Lyngdorf Audio Room Perfect TDAI 2200 - Manual (Page 12)

12
Power Supply
The high current power supply of the TDAI-2200 features a
massive 650VA toroidal transformer.
The advantage of a toroidal over a conventional C or El core
transformer is significantly less magnetic radiation, something
which can potentially induce noise (50/60Hz) which would be very
audible.
The advantage of using a transformer over a switch-mode power
supply is that the supplies for the output stage and the
microprocessors are kept completely separate since they use
separate windings on the transformer.
Thanks to the fact that the TDAI-2200 amplifier is a pure non-feedback design it is of the
utmost importance that the power supply is ripple-free. That’s why it uses more than 55,000uF
of capacitors!
The result is a power supply that delivers enough current to drive even the most demanding of
loudspeakers and a surplus of headroom that helps reproduce even the highest peaks
effortlessly and with full fidelity.
However, the truly unique aspect of the TDAI-2200 power supply is also that it actually works
as the volume control of the product. When you are playing at low volume levels, the voltage
supplied to the output stage is low - when you turn up the volume control you increase the
voltage, and thereby the output, from the amplifier.
This is implemented as a DC -> DC converter. On the ‘primary’ side full voltage is constantly
applied and then the DC -> DC converter switches the voltage needed for a given setting of
the volume control to the ‘secondary’ side (= the voltage supplied to the output stage).
In order to be able to turn down the volume fast again, the DC-> DC converter can, quite
uniquely, switch the power back to the ‘primary’ side.
Output Stage
The output stage is fed by a PCM-to-PWM Equibit TM modulator.
The modulator converts, as the description indicates, the digital PCM (Pulse Code Modulated)
signal to a PWM (Pulse Width Modulated) signal.
Below, we’ve shown a sine wave, in terms of a pulse-code-modulated signal, in the upper
panel of the figure. In a PCM signal, each discrete sample represents a specific amplitude. The
corresponding pulse-width-modulated signal at the same sampling rate (frequency) is shown in
the lower panel.
The magnitude of each PWM sample is described in terms of the pulse width, as opposed to
the pulse height in a PCM signal.
So, the 24-bit PCM digital audio signal is fed to the modulator where the audio data is up-
sampled 4 times (=@ 390kHz). The Equibit
TM modulator then translates the up-sampled signal
to a PWM signal having the same switching frequency.
The PWM signal for each channel is then fed to the H-bridge output stage.