: N-channel JFET (1mA < Idss < 5mA) (AMB audio shop, Mouser, Digi-Key)
    • 2N5484 (TO-92 inline leads)
    • 2N5457 (TO-92 inline leads)
    • J113 (TO-92 inline leads)
    • BF245A (TO-92 inline leads, note reversed pinout)

Transistor selection and matching:

Even without any special matching or selection of transistors, the amplifier should offer very good performance.

If you are very picky, you may want to match the Vgs (gate-to-source voltage) of the N-channel (Q1+) and P-channel (Q1-) MOSFETs in each complementary pair. This would assure the most linear transfer characteristics between them, minimizing distortion even before the application of negative feedback. It will be impossible to get a perfect match, but for practical purposes if the Vgs is within 0.3V it's good enough. To achieve even better match will require that you purchase a lot more MOSFETs than you need. For a tutorial on how to match MOSFETs see Nelson Pass's Matching Devices article. If you're using a 15V power supply, use a 150Ω 5W resistor instead of the value shown in the example. For a 12V supply, use a 100Ω 5W resistor.

Notes about the MOSFETs:

If you use different MOSFETs than the designated IRF models, you may have to change the value of C1 and C3, as well as the value of R7. If you don't know what you're doing, don't substitute different MOSFETs. In particular, do not use the Hitachi/Renesas 2SK213-2SK216 / 2SJ76-2SK79 series; even though they are good quality, they have incompatible pinouts than the IRFs, and are rated at a much lower current.

Do not mount the MOSFETs off-board on a remote heatsink. The added wiring from the board to the MOSFETs may cause instabilities.

Notes about the JFETs and BJTs:

Some TO-92 JFETs and BJTs are not pin-compatible with the M³ circuit board layout (in particular, the Japanese 2SK, 2SC and 2SA series). If you are substituting any of these devices please pay special attention to the pin-out as well as the device specifications.

For Q2, Q5+ and Q5-, "name-brand" transistors are recommended. Some no-name generics do not meet the required specifications.

Rail splitter

Texas Instruments TLE2426CLP (TO-92 inline leads). There is no substitute part for this. (AMB audio shop, Mouser, Digi-Key, Newark)

Heatsinks

Your choice of heatsink will affect chassis case compatibility due to height. If you use the 1" tall heatsinks, you should be conservative in setting the MOSFET quiescent current to keep the temperature comfortable (See the Initial setup section for details).
  • Aavid-Thermalloy 531102B00000 (1.5" tall) (AMB audio shop, Mouser, Digi-Key)
  • Aavid-Thermalloy 531302B02500G (2.5" tall) (AMB audio shop, Mouser, Digi-Key)
  • Aavid-Thermalloy 531202B00000 (2" tall) (Mouser, Digi-Key)
  • Aavid-Thermalloy 531002B00000 (1" tall) (Mouser, Digi-Key)

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. 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

IC sockets for opamps

DIP-8 with gold contacts

SOIC-8 to DIP-8 adapter for opamps

Needed for SOIC-8 opamps

Opamps

The default recommended opamp is either the AD8610AR or the OPA627AP. Each opamp have a sonic character of its own, although the differences are not as big as some would claim. All of the opamps in the following list have been tested and known to work in the M³:
  • Analog Devices AD8610AR (SOIC-8) (Digi-Key, Newark)
  • Analog Devices AD8065AR (SOIC-8) (Digi-Key, Newark)
  • Analog Devices AD744JN (DIP-8) (Digi-Key, Newark)
  • Analog Devices AD825AR (SOIC-8) (Digi-Key, Newark)
  • Analog Devices AD843JN (DIP-8) (Digi-Key, Newark)
  • Analog Devices AD845JN (DIP-8) (Digi-Key, Newark)
  • TI Burr-Brown OPA627AP (DIP-8) (Digi-Key, Newark)
  • TI Burr-Brown OPA637AP (DIP-8) (Digi-Key, Newark)
  • TI Burr-Brown OPA132PA (DIP-8) (Digi-Key, Newark)
  • TI Burr-Brown OPA134PA (DIP-8) (Digi-Key, Newark)
  • TI Burr-Brown OPA227PA (DIP-8) (Digi-Key, Newark)
  • TI Burr-Brown OPA228PA (DIP-8) (Digi-Key, Newark)
  • TI Burr-Brown OPA604AP (DIP-8) (Digi-Key, Newark)
  • Texas Instruments THS4631D (SOIC-8) (Digi-Key, Newark)
  • Linear Techonology LT1122CCN8 (DIP-8) (Digi-Key)

Opamps in SOIC-8 packages must be mounted on SOIC-8 to DIP-8 adapters (Browndog 970601 or Aries 08-350000-10) for fitment on the M³ board.

The OPA637AP and OPA228PA are usable for the left and right channels, and only if the voltage gain is 8 or greater. They must not be used for the ground channel under any circumstances.

More opamps may be added to the recommended list in the future after testing.

Only FET input opamps are recommended for the M³ due to the direct-coupled design. Use of opamps with BJT inputs are not recommended due to their high input bias currents, leading to severe DC offset problems that vary according to the volume control setting.

See also the notes in the Capacitors section above about compensation capacitor C1. If you do not have a function generator and an oscilloscope with which to verify stability and to tune for the best pulse response, do not use an opamp that is not in the above list.

DIP-8 sockets should be installed on the circuit board, and the opamps installed in the sockets. This facilitates easy opamp removal for testing and replacement, as well as initial setup.

Connectors

  • RCA phono input jacks, panel-mount: your choice
    • Switchcraft 3501 series (Mouser 502-3501-FP or 502-3501-FR; Digi-key SC1133-ND or SC1134-ND)
    • Vampire (various styles)
    • Cardas (various styles)
    • WBT (various styles)
    • others

  • 1/4" stereo headphone jack, panel-mount: your choice
    The headphone jack must be isolated from the chassis
    • Switchcraft N112B (Mouser 502-N112B; Digi-Key SC1123-ND)
    • Neutrik NJ3FP6C (Mouser 568-NJ3FP6C)
    • Neutrik NCJ6FI-S (Mouser 568-NCJ6FI-S)
    • Neutrik NMJ6HC-S (Mouser 550-NMJ6HCS)
    • Re'An NYS212 (Mouser 568-NYS212)
    • Pomona 6877 (Mouser 565-6877)
    • others

  • DC power jack: 2.5mm barrel type, panel mount: your choice
    The DC power jack must be isolated from the chassis
    • Kobiconn 163-4303 (Mouser 163-4303)
    • Kobiconn 163-1061 (Mouser 163-1061)
    • Kobiconn 163-1100 (Mouser 163-1100) (locking with mating plug 171-0725 (Mouser 171-0725))
    • others

  • PCB audio input block (optional, allows easy wiring connect/disconnect to PCB):
    • Molex KK 22-23-2021 0.100" header, 2-circuit (Mouser 538-22-23-2021; Digi-Key WM4200-ND)
      mating plug 22-01-3027 (Mouser 538-22-01-3027; Digi-Key WM2000-ND),
      crimp terminals 08-50-0114 (Mouser 538-08-50-0114; Digi-Key WM1114-ND)
    • other 0.100" connectors, 2-circuit

  • PCB DC power input block: (optional, allows easy wiring connect/disconnect to PCB):
    • Molex KK 22-23-2021 0.100" header, 2-circuit (Mouser 538-22-23-2021; Digi-Key WM4200-ND)
      mating plug 22-01-3027 (Mouser 538-22-01-3027; Digi-Key WM2000-ND),
      crimp terminals 08-50-0114 (Mouser 538-08-50-0114; Digi-Key WM1114-ND)
    • Phoenix Contact 1725656 0.100" screw terminal block, 2-circuit
      (Mouser 651-1725656; Digi-Key 277-1273-ND)
    • Phoenix Contact 1729128 0.200" screw terminal block, 2-circuit
      (Mouser 651-1729128; Digi-Key 277-1247-ND)
      Note: This is the recommended connector if you will be driving speakers with your M³ amplifier. It is rated at a higher current than the others listed.
    • other miniature 0.100" or 0.200" connectors, 2-circuit

  • LED connection block: (optional, allows easy wiring connect/disconnect to PCB):
    • Molex KK 22-23-2021 0.100" header, 2-circuit (Mouser 538-22-23-2021; Digi-Key WM4200-ND)
      mating plug 22-01-3027, (Mouser 538-22-01-3027; Digi-Key WM2000-ND),
      crimp terminals 08-50-0114 (Mouser 538-08-50-0114; Digi-Key WM1114-ND)
    • Phoenix Contacts 1725656 0.100" screw terminal block, 2-circuit
      (Mouser 651-1725656; Digi-Key 277-1273-ND)
    • other miniature 0.100" connectors, 2-circuit

Chassis / case

Be sure to use a case that provides enough internal clearance for the heatsinks you choose. A case with ventilation slots is strongly recommended, or you must reduce the MOSFET quiescent current settings.
  • Par Metal 20-series
    • 6"W x 8"D x 2"H custom, for use with external PSU, 1.5" tall heatsinks
    • 12"W x 8"D x 2"H standard, for use with internal PSU, 1.5" tall heatsinks

    Note: When using the 1.5" heatsinks in the 2" Par Metal cases, you should use 1/8" to 3/16" (3mm to 5mm) standoffs for the circuit board. Put an insulating plastic sheet under the board to prevent solder joints from touching the chassis bottom. Use TO-220 insulating kits on the MOSFETs, because the heatsinks will come very close to the top cover. Also, the Alps RK27112A volume/bass boost controls' shafts will be slightly below the center line of the front panel.

  • Lansing Graybox B-style
    • 8.37"W x 8"D x 1.72"H, for use with external PSU, 1" tall heatsinks
    • 16.73"W x 8"D x 1.72"H, for use with internal PSU, 1" tall heatsinks
    • 8.37"W x 8"D x 3.47"H, for use with external PSU, 2" tall heatsinks
    • 16.73"W x 8"D x 3.47"H, for use with internal PSU, 2" tall heatsinks

  • Hammond
    • 1455T2201 (metal end-caps) or 1455T2202 (plastic end-caps) 6.5"W x 9.5"D x 2"H, for use with external PSU, 1.5" tall heatsinks

    Note: When using the 1.5" heatsinks in these Hammond 1455 cases, you should use 1/8" to 3/16" (3mm to 5mm) standoffs for the circuit board. Put an insulating plastic sheet under the board to prevent solder joints from touching the chassis bottom. Use TO-220 insulating kits on the MOSFETs, because the heatsinks will come very close to the top cover. Also, the Alps RK27112A volume/bass boost controls' shafts will be slightly below the center line of the front panel. This is an unventilated case, reduce the MOSFET quiescent currents to avoid overheating.

Miscellaneous

  • Knobs for volume and bass boost controls (must fit the potentiometer shaft diameter and style, your choice)
  • DPST toggle or rotary switch for fixed bass boost on/off (optional)
  • SPST toggle or rotary switch for power on/off (optional)


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