Euraudio PSSR2S specifications

Welcome to the Euraudio PSSR2S specifications, in which you can read about the system requirements (application criteria), operation and technical data of the PSSR2S.

The PSSR2S is a symmetrical (+/-) power supply with two SPST ultra low distortion solid state relays (SSR) and with a ground loop breaker circuit. They were primarily designed for Euraudio's ultra low distortion power amplifiers, but might be used for other home-made audio amplifiers as well. Please find the PSSR2Sc assembly instructions here, which contains information about the sizing of the filter capacitors and fuses.

PSSR2S system requirements

What kind of amplifiers can the PSSR2S be used for?

They can be used for a two audio amplifier channels that needs a dual or in other words symmetric (+/-) supply voltage. Note: The PSSR2S can be used for two Euraudio LDA17 ultra low distortion, low noise audio amplifiers.

Up to what amplifier power can it be used?

The recommended maximum amplifier power is 2x125 W (speaking of class B or class AB amplifiers).

Protection board compatibility

For the control of the two SSRs, two protection boards are required. PSSR2S is fully compatible with the Euraudio DPB Protection circuit board. If you have to use the PSSR2S with the Euraudio APBF or APBM, then two components need to be reversely mounted on the PSSR2S PCB, which is covered in the assembly instructions of the PSSR2Sc.

If you wish to use the PSSR2S and its ultra low distortion SSR capability with a non-Euraudio Protection circuit board, then please contact me for the pinout of connectors J92, J93 through which you may be able to connect your own protection circuits.


The  PSSR2S rectifies the two sinusoidal AC voltages connected to its input, then smooths it by using filter capacitors, thus generating the symmetric (+/-) supply voltage that is necessary for most audio amplifiers.

To avoid ground loops, the grounding of the PSSR2S has a star-like arrangement, furthermore the PSSR2S contains a so-called ground loop breaker circuit, which prevents hum from appearing through the earthing conductor, if devices with earth ground protection against electric shock are connected to your amplifier, and the chassis of your amplifier is also earthed.

The SSR circuits are controlled from suitable protection boards by on/off voltages.

The on state of the relay can be indicated by a LED.

The SSR circuit uses a photovoltaic optocoupler to provide a floating gate voltage. The simplified SSR circuit can be seen in the following figure:

"RLYINx" is the input of the SSR x. "RLYOUTx" is the output of the SSR x (speaker hot terminal).

At the input of the rectifier bridge, there is space for a snubber RC network (R91, C91), that may be sized in order to decrease the oscillation between the leakage inductance of the transformer and the capacitance of the rectifier together with stray capacitance of the transformer. Installing the snubber network is not mandatory, and its sizing procedure is not part of the documentation. However, if you're interested, here's an article about it:

Technical data

At 25°C ambient temperature unless otherwise noted.

Supply current from the +9V supply: max. 40 mA (with an Euraudio DPB/APBF/APBM connected)

Power Supply

Bridge rectifier input voltage: max. 2x33 VAC (limited by SSRs)

Allowed continuous output current at 60 °C ambient temperature: max. 10 A

Recommended amplifier power: max. 2x125 W (class B or class AB)

Size of applicable filter capacitors:  snap-in type, max. 35 mm diameter

Solid State Relays (SSRs)

Switchable voltage: max. ±45 VDC; max. 32 VAC

Continuous current: max. 10 A (Ta=25°C); max. 7 A (Ta=75°C)

100 us pulse current before turn-off signal becomes active: max. 60 A (non-repetitive, Tcase,switching transistors=25°C)

Typical off-state attenuation on 4 ohms resistive load: >80 dB (1 kHz); 60 dB (20 kHz)

Turn-on time: < 2 ms

Turn-off time: < 400 us


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