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.

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.

Pass B1 in anodised Hammond Al case

The Pass B1 in a Hammond Al case. Nice enclosure even better sound. After assembling a vero-brd. ESP P37a for long term customer I was enspired to tackle other simple SS preamps on vero-brd. See the cct. brd. below.

As you can see above the front panel is simple with just a mini on/off switch, 4oz solid brass black chrome kbob on an Alps blue velvet pot and an aqua led. The back holds two sets of gold RCA inputs and one set off outputs. The rear switch switches between the two inputs. The 19V DC power plug is also on the rear.

I power the preamp with a 19V SMPS. Others have done similar with no complaints of noise or switch mode hash. Under test the preamp -3db points are 5hz -> 780khz. 18V p2p into a 10k load and 8V p2p into a 1k load. Impressive!

Though this preamp is more of a driver, being a source follower, than a preamp its ability to drive a reasonable voltage swing into a heavy load is obvious. The sound from this preamp is extremely raw and natural. The B1's ability to dig out absolutely the finest, earthiest detail is striking obvious the second music is passed through it.

I team this blatantly natural sounding preamp with a mid-range rich SET amp for a beautiful combination. Each time a play a different track I am struck by the rawness of the sound and the depth of the detail. The preamp stays on the warm side of clinical without taking any sonic prisoners. Build it if you can take the truth about what you are listening to.

Pass B1 driver stage

After construction of the ESP P37a I was fired up to build another vero-brd. wonder. This is the Pass B1 preamp/driver cct. brd. which went into the black anodized Hammond case. Two jFETs do all the work in this preamp. One jFET is just a constant current source (CCS) for the other. So really only one jFET sees the signal. Simple and effective. The problem is because this is a source follow there is no gain. In fact only 85% of what goes in comes out. But it comes out very well.

Two 10,000uf caps provide power filter and storage. A 50K Alps pot controls input level and large 1uf PIO Russian military caps de-couples the preamp. a 10uf poly provides output. 2SK170 (BL) jFETs are used.

Placement of components on vero-brd. is critical unless you want span the brd. with links. For me there is a lot of thought which goes into component placement to ensure links are at a minimum.

ESP P37a discrete component class A preamp

I was asked by a long standing customer to construct this ESP P37a on vero-brd. He would provide the case and PS. Basic polypropelene capacitors and metal film resistors were used. A bi-polar capacitor was used on the output stage. Low ESR caps were used in the power filtering stage. Silver based solder used throughout.

Though a simple preamp building on vero-brd. is always time consuming. I was very pleased with the build and had a short listen to ensure the cct. brd. performed well. I was pleased with the sound which appeared flat across the frequency spectrum and very natural.

I charged the customer $AU100 for the finish and tested cct. brd. and this included shipping to Malaysia. I would recommend the preamp but purchase the cct. brd. for it.

Mongrel Dog Audio/Oatley JAN6418/LM1875 chip amp kit

The near complete build of the K281 Oatley Electronics Jan6418/LM1875 power amp. The K281 kit has been built as a dual mono construction with two separate amp modules and two 24V switch mode power supplies. This was an "out-of-the-box" build with no upgrade components or "fancy" build techniques. I wanted to see what the amp would sound like with no mods at all and employing a really plane build. It is very good. Holographic sound stage from a very believable tube and chip amp. The chip is capable of better than 20Ws. Next build.