Back in those days, what separated the 'men' from the 'boys' was the output of their power amps; boys played about in the area below 10 Watts, and there was a 'grey' area between 10 and 20 Watts. The 'real' men occupied the upper echelons of 20 Watts and above. It was an expensive game when for umpteen reasons your power amp could 'teleport' itself into other worlds in a cloud of smoke, and to boot, take your precious speakers too along! And power transistors, especially matched pairs, were not exactly cheap and they surely did not grow on trees!
The 'flip side' of this power game was that in the melee, scant attention was often paid to the sonic merits of the designs. Considered from that angle, here are a couple of truly 'hi-Q' (a Philips trademark) power amps. If you have efficient speakers that do not need a connection to the nearest power house, these are wonderful options even today. I have found that the 15 W version is particularly suited to driving undemanding open-baffle speakers, and, be warned, the combination could sure sound addictive!
Perhaps what works the magic could in part be the circuit topology of these 'vintage' power amps.
Many of us could easily recall the mad race after fully complementary/fully symmetric designs. The designs looked particularly 'sexy' on paper with their picture-perfect symmetry and, of course, when well-designed, they did sound great too. But our obsession with such designs made us forget many of the golden nuggets from the past. Only recently have designers and enthusiasts like Wim de Haan and others done their bit to restore the quasi-complementary output stage as being 'sonically superior' to many other designs.
As a matter of fact the quasi-complementary design evolved out of manufacturing compulsions. It was easier in those days to fabricate high power N-P-N transistors. Fully complementary pairs were confined to the low power levels, and often used as drivers for the output devices. Now it is well documented by many designers in the field that there are subtle differences between the P-N-P / N-P-N transistors and as a result there are audible differences that mark the N-P-N pairs as being superior and "more musical" output devices. Whatever that might be, here is an opportunity for you to test that theory out with good quasi-complementary designs as these. Surely you will not be disappointed with the results!
Hi and this brings back memories. The 40 watt amp from the philips audio handbook was, and I reckon , still is the most authentic source of information on audio systems. It was the audio bible in those days. When I grew up from being a boy with 15 watt amplifiers AD149 power transistors to the rarefied levels of high power, the philips 40 watt design was my ride. The first amp i built was a stereo design in total compliance to the design hand book, except for the regulated power supply. The speakers were 4 x 8 inch philips full range per channel built as a boxed column. This was the back bone for many of our rock shows during college. I have built many a 40 watt amps later, and i must say that the design is so robust that my share of smoked up amps were unusually low. Quasi complimentary was the only way to get to great powers. Now there are many audio specific transistors in the market suitable for complimentary outputs making the design simple. With the advent of class D amplifiers, the pure thrill of building a class ab quasi complimentary amp, and setting it up with a humble multimeter, sound check with a keen pair of ears, is all but gone.
ReplyDeletecheers and may the force be with you
S.M.
My dear SM,
DeleteThere, you DID turn on the nostalgia tap... !!
The Philips Audio Handbook was The Bible for many a DIY-er in y/our generation, and nothing comes close to the thrills that resulted from following that.
After many years spent building and listening to amps (with a keen pair of ears, as you so admirably put it!), I must say I totally agree with what pundits like Vim de Haan (Elektor author) and some Japanese designers have found out --that the quasi-complementary output stage has "a sound of its own, and it is very sweet". I guess the enthusiastic following that Gainclone "chip amps" have generated is also due mainly to their output topology being qusi-complementary.
In the meantime, permit me to introduce you to another great topology, which I am sure will go on to become another timeless 'classic' -- the Circlophone. Many of my friends (abroad) who have built it swear by its qualities. (http://www.diyaudio.com/forums/solid-state/189599-my-little-cheap-circlophone.html)
Thank you and here is wishing you the joys of Onam!
Keep your iron hot, mate!
-- UKP
Hi...ukp
DeleteHello Prof,
ReplyDeleteI found your blog while Googling (what a word :) for circlophone amp. I try to open the pages excerpted from Phillips hand book you refer on this page, but still they are too small to read. Would you mind to share the bigger version of the pages? my email is on david_winarso (at) yahoo (dot) com.
Thanks,
David