Preamplifier
Introduction
This preamplifier serves many purposes in my system. It is very simple and straightforward,
the knob on the left selects the input, the knob on the right is the volume control. It also
contains a D/A Converter, and an active crossover.
The D/A Convertor
The D/A converter is the Scott Nixon design, using the CS8412 and TDA1543. The sound is amazing,
far ahead of the D/A conversion capabilities of my H/K FL8550 that I play CD's with.
Volume Control and Input Switching
This is pretty straightforward, the volume control is an Alps conductive plastic potentiometer.
The input switcher is a 4 position 3 pole rotary switch, it is all silver plated. After the volume control,
all of the signal lines go to buffers, specifically opa134 Opamps.
The Crossover
The crossover was designed for the Shorties that I built
in parallel with the preamp. It is a 4th order crossover at 2200Hz. The woofers are mounted
in a open baffle, so there is a stage of equalization for them to cancel the dipole roll-off that
starts at around 500Hz due to the width of the baffle. They also have a 3rd order high pass filter
on them at 90Hz, to cross over to the subwoofer. Following are some pictures and descriptions.
Figure 1: The
insides of the preamplifier. At the rear of the enclosure you can see the Scott-Nixon DAC, towards the front, the active
crossover is visible, and at the rear, the double-deck custom built board is the equalization for the dipole roll-off.
Figure 2: Another nice shot of the preamp.
Figure 3: The rear panel of the preamp, closest are the
inputs, with the S/PDIF input at the top, and stereo inputs below that. Next are the outputs, with the HP on
the top, the LP in the middle, and a pair of unfiltered outputs on the bottom.
If you have any questions, feel free to e-mail me.
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