Blue BOSOZ

This is a first of a series of pics of a BOSOZ. As You see, power supply is in a distinct box.
 

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...this is the underside. A 3mm panel divides the two areas.
The small circuit on the upper right is a small soft-start (or inrush protection). Another thread gives more details and a link.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=5142&perpage=15&pagenumber=4

The power supply is dual-mono, each one using two ransformers, two diode bridges for each channel; this arrangement is detailed in the original BOSOZ article by NP. Total cap bank for both channels is slightly over 22.000uf.
 

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This is the preamp front, from left to right: input selector, volume,
recording selector, output selector. The output selector lets the
signal out either on balanced connectors, unbalanced,
and (also unbalanced) to three serie of RCA, for high-mid-bass
multiamplification. Inside there is a daughter bord (see later) that
can host a passive crossover.

The chassis of the preamp (and the power supply too) is a sandwich of 3mm aluminium and 6mm plexiglass. The underside of the plexiglass is blu-violet metallized paint. I liked the contrast of the mahogany sides and blue.
 

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Space was barely enough... here you see pots axes going right between mosfets. I had some ball-bearing left and I use them to support the axes, this gives a tight hold on the axe with a zero friction effect. On the right you see the brass holders. Also visible is a copper bar where the (isolated) mosfet sits. At the time seemed a good idea to have both mosfets thermically connected... still is, but the container is so small that that would have occurred anyhow.
 

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...and the back, all together. This preamp relly shines on sound.
Difference between a direct connection to a valve amp and through the BOSOZ gives parity on every parameter, except dynamics: The BOSOZ really gives a kick in. This is on unbalanced out... as soon as the monoblock SOZs are ready we'll see what's this beast is up too.

The BOSOZ article was sitting on my shelf for a couple of years... and I peered at it time to time... had other projects going on... now I'm very happy with it and has been a lot of fun, building it.

Here seems the right place to thank Nelson too. I like to thank him for the sense of humor that peers through his posts, his site, and... his willingness and time spent to share his work.

This is all folks...:D

Roberto Amato
 

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Roberto ... again, that's beautiful stuff! If you guys are going to build such beautiful things, you might get Nelson Pass concerned ... if you know what I mean.

By the way, why does some of the capacitors looks so beaten up?

Has anybody asked you for help in machining those L metal sheets with the 3 gears on it yet? I want one!
 
fcel said:
Roberto ... again, that's beautiful stuff! If you guys are going to build such beautiful things, you might get Nelson Pass concerned ... if you know what I mean.
Not at all!! This is mostly fun, I don't do this for a living, Nelson does. This is all the difference there could be. Many people asked me to build for them. While I give a hand, sometimes two, I always turned them down. It took almost 6 month and a great deal of my spare time to build this. How much should I ask?? And nobody is giving me back my time. This is why I much appreciate Nelson's time. It's invaluable.

By the way, why does some of the capacitors looks so beaten up?
I'm answering to Skaara too. There is anti-vibration material on them, even on caps top. Is made by an aluminium foil and a chewing-gum like soft and sticky material underneath. But does it work?? Well, let's say it does not hurt anything; it dries up the sound a bit, but I like it, so it's ok. It's a side-effect of audiophile paranoia, you know... :D

Has anybody asked you for help in machining those L metal sheets with the 3 gears on it yet? I want one!
If you were a little closer I could give you a hand. That has to be done on a unit-by-unit arrangement. Remember that the turning axe has to go to the front of the amp, to the knob. So positioning and height is not trivial. Patience helps a lot... ;)

ciao,
Roberto
 
JoeBob said:
I was just admiring my latest amp, until I read your post. Dirty Jesus it looks really nice. But what gave you the idea of using the plexiglass with the blue underside? I've never seen that before, although it's a great idea.
I didn't see it before either. Two reasons. For once, the paint under can't be possibly scratched, you may mop your amp easily, with normal home cleaning stuff... I was tired of paint scratches. Moreover, having the paint under 6mm of clear plastic gives a depth and a shine no other method does... at least reasonably available to Diyers. Secondly the sandwich between plexiglass (don't use policarbonate, too soft to obtain clean cuts) and aluminium gives a very dumb material, absorbing very well all kind of vibrations.

I didn't know if this would work... the paint (car spray paint) could not look so good seen from the opposite side, the solvent in the paint could melt the plastic... any error could not be covered with additional layers... but with a light hand it worked. Beware that not all colors may work well, silver paint looks dull grey, for example. Give it a try.

ciao,
Roberto