I live in Vienna in Austria. Vienna - or Wien as it is called in German - is the gorgeous capital of Austria. Vienna is synonymous with a high quality of life, good food, beer and wine, music and gemütlichkeit. I have been living in Vienna on-and-off for the past many years and after a stay in New York, I decided to settle down in this magnificent city.
Vienna is a very diverse city where each district has its own vibe and charm. This is from my perspective one of the greatest perks of this city, because you can settle down in a district that fits your mindset.
I live in a nice penthouse with a view over the rooftops to the small mountains surrounding the city. The apartment is what is referred to as a "dachboden ausbau". What this means is that the entire roof is removed from an old house, and a brand new apartment is built on top of the building.
A very skilled young artist, Ina Fasching, lives on the same street as me. I actually met her as I went for a beer in a small "Beisl" across the street. I did not know what she actually did, but as I am a curious person I asked her: What do you do, when you are not serving me beer?
She told me that she was an art student at the famous art school here in Vienna. Of course I wanted to see her paintings, and I liked them very much.
Below some screen dumps from my PCB Editor. I plan to write a short manual, but for now intuition will have to do.
Even though digital music has been with us for decades now, I stil prefer the sound of my vinyls. Yes, I know - vinyls can be hard to deal with, they get dirty and are heavy, but still I love them. And the feeling of putting a real record on, is second to none.
I like to build Hi-Fi equipment myself. It gives me the possibility to play with various setups and change things on the fly. At the same time, I have full control over the component and build quality.
I am currently building my own version of the somewhat famous RCA power stage from 1970.
This stage is used in more commercially available amplifiers like the NAIM NAP-250. I have made quite a few modifications to the original design, most importantly I have decoupled the input stage from the driver/power stage of the amplifier to lower noise and improve stability. I have never been a huge fan of the NAIM power regulator boards as they just give a higher output impedance than a more simple rectification circuit does. So I have designed a low-impedance rectification circuit to feed the amplifier boards.
Jan Lohstroh and Matti Otala did back in the 1970's research on how to make a better sounding solid state power amplifier.
Back then, tube amplifiers were still in common use, and many did not like the "transistor sound" from the new emerging amplifiers.
The Lohstroh and Otala design has been in use ever since by the Norwegian company Electrocompaniet which has build a host of wonderful sounding amplifiers. The only drawback to most of the Electrocompaniet amplifiers is that the often break. Where a Japanese made receiver goes on and on for decades, a soldering iron is a must when you run one of those Norwegian amplifiers. Back when Per Abrahamsen was in charge of Electrocompaniet, the company was quite willing to help with schematics to be able to service a blown amplifier, but nowadays with the new owner, that has sadly enough changed for the worse, with a quite posh attitude by the company.
That is why I decided to build my own version of an Electrocompaniet amplifier, using the Lohstroh and Otala design, instead of buying a new one from the company. This way I can remedy the most common faults in the design phase and be able to easily service the amplifier.
As the Lohstroh and Otala design runs hot, and the amplifier uses BJTs, it is of utmost importance to prevent thermal runanway. Therefor the Vbe multiplier needs to be placed as close as possible to the output and driver stages and definitely on the same heatsink. I decided to build the amplifier as a semi-dual-mono, where I only share the mains transformers. By overrating those by a huge margin, the impact of not having ones for each channel is marginal.
I have made my first prototype build, and it ran perfect. Just some minor tweaks to the PCB are needed, and I am on the track to one of the best solid state amplifier designs ever made.
My first version of the LOTHALA 80 is wonderful - but there is room for improvement. The issue lies in the long-tail differential input stage, where one input is used for signal and output feedback, and the other is used to set the DC operating point via. an integrator (servo). The input impedance is so low, that I used an op-amp in a buffer configuration to drive the amplifier. As such an op-amp buffer relies heavily on negative feedback, this will impact the entire design. The soundstage is very wide, but clearly suffers from the negative feedback in the op-amp.
I decided to replace the op-amp buffer with a push-pull class A pre-stage which then will drive the long-tail differential pair - a somewhat scaled down version of the Lohstroh & Otala design itself. My pre-stage has no feedback at all, and I hope this will open the soundstage even more.
When dealing with tube based equipment it is equally important to be able to test tubes, and I realized I was in need of a tube tester. Back in the 50's and 60's, tube testers were commercially available, but nowadays they are an almost extinct species, which left me with two options. Either I had to buy a vintage tester and give it a major overhaul or build a new one from scratch. I opted for the latter as I found an excellent design done by Steve Bench. I used his basic design and modified it to my own needs.
This album shows the Step by Step process that I went through when I was building my arcade cabinet. The cabinet is used for both real arcade games where I have bought the entire electronics (boards, EPROMs etc.) from scrapped arcade machines, and for MAME. But as it takes time to change boards, I've dumped the EPROMs and use them with MAME instead. Further, I can avoid the use of the special graphics adapter that is needed when I run the original boards with a modern monitor. It was somewhat problematic to dump the very old EPROMs (eg. 2708), as they needed more voltages - often negative - than their modern counterparts that run off a single 5 volts supply.