Usual (bad) Eurorack power over ribbon cable with +12V, 0V, -12V and optional +5V, Gate and CV (latter two not used here). Module assumes each power rail is poorly regulated, with up to 0.5V droop likely.
Module uses two ribbon cables. 0V on one is treated as digital ground, and +5V on that cable powers digital circuits.
0V on the other is treated as analog ground, with +12 and -12 powering op-amps and secondary voltage regulators.
This means the connection between digital and analog occurs at the PSU busboard.
This should reduce digital return currents on analog ground. However, digital 0V to SPI DAC meets analog 0V unless isolator is used, and other connections between grounds will occur due to panel jacks and external patching.
Performance DACs, and the Global DAC which re-uses the same boards, run at 5V5 so there is headroom above the internal 5V reference. High voltage side of the logic level converters for those DACs use 5V5 also. Derived from +12V.
Pitch DACs run at ±9.5V and the Vref for those uses ±9.5V as well. No logic level conversion needed, pitch DAC is 3V3 compatible.
Use LT1763 (SOIC-8, 500mA) adjustable regulators (500mA is ample) to produce 5V5 and 9V5, with 6μ8 C0G output cap. -9V5 from LT1964-BYP adjustable (SOT-23, 200mA still plenty). LT1763 noise (10Hz-100kHz) is 20 μVRMS.
For testing, a 317 regulator (noise, 10Hz - 100kHz is 165 μVRMS). With R1 = 240R and R2 = 820R gives 5V5, while with R2 = 1k54 it gives 9V3.
Teensy 4.1 main board is a 3V3 device with onboard 3V3 regulators and a Vin pin which accepts 3V6 to 6V0 input. Use Eurorack 5V supply (reduces asymmetric loading on +12V rail). Current draw can be 100mA, depends on clock speed.
Direct from Eurorack, perhaps with Schottky diodes for reverse power protection. Usual electrolytic caps onboard, and small ceramics by each op-amp package.
Pitch DAC op-amps can run on ±9.5V to handle ±5V CV. Perf DAC op-amps, if RRIO, could run on unipolar 5V5 but bipolar 12V makes it easier to hit 0V easily. Depends on opamp choices.
Vref power is same +9V5 as Pitch DAC power.
To be determined. Options for (about) 5V, 8V gates useful. Exact level not critical.
Same Gate and LED board needs voltage level conversion and current drive for the two RGB LEDs.
Eurorack power connector, usual 10μF smoothing caps (or greater)? Top plane mostly gnd (for low impedance and also cooling) with traces for ±9V5 and for +5V5 outputs; bottom plane gnd (again for cooling), well stitched to top, with traces for ±12V inputs.
Maybe locate on back of the perfdac-jack and pots board, which is otherwise unused, and add two standoffs after the pots to make it more stable?
Output Capacitance and Transient Response The regulators are designed to be stable with a wide range of output capacitors. Output capacitor ESR affects stability, most notably with small capacitors. A 3.3μF minimum output value with ESR of 3Ω or less is recommended to prevent oscillation. Transient response is a function of output capacitance. Larger values of output capacitance decrease peak deviations, providing improved transient response for large load current changes. Bypass capacitors, used to decouple individual components powered by the regulator, increase the effective output capacitor value. Larger values of reference bypass capacitance dictate larger output capacitors. For 100pF of bypass capacitance, 4.7μF of output capacitor is recommended. With 1000pF or more of bypass capacitance, a 6.8μF output capacitor is required.
The shaded region of Figure B1 defines the regulator’s stability range. The minimum ESR needed is set by the amount of bypass capacitance used, while maximum ESR is 3Ω.
(source: DEMO MANUAL DC368A)
10μF input cap, 1nF noise bypass cap, 6μ8F to 10μF output cap (see Fig 3. Stability and discussion of ceramic dielectrics: go for X7R).
Minimum top resistor (R2) value is 2.6k. Try with 47k. First approximation:
9.5 = 1.22(1 + r2/r1)
9.5 = 1.22 + 1.22 × r2/r1
8.28 = 1.22 × r2/r1
r1 = (1.22 × r2)/8.28
r1 = (1.22 × 47000)/8.28
r1 = 6k98 which happily is an E96 value.
Second approximation:
Vout = 1.22(1 + 47000/6980) + 30E-9 × 47000 = 9.436V. Second term is 1.41mV so ignore.
Current through r1 is 1.22/6980 = 170μA Current through r2 is (9.5-1.22)/47000 = 170μA.
Power = output current times in-out voltage differential, plus ground current times input voltage. Say 50mA × (12.5 - 9.5) + 2mA × 12.5 = 175mW.
From datasheet, table 2: use 100mm² top-side ground plus 25000mm² lower ground plane = 10 × 10mm top; no go bigger, 1000mm² = 32 ײ 32mm top. 50 × 500mm bottom seems unfeasibly large (19 inches!!). Going to need much better current draw estimates!
But assuming 74C/W, rise above ambient is just 13C.
Higher rise due to bigger voltage drop.
5.5 = 1.22 + 1.22 × r2/r1
4.28 = 1.22 × r2/r1
r1 = (1.22 × 47000)/4.28
r1 = 13k4, closest E96 is 13k3.
Vout = 1.22(1 + 47000/13300) + 30E-9 × 47000 = 5.53V.
Power = 50mA × (12.5 - 5.5) + 2mA × 12.5 = 375mW.
At 74C/W, rise above ambient is 28C.
10μF? input cap, 1nF noise bypass cap, 6μ8F to 10μF output cap
-9.5 = -1.22(1 + r2/r1)
-9.5 = -1.22 + 1.22 × r2/r1
-8.28 = -1.22 × r2/r1
r1 = (-1.22 × r2)/-8.28
r1 = (-1.22 × 47000)/-8.28
r1 = 6k98
Vout = -1.22(1 + 47000/6980) - 30E-9 × 47000 = -9.436V.
Power = -50mA × (-12.5 - -9.5) + -2mA × -12.5 = 175mW.
At 135C/w, 23.5C above ambient.
Measure current draw of perf DAC board (5V5 regulator needs to power 2) before ordering PSU parts, to be sure the SMD 5V5 will be suitable. Might need a 3-pin regulator.