The α10 stereo pre-amplifier

Parts list

The table below illustrates the parts needed to populate the α10 backplane board, the σ10 power supply, the enclosures, their associated panel components and wiring. The list does not include the parts needed to populate the α20, LCDuino-1, δ1, δ2, σ22 or σ25 boards. Please see the websites of each of these modules for parts information, as well as the special notes below.

Some parts listed are the ones used on AMB's reference build, but you may choose others to your liking (e.g., LED, switch, knob, etc.).

Visit AMB audio shop for parts that are marked accordingly.

α10 stereo pre-amplifier
PartQuantityDescriptionMouser #Digi-Key #Notes
PCB1α10 backplane circuit boardAMB audio shop-
SW1Pushbutton switch, momentary contact, panel-mount
(Bulgin MP0045/1D0NN000)
117-MP0045/1D0NN000-also Allied 566-0036 or
Newark 95M9945
POT1Potentiometer, linear taper 100KΩ, motorized 5VDC, panel-mount
(Alps RK16812MG099)
AMB audio shop-
KNOB1Knob for potentiometer(your choice)Goldpoint K1.1-S-SA
PH363Pin header, 36P (break-apart, 0.230" or 0.235" mating length)517-647-01-36S1011E-36-ND-
PH61Pin header, 6P (0.318" mating length)AMB audio shop-
PR224Pin receptacle, 2P-S7035-NDsee Note 1
PR32Pin receptacle, 3PAMB audio shop
PR42Pin receptacle, 4P517-850-01-07
(cut to size)
S7037-ND
PR52Pin receptacle, 5PAMB audio shop
PR62Pin receptacle, 6PAMB audio shop
PR71Pin receptacle, 7P517-850-01-07S7040-ND
MH213Molex KK 254 header, 2P538-22-23-2021 (tin) or
538-22-11-2022 (gold)
WM4200-ND (tin) or
WM2700-ND (gold)
-
MR213Molex KK 254 crimp housing, 2P538-22-01-3027WM2000-ND-
MH32Molex KK 254 header, 3P538-22-23-2031 (tin) or
538-22-11-2032 (gold)
WM4201-ND (tin) or
WM2701-ND (gold)
-
MR32Molex KK 254 crimp housing, 3P538-22-01-3037WM2001-ND-
MH48Molex KK 254 header, 4P538-22-23-2041 (tin) or
538-22-11-2042 (gold)
WM4202-ND (tin) or
WM2702-ND (gold)
-
MR48Molex KK 254 crimp housing, 4P538-22-01-3047WM2002-ND-
MH52Molex KK 254 header, 5P538-22-23-2051 (tin) or
538-22-11-2052 (gold)
WM4203-ND (tin) or
WM2703-ND (gold)
-
MR52Molex KK 254 crimp housing, 5P538-22-01-3057WM2003-ND-
MH61Molex KK 254 header, 6P538-22-23-2061 (tin) or
538-22-11-2062 (gold)
WM4204-ND (tin) or
WM2704-ND (gold)
-
MR61Molex KK 254 crimp housing, 6P538-22-01-3067WM2004-ND-
MCT80Molex KK 254 crimp terminal538-08-50-0114 (tin) or
538-08-55-0102 (gold)
WM1114-ND (tin) or
WM2312-ND (gold)
-
RCA16RCA jack, panel-mount, isolated(your choice)RCA-622FG
UMB_CONN1Circular locking connector, 7 circuits, female, panel-mount
(Amphenol C016 30G006 100 12)
523-C01630G00610012361-1082-ND-
1Circular locking connector, 7 circuits, male, cable-mount
(Amphenol C016 30H006 110 12)
523-C01630H00611012361-1352-ND-
JP1Jumper shunt, 0.100"649-68786-202LFS9001-ND (10-pack)-
--Hookup wire, 22AWG and 24AWG, stranded copper, various colors(your choice)-
--Heat-shrink tubing, various diameters(your choice)-
-1Aluminum enclosure (see below)--Par-Metal 20-12122N with two front panels
-4Rubber feet(your choice)-
STANDOFF181/4" #4-40 (or 6mm M3) threaded standoff, male-female534-8712-McMaster-Carr 93505A430
STANDOFF2247/16" #4-40 (or 11mm M3) threaded standoff, female-female--McMaster-Carr 91780A431
STANDOFF3101/2" #4-40 (or 13mm M3) threaded standoff, male-female534-8401-McMaster-Carr 93505A432
SPACER21/8" #4 (or 3mm M3) unthreaded spacer--McMaster-Carr 92510A688
--#4-40 (or M3) machine screws, #6-32 machine schrews, washers, nuts and other hardware(your choice)McMaster-Carr
σ10 power supply
RLED1680Ω 1/8W resistor (carbon film or metal film)299-680-RCCF18JT680RCT-ND-
LED13mm blue LED, tinted/diffused78-TLHB4400751-1092-ND-
IEC_MODULE1IEC power entry module with fuse holder562-723W-X2/04Q206-ND-
FUSE15x20mm fast-acting fuse, 0.6A (for 120V mains)576-0235.600HXPF2674-ND (5-pack)-
5x20mm fast-acting fuse, 0.3A (for 240V mains)576-0235.300HXPF2671-ND (5-pack)-
T1115V+15V (or 18V+18V) 7VA toroidal power transformer-1295-1055-ND or 1295-1057-NDsee Note 2
T219V+9V 5VA toroidal power transformer-1295-1110-ND-
SSR1Solid state relay, 3VDC trigger, 5A 240VAC load, zero-crossing558-CL240D05CC1762-NDSee Note 3
2#8 Ring terminal, 18-22AWG, crimp style517-9472794727-01-ND
2#6 Ring terminal, 18-22AWG, crimp style517-9472594725-01-ND
UMB_CONN1Circular locking connector, 7 circuits, female, panel-mount
(Amphenol C016 30G006 100 12)
523-C01630G00610012361-1082-ND-
1Circular locking connector, 7 circuits, male, cable-mount
(Amphenol C016 30H006 110 12)
523-C01630H00611012361-1352-ND-
--Hookup wire, 18AWG and 20 AWG, stranded copper, various colors(your choice)-
--Heat-shrink tubing, various diameters(your choice)-
-1Aluminum enclosure (see below)--Context Engineering 3008H-5N or LMB Heeger EAS-200
-4Rubber feet(your choice)-
--Umbilical cord sleeving(your choice)Techflex braided monofilament
--#4-40 (or M3) machine screws, #6-32 (or M3.5) machine screws, washers, nuts and other hardware(your choice)McMaster-Carr
-1AC power cord, IEC standard(your choice)Wall-plug style vary by country

Notes

  1. You may purchase 36P receptacle strips (Mouser 517-850-01-36) and cut them to size for each of these. Count on losing a circuit position at each cut point, because it does not break cleanly. Fix up each end with a flat file after cutting.
  2. Use a 15V+15V transformer for ±12V DC analog supply rails, or a 18V+18V transformer for ±15V DC. ±12V DC is usually sufficient voltage for most applications, but ±15V DC will provide extra output voltage swing capability (see the Specifications section).
  3. See the Other options section for using a "buffered" electro-mechanical relay module instead of a solid state relay.

Parts sources

Apart from those items offered at AMB audio shop, you can obtain everything else from the vendors listed on the AMB Audio DIY Page. The recommended US vendors are Mouser and Digi-Key. Builders in other countries may search Farnell or RS Components.

Enclosures & panels

AMB's reference α10 is housed in a Par-Metal 20-12122N enclosure in natural brushed aluminum finish. The size is 12"x12"x2" (WxDxH). The enclosure was ordered with two front panel frames and no rear panel. Custom 6mm milled aluminum panels were then ordered from Front Panel Express to replace the stock panels. All screws on the Par-Metal enclosure have #6-32 threads, and stainless socket cap screws were used throughout (standard head on the front/rear panels, button head elsewhere).

Note: Some Par-Metal enclosures have #8-32 threads on the panel frames.

AMB's reference σ10 power supply enclosure is a Context Engineering 3008H-5N split-body enclosure in natural brushed aluminum finish. Its front and rear panels were also discarded in favor of custom 4mm milled aluminum panels from Front Panel Express. The enclosure was then tapped for #4-40 threads and used with stainless standard head socket cap screws.

If you would like to replicate AMB's reference build, you should download and install the Front Panel Designer software (for Linux, MacOS and Windows), and download the following α10 and σ10 FPD files (ZIP compressed bundle, 3KB): alpha10_sigma10_panels.zip These FPD files were created for perfect alignment with the α10 backplane board. Be sure to read the README.txt file in the ZIP bundle. All holes and cutouts pertain to the panel parts selections listed in the table above. If you use different parts then the design should be modified to match. Be sure to double-check all measurements before submitting an order to Front Panel Express.

The rear panel is grouped and labeled for four sets of inputs and four sets of outputs. The α10 (and δ2) is actually configurable at build-time to support a variable number of inputs and outputs as long as the total number does not exceed eight.

Note that this is an "exported" version of the FPD files, and does not have the AMB logo or the "AMB Laboratories" text. If you want a logo, please create your own.

In order to fit everything into the low-profile 2" Par-Metal enclosure, pay special attention to the following:
  • The σ22 board heatsinks must be no taller than 1". Use Aavid-Thermalloy 531002B00000G (Mouser 532-531002B00; Digi-Key HS231-ND) or Aavid-Thermally 513002B02500G (Mouser 532-513002B25G; Digi-Key HS403-ND).
  • The σ22 board C5 and C6 capacitors must be no taller than 1". Use 1500µF 35V Panasonic EEU-FC1V152S (Mouser 667-EEU-FC1V152S; Digi-Key P11243-ND) or similar.
  • The Par-Metal panel frames need to be trimmed to clear the LCD display on the front, and to clear the RCA jacks at the rear. You may use a combination of nibbling tool and flat file to do so. See the Instructions section for more details.
  • Use board standoffs and pin headers/receptacles exactly as specified in the parts list above. Their use is shown in the table below:

    PartUsage
    STANDOFF1For mounting the backplane board to the bottom of the enclosure
    STANDOFF2For mounting the α20, δ2, σ22, and σ25 boards to the backplane
    STANDOFF3For stacking the δ1 board on top of the δ2 board, and for mounting the LCD display to the LCDuino-1 board
    PH36, PR2, PR3, PR4, PR5, PR6, PR7For connecting the α20, δ2, σ22, and σ25 boards to the backplane
    PH6, PR6For connecting the δ2 board to the δ1 board

    Using the correct parts will ensure the following:

    • Proper fitment in the enclosure.
    • All pin headers and receptacles are mated securely and completely.
    • There is sufficient space between the δ1 and δ2 boards for parts clearance.
If you use the 3" high version of the Par-Metal enclosure (part number 20-20123x), or an entirely different (taller) enclosure, then the first three requirements in the list above no longer apply, but you should still follow the standoff and pin header/receptacle recommendations. Of course, if you're planning to have custom panels fabricated for a different case, then you'll have to create your own FPD files.

Additional per-module notes

The following is a list of per-module notes about parts. Please read through this carefully before you order any parts. Please see the Instructions section for details about building the α10 pre-amplifier.

α20 line stage amplifier

The traditional audio pre-amplifier line stage usually has a voltage gain of 5x to 10x (14dB to 20dB). This is usually enough for a combination of weak sources, low power amplifier gain and inefficient speakers. Many modern digital sources have very "hot" output, and with efficient speakers one could still get reasonable volume control range when the pre-amplifier line stage gain is set between 1x and 5x. You should evaluate your system needs and choose an appropriate gain. The δ1 volume attenuator has a very wide control range and 256 steps (from 0dB to -127.5dB in 0.5dB steps), so it's very tolerant of high gains. Nevertheless, setting the gain to a moderate level ensures that the noise floor is as low as possible.

LCDuino-1 display I/O processor

SW, POT and SSR in the α10 parts list above are redundant in the LCDuino-1 parts list. Populate all parts in the LCDuino-1 parts list, except R4, J7 and J8.

δ1 stepped attenuator

You should keep the δ1 board in one piece (i.e., do not break apart the driver and attenuator sections). Use the cable-less pass-through connector option as shown in the δ1 parts list. Populate all required parts on the δ1 board, except R3, R4, L1 and J1. If you are mounting the IEC power entry module, solid state relay and power transformers in the main pre-amplifier chassis (rather than a separate power supply box), then populate the ground loop breaker parts RG[LR] and CG[LR]. Otherwise, leave these locations vacant.

The default attenuator input resistance of 25KΩ is recommended unless you have some peculiar requirements.

δ2 input/output selector

You should keep the δ2 board in one piece (i.e., do not break apart the driver and attenuator sections). Use the cable-less pass-through connector option as shown in the δ2 parts list. Populate all parts on the δ2 board, including R3, R4 and L1, but not any of the Molex KK 254 headers. You will be installing pin receptacles on the bottom of the board.

The AMB reference α10 is set up for four stereo inputs and four stereo outputs, and the rear panel is labeled accordingly. You may choose a different configuration, please refer to the δ2 website for details. Rather than using pin headers and jumper shunts for JP[0-7][SG][LR], you may simply solder resistor lead cutoffs to hard-wire the settings.

σ22 regulated power supply

Configure the σ22 for ±12V or ±15V DC output. Note the power transformers needed for each of these in the parts list above. Do not populate the terminal blocks as specified in the σ22 parts list. Instead, you will be installing pin receptacles on the bottom of the board.

σ25 regulated power supply

Configure the σ25 for 5V DC output (i.e., use a 7805 regulator). Do not install the Molex KK 254 headers as listed in the σ25 parts list. You will be installing pin receptacles on the bottom of the board.

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