Greetings!

[sbrook]

I arrived here after looking for some online source for the "New Approach in Class B Amplifier Design" by Peter Blomley. I have the circuitry and words in an old Wireless World publication of Audio circuitry from MANY years ago.

I started off my Audiophilia (if you can call it that ... my requirements are much less than that of an audiophile, but I hate the sound of BAD speakers/amplifiers etc as were and are all too common in the past and still today ) in the UK back in 1970 with a pair of EMI 13x8 Elliptical speakers in home made cabs. I built the comparatively inexpensive "Peak Sound" Englefield Amplifier with Germanium output transistors (in its effort to reduce crossover distortion). It sounded WONDERFUL compared to the commercial boxes my friends and family owned.

Eventually, I realized that the speakers still left TOO much to be desired and splashed out on a pair of Kef Chorale bookshelf speakers. I've still not heard much better to this day amongst speakers of that size and price range.

Then I realized one day after accidentally blowing up the AD142/3 output transistors for about the 10th time, that it was time to try something different. So, in about 1980, I built the Blomley power amps. The sound was astonishingly good. I kept the old very basic preamp and tone controls from the Peak Sound. They were so much standard of all common inexpensive designs, it was a case of why change what works.

Well, now, 20 years later, I've got some leaky electrolytics in the preamp putting some volts onto the volume control with the inherent horrible sounds. Quick repairs have resolved that.

But the time has come to replace these preamps with something a little more up to date. Component or IC doesn't bother me although I do want low noise ... something IC/op-amp preamps in the past were good at generating.

So, anyone with any ideas on what I might build to replace this bit of pre-amp history with?

I still use vinyl with a Dual turntable and Ortofon cartridge.

I'm contemplating repeating the Blomley circuitry to build a 5.1 or otherwise extensible system (I'll have to buy more good speakers I guess!) Need to upgrade the PSU if I do that!

[Cal Weldon]

A warm welcome to the capital from the left coast.

[sbrook]

I've been reading and maybe contributing half a penny's worth of my little (now) knowledge mainly from daze of yore when electronics stores meant components and they littered parts of London. I find it interesting that there is so little interest in hobbyist electronics anymore and others have commented on this too.

That said, I think the "do everything IC" and the computer have a lot to answer for.

I look at all these circuits for attempting to squeeze the last little bit of distortion out of amplifiers like these IC gainclones, or different packaging. It's taking the ingenuity out of the designs.

I just found a copy of Wireless World's High Fidelity Designs (1974) for which I paid the princely sum of 1 pound. It has designs for tape recorder electronics, a turntable, a pickup arm, an FM Stereo Tuner, a PLL Stereo Decoder, a couple preamps, a couple preamps, a couple Class B amps, a Class A amp, a couple loudspeaker enclosures, a pair of electrostatic headphones and an IC Peak Program meter.

An absolute wealth of talent from Bailey, Burrows, Stuart, Blomley and Linsley-Hood.

Now, all these folks talent in getting the electronics perfect has become second to IC amps with reasonable but not necessarily the best of characteristics. So, now, instead of innovating with descretes, people are looking at deoxygenated cables, variations in capacitors, variation in hookup wire, variation in metal film vs carbon film etc.

It makes me scratch my head a bit as I sit here trying for find parts to recreate my build of the Blomley class B and a variant on a Bailey preamp (with Baxendall tone controls). I can buy 2000 BC182Ks from some company, but try to find say 10! I'm not sure I want to buy house brand equivalents.

Of course one of the big problems we face is that the players in the semiconductor manufacturing (and some of the other components) industry have changed ... TI, Motorola, National Semiconductor, Signetics, Ferranti, Mullard (Philips) are now all in different hands, so you have to be creative in coming up with equivalents, especially when you find that stockists have say the NPN but not the complementary PNP transistor. So, you end up chasing over lots of different stockists and discover minimum orders or line item charges or astronomical shipping charges.

It's quite disheartening really.

And as we head into digital media with DRM layered on and design licensing, it becomes impossible for the hobbyist.

Oh well ... I guess I'll get my new super Blomley amps built with multi-preamp channels for surround sound built, with digital and remote controls, with all manner of other bells and whistles. And I won't be bickering over what wire sounds best or what caps sound best, because I know that the amp I have now sounds just as I like to hear it!

I'm not into valves (tubes) any more ... I got splattered across too many walls in days of youth from 250 V shocks!

[latala]

I have just unearthed my own englfield power amp Do you still have schematic for the power amplifier at all?
I am very interested in this short lived period of design Silicon drivers and Germanium output devices!
As you say it was an attempt to minimise crossover and cost
regards for now Trevor

[planet10]

Welcome to the forum.

I personally think that forums like this are bringing a diy renaissance. There is a rich set of things one can set about building where others have blazed trails.

dave

[sbrook]

Somewhere or another, yes, I do have the circuit, but it may take me a while to find it ... I can't quite remember it well enough to pull it out of my head ... It was just too many years ago :-)

I certainly remember visits to Englefield Electronics (RIP) to get parts ... funny little shop front ... next to nothing on display. Go in with your list and out comes the guy with a bag of your goodies :-) I liked them a lot because they carried a limited range of stuff ... didn't try to sell more than a typical hobbyist would actually need.

[sbrook]

D'Oh ... make that electrovalue ... not englefield electronics ... brain seems to skip a beat every now and then.

A circuit diagram of the PW Double 12 amp is attached which should be virtually identical to the Peak Sound Englefield. A couple of Resistor values are a little suspect and some of the capacitors have been adjusted in value to their nearest E range equivalent.

[latala]

yes thats the one!
many thanks trev