Friday, November 26, 2010

Pass capless BoZSE

My new Oppo BDP-83SE has input caps but my 6AS7 SET has no input caps. So make a preamp with no input caps but good output caps. In this capless SE version of BoZ I have no input caps but retained the 10uf polypropylene caps for the output. Also the output caps have been snubbed by 0.1uf polies.

Nelson suggests a total of 30,000uf for his B1 whose PS I stole a few ideas from. But only having 10,000uf caps I used three to get the filtering/storage up. Also I used a simple RCRCRC filter network. 1ohm/10,000uf/10ohm/10,000uf/1ohm/10,000uf. Each 10,000uf cap is snubbed. Silver plated wire wrap wire is used throughout. Input hookup wires and power wires were threaded through tiny bead chokes. Multiple earths (negative voltage) connections were made. Bitumanised Al foil laid in the top and bottom of the Hammond anodised Al case. Silver solder, Alps pot and 4oz brass added once more to a quality build.

The sound stage is massive, stage depth multi-dimensional. The mids are excellently rendered with transients laid bare. Treble smooth is silky-smooth. You almost feel there is no treble because it is just parts of the mix, part of the overall music. Bass is weighty and well extended.

Where I thought the B1 was the Bee's knees this capless SE BoZ may be much better on all fronts. And it has gain.

Monday, November 1, 2010

Pass BoZ cct. brd.

See the finished BoZ below. As with the B1, Russian PIO caps on the input and polies on the output. The simpler BoZ I built here came with no PS. So I borrowed some of the PS ideas from the B1. A 1ohm resistors feeds the first 10,000uf cap and a 10ohm the second. Where the B1 has Nichicon filter caps BoZ has a cheaper filter cap. Alps blue velvet pot and 4oz solid brass knob.

Also I placed the components in mirrored style on the vero-brd. One channel reflects the other. Not sure this will increase fidelity but it looks good. With the B1 I simply copied on channel on the second half of the brd. to provide a second channel.

Pass BoZ (Bride of Zen)

After completion of the Pass B1 I decided to try BoZ (Bride of Zen). Once more this is a single jFET (2SK170) preamp but where the B1 is a line driver this preamp has gain. And it has plenty of gain. I used the same Russian 1uf PIO caps and the same 10uf polypropylene (snubbed this time) output caps. In many ways the the preamps share a lot of components. But they sound very different.

Hook-up wire this time is wire wrap wire (WWW). After reading a book on cable construction, less (with regard wire thickness), is more. The Hammond anodised Al case is slightly smaller then the B1.

BoZ is very sensitive to PS noise. Where the B1 is more tolerant of PS noise any PS hum, whistle or buzz can be heard and is amplified. I am currently running BoZ on 4 X 9V lithium batteries for 36V. Both preamps have a less than 20mA current draw.

Sonically the B1 is superior. But BoZ has greater bass weight. B1 can etch greater mid-range and treble detail and produces the music in a very raw and uncoloured manner. Other serious listeners made this comment too.