K295 Production Version

In an earlier blog I constructed a prototype K295 for a bass player. It proved to be a great success and produced richer harmonics making the bass sound fuller and a lot warmer. This build is the production version of the K295 and the kit can be purchased from Oatley Electronics in Australia In this version only a single tube is used. The PS, including a tiny mains power transformer, is mounted as part of the whole cct. brd. but can be snapped away.

As in the earlier preamp I used a plastic case lined with bitumanised Al foil. Single pots were used to allow separate channel control and large numbered knobs used so setting can be noted for future used. The central blue "on" led marks "0" for both pots. Guitar 6.5mm jacks are on the back to allow music instruments to be plugged in. All hook-up wire is twist single strand copper.

On a short listen through my system the preamp appeared to work very well providing gain and and good control over volume levels. The left channel has a slight buzz due to it being closer to the tiny transformer than the left. A larger case would solve this problem by allowing the input and output jacks to be mounted further from the power tranni and mains (110 or 240V). Or break the PS away from the amp cct. brd. and mount it separately. All in a good build and good result.

K295 - JAN6418 buffer/preamp

In this small plastic enclosure is the new Oatley K295 kit. But in this build an early dual tube prototype brd. has been used. The intended use for the build above is for preamping of a double bass for a player in a Rock-a-billy band. Red LEDs are mounted on the brd. to light the JAN6418 tubes.

From early reports Ray, the bassist, is very impressed with the sonic results so far from his electric bass.

BoZ on a Cap (BoZoaC)

BoZoaC (BoZ on a Cap) uses a recursive component-2-component construction method to build the whole of the preamp cct. on the output caps. See the posted images below of the BoZoaC engine.

In my system input caps are not required and an earlier BoZSE build (input capless) proved that removing these caps improved overall performance of the preamp. Anytime signal path can be reduced in length and component-2-component construction methods used, sound quality has to improve. If look at the BoZoaC engine below it is obvious the signal path on the cct. is reduced to component length.

Some very high-end preamp manufactures will not use metal cases to enclose the boutique components claiming magnetic and eddy current issues. I chose this plastic case for similar reasons and wanted a non-resonant slim case to enclose this unusual build.

Though only a few hours of play have pasted through this tiny little preamp cct. I am convinced the sound equals or betters that of BoZSE which is supported by 30,000uf of storage caps. There appears to be a greater immediacy of the music with equivalent bottom end. Only comparative listening will prove this but this whole build is very satisfying so far.

BoZoaC exposed

A ridged plaster instrument case was chosen to house the recursively constructed BoZoaC. Three 9V lithium batteries sit at the rear where two sets of gold plated RCAs are mounted. The output for the preamp can be found on the left of the case with the input selection switch.

On the right rear of the case the banana style low profile sockets are mount to allow battery checking. If the batteries are removed an external PS could power BozoaC. Silver solder and wirewrap wire are used throughout.

BoZ on a Cap - BoZoaC

Due to the low component count of the BoZ cct. it is quite possible to build the whole preamp on a the output caps. In my other BoZ constructs I employ 20,000uf of storage caps. To keep the whole build very compact I used 2 x 1000uf low ESR caps for storage caps.

There is no input caps or attenuator with this build. It is not required in my system but other systems may require those components. A big plus of a genuine component-2-component build is a very short signal path and a minimum number of solder joints. These two factors help to improve the over performance of the preamp. There is no additional wire used in the build, all components are directly silver soldered to each other components.

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.

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.