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BDP 31st October 2003 07:19 PM

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I first built the BOZ single ended preamp and the sound was OK but when the balanced version BOSOZ came out I couldn’t resist and had to build it. I wanted to run constant current sources so I didn’t need the full voltage on the negative power supply. I figured -30 volts for the CCS would be adequate for the job. I used bipolar CCS’s with diode references. I already had the transformer from the BOZ and thought there has to be a way to use this transformer, so after some thought it occurred to me that I could use a voltage doubler for the positive voltage and simple rectification for the negative voltage. The front end power supply for the A75 uses doublers and it also has some discrete regulators all on one board and the etched boards are available from Audio Express. With a few modifications to the board one power supply rail could be doubled and the other modified for normal with out the voltage doubler. The gain of the discrete opamps were changed to give a regulated output of -30 volts and + 60 volts. The main board is point to point wiring as you can see. The volume pots are 5K Elma and are used at the output. For the input I used a simple voltage divider to attenuate the input signal from the CD player to the appropriate input level.
I have very much enjoyed this preamp. It is interesting to be able to change so my parameters, balanced, single ended, gain, input levels and see how they all sound. One of these days I will try some better caps at the output and maybe X- it.


BDP 31st October 2003 07:21 PM

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Here are more pictures.

BDP 31st October 2003 07:22 PM

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The case is aluminum painted with truck bedliner coating.

moe29 31st October 2003 08:42 PM

very cool, the paint job looks good to, good idea.

fill us in on the POTS... what did you use?

BDP 31st October 2003 11:14 PM

The coating is about six years old now and has held up well.
The POTS are 24 position 5K series attenuators using Elma BV22568. Two stereo POTS, one for each balanced output. Some might think that 24 steps are not enough, but it works for my setup.

:cheerful: :Pumpkin:


Nelson Pass 1st November 2003 01:56 AM

Very impressive effort.

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