I suppose the story of the Brio-r starts back in 1992 when we used to frequent a used test equipment supplier based in Reading. These were the early days of the Rega electronics department and we had a limited budget for test equipment, so we would regularly scour the used test equipment suppliers for that elusive piece of equipment at a reasonable price. During one of these visits accompanied by Rega’s general manager, Phil Freeman, I unearthed a massive collection of Wireless World magazines dating from the late 40’s to the 70’s. I was told these magazines came with a selection of test equipment from a recently closed audio/visual company. To say I was eager to buy these magazines was an understatement, as they contained oodles of articles about audio equipment, and for me this was the golden era of ‘discrete’ audio analogue design. I persuaded Phil to load up his Escort RS to the gunnels with these magazines; putting a rather heavy load on the suspension, but the Escort RS made it safely back to Essex.
I saw in one of these magazines the 1952 article by Peter Walker about the Quad II amplifier. This wetted my appetite to read the rest of articles as the Quad II is in my Top 10 best amplifier list, and was the first serous valve amplifier I encountered at the age of thirteen.
I have to point out that this was before the advent of the internet when you had to find information where you could, which includes looking for magazines and books in dusty store rooms, swapmeets & jumbles which I still do!
I spent the next 8 years reading these magazines soaking up all the audio and related articles. A series of articles by an Audio Engineer I held in high esteem caught my eye giving me the inspiration for a power amplifier, which could have all the advantages of a solid state amp with some of the sonic properties of a valve amplifier. Using the Mk 3 Brio pre-amplifier and power supply as basis, I designed a new power amplifier for the Brio-r based on the above article, to my mind vastly improving on the Mk3 amplifier.
Neck on the block
However at Rega the Mk 3 version of the Brio was currently in production and was accepted as cracking sounding amplifier. All the Rega sales people felt the new Brio-r should use the existing Brio MK3 circuit so as not to change the sound. On hearing the new Brio-r, Roy put his neck on the block and pushed the new circuit into production against sales and distributor advice! However any controversy disappeared as soon as the Brio-r was auditioned.
Whilst I was reading the magazines I noticed that a few of the seminal audio articles had been highlighted, so they must have been of interest to the previous owner. I did suspect the previous owner was in some way connected with audio equipment and the Pirate Radio Station Radio London, as in amongst the pages of the 1965 edition that has the Bailey transmission line speaker I found, drawn on the back of a piece of Radio London headed paper, the drawing of a speaker cabinet using a B139 LF speaker and a HF unit. This drawing is now held by the Lighthouse Radio Museum in Harwich, Essex.
The Brio-r prototype
I did occasionally wonder who the original owner of the magazines was. I’d noticed there was a delivery name of M. Howell written on the back of some of the magazines, but this stayed unanswered up until the advent of Pirate BBC Essex in Easter 2004. Due to the renewed interest in the world of Pirate Radio in the UK I found out that M. Howell was Mike Howell, one of the engineers on the Pirate ship Radio London in the mid 60’s. This has subsequently been confirmed by the Radio presenter Dave Cash. This also explains why all the audio articles were highlighted! I have been informed that Mike Howell sadly passed away in the early 90’s, and because of his unfortunate passing I came by this collection of Wireless World magazines.
Stereo 20
Now for the technical stuff on the Brio-r. It’s hard to describe the action of the Brio-r amplifier without using technical terms but I’ll try to make it as straightforward as possible. The output stage comprises of a single Class A emitter follower, which drives a pair of complementary Class AB Darlington output transistors. This forms a cascaded emitter follower output stage with a pair of complementary Darlington output transistors (running in Class AB) driving the speakers. Although the amplifier is operated as a complementary class AB circuit, the output transistor arrangement can be seen as a single emitter follower output which can drive a speaker with class A sonic performance with the heat of a class AB amplifier. This could be best described as class A – AB amplifier.
This configuration also means the output transistors are being driven by low source impedance, which improves the bass drive conditions for the output transistors at the all-important crossover point. Another advantage of driving the output stage with a single emitter follower, or in other words a buffer, is that it reduces the load on the all-important voltage amplifier, which improves the linearity.
The circuit in the original 1970 article was to some extent impractical because of the rather high standing current in the driver stage. Thirty five years on from the original design I was able to solve this by using high gain Sanken Darlington transistors. Also the Sanken Darlington transistors have an embedded thermal bias network giving very good thermal stability.
One of the amplifiers I was using as a reference was a Leak ST20 valve [tube] amplifier with a pair of Class A push-pull connected EL84’s [6BQ5] in the output stage. Comparing the Brio-r to this amplifier enabled me to confirm that the cascaded emitter follower output stage in the Brio possessed Class A sonic performance.
To conclude this article I have to mention my wife’s perspective on finding these magazines. Her face said it all when umpteen copies of Wireless World emerged through the front door into the hall way. Thankfully I was able to plead professional dispensation; otherwise the Brio-r may not have existed.
Terry Bateman, 7th October 2011