Product Description

SYMEF TYPE S220 Watts Class AB amplifier

Product Overview

Class A/B amplifiers provide the warmest fullest bass. SYMEF has a huge Soundstage, vocals are accurate and highs are detailed. Overall the sound is very balanced in the whole audio range, no slamming bass or shrill voice. It's just perfect. THD 0.002%, 1 Watt, 1kHz, 4 Ohm. This is a very unique and exceptional amplifier. It's like a tank and won't disappoint. Kindly consider purchasing our or any other speaker delay and protection circuit.


170mm * 125mm . Allowing for creation of a multichannel amplifier and or active speaker system.

Power Source

Unregulated +/-40VDC to MAX +/-60VDC, checkout our power supply module.


You will need a suitable heatsink with at least 0.6 C/W dissipation and mounting kit. The module has holes for mounting. M3 screws and standoffs would be suitable for attachment.


The amplifier should reach full power at line level voltages. You may use a preamplifier of your choice.

1. Connect the output transistors to a suitable heatsink using thermal pads, washers and


2. Ensure short circuit protection fast blow 6.3A are fitted on the board

3. Short the input with a jumper for initial power up and bias testing.

4. R28 is a 25 turn pot, center it at 12 turns.

5. Before attaching power,let the main power supply discharge by itself before connecting

its leads to the board.

6. While power supply is powered down and discharged naturally connect the ground lead of the power supply first, then the negative lead and finally the positive lead

7. Use a multimeter to measure the voltage between speaker ground and speaker out

terminals. This should preferably be less than 50mV.

8. For bias adjustment measure the voltage across R29 with a multimeter and adjust R28 until the voltage across R29 reads between 10mV to 20mV. Depending on warmup time and rail voltage bias the output devices between 15mA (3mV) to 100mA(20mV). Higher rail voltage and lower warmup times use 15mA(3mV). Lower voltage rails and longer warmup times use 100mA(20mV)

WHERE More elaborate testing is required

Power the board from dual DC lab supplies limited at 300mA at -/+ 20VDC

1. Use a function generator to apply 20Hz, 1kHz and 20kHz sine waves of 0.2V to the signal

and GND terminals of the PCB.

2. Using an oscilloscope between the speaker GND and SPEAKER, observe the resulting

signal. There should be no ringing or oscillation.

Although fitted with series input resistors, do not accidentally use unreasonably high waveforms as those of other power amplifiers or mains AC at the input as you risk damaging the input stage. Public address systems and touring gear where such mistakes can happen are usually outfitted with input stage clamping diodes.

Have fun and let us know what you think

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