Bamboos and boxes

Provide the base support for the chanter

So when I started to learn to play the bagpipes, the first thing I had to purchase was a practice chanter. The full set of bagpipes uses a hide or synthetic bag to provide a steady flow of air through the chanter and the drones. The drones are the three pipes that rest on the pipers shoulder and they just make different bass notes to support the chanter. IMG_0505The chanter itself though is the pipe with finger holes in it that makes the notes of the tune. Here is a photo of yours truly taken by my bagpipe teacher when I went for a lesson with my new Chanter reedpipes. There is a reed in the chanter that vibrates when a stream of air from the bag passes over and through it. But here’s the thing. A bagpipe chanter makes a heck of a loud sound (so,me would say noise), and so do the drones. If you practiced playing them in your apartment, some neighbour would sooner or later shoot you. So in modern times, the practice chanter was developed. It is similar to the actual chanter, but the reed is made of plastic and is relatively un-noisy. There is no bag so the air to sound the practice chanter is provided directly by the player blowing down a blow stick which is connected directly to the practice chanter.

So having set the scene, let’s get back to the title of this blog article, i.e. ‘Bamboos and boxes’.

Chanter quiver comp
Chanter quiver

Any musical instrument should be protected for transportation and since I had some bamboo lying around, I sawed off a length and used it to make a carrying case for my practice chanter. The cap and strap are made of leather. I thought it was quite arty looking and would be a convenient way of carrying the chanter around. Here is a picture of what I called ‘The Quiver’. It worked O.K. but it is quite a long and bulky object and I realised after a while that it was not very practical. So I made a container of a different design for the chanter. It is a little foam lined, hinged box with cutouts in the foam to cushion the chanter.

To transport the chanter in this box, one unplugs the blowstick from the lower part and stows them side by side. The reed has to be removed too because it would be too vulnerable if it was left protruding from the playing tube. The reed and also a couple of spare reeds get popped into a small plastic pill box with a desiccant to keep the reeds moisture free. Piper 2 nealPractice chanter reeds are made of plastic and don’t work well when wet. Real chanter reeds are made of special Indian reed and they have to be moist if they are to be coaxed into making any sounds at all.

Tape-recording Video

We saw that when recording analogue sound on tape, head to tape speed was critical. Some musical notes sound higher pitched to us because their wave patterns have higher frequencies and shorter wavelengths. If the wavelength becomes so short that it starts to approach the length of the gap between the recording head poles, the waves are cancelled out as they pass the head. We can increase the maximum recordable frequency by reducing the width of the head gap or by speeding the tape up so the magnetic flux is spread over a longer section of the tape.

But head gaps can only be made so small and tape speed cannot be increased 300 times to make it possible to record the 5 million cycles per second (5MHz) that video requires as opposed to the 15 000 Hz that good quality audio requires. To record analogue broadcast video on a tape moving across a fixed head, the tape would need to run at about 140km/hr. Giant reels of tape would have to be managed and the whole thing would be highly impractical. So how do they record analogue video then?

Simple really. The tape does move, as before, at about 38 cm/sec but the head is not fixed. TRacks on quad tapeThe head is a tiny construction on the rim of a lightweight wheel and spins at a very high speed across the width of the tape. i.e. If we dip the recorded tape into alcohol containing very fine iron filings in suspension, and then dry it out, the recorded track appears as a series of stripes running almost transversally across the moving tape. Professional recording tapes were 2″  (about 5 cm) wide, and were sucked into a curved guide by a vacuum pump whilst they moved past the spinning recording head. Looking at the tape guide side-on, it looked something like this. This curving of the moving tape enabled the head-wheel to spin in an arc making contact with the tape throughout .

Quad head guid

The spinning head would start touching the tape at the top and lay down a track till it reached the bottom (Not strictly true but it works for now). You will see that there are 4 heads on the spinning wheel and each one would record a quarter of a complete TV picture onto the stripe on the tape. By the time the next head reaches the tape, the tape itself will have moved on a bit and the second head then records its stripe.After a full circle of the wheel, there would be four parallel recorded stripes across the tape containing the information for one whole TV picture. This ingenious approach produced a head to tape speed fast enough to record the 5 MHz waveshape which described the frequency modulated, broadcast standard,  video signal.This was known as a quadruplex system. There were other systems such as helical alpha-wrap etc but let’s deal with one at a time. They are all variations on the same principal.

During playback, the tape was synchronised by pulses recorded along the bottom edge so that the heads would find the recorded patterns and be able to track them and read the magnetic record on the tape. There was a lot of circuitry involved and the process required extensive mechanical and electronic stabilising, but it was done and high quality video pictures were recorded and recovered.

Acknowledgement: pictures taken from website http://archive.totterslane.co.uk/tech/quad.htm. Content is my own.

An electronic metronome

I am retired and live in a small apartment, so the days of having large workshops and rooms full of electronic bits are all gone. I do occasionally build a little gadget or a box though, just because I like doing that. As my current preoccupation is learning to play the bagpipes, most of the things I have made lately are to support my music making.

Metronome circuit diagram

I needed a metronome to provide rhythmic clicking sounds and flash LED lights in time to the music, or rather to keep me playing at the speed the music should be played. 

One can of course just download a metronome app on one’s cellphone but that is not in the spirit of building things. So I scratched available components out my spare parts box and reassigned a plastic container from my kitchen to build the thing into. Here’s how it all went together. Above is the circuit diagram. It is a  pretty standard design except that component values have been selected for this specific purpose.

Board drilled inc 555I used ‘Veroboard’ to mount the components onto. It consists of copper strips on the surface of an insulating board. The strips can be cut into sections using a drill, This provides wires that connect those things that need to be connected. Here’s a view of that process. The components mount onto the other side of the board and their wires are poked through holes in the tracks and soldered to the tracks.

Here is a view of  the underside of the board with all the components soldered into place. The purpose of the terry clip is to hold the 9V battery. The holes in the corners are for mounting screws. The wires you see connect to the controls which are mounted on the lid of the plastic box. Nothing is mounted to the bottom or sides of the box , so the whole thing can be accessed by simply removing the lid from the box.  Board underside soldered & bat clip compHere is a view of the component side of the board. It is shown in the maintenance position where everything can be accessed. During operation it moves inside the box next to the speaker and above the controlks so the box can be closed and clipped together.  Top of board in maintenance position

Here is a view of the whole unit, assembled and ready to operate. There is an ON/OFF switch and the click speed and volume can be set on the controls.

Completed unit - angle shot

My Blog does not support videos so I cannot show you how it looks and sounds. But because it makes a cheerful clip-clop sound at the pace of the music, I have nicknamed it “Pony”.

 

 

Chapter 2
A friend of mine once learned to do morse code and I also used to do that when I was a practicing Radio Ham. So the friend asked if I could build an oscillator which we could use to practice Morse code with. But a code oscillator is nothing different from a metronome except that it runs about 1 000 times faster. If I set the metronome to run very very fast, the rapid clicking sounds to the human ear like a musical or whistling tone. Click here t6o get the effect.   The metronome controls don’t adjust the speed of the clicking to go that fast, so I just added a switch to the top which switches in different timing components and turns the metronome into an oscillator. I then also installed a jack socket on the box (not jack-in-the -box), into which I can plug a morse key. It is just a contact on a spring loaded arm and when you tap the contact arm. it completes the circuit and sends out a burst of tone. A short burst becomes a dot and a longer burst becomes a dash. The metronome speed control becomes a pitch control to vary the note it gives out up  and down the scale.

Here are the Morse code alpha-numerics in case you would like to practice your Morse code. LOL.Morse code

The rise & fall of recording tape

Part 2 – 0 Audio tape basics

During the 1950s and 60s, magnetic audio recording tape came very much into its own. It had been around for a long time but it was not robust and the quality was poor. The detail is not for a blog like this.

The modern tapes of the time were 1/4″ wide single track tapes made of a plastic called cellulose acetate. It was strong and flexible and did not easily stretch. If a recorded tape is stretched out of shape and then played back, the sound will be distorted. To make recording tape, small magnetizable metal-oxide particles, suspended in a lacquer that hardens into a flexible layer when it dried, is spread on the surface of the acetate ribbon. I have heard such tape laughingly described as a strip of plastic with rust painted onto it.

Now whilst the particles in the emulsion can be magnetised to remember the music waveform that had been recorded, the magnetism does not spread on the tape as it did in the old wire recorders. This is because the particles tape-headare discreet from each other and not contiguous. Tape from the supply reel is drawn over the recording head and taken up on another reel.The head itself is a metal ring cut through at a point to form an extremely narrow gap. A coil of wire is then wound around the head ring and the audio signal that needs to be recorded is passed through the wire. The signal current flow causes a magnetic field across the head gap with a magnitude proportional to the audio signal being recorded. Louder signals cause a stronger current in the head and magnetize the tape more. As the tape is drawn across the head gap, the particles on the tape are magnetised and when that tape is again passed over the head later, it will induce a current into the coil which can be read out as the original music.

All was well in theory but in the original systems the quality was poor due to losses and distortions. For one thing, the amount of magnetism induced onto the tape was not directly proportional to the magnetising force. Small magnetizing signals magnetized the tape to a certain extent but doubling the input signal did not double the magnetization. This led to a distorted copy of the original when played back.  The problem became less severe at higher tape magnetization levels and the reproduction was reasonably good in the middle range, or so called linear part of the tape’s magnetization curve. So a way had to be found to use just that linear range of the tape magnetization curve over which the recorded signal remained a fairly accurate facsimile of the original signal. This was done originally using either a fixed magnet  or a small DC magnetizing current through the head-coil, to pre-magnetize the tape to the point that it started operating on the linear portion of its magnetization curve. This was called DC bias.  The varying signal current was then also passed through the head to create the recording using only the linear part of the magnetization curve. The trouble with that approach is that there is a limit to how much you can magnetise the particles on the tape. At some point the tape is fully magnetized or ‘saturated’. So if the DC bias is too strong, there is not much headroom between where the DC bias leaves the tape magnetization level and and the saturation point of the tape. To fix this, the DC biasing system was replaced by a high frequency AC biasing signal. To understand how this works though we need to understand the importance the head gap and tape speed.

The audio signals we want to record are alternating electrical signals. i.e. they swing from positive to negative and back to positive rapidly. We say they are AC (alternating current) signalssine. If we draw a graph of a pure musical tone it will be a simple Sin wave, i.e. one that varies in intensity in a constant repetitive fashion in time, it could look like this. The sound we hear when we strike for instance a middle A note on the piano changes polarity 440 times per second. The horizontal axis of the graph indicates the point of zero magnetising current. As the current gets more strongly positive it will rise above the line and as it becomes negative it will be shown below the line. But this graph is a snapshot of a moment in time. If you look at it a moment later it will all have moved a bit to the left. So the graph depicts how positive or negative the current is at various moments in time. Click on the arrow below to hear  what it sounds like. . So if you look at this graph you will see that one cycle of the sound or one wavelength if you prefer that term, is from any point on the graph through till when it gets back to the same point and starts repeating itself. If there are 440 repetitions per second as in the case of middle A on the piano, each cycle will last for 1/440th of a second. i.e as the tape moves past the record/playback head, 440 wavelengths will pass the gap each second. It all works fine unless the head gap is too large. If the gap is the size of a wavelength, both halves of the cycle, positive and negative will be in the gap at the same time and the magnetic fields being produced will cancel each other out leaving no recording on the tape. So the gap needs to be very small compared to a wavelength so that it can leave a recorded pattern on the tape which truly represents the original signal. This is what defines the quality of a tape recording head. It is much harder and more expensive to make a head with a very small gap but the smaller the gap, the shorter the wavelength it can record or play back. If the wavelength gets shorter, the frequency (pitch) rises. The sound-wave travels past our ears at a more or less fixed rate so if the wavelength is shorter, more cycle will pass our ears and that means we hear more frequent peaks and valleys. We say the frequency increases as the wavelength shortens. Young people can hear frequencies of 15 000 Hz (vibrations per second) or even higher. That’s a very short wavelength and a head gap has to be really small to reproduce it. But then again it depends how fast the tape moves past the head. if we speed the tape up, each cycle of the recorded signal stretches out on the face of the tape. Or said differently, at high speeds, a wavelength representing a certain musical note covers a longer piece of tape. This means that a given head gap can record higher frequencies if the tape speed is higher.

So then, back to bias. We said that DC bias compresses the useable range of magnetic tape and therefore we get a poor signal to noise ratio and we hear noise on playback. if we use a high frequency signal to pre-magnetize (bias) the tape we have a different result. If the bias current vibrates at several times the highest frequency we need, it will lift the recording on its back onto the linear portion of the tape’s magnetic response but the gap cannot record this high frequency and the bias disappears as the tape leaves the head. This enables the tape to eventually record a much larger range of signal levels than DC bias does.

Its complicated to understand but it actually does work and high quality tape recording uses high speed biasing to improve the quality. This is dry stuff anyway so next time I write on this topic we can move onto video tape recording which is another thing altogether.

bar_magnet field

When is a lunch box not a lunch box?

I was most interested to see on Benjay’s Google+ page, he made use of items such as his daughters shape boxes to house amplifiers, speakers etc. It’s alway been a challenge to find non-expensive cases and cabinets for one’s projects and I think Benjay’s solutions are pretty innovative.  I’ll work back to that but I have to start the story differently.

When I worked in the Broadcasting industry in the 1960s and 70s, a lot of the programs we packaged for broadcast were still recorded on large, 12″, gramophone records. We even used to receive the ‘Goon Show’ by mail from the BBC on 12″ records. Tape recorders had been around for quite a few years but if you wanted a truly high quality recording, it was still done on disc. When the SABC wanted to broadcast a symphony concert from the city hall or wherever, a truck would be used to transfer the massive Neumann cutting lathe down to the venue. The machine would have to be manhandled into the building by two strong young technicians and set up with spirit levels to be truly horizontal on a solid base. A virgin wax disc was placed on the turntable and the concert would be cut on that. This precision, German-built Neumann record-cutting lathe was a really solid piece of equipment and the recordings it made were of a very high standard. For instance, the cutting head was not mounted on a swinging arm as we see with domestic record players. With a swinging arm, the cutting stylus would only run exactly true to the direction of the track at one point in its tracking arc. At all other angles of rotation, the cutting tip would be at a slight angle to the track and this would cause distortion. Later on, Hi-Fi record players in the studio and at home minimized this error by using the longest possible tone arm so that the total arc transcribed by the stylus was as flat as possible. But in the cutting lathe, no error at all was allowed and this was achieved by using a headstock that advanced the very solid and precise cutting head across the disc from edge to centre in a straight line as the recording took place. Neumann disc-cutting lathe

The delicate recording on the wax disc was then taken back to a laboratory where it was electroplated with a nickel alloy in a complex multi-stage process. When the nickel plating layer was then removed from the wax original, it was an accurate and hard, negative copy of the original. This could then be used as the die for stamping out playable records.  In the days before Vinyl records, the old commercial 78 speed discs were made of shellac, and if you dropped them they smashed into pieces much as a teacup would do today if you dropped it. But the records made specifically for high quality broadcasting of recordings such as the concert we have been talking about were pressed into shellac which was just the skin on an aluminium base disc. This made them more robust than commercial discs but of course they were still vulnerable and quickly developed surface noise etc. with usage. They were however only ever played a few times for broadcast purposes after which they were either archived or simply discarded.

Now this is where my story started. The shellac covered aluminium discs that were not archived were simply tossed out and we who worked in the technical department got to take boxes of them home with us for free. We would chuck such a disc into a basin of boiling water and this would cause the aluminium inside to expand and simply burst the shellac off it. We were left with a beautiful shiny aluminium disc you could see your face in, and this we could use for making equipment chassis, faceplates etc. How marvelous that was to those of us who wanted to build, amplifiers and radios and other gadgets. We would build those valve amplifiers etc. with great care so that they looked really good, The little glowing bottles would all line up like well trained soldiers and the wiring under the chassis was done painstakingly and attractively. Sometimes they looked so good that we used them just like that so everybody could see how neatly we had worked, but there were high voltages running round in those valve circuits and for this and other reasons we sometimes wanted to build our creations into outer boxes. This was however one of the trickiest tasks and we were always looking for readymade stuff to house things in just as Benjay does when he mounts his   “Zinky Smokey amp and Takamine acoustic preamps” in his daughter’s old shapes boxes.

But I have become lazy in my old age and these days if I need to knock up a device for some purpose, I don’t gCompleted unit - angle shoto to so much trouble. This electronic metronome I built recently using a 555 timer chip for instance was simply installed in a plastic lunch box. I’ll do another blog on the detail of building that thing but for now, here’s just a picture to show what it looks like. Nearly every part of it came from my spares box or from the kitchen cupboard.

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The rise and fall of recording tape

Part 1 _ Wire recorders

When I was a kid back in about 1949 or so, we were all very excited because my Dad had acquired a Webster wire recorder. Up until then, the only recordings we ever heard were on gramophone records but that’s a whole ‘nother story. 

The Webster was an American machine in a box with a flat top. Against the back edge of the top but central between the sides was a record/playback head. Silver wire was drawn from a bobbin on the left of the deck, passed through a groove in the head and rolled up onto an initially empty spool on the right hand side. During recording, Webster wire recorder_1the sound from the microphone amplifier or radio created a magnetic field in the groove of the head and as the wire passed the head, it was magnetized to a varying degree in accordance with the sound.  Later, the same wire could be run past the same head and it would create an electrical signal in proportion to the magnetism in the wire, thereby theoretically reproducing the original sound. The wire would frequently break or stick, and the speed would vary depending on mechanical limitations in the system. The playback sounded pretty lousy. It was also true that the magnetism induced in the wire did not stay exactly where it was put because each particle of the wire slightly re-magnetized the adjoining particles. In other words, the magnetism spread in the wire to some extent and this caused a loss of fidelity when the wire was played back.

Everybody had lots of fun sending each other recorded messages etc but the wire recorder wasn’t much good for anything else. You couldn’t go down to the store and buy a piece of music recorded on wire. A better system was needed and sometime in the 50s or so, domestic tape recorders started to become available. Professional tape recording had been around since the 1930s but home equipment only happened about 20 years later. It was better than wire for various reasons. The tape was made of an acetate base of some sort with a layer of very fine metallic dust embedded into a varnish-like surface. The tape would be passed over a recording head and the magnetic field in the head would magnetize the separate metallic particles in the surface layer. Because these were not touching each other, the magnetism could not easily spread through the tape and the reproduction was very much better that wire recording. The system was however still fraught with problems and the quality was still not good.

But more about that in a few days time.

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A haven to practice bagpipes

If this were Zen I would ask the question, If bagpipes are played in a concrete room with nobody there to hear them, are they played?

Most people know that the bagpipes are a very loud instrument and any piper who lives in a built-up area has the problem of finding a place to practice that will not disturb the neighbours. I live in an apartment block and practicing the pipes inside the building is definitely a no-no. My cat would report me anyway. But luckily for me, there is a concrete room on the basement level of our block with no connection to the main buildings.  The painters and maintenance men use as it a common room for their lockers, lunches etc.  It can best be described as a bomb shelter or concrete bunker and when the maintenance staff knock-off work at 5 PM, nobody uses it. I have fast-talked my way into getting a set of keys for this room and that is where I will practice making my pipes produce music.

Driveway to pipe room web

Here we are going down the driveway from the road to the under-building parking. Note the Red picket gate on left hand side away from building.

Pipe room outer gate web

We have turned left off the driveway and are now facing the gate we saw in the previous picture. Note that it is not under the building at all.

Pipe room yard web

 

 

 

Behind the gate is a small yard full of junk and the door of the piping room can be seen at the far end from the gate.

Pipe room_1 web

 

 

The room is a pigsty but who cares? It is large, 7m X 5 m and is full of sound       absorbing junk so it does not echo.

Pipe room_3 web

As you can see it is a veritable concrete bunker.  I will run there when the bombs start falling.

I have started increasing the lengths of my squawks on the bagpipes. From an initial, cat terrifying, three second skirl, I have managed to sustain a single note on the chanter, without drones, for almost a minute continuously. With the chanter corked and the three drones opened, I have been able to get all three drones to sound for quite a long time. I am learning that the piper does not so much squeeze the bag under his arm but rather holds the bag steadily under the arm and allows the expansion of his chest to compress the bag. This way, the pipe bag becomes a sort of extra lung. When the piper breathes in, his chest expands and compresses the bag making it play. Then as be exhales into the bag, the bag inflates again and his chest deflates. The theory is simple. Actually doing it is another thing altogether.