Based on designs from these sources:
- Precision, AC Reference Signal Attenuator Using the AD5546/AD5556 Multiplying DAC
- New High-Resolution Multiplying DACs Excel at Handling AC Signals
This design is also used by a number manufacturers:
- Mark Levinson preamps
- Luxman LECUA (Luxman Electronically Controlled Ultimate Attenuator)
- Accuphase AAVA
Features:
- 65536 linear steps
- Gain possible, set by op-amp and resistors
- Excellent performance
- Can drive headphones
- Compact
- SPI controlled
Here is the DIYAudio forum thread with my prototypes and questions: Solid state R2R attenuator using analog switches or multiplying DAC
Python module is here: code/modules/mdac_attenuator.py
| Reference | Quantity | Value | Footprint / Notes |
|---|---|---|---|
| C1A1, C1B1 | 2 | 2pF | 0805 |
| C4, C6, C7 | 3 | 100nF | 1206 |
| C2, C3, C5 | 3 | 100uF | Radial 10/5mm or SMD |
| IN1, OUT1, PWR1 | 3 | 1x3 | Molex KK 254, Multicomp MC34 or any 0.1" socket header |
| J1 | 1 | 1x6 | Molex KK 254, Multicomp MC34 or any 0.1" socket header |
| J2 | 1 | 1x6 | 0.1" socket header, for passthrough to input-selector |
| LED1 | 1 | LED | 1206 |
| R1 | 1 | RLED | 1206 |
| R1A1, R1B1 | 2 | 91R | 1206 |
| R2A1, R2B1, R4A1, R4B1 | 4 | 120R | 1206 |
| R3A1, R3B1 | 2 | 360R | 1206 |
| U1 | 1 | AD8599ARZ | SOIC-8 |
| U2 | 1 | DAC8812ICPWG4 | TSSOP-16 |
Values for R1, R2 and R3 above give a gain of 4.
To calculate gain use this formula:
gain = (R2+R3)/R2
R1 = (R2*R3)/(R2+R3)
Refer to the AD5429/AD5439/AD5449 datasheet