One Four All Guide

Following is additional information on using Kaamos One Four All power supply board. Please also see the product description. If something is still unclear, please contact us. We will try to update the information based on feedback.

The concept

One Four All (OFA) is a high-quality all-in-one power supply that generates four supplies from a single 5V input. It has multiple power outputs to easily power several Kaamos (or other) audio boards. In addition, the board provides comprehensive protection and safety features for increased reliability and robustness – and peace of mind.

In the heart of the design are three switching converters: two boosts and one inverter. The switched voltage rails are filtered with snubbers and CLC-filters designed based on lots of measurements, and the final output power rails are provided by very high-performance LT30xx linear regulators with very high and wide-bandwidth PSRR and low noise.

The board can be supplied by a generic USB-charger or power bank for isolated power. The PSU is not sensitive to input power noise and interference as the input goes through the converters, filters, and LDOs. However, a decent quality input supply is still preferred to avoid any issues.

Power outputs

There are two types of Molex Micro-Fit output power connectors with following supplies:

• 2-pole digital-only power output:
  • VD (5V digital).
  • GND.
• 6-pole mixed-signal power output:
  • VD (5V digital).
  • VA (6V analog reference).
  • VP (+13-14V analog amplifier/opamp supply).
  • VN (-13-14V analog amplifier/opamp supply).
  • Two GND pins.

OFA has three output connectors (in parallel) of each type to power up to six boards, given that the following total output currents are not exceeded:

• VD: 400mA.
• VA: 150mA.
• VP: 250mA.
• VN: 250mA.

Each supply is equipped with a current-limit and under-voltage monitor. If any one output supply turns off, all turn off. Soft-start or power-toggle restarts the PSU.

Power input

Power input is 5V via USB-C or wires soldered onboard. Maximum input voltage is around 5.3V. Over-voltage protection kicks in at around 5.5V and the input also has a reverse polarity protection.

Board input voltage

The board takes significant current from the 5V input supply and there is always a voltage drop due to wiring resistance. If the board is heavily loaded, the input wires should be thicker and shorter. The board input voltage can be measured under full load to see how much it drops. It is recommended to keep the board input over 4.7V. If the input drops under 4.3V (exact limit depends on the current), the board turns off.

Power switch

We always recommend turning the board off completely when not in use. An easy option is to unplug or turn off the input supply but if this is not viable, there is a connector for external ON-OFF power switch onboard. As the power switch is in series with the input and carrying all the input current, the switch must have low enough on-resistance to meet the board input voltage requirement. Switches rated for several amperes should meet this requirement.

Input current

Fully loaded the PSU can take up to 3A of input current. Even if not fully loaded, the input supply should have sufficient current rating due to inrush current. 5V/2A supply is sufficient for most use cases but higher loading requires 3A supply; see examples below and leave some headroom. There is no USB-handshaking; OFA has sense resistors to tell the host it needs up to 3A current but does not check if the source can support that.

Following input supply currents are guidelines, the exact voltage at the board input has impact on the current (higher voltage drop means lower input voltage and higher current).

• Outputs on, no load: 90mA.
• Outputs off: <2mA.
• VD 100mA, VA 100mA, VP/VN 100mA each: 1.2A.
• VD 200mA, VA 100mA, VP/VN 200mA each: 2.2A.
  • It is normal the board gets very warm under this loading; the hottest components can get near 80C – and even hotter if loaded to the maximum. VP/VN loading stresses the board more than VD/VA loading.

For reference, Kaamos converter boards take approximately:

• W-DAC + XLR add-on
  • VD 35mA, VA 40mA, VP/VN 40/35mA + VD 20mA, VP/VN 30/30mA.
• ADC AK5572
  • VD 15mA, VA 30mA, VP/VN 70/70mA.

Soft-stop and soft-start

Soft-stop puts the PSU in standby and soft-start turns it back on. These can be engaged with a push-button (ON)-OFF type switches. Note that the soft-stop turns off all outputs but the PSU logic remains on.

The PSU turns on all outputs upon power-up and can be turned off by a hard power switch or unplugging the input; therefore, soft switches are optional.

Mute output

Mute Out is active-high with around 4.8V level when the PSU is powered with outputs off (either because of soft-stop or output failure). It can be connected to W-DAC EMUTE input, for example, to quickly mute the output if power turns off (as the DAC already has its own power monitor mute, this may not make any difference).

Mounting hardware

OFA has a mounting hole on each corner of the PCB like other Kaamos boards. Normal standoffs can be used on each corner but we also provide small L-brackets for panel mounting. The L-bracket pads and holes are plated with low-inductance connection to the casing of the USB-connector.

Startup troubleshooting

Due to extensive protection features, the PSU may fail to power up under certain conditions. This is indicated by OFF-LED after power-up and non-functional soft-start. Here are some troubleshooting steps.

Too low input voltage may cause startup failure. This can occur due to several reasons:

• Input voltage supply is too low.
  • Worth checking but this is unlikely the case if using a 5V supply.
• High input wiring and/or power switch resistance. Too high series resistance causes the input voltage to drop too much at power-up when the PSU loads the input. There is always an inrush current at start-up as well that makes the input voltage momentarily lower than steady-state loading.
  • What is too high resistance? It depends on the loading. We recommend aiming to keep the board input voltage at 4.7V under load. With lighter load it should work down to 4.3V but this gives some headroom for heavier loads.
• Input supply current limit. The above-mentioned startup-droop gets worse if the input supply cannot provide sufficient startup current. Hence we recommend at least 2A 5V supply even with light loads.
  • If you think the input wiring resistance is low enough, please try another USB-supply.

Another source of failure may be due to output supplies not reaching their final values within the startup sequence time (200ms) because of:

• Too high load current. If the output current limits are exceeded, outputs are turned off.
  • Check combined output load current and see the limits are not exceeded. Check that connected boards are working fine, maybe one at a time.
• Too high load capacitance. As all output channels are current-limited, charging high capacitances take time, causing voltages to go up too slowly.
  • What is too high capacitance? It depends on the combination of capacitances between channels and overall loading. If overall loading is low, there is more current available to charge the capacitances than if we are already near the current limit. We have tested the PSU with 1000uF on each channel (VD, VA, VP, VN) at moderate loading successfully. At low loads the capacitances can be higher, but being close to the limit this may be too much.

Other questions

Can I use OFA with a 4.2V Lithium battery?

As it is now, no. Currently the input under-voltage shutdown engages at around 4.1V. We have evaluated the performance down to 3.5-3.2V what it should support in such case. Some output channels work fine but VN struggles especially if input voltage drops slightly. With minor changes (maybe just a different BOM) we could make a variant with significantly lower output current capability (likely to power only one ADC or DAC) that supports Li-Ion use. If you are interested in such use case, please let us know. No promises but if there is enough interest, we’ll look into it. Some of the work is already done. Note that any battery management circuitry would need to be external.