4
Cleaning the cabinet
The front panel is made of aluminium. It can be cleaned by using normal mild solvents and clean paper
tissue or cloth. Do not use excessive amounts of solvents, and do not let any of the solvent spill into the
amplifier. The Brass logopanel is covered with a protective layer.
DO NOT USE ANY BRASS POLISH. This will remove the protective layer.
The protection circuitry
The ideas for the protection circuit come from our professional amplifiers, where it has worked well since
1982. Due to the rugged MOSFET, we can allow high peak currents , and we only need to mute the
input signal in case of long-term overload.
The protection detects DC errors, high level subsonic signals, long-term ultrasonic signals, high tem-
perature, and to low impedance loads or short circuits.
If needed, the protection will simply mute the input signal, and if necessary open the output relay. The
relay will normally open only after muting the input signal to avoid relay switching of strong currents that
could corrode the relay contacts.
So in case of i.e. a short circuit, the input is muted for a second. Then a 1 millisecond long pulse is sent
out to test again. If the short circuit still is present, it waits a second and tries again, and so on. One
second after the user has removed the faulty cable, the system will quickly remove the muting.
The protection also detects too low impedance loads, and alerts the user by muting for a second. So the
user can be sure to hear only clean non-distorted audio. The normal current limiting and momentary
distortions of the music are avoided in the GamuT M250 power amplifier.
A second of silence
You may experience a second of silence while the music is playing loudly. This is the protection acting to
protect your tweeters. Any amplifier will start to clip the top of the music if you exceed the maximum
power level. Technically, clipping generates a lot of high frequency energy, which can burn out the
tweeters in your loudspeakers. The protection constantly checks the energy above 20 kHz, which
humans do not hear. The distortion is momentarily very high anyway, because you have exceeded the
maximum power, so just reduce the level a bit.
You can also provoke the subsonic protection by playing warped records without using a subsonic filter.
Please check your tonearm/cartridge resonance frequency, which should be about 8-12 Hz to reduce the
effect of warped records.
Connecting your loudspeakers to the output terminals
Normal power amplifiers have a coil in parallel with a resistor between the amplifier and the output
connector. Its purpose is to protect the amplifier against capacitive speaker and cable loads. However,
this will slightly reduce the fidelity of the sound in the treble range, when the amplifier is used with normal
loudspeakers. So we have added a direct output in addition to the normal filter protected output.
The red terminal closest to the heat sinks is the direct output. The other red terminal is the filter output.
The white terminals are ground
This also gives you the ability to connect biwiring nicely, using the filter output for the bass. and the di-
rect output for the treble
In case of biwiring an electrostatic loudspeaker, the reverse should be done.
Inside the cabinet the ground terminals are kept biwired until they meet at the main star ground point.
So please do not connect them together.
