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.

Mongrel Dog Audio Jan6418 valve phono preamp

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.

Mongrel Dog Audio valve phono preamp

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.

Portable Triode Headphone Amplifier

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.