One Four All – Low-Noise Audio PSU

5V input via USB-C or wires:
- At least 2A USB supply recommended, heavy loading requires 3A.
- Use USB power bank for fully isolated power.
Generates the following supplies from a single 5V input:
- VD – 5V digital, up to 400mA.
- VA – 6V analog reference supply, up to 150mA.
- VP/VN (+/-13.3V analog amplifier/opamp supply), up to 250mA per supply.
Molex Micro-Fit power output connectors to power multiple Kaamos boards (subject to current limits) with simple connections:
- 2-pin Molex for digital-only boards.
- 6-pin Molex for mixed-signal boards.
- All output connectors are in parallel so total current per supply must be within the limits.
Extensive protection features for increased reliability and robustness:
- Power-up sequencing to decrease inrush current.
- Input reverse polarity protection.
- Input over-voltage protection and under-voltage shutdown.
- Current limit and under-voltage shutdown on each output channel; if one shuts down, all shut down.
Soft power button to toggle the PSU between standby and active states.
Hard power switch to fully turn off power (recommended when not in use).
Mute output to quickly mute DACs in case of output failure.
PCB is 107×52.5mm (slightly larger than v1.5).

Power input

Input is nominal 5V (4.8-5.2V). Due to voltage drop in the cable and input circuits, a slightly elevated voltage of 5.1-5.2V eases thermal stress of the PSU with heavier loads. We have used official Raspberry Pi 3A (27W model) and 5A (45W model) supplies in our tests and they have worked really well.

Under heavier load the USB cable also matters. We recommend a short or thick cable; low resistance is key.

See the board guide for examples of current consumption.

Notes:

VIN connector / wiring is in parallel with USB-connector – do not use both simultaneously.
USB is power only (type C USB2). There are no data or handshaking, only 5.1k resistors on CC pins.

Hard power switch

Toggle power switch (new in v2) completely turns off power which is recommended in DIY electronics when not used. If the board is mounted on a panel, the switch is accessible next to the USB power input.

There is an ‘EXT SW’ placeholder next to the onboard switch which allows wiring an external power switch, e.g. if another style or location of switch is preferred. This is in parallel with the onboard switch so the onboard switch must be off. Any external switch must be rated for 3A DC or higher.

Soft power button

Soft ON/OFF button (new in v2, v1.5 had separate ON and OFF headers) toggles the PSU between ON and OFF (standby). Besides the onboard button, an external button can be wired between the ‘GND’ and ‘ON/OFF’ pins of the header. It is only for logic signal and can be a small signal switch with thin wires.

Due to limitations of the already complex hardware state-machine, when toggling from OFF to ON and keeping the button depressed for longer than around 1 second, the PSU toggles back from ON to OFF.

Soft ON/OFF button on the right edge, or external button between ‘ON/OFF’ and ‘GND’ on header.

Power-up

Upon power-up, the PSU turns ON automatically (this can be changed, see below). All output channels (5V, 6V, +/13V) are turned on in a sequence to minimise start-up current spike. Successful ON-state is signalled by the ON LED. MUTE output is low.

OVL/FAULT LED signals a state where the PSU tries to be ON but there is a fault in the outputs. It is normal it to blink when transitioning between OFF and ON. This state should never be longer than a blink since any fault should turn off the outputs and go to OFF state.

If the PSU fails to power-up (not staying ON), please see capacitance options below or startup troubleshooting in the OFA Guide.

If you connect a high capacitance load when the PSU is ON, it is normal it turns OFF because the current spike triggers over-current protection. When the PSU is turning ON, the over-current protection is temporarily disabled so it can charge load capacitances.

Input capacitance options

New in v2 are options for input capacitance. By default, the PSU has 470uF input capacitor. This is already a high capacitance in a USB device but it has proven to be beneficial to help the PSU start up in different scenarios.

However, 470uF is not enough for a robust start-up in some cases. For example, if the PSU is powered by Raspberry Pi, this can lead to an oscillating state where the PSU tries to start up, but RPi cuts off the power due to high start-up current, and this keeps repeating. Adding more input capacitance helps. Therefore, there are two additional 470uF capacitors that are disconnected by default but can be added via shorting links on the bottom side. In our tests adding one more was enough for Raspberry Pi 5.

Short JP101 and/or JP102 to add more input capacitance, 470uF each.

Changing default power-up state

By default, the PSU turns ON when power is turned on. This can be changed with a shorting link on the bottom side. By shorting the link, the board defaults to OFF after power-up. Engaging the soft power button (or header) turns the PSU ON.

Short JP201 to remain OFF after power-up.

Mute output

Active-high (around 5V through 1k resistor) mute output can be used to signal standby-state to external circuits. It is high when the PSU is OFF, and low when it is ON. Alternatively, this could be used for an external standby LED.

Using with non-Kaamos modules

If you want to use the PSU with boards that don’t have Molex power connectors, the best option is to get a power cable (6-pin / 2-pin) and cut the connector off at one end, and solder the wires to your circuit.

Important information on order

All required components are soldered down and the board is fully tested.
Please ensure you have the skills to solder the remaining components and wires to connect the board in your system – and most of all understand what you are doing.
If you need help prior to purchase, please contact us.

Order contents

The board is delivered with following parts included, shown in the photo below:

Fully tested board with all components populated.
VIN Molex connector.
PCB panel mount kit for USB-end:
- 2pcs small L-brackets.
- 4pcs 4-40 1/4″ screws (hex head, likely imperial but around 2.5mm).
PCB bottom mount kit:
- 2pcs 6mm standoff.
- 2pcs M3 bolt (2.5mm hex head).
- 2pcs M3 nut.
- 2pcs M3 flat washer.
- 2pcs M3 spring washer.

More information

See the One Four All Guide for more information on the following topics:

Input voltage range and impact of wiring resistance.
Number of boards OFA can supply.
Soft-start and soft-stop.
OFA startup problems.

Files

We do not guarantee the files are 100% match with the board. Especially when it comes to mechanical design based on the 3D-model, please verify any dimensions on the actual board since the model relies on 3rd party component models we have not verified.

Schematics may be released later on
Component placement and board dimensions
3D-model (.step, 75MB)
Older version v1.5 product page in PDF

See board version history at the bottom of the page.

Measurement results

Measurements are from v1.5 but the core PSU circuits are unchanged in v2.

Audio performance

Comparing W-DAC and ADC AK5572 performance when using linear bench power supply or One Four All, no differences have been measured in the audio performance figures such as dynamic range and THD+N.

Current consumption

Following are examples of current taken from 5V input supply. The current depends on the exact board input voltage; any voltage drop in the input wiring means higher input 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.

Cleaning input supply

This example uses Anker 735 USB-charger to supply One Four All, and the noise of the 5V input and 5VD output is compared.

5V input from USB-charger.

VD output.

As we see, the PSU effectively cleans the input and the 5V input is not used directly for VD output. Instead, it goes through a switcher, filters, and a high-performance LDO.

Output noise

Noise has not been characterised accurately but to see it is roughly as expected. The noise of the power rails was lower than the measurement instrument capability; therefore, the values are only given as "better than" the instrument limit.

Measurement conditions:

Source: Anker 735 USB-charger.
Loading: 100mA per output rail.

The following results apply to all rails (VD, VA, VP, VN):

Noise in 20kHz bandwidth: <1uV RMS
Noise in 90kHz bandwidth: <2uV RMS
Noise in 1MHz bandwidth: <10uV RMS

The noise floor is almost flat at least until 1MHz in our measurements, except for the slight increase in the low frequencies, shown below. VD is better, while VA, VP, and VN look practically identical.

VD noise floor (256k FFT).

VN noise floor (256k FFT), VP/VN are similar.

These measurements do not show the switching frequencies; we will try to get higher bandwidth results one day but currently do not have measurement kit for that.

Switching transients

The converters work at a bit over 1MHz switching frequency which is the fundamental frequency of the ripple; however, CLC filters and LT30xx LDOs with very high PSRR push the ripple below the noise floor. However, when the switches (FETs and diodes) turn on and off, they create spikes with ringing in the 250-350MHz range which is more difficult to work with. Moreover, getting reliable measurement results is not straightforward as probes and cables easily pick up this ringing.

A lot of effort has been spent to attenuate the transients. The first line of defence is at the switching node where a properly calculated RC-snubber greatly attenuates the ringing (by sacrificing a bit of efficiency), verified by careful active probe scope measurements. Then we have small capacitors plus a high-bandwidth ferrite followed by another set of small capacitors, forming a CLC-filter. Finally, we have the LDOs with capacitors. However, transients at this high frequency just go through the LDOs so we need to rely on the passives and parasitics for filtering. Overall result is significant attenuation of the switching spikes but the reality is that they are never completely gone - we just need to push them as low as we can.

It is worth noting that switching transients are not only present in switching power supplies. Rectifier diodes in linear power supplies are switching elements as well, causing similar switching spikes that need attention.

Load transient response

Load transients cause no ringing at the output. There is a small step due to DC-resistance and shared output path between all the output Molex connectors. Below is an example from VD where it is the worst due to the highest current output. The load is stepping between 50-350mA (pink), while yellow is the voltage before the LDO and green after the LDO. This small 7mV step is due to the voltage drop in the output trace resistance when the measurement is done at the output connector.

VD load transient response.

Board version history

First sold version was v1.5, except early bird boards were v1.4. The changes between the two are minor, mostly in clarifying the silkscreen.

Version 2 has the same switcher and LDO circuits. Inductors have changed due to availability of the original inductors, but the performance is on par with the previous ones.

Main changes in v2 are:

Hard power switch.
Combined ON/OFF button instead of separate ON and OFF headers.
Option to start up in OFF state.
Higher input capacitance and option to add more in.
VIN Molex header for future options.
PCB is slightly larger: 107x52.5mm vs 100x50mm.
New PCB styling to match recent Kaamos boards.

Difference between v2.1 and v2.2 are only small footprint tweaks.

One Four All – Low-Noise Audio PSU

Power input

Hard power switch

Soft power button

Power-up

Input capacitance options

Changing default power-up state

Mute output

Using with non-Kaamos modules

Important information on order

Order contents

More information

Files

Measurement results

Audio performance

Current consumption

Cleaning input supply

Output noise

Switching transients

Load transient response

Board version history

General Info

Contact

One Four All PSU

One Four All – Low-Noise Audio PSU

Power input

Hard power switch

Soft power button

Power-up

Input capacitance options

Changing default power-up state

Mute output

Using with non-Kaamos modules

Important information on order

Order contents

More information

Files

Measurement results

Audio performance

Current consumption

Cleaning input supply

Output noise

Switching transients

Load transient response

Board version history

Related products

Power Splitter Board

LT30xx LDO Module

General Info

Contact