Euraudio PSS701/PSS702 specifications

Welcome to the Euraudio PSS701/PSS702 specifications, in which you can read about the system requirements (application criteria), operation and technical data of the PSS701/PSS702.

The PSS701 and PSS702 are symmetrical (+/-) power supplies with an SPST ultra low distortion solid state relay (SSR) and with a ground loop breaker circuit. The only difference is that PSS701 has place for one filter capacitor pair, while the PSS702 has place for two pairs. 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 PSS701/PSS702c assembly instructions here, which contains information about the sizing of the filter capacitors and fuses.

PSS701/PSS702 system requirements

What kind of amplifiers can the PSS701/PSS702 be used for?

They can be used for a single audio amplifier channel that needs a dual or in other words symmetric (+/-) supply voltage. You need as many PSS701/PSS702's as the number of the separately grounded channels is within your amplifier chassis. For example for a dual mono amplifier, you need two PSS701/PSS702's. It is not recommended to use them in stereo amplifiers, because the shared grounds create a ground loop with possible hum ingress. Note: The PSS701/PSS702 can be used for the Euraudio LDA17 and LDA172 ultra low distortion, low noise audio amplifiers as well.

Up to what amplifier power can it be used?

The recommened 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. PSS701/PSS702 is fully compatible with the Euraudio APB Protection circuit board. If you have to use the PSS701/PSS702 with the Euraudio APBF or APBM, then two components need to be reversely mounted on the PSS701/PSS702 PCB, which is covered in the assembly instructions of the PSS701/PSS702.

If you wish to use the PSS701/PSS702 and its ultra low distortion SSR capability with a non-Euraudio Protection circuit board, then please contact me for the pinout of connector J92 through which you may be able to connect your own protection circuits.


The  PSS701/PSS702 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 PSS701/PSS702 has a star-like arrangement, furthermore the PSS701/PSS702 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, but also has its own pull-up resistor. You can decide where you install the pull-up resistor. If you install it in the PSS701/PSS702 board and you disconnect the protection board, then the relay is always on. If you install the pull-up resistor in the Euraudio protection board and you disconnect the protection board, then the relay is always off. The latter is recommended.

The on state of the relay is indicated by a green 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:

"RLYIN" is the input of the SSR, "SPKHOT" is the output of the SSR (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 +12V supply: max. 40 mA (with an Euraudio APB/APBF/APBM connected)

Power Supply

Bridge rectifier input voltage: max. 2x50 VAC

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

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 (SSR)

Switchable voltage: max. ±70 VDC; max. 50 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. 80 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: < 1.2 ms

Turn-off time: < 400 us


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