And if you think that’s smooth…..

This one gets us a bit further along the road to nowhere (famous last words of a lemming) and still on the same track as the Selmer blog. 

As an electronic power source, this shape of voltage is useful to man nor beast. It might pass muster as something that would charge a battery, or as source of electrocution. (If that’s what turns you on. So to speak.)

 This drawing is so confusing (even to me, and I drew it) that it needs an apology. So, first of all, I’m very, very, sorry. (Add any number of ‘verys’ to taste.) Here’s a list of excuses.

1) I was drunk when I drew it.

2) My pencil slipped.

3) This computer wants to see me dead.

You got to admit that that is not a very long list of excuses. But I ‘m not a politician. If I was, I could fill a complete hard drive with them. My team of  excuse manufacturers would have field day and ‘brainstorm’ until they drowned in the monsoon. Yes, I know, it’s a forlorn hope.

And now, back to the plot. I think I left it in the back of this drawer somewhere………..

The major difference between  the top diagram and the lower one (That’s not counting that they’re as similar as a stoat and an octopus) is that the top one has one nobbly-thing (technical eh?) and the bottom one has two nobbly-things AND A LINE. I could (were  I in full possession of a brain cell) just keep repeating the upper drawing and I would get a lot more of the same thing. That’s more of the technical stuff, of course.

If the long-suffering reader would care to look down a bit, that’s instead of staring at the ceiling and wondering when it will all end (‘lay down and think of England’ about covers it. Or Brazil. Or Australasia.) he/she will notice that at A, which looks a lot like A in the last blog, there is a subtle difference. That partly to demonstate that I can in fact spell ‘subtle’ and partly to introduce a component called a ‘Capacitor’. The capacitor  is labelled ‘C’, ingeniously. It is this single component that can convert the unusable voltage in the top diagram, to the almost unusable diagram underneath it.

The Line X-Y on the lower diagram is an approximate discharge path for the capacitor.

“So what?” you might well ask.  That’s where I can tap the side of my nose and do my Ron Moody impression in ‘Oliver’. Or was it ‘Fiddler on the Roof’. One of them, anyway. 

This leads (onwards and upwards) to explanations of what a capacitor is, what it does and how it does it.

It also leads to me getting a cup of tea, and you not. Nothing personal you understand.

Selmer Treble ‘n’ Bass Rectifier is to Blame.


A very nice bit of work on the cabinet of this old Selmer Treble ‘n’ Bass, done by Delwyn, a local guitar/vocal musician. He found it in a skip. He sorted out the casework and I sorted the insides. Sadly, they just don’t have this class of skip where I come from. 

This Selmer Treble ‘n’ Bass (probably late sixties) was a recent repair that someone had ‘repaired’ somewhere in the dim and distant past, and it served as a reminder that I’ve not yet got to rectifiers and how they work. There is some stuff on the function of a power supply somewhere in here, but nothing very specific.If you’d like to know why we might want one at all, I’d have to direct you to a load of blogs on here about power amplifiers.

So, first, what does it do? (that’s before we find out about how it does it).

The stuff that comes in  through your wall socket is a.c. This stands for ‘alternating current’, and this means that it alternates between positive and negative. “Why does it bother to do that?” you might ask. “Because it can be ‘transformed’ into higher or lower voltages and currents” I would answer, simplistically avoiding a million details.  But, although an over-simplification to the point of a matchstick Mona Lisa, still correct, in essence.

Here’s another oversimplification, as if one weren’t enough. The drawing at A is the symbol for a diode, and a diode is at the root of all rectifiers.

I would have put heaps of pictures of various diodes just about here   X   but my camera has bust. So my next blog might be something to do with fixing (or not fixing) a Fujifilm S5000. Suffice it to say, they (diodes) can look as different as a glass stick insect and an octopus. But they all do the same thing.

At A, the diode is pictured as an arrow-shaped thing, and that’s a pretty sensible diagram for it. If we put a battery with the positive at +, and the negative at -, the diode will pass a current in the direction it looks like it might. The way the diode is pointing, in other words. The R resistor is there to limit that current flow because the diode acts almost as a short circuit, and to drop that across your battery would not do battery or diode any good at all.

The opposite polarity (putting the negative of the battery to the + and positive to -) has a completely different result. Nothing happens at all. The diode behaves like an open switch. The diode then, is the simplest form of semiconductor. A conductor passes current, an insulator doesn’t, and a semiconductor is a bit of both. It conducts in one direction and not in the other. How might that rectify, then?

Well, an a.c. current swops polarity. (this has also been discussed in other blogs). If this a.c. is put to the + and – points in diagram A, the positive part of the signal will push current through the diode, and the negative part will, effectively, see an open switch. This is called ‘reverse biasing’ the diode and it means that the resistor R  will only receive positive-going stuff from the a.c. input.

Here (again) is my excuse for sine wave. The important bit, in this case, is also the simplest. Volts + and Volts -  and the horizontal line between, which is volts zero. The negative part of the sine (negative half cycle) won’t pass through the diode. So what actually appears at the resistor R (we’re still on the ‘A’ drawing here) looks like the bottom drawing.

This now approximates to d.c. The big difference between a.c. and d.c. is polarity. D.c. is polarised which means that it has a positive and a negative supply. A.c. alternates (a.c. stands for ‘alternating current’; no mystery there, then) between positive and negative, so, effectively, the polarity changes round at a certain frequency. BUT……. if the bottom half of the cycle is missing (because of the diode) it doesn’t change over, it stays positive-going. So it’s always positive. So it’s polarised, so it’s d.c. in other words.

Unfortunately, rectified a.c. is not pure d.c.

So more problems. I got a gas bill this morning. I know about problems. These specific problems, however, are with respect to a property called ‘SMOOTHING’. (I had thought of offering to donate my own internal gas to national grid of gas, if there is one; but I’ve so far had no reply. I did send them a sample in the envelope, just to help out.)

Rather than sending the reader into the realms of chewing his/her own legs off having been shocked out of his/her mind by the threat of more of this ridiculousness, I’ve decided to deal with the untrammelled issues of ‘Smoothing’ in a later blog.

So I can get a cup of TEA; and you can do something more fun. Maybe.


Well, clever git, you build one, then.

I can’t argue with anyone who might level the criticism that I’m less than charitable with my comments about new gear. But then, its my ball, so I get to take it home if you don’t let me win.

It’s not really about spite though. Much. The upsetting issue for me is rarely with the gear itself (even if I do call it everything from hyena dung to garbage bin balast). It’s mostly with the thinking that, by quoting a heap of meaningless numbers, dug out from the obscurity of their CAD program cave, manufacturers raise themselves above the mundanities of their unfortunate customers.  And supply themselves with loudhailers and parachutes (the better by which to talk down to us from etherial heights).

And another thing. Just while I’m about it. The fabulous cleverness of today’s technology has a flaw. A lot of it is unnecessary. For instance, what’s the point of constructing an amp to amplify light speed frequencies when the human ear can only hack stuff a lot lower than a dog whistle? I’m just not going to spend that much on my dog’s education.

And another thing, on the same sort of topic; why do I want to microminiaturise my amp down to a pin head when I can’t lift the speaker cabinet into the boot of my car?

Loads of these things run through my head (sadly) when I open up an amp and see the results of the western hemisphere’s manufacturing skills relocated to the eastern hemisphere. For a start, does it really matter which nationality robot built it? Not to me it doesn’t. It’s just that, if all the knives and forks are eventually made in China, and they suddenly decide they’re only making chopsticks, a lot of us would starve to death. Back to the plot. Whatever it was.

My guess at the starting point of most amp design would be the marketing dept. They would do a lot of market research into the ‘affluence band’ (never heard of that band), the ‘geographical locations’ (how many folks might use the amp in a desert), the ‘age band’ (whether or not they might be able to read or should they put cartoons on the controls), what ‘zines’ do they read, what did they have for breakfast, what colour underpants do they prefer on Wednesdays, is their dog called ‘Larry’?

What happens to this essential (and expensive) information? They put it into Chinese crossword puzzles, and hang it onto the price tag of the amp.

This naturally leads on to design criteria. The first being ‘How many multiway connectors can we fit into this thing?’ ‘Can we get the word ‘Valve’ in there, somewhere?’ (Just as an aside, the company H/H had a line of amps in the ’80′s they called ‘Valvestate Technology’ which didn’t actually have a valve in there anywhere. Just thought you’d like to know.) ‘Will the robot in China be ok with English lettering, or should we write it top to bottom?’

As essential as these issues doubtless are, my own take on the first steps of design would be nothing like that, at all.

My fundamental question would be, “what don’t I like about current amps?” And as the answer to that would be a fairly unhelpful “More or less everything”, I would then need to delve into the annals (anals?) of  the manufacturing of electronic equipment. Why? Because it’s all there laid out before us. The ‘what worked brilliantly well’ and the stuff that finished up on the bomb site. That way we could sift through the great ideas that didn’t quite get there, apply some modern technological stuff to it. Just to see how the original idea would have worked had it had that chance, way back when.

People daren’t experiment these days (unless it’s on a computer, which requires no commitment at all. If you have to make it to find out if it works, you have to put your heart and soul into it. It’s a different planet); you really can’t experiment with something that’s going to be cloned a million times, and cost your company a possible bankrupcy if it gets it wrong. ‘Safe’ is the watch word.

Presumably this is the same sort of thinking that Sony, Apple, Microsoft, and all the rest, employ when they sell a phone (or whatever) that’s already been superceded a half a dozen times when they sell it to you as the ‘latest model’.  The other models are all in mothballs, ready for the next ‘big launch’.

Not much in this related to designing my nice little amp. But it’s got me at least thinking about it. And a few things I’d probably rather not think about.

Time for tea; definitely worth thinking about.