| .: Home :. | .: Productions :. | .: Misc :. |
Audio input and output modules
About
This is a collection of small audio input and output modules. They are building blocks easing the realization of sound processors or synthesizers.
The modules are ready-to-use input buffers and line drivers for common but non-trivial types of audio signals, like balanced lines or hi-Z instruments. Thus, the main circuit board can focus on its own job without having to deal with the outside world interface.
Each board is made of 4 units. It is possible to cut a board with a saw to get the desired number of units. The power bus can be daisy-chained between several boards, possibly of different types.
- Input modules :
- XLR + ¼” jack combo, balanced line
Input impedance : 2×18 kΩ
Bandwidth at −3 dB : 0.5 Hz–723 kHz
Gain : 0.909 - ¼” jack, balanced line
- ¼” jack, high-impedance instrument level (electric guitars)
- XLR + ¼” jack combo, balanced line
- Output modules :
- XLR, balanced line
- ¼” jack, balanced line
The picture above shows the 2 combo input modules and 4 XLR outputs in an active crossover filter for a dual stereo amplification system.
Notes
The XLR input is for line only, it is not suitable for microphones (level too low, no phantom power).
Power requires clean ±15 V DC supply. However any voltage will do, as long as it is symmetric and allows the operational amplifiers to work in their duty range. Bulk capacitors must be provided upstream, as the modules only include local decoupling caps per chip. Current amount mostly depends on what the total opamp population needs.
Input modules have protection diodes against overvoltage. They are standard 1N4148, but it is possible to replace them with other types like Schottky to reduce the tolerance threshold.
Boards are held on the enclosure only with the audio connectors. This should be sufficient as they are quite lightweight. The PCB is distant from the inner edge of about 1 mm. The pitch between units of any type is 25 mm.
Resources
Bill of materials
For a single unit. Version : 2024-06-18
Input / combo, balanced
| Name | Qty | Value | Specific contraints or model |
|---|---|---|---|
| C1 | 1 | 100 nF | Ceramic X7R, 50 V, pitch 2.5 mm, must fit in a DIP-8 socket |
| C2, C4, C12, C14 | 4 | 22 pF | Ceramic C0G/NP0, pitch 2.5 mm, 2.5 mm thick |
| C3, C13 | 2 | 47 µF | 35 V, pitch 2.5 mm, Ø 6.3 mm |
| D1, D2, D11, D12 | 4 | Small signal silicon diode | Reverse voltage > 60 V, 1N4148 |
| J1 | 1 | Pin header 1×3 | Optional (power) |
| J2 | 1 | Pin header 1×2 | Optional (audio) |
| J3 | 1 | Female XLR-jack combo on PCB | Neutrik NCJ6FAH |
| R1, R11 | 2 | 1 kΩ | 500 mW is safer |
| R2, R12 | 2 | 100 kΩ | |
| R3, R4, R13, R14 | 4 | 10 kΩ | |
| U1 | 1 | Dual operational amplifier + socket | DIP-8 package, NE5532 |
Input / jack, balanced
| Name | Qty | Value | Specific contraints or model |
|---|---|---|---|
| C1 | 1 | 100 nF | Ceramic X7R, 50 V, pitch 2.5 mm, must fit in a DIP-8 socket |
| C2, C4, C12, C14 | 4 | 22 pF | Ceramic C0G/NP0, pitch 2.5 mm, 2.5 mm thick |
| C3, C13 | 2 | 47 µF | 35 V, pitch 2.5 mm, Ø 6.3 mm |
| D1, D2, D11, D12 | 4 | Small signal silicon diode | Reverse voltage > 60 V, 1N4148 |
| J1 | 1 | Pin header 1×3 | Optional (power) |
| J2 | 1 | Pin header 1×2 | Optional (audio) |
| J3 | 1 | ¼” female jack, stereo, switched, horizontal on PCB | Neutrik NMJ6HCD2 |
| R1, R11 | 2 | 1 kΩ | 500 mW is safer |
| R2, R12 | 2 | 100 kΩ | |
| R3, R4, R13, R14 | 4 | 10 kΩ | |
| U1 | 1 | Dual operational amplifier + socket | DIP-8 package, NE5532 |
Input / instrument
| Name | Qty | Value | Specific contraints or model |
|---|---|---|---|
| C1 | 1 | 100 nF | Ceramic X7R, 50 V, pitch 2.5 mm, must fit in a DIP-8 socket |
| C2 | 1 | 22 pF | Ceramic C0G/NP0, pitch 2.5 mm, 2.5 mm thick |
| C3 | 1 | 100 nF | Film, pitch 5 mm, 7.2 × 4.5 mm² max Ideally a material suitable for linearity (polypropylene) |
| D1, D2 | 2 | Small signal silicon diode | Reverse voltage > 60 V, 1N4148 |
| J1 | 1 | Pin header 1×3 | Optional (power) |
| J2 | 1 | Pin header 1×2 | Optional (audio) |
| J3 | 1 | ¼” female jack, stereo, switched, horizontal on PCB | Neutrik NMJ6HCD2 |
| R1 | 1 | 1 kΩ | 500 mW is safer |
| R3 | 2 | 2.2 MΩ | |
| U1 | 1 | Dual operational amplifier + socket | DIP-8 package, FET-based, OPA2134 |
Output / XLR, balanced
| Name | Qty | Value | Specific contraints or model |
|---|---|---|---|
| C1 | 1 | 100 nF | Ceramic X7R, 50 V, pitch 2.5 mm, must fit in a DIP-8 socket |
| C2, C4, C14 | 3 | 47 µF | 35 V, pitch 2.5 mm, Ø 6.3 mm |
| C3, C13 | 3 | 22 pF | Ceramic C0G/NP0, pitch 2.5 mm, 2.5 mm thick |
| J1 | 1 | Pin header 1×3 | Optional (power) |
| J2 | 1 | Pin header 1×2 | Optional (audio) |
| J3 | 1 | Male XLR connector on PCB | Neutrik NC3MAH |
| R0, R1, R10, R11 | 4 | 4.7 kΩ | |
| R2, R3, R12, R13 | 4 | 10 kΩ | |
| R4, R14 | 2 | 100 Ω | |
| R5, R15 | 2 | 1.5 kΩ | |
| U1 | 1 | Dual operational amplifier + socket | DIP-8 package, NE5532 |
Output / jack, balanced
| Name | Qty | Value | Specific contraints or model |
|---|---|---|---|
| C1 | 1 | 100 nF | Ceramic X7R, 50 V, pitch 2.5 mm, must fit in a DIP-8 socket |
| C2, C4, C14 | 3 | 47 µF | 35 V, pitch 2.5 mm, Ø 6.3 mm |
| C3, C13 | 3 | 22 pF | Ceramic C0G/NP0, pitch 2.5 mm, 2.5 mm thick |
| J1 | 1 | Pin header 1×3 | Optional (power) |
| J2 | 1 | Pin header 1×2 | Optional (audio) |
| J3 | 1 | ¼” female jack, stereo, switched, horizontal on PCB | Neutrik NMJ6HCD2 |
| R0, R1, R10, R11 | 4 | 4.7 kΩ | |
| R2, R3, R12, R13 | 4 | 10 kΩ | |
| R4, R14 | 2 | 100 Ω | |
| R5, R15 | 2 | 1.5 kΩ | |
| U1 | 1 | Dual operational amplifier + socket | DIP-8 package, NE5532 |
Unless specified :
- Resistors and diodes must be at most 7 mm long (DIN 0207 form factor).
- Resistors must support at least 250 mW.
- Resistors should be 1 % accurate, especially for balanced output modules. But most of the time 5 % is still acceptable.
- As usual with my THT designs, ICs must be mounted on sockets to make room for the decoupling capacitor underneath. However it is possible to solder the capacitor on the back of the board to remove the socket constraint (and use an SMD equivalent if available space is tight).
Schematics and PCB
Electronic schematics, Gerber files for the manufacturing, layouts and
KiCAD 8 source files are
located in the following archive:
audio-inout-2024-06-19.zip
(3015 kB).
Pictures below are for illustration purpose only.
Use the files from the archive as reference, layouts are located in the
print subfolders.
I packed the components tightly to reduce the board area, so labelling them was a bit challenging. Sorry for the lack of readability.
I can provide PCBs at cost price + shipping fees (from France). These PCBs are earlier versions shown on the top picture, their dimensions are sligthly different of the provided files (24 mm wide and shorter) but they are electrically identical. Please contact me if you are interested.
| [Home] [Productions] [Misc] | Website by Laurent de Soras, 2003-2024 |