Thursday, 28 July 2016

Useful Software

Designing amplifiers is a complex task; while there are very well-documented circuit topologies in the literature, for each implementation there are voltages, gain factors, bias currents and resistances and capacitances to be taken into account.

Deciding on these factors requires an understanding of electrical principles and usually quite a lot of calculation.

In the golden age of valve gear – the 1950s and 60s, there was no software, the calculations needed to be done manually. Like the constipated accountant, circuit engineers needed to work it out with a pencil and paper.

Now we have it easy. Software which allows you to select your topology and simulate it, and giving recommendations for correcting anything that would cause a problem. Like this:

Do you think the program author might be a trekkie?

This is from Tube CAD by glass-ware software. Legacy software that you'll need a Windows XP machine (physical or virtual) to run it on.

There's also PSU Designer 2 for designing power supplies. With valve gear the power supply is usually a complicated mix of capacitors and inductors requiring careful balancing to get multiple different voltages to different parts of the circuit.

Finally there's Circuit Maker for drawing circuit diagrams. Bit like this which is a long-tail pair phase splitter idea I was playing with, something like this might make it into the final design, maybe...

Wednesday, 27 July 2016

What's this blog about?

[Admin note Mar 2018 – this post has been preserved unedited from when it was first posted. At that time, the intention on this blog was just to chronicle one project. It has since grown from that, but this initial post is preserved for nostalgic purposes!]

We all have some kind of unobtanium – something which represents the pinnacle of whatever particular interest we have... for example car enthusiasts have their dream car, camera enthusiasts always lust after the new lens or camera body, gamers are always after the latest rig with the fastest graphics.... that sort of thing.

In my case I was been bitten by the hi-fi bug at a very young age, which resulted in me diverting money into purchasing equipment to satisfy the quest for pure sound. A variety of black-box (usually) Japanese equipment has served my listening purposes through the years of my adult life, usually mated to well-mannered English speakers – my taste has always been toward the pure and clear sound with pinpoint imaging, instead of blasting out phat beats, yo!

By a varied path I came to be exposed to some rather delicious valve gear a few years ago which led to an instant epiphany... despite my extreme cynicism and scepticism about audiophiles (who at the time I saw as guys who just wanted to brag about how expensive their gear is), this valve sound was something that I couldn't just condemn as pretentious.

(Admin note: I am not American, so throughout this blog, I'll be calling them valves. Go ahead and read "tube" if you want... I don't make any judgements... tomato/potato)

Having also tinkered with electronics for all of my life, I decided on the idea of building my own personal unobtanium: a no-compromise design valve integrated amplifier, with sufficient power to drive my big KEF floorstanding speakers.

This means around 40-50 watts, which dictates the amplifier configuration.

Rather than blindly working off a published schematic, I plan to pick a tried-and-tested topology but design the circuit myself. This gives me the chance to learn how these things work, rather than just following a plan. I want to know about the pros and cons of the different designs of phase splitter, about building power supplies, and so on.

Yep, I want to do this the hard way... researching, learning and designing every step of the way – that's why I am doing this blog. I expect it will be several months before I have something that works and is not too dreadful aesthetically to sit on display in the living room.

If this works out well, it will not be the last amp I build.

Stay tuned for updates.