Euraudio PSSR350 specification

Welcome to the Euraudio PSSR350 specifications, in which you can read about the system requirements (application criteria), operation and technical data of the PSSR350.

The PSSR350 is a symmetrical power supply with an SPST ultra low distortion solid state relay (SSR) and with a ground loop breaker circuit. It was primarily designed for the Euraudio LDA172hc low distortion power amplifier, but can be used for other home-made audio amplifiers as well. Please find the PSSR350c assembly instructions here, which contains information about the sizing of the filter capacitors and fuses.

PSSR350 system requirements

What kind of amplifiers can the PSSR350 be used for?

It can be used for a single amplifier channel that needs a dual or in other words symmetric (+/-) supply voltage. You need as many PSSR350's as the number of the separately grounded channels is within your amplifier chassis, for example for a dual mono amplifier, you need two PSSR350's. If you want to use them in stereo amplifiers, then be careful, because the shared grounds may create a ground loop with possible hum ingress. Note: The PSSR350 can be used for the Euraudio LDA162mc, LDA162hc, LDA172mc and LDA172hc low distortion, low noise audio amplifiers as well.

Up to what amplifier power can it be used?

The recommended maximum amplifier power is 250 W (speaking of class B or class AB amplifiers).

Protection board compatibility

For the SSR control, a protection board is required. PSSR350 is fully compatible with the Euraudio APBM or APBF protection circuit boards. If you have to use PSSR350 with the Euraudio APBT or APB, then a simple workaround is needed, which is covered in the assembly instructions of the PSSR350.

If you wish to use the PSSR350 and its ultra low distortion SSR capability with other protection boards (not with Euraudio's APBM, APBF or APB), then please contact me for the connector J92 pinout through which you may be able to connect your own protection circuits.


The  PSSR350 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 void ground loops, the grounding of the PSSR350 has a star-like arrangement, furthermore the PSSR350 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 circuit is controlled from a suitable protection board by a on/off voltage. If the protection board is disconnected, then the relay is off.

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

"AOUT" is the input of the SSR (amplifier output), "SPKHOT" is the output of the SSR (speaker hot terminal).

Technical data

At 25°C ambient temperature unless otherwise noted.

Power Supply

Bridge rectifier maximum input voltage: 2x50 VAC

Maximum allowed continuous output current at 60 °C ambient temperature: 10 A limited by the heatsink of the rectifier bridge)

Recommended amplifier power: max. 250 W (class B or class AB)

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

Solid State Relay

Maximum switchable voltage: ±70 VDC; 50 VAC

Maximum continuous current: 10 A (Ta=25°C); 7 A (Ta=75°C)

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

Maximum 100 us pulse current before turn-off signal becomes active: 80 A (non-repetitive, Tcase,switching transistors=25°C)

Turn-on time: < 1.2 ms

Turn-off time: < 400 us


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