Sunday, June 11, 2017

Owston - a visit to DIY Audio Land

Some of you may know that one of my major hobbies is building amplifiers and loudspeakers. I realize that most of the pictures will mean nothing to most of you, but think of them as exotic flowers in an unusual garden. Even if you have no idea of what I will be talking about, maybe you will understand a bit more by the end of the blog. Perhaps not.

When I was in hospital recovering from my heart surgery in early 2016, I passed the time thinking about how to design a light weight amplifier. As part of my research, I came across a UK group called Audio Talk and I got a number of ideas from their forum. They hold a meeting each year and I discovered that I would be in England when it was held. I asked if I could come and they were happy for me to attend.

This amplifier is known as the Tower of Power and illustrates an important principle in all amplifiers, be it a monster like this, or even a tiny amplifier in a cell phone. This rats nest is the amplifying part where the large two tubes (valves) towards the top back provide the power. There are lots of different types of tubes and these are a very old design known as an 801. They only produce about two watts but these are hot-rodded with special regulated electrical supplies.

Every amplifier needs power to operate and here is the main power supply which takes in alternating current AC from the wall and converts it to direct current DC. This is so big and heavy because it is designed to produce a high voltage and a lot of current and it needs to be free of interference and very stable to get really good sound.

The whole shebang is on casters so that it can be wheeled around.

Out of focus closeup of the rats nest which is an inspiration for me. I have never quite achieved anything like this. Maybe the builder added some extra non-functional wires that don't do anything but just add to the Jackson Pollack ambiance. The silver cylinders are motor run caps which is the part that usually is the cause of your air-conditioner failing. Your friendly electrician makes a lot of money by replacing this rather inexpensive part and charging you a lot.

Many DIY builders go through a process known as bread-boarding which is just what it sounds like. When trying out a new circuit for the first time, they get a piece of board and lay the components out in a simple fashion and then try to make it work. It is relatively easy to correct or adjust compared to trying to do it in a box. If all is well, then you rebuild it inside a beautiful looking box or container. Or you just leave it as an unfinished piece of work on the breadboard.

A power supply box. Some builders keep the power supply separate because the large transformers and chokes are very heavy.

One of the reasons I went to this DIY meet was to see and hear this amplifier.  A couple of years ago I went to another DIY meet on our way to Australia. It was held just south of San Francisco and is known as the Burning Amp Festival. It is mostly devoted to solid state transistor amplifiers based on designs by a commercial manufacturer named Nelson Pass. Each year, he encourages the DIY community by releasing a relatively simple amplifier which demonstrates some interesting topology. In 2015 he stood a few feet away from me and showed this schematic.

This is Nelson along with the schematic of the 50 watt Single-ended BAF2015 Schade amplifier. You can read about it here.

Although there has been a lot of discussion, I believe very few of them have been actually built and I suspect this is the only one. To the left is the power supply and on the right is the amplifier  for one channel.

The other channel. The large spiky thingie to the left is a heatsink. The design calls for over three amps of current and 60 volts which means approximately 200 watts of heat to be dissipated. Even though the aluminium heatsink is 13 inches high by 8 inches wide and the prongs are 3 inches deep, it still needs a very quiet fan to keep the temperature down.

The fan worked very well and even after the amplifier had been turned on for some hours, it was only a little warm. Years ago I built another of the Nelson Pass designs called Son of Zen that put out a huge amount of heat. I needed three separate containers and one of them got so hot that somebody said you could cook a chicken in there. You can see pictures here.

The amp sounded very good and I will probably build it since I have most of the parts I need.

Many in the DIY community also build loud speakers. Since many of us don't have room for workshops to build large boxes, many of us have turned to building what is known as Open Baffle Speakers. Essentially you take a large piece of wood, cut appropriate holes, attach your drivers and work out a way to make sure they whole thing does not flop over in a strong breeze. Yes, it's more complicated than that but it works and it often sounds very good in typical listening rooms.

For those of you who are thinking the baffle is too small to allow much bass, you should read about high QTS and large woofers here.

You can see more detail in the following photos. The first few are from the speaker on the left and the others from the speaker on the right.

These speaker drivers are 15" wide.

This is 18" wide and can move a lot of air.

In the esoteric world of high end audio, many prefer the sound of vinyl records to digital CDs. The DIY community often uses old record players, restores them and then mounts them in fancy new plinths of interesting design.

There were quite a few Goldring Lenco turntables. The company was Swiss and there are still quite a lot of them around. They were well made and apparently still work very well.

The guts.

Headphones are very popular these days and of course, the DIY amp builders construct high quality amplifiers for headphones. They are not very portable however.

An unusually small speaker that sounded much larger than it looked.

When I found out that this meet would be held while I was in England, I asked if anybody was coming close to Worcester on their way to Owston and a very nice bloke from Taunton volunteered to give me a lift. His name is also Ray and he built these really interesting amps. This photo shows the amps without their tubes. The amp is an OTL design which uses four 300B tubes in a cathode follower arrangement and produces one and a half watts per channel. Ray used a box for each channel and a box (back right) for the heavy power supply. By the way, each 300B tube costs over 100 pounds. More about how they sounded later.

You can read more about building this amplifier here.

Another breadboard.

Another amplifier. It's a Transcendent Audio kit that you can build yourself.

A different kind of open baffle speaker where fabric covers the speakers and holes. I liked the orange trim. We used these speakers towards the end of the day to compare various amplifiers.

Three speakers. From the far left in the background is a small junky bookshelf speaker that was refurbished and substantially improved. As a rescue job, it was very impressive and sounded much better than it should. In the middle is one of the open baffle speakers and on the right, the large boxes are from a public address system and designed to play loud in a very large room. 

A modern recording studio.

A push-pull amplifier.

Another OTL of a different design using 6080 tubes as output tubes. You can read more about it here. The dome hides a toroid transformer and the whole thing is quite tiny, probably about 9" by 12".

The insides.

Some people are real craftsmen who can build something like these.

About noon, the serious listening started. There were about two dozen of us, mostly of a certain age and a certain colour hair or lack thereof. There was one woman who was really enjoying the music. Unfortunately it does seem to be a male dominated hobby especially it is generally reckoned that women have better hearing than men.

Everybody got to demonstrate their system with three tracks. Most people used vinyl records. Naturally the music varied a lot. It's one of the best parts about going to this kind of meeting. You get to hear music that you haven't heard before. However there were a few tracks that I would not care if I never heard them again.

It made me think about which three tracks I would have selected.

And something additional that would have outdone the Graham Central Station track of Earthquake.

My daughter Robin introduced me to this.

I noticed that a few blokes had gone outside to look at this motor bike.

You can read more about these Ural motorcycles here. They all come with a side car.

It would probably work well for a couple of fat ladies, or gentlemen.

Detail of a special board with associated stuff suitable for heating the filaments of direct heated triodes. Nicely twisted wires. By the way, twisted wires normally mean that they are carrying AC.

Lunch arrived. We each paid 15 pounds to cover the rental of the room, coffee and tea as well as the lunch.

The builder of the amp with the small dome also brought this along. He won the prize for best pants of the day with his tartan legs on the right.

The spectacular tubes for this amp dated from the 20's and 30's of last century. When the builder bought them years ago they were quite inexpensive. No longer. 

I was very impressed by the sound of this amp which produces five watts.

The back side of the amp.

Ray's 300B OTL amps in action. Although they struggled to produce a big sound in such a large room, they really sounded good with a wonderful treble. Towards the end of the day, we settled into a routine of playing the same song (Walk on the Wild Side) with different amplifiers using the same speakers. I found this was very useful to compare the amps and although there are not huge differences between them, they all sounded excellent.

Finally, a pair of white coffins for small children were carried in. They turned out to be speakers with curved sides wrapped in white blankets but it was time for Ray and me to leave and drive back home.

I really enjoyed my time at the show and it was much like all the other meets I have been to over the years. We DIYers are friendly, helpful people who enjoy seeing what other people have built so that we can get new ideas for future projects.

And many thanks to Ray from Taunton for taking me to the meet.

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