Guest Post : Olivers Amplifiers

Hi!

Oliver who built some amplifiers based on kits from me was so kind to share his experience...

Hi, I'm Oliver and I live in Brooklyn, NY. Some time ago Thomas asked me to write about my experience building a 10y/45/50 amplifier, finally here it is!

I've always been a music lover/collector but discovered tubes accidentally when I inherited a pair of Altec Model 19 speakers along with some old Quad 2 amps and matching 22 preamp. Like most children of the 80's I had no idea what those strange light bulb things were but they sure sounded nice so after some research and soldering practice the Quads were restored and my first tube guitar amp built.

Pretty quickly I was hooked! I discovered the long out of print Sound Practices magazine which helped feed my tube addiction and I began building stereo amps of various kinds but especially single ended types with the wonderful 45. I also became aware of Thomas from the Sound Practices 'homebrewer of the month' feature where he detailed very intriguing 211/211 amplifier with an elaborate 3 phase power supply, this captured my imagination and I immediately hunted to find some of the Tango NC-20 interstage transformers mentioned.

A few years and many amplifiers later I stumbled upon the Vinyl Savor Blog when Thomas first posted his 45/2a3 amplifier, As soon as I saw it I knew I had to have one. Before mustering up the courage (and finances) to build that particular amp however I decided to start with one of the simpler circuits generously published as the Single Ended Amplifier Concept. The basic design appealed on many levels, it was elegantly simple, had no cathode bypass capacitors, lots of iron including choke loaded power supply and was versatile in driver tube choice between 6j5/6p5/6n7, of which I had many examples. Another huge bonus was that I already had most of the Lundahl iron from a previously aborted project so the additional investment wouldn't be that large.

The Lundahl power transformer I used didn't have a centre tap on the high voltage winding so I settled on a hybrid bridge rectifier with 6ax4 and BY229 diodes and in the end chose 45 over 46 in the output stage, otherwise it was simply built as drawn. All the fabrication was done the old fashioned way (no CAD or CNC) with ruler and pencil, it was time consuming but relatively simple and all carried out in my garage with rudimentary tools. I tried as much as possible to remain faithful to Thomas' aesthetic and layered sub chassis approach using standoffs and aluminium angle stock to secure the many pieces of iron, it took a lot of planning the first time but after the layout was finalized and all the iron mounted completing wiring was very fast and now I am a big fan of this layered approach.

As often happens there was some trouble shooting to get things working correctly but once the problem was found (incorrect connection of the output transformer secondary) I was immediately impressed by what I heard. It seemed to magnify all the strengths of 45 tube and I couldn't find any audible weakness, especially impressive was the rock solid low end and the sense of focus and composure on more complex music.

Before long my friend Daniel heard the music at my place and decided he needed to build a Thomas Mayer 10y/45 amp too. After the initial planning stage all the necessary iron was ordered from Thomas and we sourced the passive components ourselves, soon packages full of exotic parts started arriving from around the globe. Since I had some 50 and VT-52 triodes I wanted to try in the output stage I added a few features to the basic design including a switch arrangement to increase/decrease the B+ and 2 additional passively filtered DC filament supplies for the output tubes, also switched, to alter filament and bias voltage. Since I had larger Tango XE-60 output transformers I ended up with a larger footprint and made some slight changes to the existing layout, all the capacitors were moved to the top plate and the 6 additional transformers and necessary passive components were mounted inside their respective chassis. I also really wanted the impressive blue glow of mercury vapour rectifiers so with some help from Thomas we were able to devise a way to do this using 816a and the filament windings on the existing power transformer. The power supply also got a little extra reservoir capacitance and a dual switch arrangement for preheating those precious antique triodes, although the high voltage rises slowly enough with the 6ax4 damper diodes.

Again all the construction was slowly done by hand, so slowly that I was able to hear Daniels' finished amp before my own. Needless to say we were both extremely pleased by the results, the transparency and air that the 10y contributes to the top end is fantastic, realism and tone abound and it uncovers all kinds of previously hidden details. To me this is the ultimate realization of a 45 amplifier and something I will never let out of my hands.

Since it was made with ease of modification in mind I've been able to try many combinations of DHT in both driver and output sockets and one of my favourites has been 801a/801a, although not an ideal match for the output transformers it was a very pleasant surprise and so lifelike the equipment simply disappeared leaving just music floating in space. Definitely something I want to investigate in the future. Also possible for the future is trying out the Elrog 300b which will fit right into the circuit with only the slightest modification.

Lastly I wanted to share a recently finished project which is a redux of the initial 6n7/46 build. This time I used a set of NOS Tamura iron and decided to go with the separate bridge rectifier power supply for a no compromise approach. One drawback commonly mentioned of the Tamura transformers is the slightly narrow bandwidth but I certainly don't notice this, very clear and extended with simply beautiful tone. Next is a matching LCR d3a phono stage built up in the same style, can't wait to get my soldering iron in it's heated state again.

 
Big thanks must go to Thomas for sharing his wonderful designs and providing the critical parts to make them a reality. Always willing to answer my questions (of which there were many) and a great source of inspiration. I'd encourage anyone out there considering building one of Thomas kits to go for it. A great learning experience and a truly world class finished product, I simply can't imagine building anything better!

Many thanks to Oliver for sharing his story!

Best regards

Thomas

Guest Post: D3a LCR phono built by Claus

Hi!

At last years ETF I had the pleasure to meet Claus from Denmark. He built a D3a LCR phono based on a partial kit from me and brought it to the ETF where it was shown in the danish room.

The unit was beautifully built and sounded wonderful. Claus put a lot of effort into the chassis and the result is stunning. He agreed to write up an essay about his experience while building it. And I am vary happy to be able to share his story with you:

How I ended up with a Thomas Mayer LCR phono stage

By Claus Fonnesbek, Denmark

Where do I start… Not at the beginning, I’ll skip all the boring stuff.

I have been building audio amplifiers and preamplifiers for many years, there even was a time where I thought I would do it as a profession, but that never happened instead it ended up being just a hobby.

I switched from vinyl to SACD 15 years ago, but sadly this format never got to be a huge success, now streaming is the “right” thing, but not for me, I like putting on a album and listening to the whole thing.

I first saw some of Thomas Mayer’s constructions at the triodefestival back in 2000, in fact a LCR riaa if my memory is correct.

After some years with different silicium based gear, I build a 300B power amp a few years ago, and after a long search I found a Thorens TD124 mkII in pristine condition I decided to return to vinyl.

I knew that I wanted something based on tubes and LCR riaa correction, my recently finished 300B power amp is using the C3m pentode, which I looked at first, but having a small stock of D3a tubes the Thomas Mayer LCR phono stage was the natural choice.

I got in contact with Thomas and it turned out that he was selling “kits” we agreed on a price for a kit including all the “iron” and oil capacitors, I would source the rest my self.

Thomas was kind enough to let me borrow his "portrait style chassis” design, so I have ended up with a LCR preamp very similar to the original.

To make sure that all the chokes and transformers would fit in the chassis, I started out with a 3D model, my chassis is a bit smaller then what Thomas uses and my arrangement of transformers and chokes is different.

To save space I’m using the LCR module from http://www.acoustic-dimension.com/ which I can recommend, I would have loved using a Tango module, but it is beyond economical reach.

A week after ordering the parts from Thomas, I received all the Iron and caps, all was very well packed so no issues at all.

Shortly after I received the rest of the parts.

I could finish the design of all the mechanical parts, all the aluminum parts were ordered from Schaeffer AG, they do really nice work and I have used them for several projects.

The first test fit of the amp chassis can be seen in the picture.

I sandwiching the capacitors between the top plate and a sub plate which also acts as fixing point for the chokes and interstage transformers, this was done to keep all the screws hidden, in total there is only 8 screws visible.

Now the build could start, I started with the power supply, a purely passive power supply no regulation at all, B+ is L-C-L-C and filament supply is L-C, TV dampers for B+ and schottky for the filament.

The completed power supply before testing.

All the chokes and transformers are made for Thomas Mayer by Lundahl and Weiss.

Both the B+ and filament transformer has is a lot of tabs (different voltage combinations) on, which makes it possible to trim the voltages, making it possible to end up with the right voltages without any regulation.

Testing the power supply.

Nice glow from the tv dampers, they take up some room, but they look nice and they have a fairly slow start, which will help extend the life of the D3a tubes, and lastly they have the big bonus of being very cheap.

Now for the amp, a simple circuit, but a lot of big parts. Having made a 3D model first helped making the amp as compact as possible, with the added problem that everything has to be assembled in the right order, there is no room for mistakes and replacing a part requires a lot of skill or time to take it apart.

Half of the amp done, all chokes, small parts and most of the point to point wiring done.

The LCR modules are on top of the amp resulting in the shortest signal path possible.

Still missing the interstage transformers and the last wiring.

The last parts are fitted, interstage transformers and the final wiring, it ended up being quiet a challenge to solder the last wires.  One thing is making a 3D model, it is totally different assembling it in real life.

After some quick measurements I was ready for the listening test, so how does it sound ?

Well I’m not the right person to judge that, it will be really difficult for me to be neutral, I could of course use all the standard acronyms, but I wont.

A very good friend of mine gave it a listen recently, his judgment was very positive.

We listened to a stack of very well known records and one of the things that were most noticeable was that we heard new thing from the groves that wasn’t heard before.

Inspired by Thomas’ outdoor model shoots, here is a couple of photos of the finished amp, the chassis is solid walnut treated with tru-oil, a lengthy process where one can keep going indefinitely, oil, sand, oil, sand, oil, sand, oil and onwards, I stopped after oiling about 20 times.

Last words, a very big thanks to Thomas for his assistants during the build, always ready to answer my at times stupid question.

So what’s next ? maybe a matching preamp.

Thanks

Claus Fonnesbek

Thanks a lot to Claus for sharing this story! And congratulations for the wonderful build!

Best regards

Thomas