Monday, December 27, 2010
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.
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.
Friday, December 24, 2010
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.
Friday, November 26, 2010
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
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.
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.
Saturday, October 23, 2010
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.
Friday, October 22, 2010
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.
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.
Monday, May 31, 2010
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.
Monday, March 22, 2010
In this build the soon to be released, JAN6418 valve based, phono preamp kit has been enclosed in a die-cast Al enclosure. The enclosure was finished in a hammered copper epoxy enamel paint.
The sound is excellent. I worked closely with Branko, the developer, to ensure the preamp could deliver its best at a real budget price. This two stage valve based, FET buffered phono preamp utilises an international wall wart to allow the kit to be plugged in to the mains any where in the world.
At the time of writing this kit form valve based phono preamp for MM had not been released. I was invited by Branko of Oatley Electronics to help put the finishing touches on his latest kit. After the replacement of four small caps the phono preamp was sounding very good. This kit would couple well with the K272A tube preamp.
The kit employs a switch mode 5V wall wart to power it. The beauty of this kit is the wall wart comes with auto mains AC voltage sensing and multiple international mains adapters. So no matter which country you are in the world you can plug this kit straight into the wall.
Inside the 5V is converted to 30V with yet another SMPS. Not to worry Branko has gone to a lot of trouble to ensure that no SM hash reaches the sensitive ccts. To produce a truly linear output the tiny JAN6418 valves had to run on 30V. Not only that valves are operating in pentode mode. How may phono preamp kits do you know are using pentodes? This kit is a first on two very distinct fronts. Firstly a truly international mains power supply and a two stage pentode phono preamp.
But wait there is more: Each tubes stage is buffered by low noise FETs. This phono preamp would have to be one of the strangest ever. Pentodes, FETs, SMPS, international SM wall warts. And it sounds so good.
The kit is complete and comes with very standard componentry. If you are a first time builder don't change a thing. The more experienced constructor may swap-out some of the components for more high-end parts. But isn't this the great thing about inexpensive kits that you can put your own signature on the build. Try the kit if you have an analogue system (TT) and see if you are not very impressed by the quality of the kit and it's performance.
The cct. brds. are solder masked and the brd. plated through. Most of the cct. brd. is earth plate. This keeps noise extremely low. Apart from a small amount of valve hiss the board is dead quiet. At one meter from the speakers (and mine are 91db sensitive) no noise can be heard.
The enclosure is a double layer of Hammered Copper epoxy enamel paint. A layer of bituminous heavy Al foil lines the base and lid for enclosure dampening and additional shielding. Gold plated isolated RCA connections are on the back with the power socket. Tightly twisted telephone wire is used for the internal hook-up. Why telephone wire? One it is a very pure copper and two it is single stranded. Tightly twisted: noise is locked out with no shielding capacitive issues. The feet are small rubber finished types, cheap but nicely isolate. A rubber seal is clamped between lid and enclosure to provide even more resonance deadening.
The sound is excellent.
Monday, February 22, 2010
A portable Triode Headphone Amplifier is rather a unique piece of gear for a world which is solid state and integrated chip driven. But this very warm and musical sounding preamp is truly portable relying on two 9V lithium batteries for its energy.
The circuit is based on the Oatley Electronics K272 triode preamp kit. There are many upgrade components added to the original kit. The input comprises two JAN6418 sub-mini pentodes in triode mode. The output is buffered by a PT2803 OP amp driver chip. This chip is a low distortion headphone driver/amplifier but here is used with unity gain. It has sufficient power to drive low impedance headphones.
Coupled with your iPod or more high performance portable player, this Mongrel Dog Audio headphone amp provides a unique and intoxicating listening experience. Compact and not too heavy for daily use and with a battery life of hundreds of hours there is now no excuse not to listen to your fav. music with the full tone it had been recorded.