Installation and instructions of use

Thank you for purchasing our product.

Before connecting and switching on the amplifier, carefully read the enclosed operating instructions and information about its installation. The user manual in electronic format is also available on the manufacturer’s website.

The Struss DM 250 amplifier has been designed and manufactured using the very latest technology and in accordance with global standards of quality, reliability and safety.

Recommendations for installing the amplifier

The device must be used indoors. It is intended for home use as general-purpose equipment. If the amplifier has cooled down heavily, e.g. due to being transported in cold weather conditions, wait a few hours before commencing set-up to bring it to room temperature.

The amplifier is not resistant to weather conditions, high humidity, flooding with water or other liquids.

Do not put objects filled with liquids on the device, e.g. vases, tea or coffee, bottles and glasses with alcohol, etc.

It is not recommended to use the amplifier for amplification, under conditions that cause long-term loads with a high-power output signal, e.g. mass events.

Damage to equipment resulting from use not in accordance with the manufacturer’s instructions is not covered by the warranty.

Transport of the amplifier

The amplifier is best transported in the factory packaging. With large temperature differences from outdoors to indoors, the cold device should be unpacked, and a few to a dozen or so hours should be allowed to let the equipment reach room temperature, and any condensation to evaporate.

Location of the installation of the amplifier

During operation, the amplifier emits heat. Do not to cover – block the ventilation openings in the casing of the amplifier. The top cover must not be exposed to direct sunlight.

The amplifier should not be installed near intense heat sources such as radiators or heating.

Do not place heat sources or open flames, such as lighted candles, on or near the device.

Connecting external elements

WARNING! Connect the power cord last of all.

Turn the POWER switch to the OFF position.

Turn the VOLUME potentiometer to the left-most position (loudspeaker volume control).

Connect the right speaker column to the right terminal marked (R) and the left speaker column to the left terminal marked (L). Attach and turn the terminal nuts by hand (not the banana plugs). Do not use a spanner or any additional tools to help you.

The amplifier can work with 4 Ohm and above impedance loudspeakers.

Connect sound sources in any order.

It is recommended to use high-quality cables to connect audio sources and loudspeaker cables, to ensure the highest quality of sound reproduction.

The separated line-in input with XLR sockets is designed for connecting sound sources that have a balanced (symmetrical) output. This input has a smaller capacity than the others and guarantees better sound reproduction. The other low voltage signal inputs will allow the use of cables with RCA plugs.

In the case of using PRE output and PA IN input, special care and attention should be taken to avoid possible overloading of the amplifier and loudspeakers, where the level of the signal from the sound signal source is too high.

Connect the power cord to the amplifier, ensuring that the power plug is pushed into the end of the power inlet and is connected securely.
It is allowed to use power cables of any company that meet the safety requirements and have the appropriate certificates in the field of electrical safety (designations).

Connect the power cord plug to the power supply – 220/240 V AC, 50/60 Hz.

Turn on the sound source and amplifier with the POWER switch to the ON position.

Select the appropriate sound source with the rotary switch – the selection will be indicated by the lighting of the corresponding blue LED.
Use the VOLUME potentiometer to set the appropriate volume or perform this operation using the remote control.

The RCA output marked PRE OUT is used to use the preamplifier to control external power amplifiers.

The RCA input marked with PA IN is only used to utilise the end power amplifiers in the amplifier. To use this amplifier’s operating mode, the source selection switch should be switched to the PRE IN position.

Breaking in time of the amplifier

During the production process, the amplifier undergoes a breaking in process, after which a repeated control test of parameters is carried out.

The complete breaking in process takes place at the end user, after about 1-2 weeks of use. Minimum of 100 hours of functioning.

The amplifier and loudspeaker protection system against damage

In order to protect the amplifier and loudspeakers, mainly tweeters, the amplifier is equipped with 2 types of safeguard measures:

Short-circuit protection

When you switch the speaker cords during music playback (not recommended), short-circuits of wires or output terminals may occur. The protection system will disconnect the loudspeakers for approx. 2 seconds. If the short circuit in the amplifier output circuit is permanent (e.g. error in the installation of cables), the amplifier should be switched off as soon as possible and the cause of the short-circuit should be removed. Do not test the safeguard system when the power output of the amplifier is permanently shorted, as this may lead to failures not covered by the warranty.

In the case of exceeding the maximum allowable power output, distortion (clipping) appears on the output of the amplifier that may cause damage to the tweeters. In this situation, the amplifier will disconnect the loudspeakers for a period of about 2 seconds. You should immediately lower the volume by using the Volume or remote control knob.

Specification of technical parameters of the DM 250 amplifier

Output power: 2 x 130 W/8 Ω, 2 x 250 W/4 Ω (DIN 45500)

Operation in class A: 2 x 10 W/8 Ω

Minimum load: 1 Ω (instantaneous)

Output impedance: 0.1 Ω

Distortions – THD:

  • 0.1 % at1 W/8 Ω,
  • 0.025 % at 120 W/8 Ω

Bandwidth: 5 Hz – 100 kHz – 3 dB/1 W/ 8 Ω

Nonlinearity within the band 20 – 20,000 Hz: ± 0.1 dB

Band irregularity in relation to RIAA curve for the gramophone input MM: ±0.15 dB

Slew rate: 150 V/μs

Total interference on speaker outputs in the band 20 – 20 000 Hz: 0.25 mV

Signal-to-noise ratio: 135 dB (IHF – A)

Preamplifier amplification: 4 dB, output impedance 50 Ω


  • 2 x universal – RCA,
  • XLR,
  • separated CD/DAC – RCA,
  • phono MM (gramophone) – RCA

Sensitivity of inputs:

  • 500 mV – universal inputs and CD/DAC,
  • 250 mV – XLR input,
  • 3,5 mV – MM input,
  • 0.775 mV – power amplifier inputs

Input impedance:

  • 47 kΩ – power amplifier inputs,
  • 100 kΩ – universal inputs and CD/DAC,
  • 22 kΩ – XLR,
  • 47 kΩ/100 pF – MM (gramophone)

Potentiometer (volume): precise Alps – Blue Velvet

Transformers: 2 4 x 15,000 uF – Nippon Chemi-Con

Advanced protection system: against speaker short circuit and DC voltage occurrence on the output

Remote control: kod RC5 (volume)

Power consumption: 37 VA – 800 VA (peak)

Dimensions: 430 x 102 x 338 mm

Net weight: 15.4 kg; remote control 0.370 kg

Power cable

Socket: Voltage requirements –
(EU) AC – 230/240 50/60 Hz
(US) AC-100/125 50/60 Hz

Power cable

Connecting speakers

Speakers Binding Posts: Right (Red +), Left (White -) / speakers 4 – 16 Ohm

Connecting speakers


Power amplifier input connection

RCA (CINCH) : (PA IN Right (Red +), Left (White -)

Power amplifier input connection

CD / DAC player

Input RCA (horizontal): CD – DAC (Red -right, White -left)

CD / DAC player


Inputs RCA (vertical): AUX 1, AUX 2 (Red -right, White -left)


Gramophone grounding

Terminal: GDN

Gramophone grounding

External power amplifiers connection

Inputs RCA Vertical) : PRE OUT (Red -right, White -left)

External power amplifiers connection

Remote control

Remote control

Environmental protection and preservation

For the sake of the natural environment, please remember that damaged amplifiers should be sent to specialised companies dealing in the utilisation and disposal of electronic devices. Dispose of used batteries from the remote control in special containers.


Szanowni Państwo, informujemy, że właściciele Struss Audio podjęli decyzję o zmianie nazwy spółki na Soundastic. Pod nową nazwą nadal będziemy produkować sprzęt audio, stawiając sobie za cel umożliwienie Państwu obcowania z pięknym i czystym dźwiękiem.

Dear Sirs, we would like to inform you that the owners of Struss Audio have decided to change the company's name to Soundastic. We will continue to produce audio equipment under the new name, with the goal of enabling you to experience beautiful and clear sound.

Holler Box