The δ1 relay-based R-2R stereo attenuator

Parts list for standard configuration

The table below illustrates the parts needed to populate the δ1 board. This list does not include any parts for the LCDuino-1 board, the power supply, wires or enclosure-related items. For parts not offered by AMB audio shop, Mouser, Digi-Key, Newark, Farnell, RS Components stock numbers for the recommended parts are listed below for your convenience. Additional alternative parts are listed in the Parts selection guide section below.

Some parts are optional, if they are not populated then certain features will either be disabled or degraded. While it is recommended that you install all parts for maximum functionality, you should look carefully at the notes below to find the combination of features that best fits your needs.

Part ID Qty Description Mouser # Digi-Key # Farnell # RS # Notes
Circuit board
PCB 1 δ1 PCB AMB audio shop -
R1+, R1- 2 resistor array 1KΩx10, bussed (SIP-11) AMB audio shop see Note 5
R2+, R2- 2 resistor array 47Ωx8, bussed (SIP-9) -
R5+, R5- 2 resistor array 47KΩx8, bussed (SIP-9) -
R3, R4 2 miniature 1/8W resistor 3.3KΩ 270-3.3K-RC S3.3KCACT-ND 9343040 165-0296 see Note 1
RSnL, RSnR, RPnL, RPnR, RTL, RTR 22-34 attenuator resistors (your choice) see Note 2
RGL, RGR 2 wirewound resistor 10Ω 5W 280-CR5-10-RC,
71-CW5-10 or
PPC5W10.0CT-ND 1735130 683-0983 see Note 3
C1, C3 2 aluminum electrolytic capacitor 470µF 10V 647-UHE1A471MPD P10221-ND 9691944 315-0338 -
C2+, C2-, C4 3 multilayer ceramic capacitor 0.1µF 50V X7R 80-C320C104K5R 399-4264-ND 1457655 or
538-1310 -
CGL, CGR 2 suppression capacitor 0.1µF 250V 539-158X104 P11116-ND 1198295 148-474 see Note 3
Ferrite bead
L1 1 per δ1/δ2 stack Ferrite bead, axial-lead AMB audio shop See Note 1
Integrated circuits
U1+, U1- 2 PCF8574A or PCF8574
I²C port expander (DIP-16)
AMB audio shop
(PCF8574A only)
See Note 4
U2+, U2- 2 ULN2803A darlington transistor array (DIP-18) 511-ULN2803A 497-2356-5-ND 1094428 714-1167 -
LED+, LED- 2 10-LED bargraph array (DIP-20) 604-DC-10EWA 754-1176-5-ND 1208882 247-3056 see Notes 5, 6
K0-K7 5-8 miniature latching DPDT relay
Panasonic AGN2104H
AMB audio shop -
IC sockets
- 2 DIP-16 low-profile socket, gold contacts 575-393316 ED5316-ND 1077315 813-137 for U1+, U1-
- 2 DIP-18 low-profile socket, gold contacts 575-393318 ED5318-ND 1077318 813-143 for U2+, U2-
J1 1 6P Molex KK 254 headers, right angle,
tin or gold
538-22-05-3061 or
WM4304-ND or
1756799 or
679-5473 or
see Note 7
1 6P Molex KK 254 crimp housing 538-22-01-3067 WM2004-ND 1654529 679-5391
J2, J3 1 6P vertical pin headers
tin or gold
538-22-03-2061 or
WM4004-ND or
9731113 479-181
1 SIP-6 pin receptacle AMB audio shop
J4 1 16P dual-row header, right-angle, unshrouded 538-10-88-3161 SAM1049-08-ND 1248191 681-2581 see Note 8
J5 1 16P dual-row receptacle, right-angle - SAM1006-08-ND 1766333 -
J4, J5 2 16P dual-row header, right-angle, shrouded 517-D2516-5002-AR MHE16E-ND 1099247 542-8920 see Note 9
2 16P dual-row IDC socket with strain-relief 517-D89116-0131HK and
MKC16E-ND and
1099238 192-7372
1 16-conductor 0.050" ribbon cable 517-3365/16FT MC16G-5-ND 297318 289-9874
INPUTL, INPUTR, OUTPUTL, OUTPUTR 4 2P Molex KK 254 headers, right angle,
tin or gold
538-22-05-3021 or
WM4300-ND or
1756797 or
679-5448 or
see Note 10
4 2P Molex KK 254 crimp housing 538-22-01-3027 WM2000-ND 1462825 679-5363
INOUTL, INOUTR 2 3P Molex KK 254 headers, right angle,
tin or gold
538-22-05-3031 or
WM4301-ND or
1462932 679-5451 or
see Note 10
2 3P Molex KK 254 crimp housing 538-22-01-3037 WM2001-ND 1462838 679-5375
- 20 Molex KK 254 crimp terminals,
tin or gold
538-08-50-0114 or 538-08-55-0102 WM1114-ND or WM2312-ND 1462641 or
172-9178 or
for all Molex KK 254 crimp housings
JP1A+, JP1B+, JP1C+, JP1A-, JP1B-, JP1C-, JP2, JP3 1 36P pin headers, break-apart 517-647-01-36 S1011E-36-ND 1097955 - for all jumpers
- 8 jumper shunts, 2P, 0.100" 649-68786-202LF S9001-ND (10-pack) 1097979 (10-pack) -
- - PCB standoffs, 0.5" or 13mm long, imperial #4-40 or metric M3 threaded (your choice) McMaster-Carr, etc.
- - Machine screws, imperial #4-40 or metric M3 (your choice) McMaster-Carr, etc.


  1. If you will be stacking multiple δ1/δ2 boards, then only one of them needs to have R3, R4 and L1 installed. L1 connects the driver section's digital ground to the chassis through the mounting hole.
  2. Use the Resistor calculator to calculate the resistor values, and select your preferred resistor type. See Parts selection guide below.
  3. Optional: Install these if your build requires a ground loop breaker. See the δ1 board assembly instructions section for details.
  4. PCF8574A and PCF8574 occupy different I²C addresses spaces. AMB recommends that you use the same chip type for U1+ and U1- on a per-board basis. See the Initial setup section and the LCDuino-1 website for more information.
  5. Optional: Install these if you want relay coil activity indicators, useful for debugging purposes.
  6. No IC socket is specified for LED+ and LED- because it would make them too tall to fit between stacked boards. Solder them directly to the board.
  7. If you are building the α10 stereo pre-amplifier using the special backplane board, use the α10 parts list for these parts.
  8. If your δ1 board's driver and attenuator sections will remain in one piece, use these for J4 and J5.
  9. If your δ1 board's driver and attenuator sections will be snapped apart, use these for J4 and J5.
  10. δ1 supports two styles of input and output connection options:
      Separate 2P input and output Molex KK connectors per channel.
      3P input/output Molex KK connector per channel (similar to conventional volume potentiometer).
    You need to populate only one of these options. If you use the 3P option, then install wire jumpers in JP4L and JP4R.

Parts selection guide

The following is a list of recommendations and options. Please read through this carefully before you order any parts.


R1+, R1-, R2+, R2-, R5+, R5-: These are all "bussed" resistor networks. R1+ and R1- are SIP-11, each with ten internal 1KΩ resistors. R2+, R2- are SIP-9, each with eight internal 47Ω resistors. R5+ and R5- are SIP-9, each with eight internal 47KΩ resistors. One pin of each of them are connected to a common bus. The lead pitch is 0.1" (2.5mm) for all of these.
R3, R4: These resistors are 3.3KΩ miniature axial lead types with a body length no longer than about 4mm and no wider than 1.9mm. Carbon film, thin film or metal film types are acceptable, with 5% tolerances or less.
RSnL, RSnR, RPnL, RPnR, RTL, RTR: These are the main resistors for the R-2R ladder attenuator network. The δ1 PCB accommodates through-hole resistors with lead-pitch from 5mm to 12.5mm, and several intermediate sizes. Please use the Resistor calculator to determine the appropriate resistor values. The calculator shows one channel, you'll need to obtain two of each resistor per board (for stereo). The resistor type to use depends on your preference and budget. These resistors will dissipate negligible power so the wattage rating is not important. Carbon-film, carbon-composition and wirewound types are not recommended.

You should save a record of your resistor calculator parameters (such as doing a screen-dump or printing a hardcopy) for future reference.
RGL, RGR: Optional resistors for ground loop breaker, 10Ω 5W wirewound type, axial lead, lead spacing 23mm.


C1, C3: Aluminum electrolytic capacitor 470µF 10V, radial lead, lead spacing: 3.5mm;, diameter: 8mm, height: 11.5mm maximum C2+, C2-, C4: X7R multilayer ceramic capacitor 0.1µF, radial lead, lead spacing 2.5mm CGL, CGR: Optional capacitors for ground loop breaker, 0.1µF 250V, suppression capacitor, class X or Y rated, radial lead, lead spacing 15mm, 12.5mm, 10mm or 7.5mm.

Ferrite bead

L1: Ferrite bead, axial-lead (AMB audio shop)

Integrated circuits

U1+, U1-: I²C port expander (DIP-16)
U2+, U2-: Darlington transistor array (DIP-18)


LED+, LED-: 10-LED bargraph array (DIP-20)


K0-K7: Miniature DPDT relay 4.5V DC latching
  • Panasonic AGN2104H (AMB audio shop)
  • Omron G6JU-2P-Y-DC4.5
  • Note: You may use another single-coil latching relay in the Omron G6JU-2P-Y or Panasonic AGN series with a different coil voltage, but you need to have a separate power supply. See Power options for details.

IC sockets

DIP-16 and DIP-18 low profile sockets with machined contacts


J2, J3: (for board stacking)
  • Vertical 6P single-row pin header with solder tails, .100" pitch, .318" mating length
  • Vertical 6P single-row pin receptacle with solder tails, .100" pitch (AMB audio shop)
J4, J5: (one-piece δ1 board option)
  • J4: Samtec TSW-108-08-T-D-RA 16P dual-row pin header, right-angle, unshrouded
  • J5: Samtec BCS-108-L-D-HE 16P dual-row pin receptacle, right-angle
  • other similar
J4, J5: (separated δ1 board option)

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