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New: guitar FUZZ circuit built on a drawing pin board

 See a bit further down for PMR engineers' anecdotes and 80's pictures of London

Alternative Electronics

Simple electronic circuits that can be built without a printed circuit board that don't cost much to build and work well. With a bit of thought they can be made to look good too. Most are on a wooden base board with drawing pins although vero-board makes an appearance sometimes.

Designing a Simple Transistor Circuit

This may be of interest to electric guitarists who want to become more of an anorak about their craft!

Here we will deal with a ubiquitous transistor BC547, for use in audio frequency applications. It’s the same as a BC 107 NPN, although in a plastic TO92 package for cheapness. Supply is a 9 volt PP3, bias: class A and common emitter configuration. For simplicity let's ignore the 0.1u and 10u capacitors and consider only the DC conditions, it’s all bog-standard Ohm’s Law; V = R X I or R = V /I or I = V/R, and another transistor quantity: hfe. Seen on digital multi-meters, its purpose is to test transistors for gain amounts. Also known as Beta, hfe is the ratio of current (I) difference between the collector and base of a transistor and the higher this figure, the higher the gain. The required collector current depends on the signal level that our transistor needs to work at. This could be up to thirty milliamps (30mA) driving a 65 ohm loudspeaker in an intercom for example. At the opposite extreme transistors used in low level pre-amp stages, may require only 100 micro-amps collector current. In fact, 100uA – 30mA is the approximate usable working current range of a BC547 although it will pass 100mA max Ic, @ full saturation, for our purposes, more than 30mA makes it overheat, causing burns, and at less than 100uA the gain drops below a useful level: In such circumstances we’d need to select an alternative type. We will design a one stage, single transistor amplifier, useful as a guitar tube-driver: This will enable the instrument to push an amplifier into overdrive distortion. 1 mA will suffice for the collector and next comes Ohm’s Law. In the diagram there’s an X and is the junction of collector, RB, RC and one end of the 10uF. When working, point X should be half supply voltage: 9/2 = 4.5Vwith respect to the grounded emitter.  In practice, this could be anywhere between 3 – 7 volts but half supply is ideal. The current, as mentioned, is 1mA: same as 0.001 amps. Press ‘ON’ on your calculator and enter 4.5 (half 9) then press divide - by your current which is 0.001 (1milliamp). You’ll get 4500. This is your value for RC. You’re unlikely to find a 4.5k so instead we use 4.7k; nearest preferred value: hereon abbreviated NPV.

Transistor Bias Project1.jpg 

Determining the value of the Base Bias Resistor.

The transistor won’t do anything until a base-bias resistor is connected. Working out RB (Resistance Base) is more difficult and you must find the hfe of your BC547. Do this with the hfe function on a multi-meter. My drawing of a BC547 is used for connection reference. To make remembering easy, the three wires hanging downwards, as would be when board-mounted and viewed from above, the collector (C) is top, corresponding with the circuit diagram. Likewise, with the base (B) middle and the emitter (E), bottom. Correctly identifying the connections is very important. You must insert the three leads into the hfe socket on your multi-meter accordingly, noting that a BC547 is an NPN. The resulting number displayed on the meter’s LCD is the hfe rating for that specific device and it’s important to remember that other BC457s may differ, owing to manufacture tolerance spread. When working, the voltage between base and emitter is about 0.65 volts, so between collector and base should be 4.5 minus 0.65, equals 3.85 volts. The one pictured was found to be 200. Our 0.001 amp collector current is then divided by this 200 and you get the required base current: 5uA. Divide your 3.85 volts by 5uA (0.000005) and you get 770000 or 770k. You’re unlikely to find this value in your collection so 750k nearest preferred value will work instead. A NPV in the more common E12 range is 820k, although you can go as far as 1M and it will probably still work.

A Much Easier Way To Work Out Base-Bias Resistance.

Build the circuit as in the diagram using drawing pins on a wood base-board and solder components onto the drawing-pins: simply copy what I’ve done in the photo. Using only one of the outer tags and the middle one of a 2 megohm potentiometer, connectbetween base and collector instead of RB using crock-clips or soldering. Connect the PP3 and adjust the 2 meg pot until you get half of the supply voltage between point X and emitter. Keeping the shaft still, disconnect and measure the potentiometer’s resistance: this will be your value for RB and the resistor selected accordingly. This circuit should work with transistor types: BC107, BC108, BC109, BC547, BC548 and BC549. In fact, any bi-polar transistor will work as long as the correct connections are adhered to: Please consider that some transistors, such as the amazingly high-gained BC169C have collector connection in the middle and base where the collector would otherwise be.

Transistor Bias Project2.jpg 

Pre-Worked RB RC Table for a BC547 (hfe = 200) using VCC at + 9 volts.

Collector Load Resistor: Ohms

Base Bias Resistor: Ohms

Collector Current (Ic)

180

47k

25mA

220

82k

20mA

470

130k

9.5mA

1k

270k

4.5mA

2.2k

373k

2mA

4.7k

770k

1mA

10k

1.8Meg

450uA

It doesn’t take much imagination to occur that you can feed an output of one stage into another one and get more volume, as done below. This can be done by connecting two or more of these circuits in cascade. From a design point of view it is better to start from the premise that we require a clean signal so we’d then select appropriate resistance values to pass a higher (25mA) current for the last stage: the first stage is left as above and the second would have 180R as RC, 47k as RB. We could substitute the 180R collector resistor with a high impedance loudspeaker. Commonly available loudspeakers of this type are 65 – 80 ohms. It's not capable of marshal 200 watt performance: the best this simple amplifier can manage is a quiet practice amp for use in a personal space, primarily, presented as a means of grasping fundamentals of amplifiers/effect pedals electronic operation.

Stain’s Three Transistor Guitar Amplifier

Like it says  on the bocs ! Drawing pins come in varous sizes but these little cheaper ones are best for these projects. If you use the more common larger ones, they need to be spaced out a bit more, which will involve using a bigger bread-board.

Drawing pin as it looks when separated from it's mates and taken out of the bocs. They need to be kept in a tin with a tight fitting lid to prevent escape: Standing on them barefoor by accident is excruciating !

Calling all inventors: please invent this! Solder fumes contain nasty substances that irritate noses. We need to dissipate them into the surrounding air away from our face, the fan positioned close to our workpiece. Solder extraction gear is costly: this simple device, consisting of an old angle poise lamp frame and a computer fan does the trick.

Wire: so much of this thin solid core stuff is thrown out by telecomm engineers and sold off cheap in electronics shops that it's worth collecting up. It's perfect for these 'pintronics' projects.

This simple amp can be used for other purposes: forming the basis of an intercom or amplifying a crystal radio. Being limited in output power, it overdrives easily giving a crunchy sound desired by some guitarsts. The BC 337-16 is available; 99p for 25 (eBay). They’re obsolete, because the hfe, Beta or Gain is low: the examples I bought from eBay were only 40 - 70. However, the low gain enables simple construction such as the old-fashioned drawing-pins-on-wood method: unsuitable for BC 109Cs or similar high gain types as we may get resistive coupling causing transistor bias problems. This produces poor sound quality/unwanted noises from the speaker: wood is not a great insulator, according to Sir Clive Sinclair, getting worse in damp environments.

For improved screening, also necessary for high-gain transistor  types, we'd need a metal case because wood provides no screening. Metal working makes hard work of our project and is costly. Circuit instability makes noises at the speaker and consumes a power amplifier’s limited output by emitting inaudiable frequencies. Some circuit designers use shunting capacitors in selected places but it may cause other instabilities and reduces the HF response. Terminating resistors can be used, also adding to circuit complexity: to be discussed later. Unstable circuits, though, can be used for sound effects. During project planning, the thought occurred of using Germanium transistors. However, a typical type number such as OC81, is £2.50, being rare.

!

Transistor hfe or gain does more to affect input impedance of an amplifier than make what it's working in louder. Electric guitars have inbuilt volume/tone potentiometers, typically 250k and there's also the parallel wired pick-up coil, so combined matching would probably be less than 100k. For this reason there’s no point in having a 1 Meg input impedance amp for a guitar. If you wanted to connect a Xtal mike or pizo record player P U, then this order of impedance is appropriate.

A hoofbags music/sound engineering trick is to feed an output of one of these amps, via screened lead, to a remote speaker in a box, also containing a microphone. The microphone’s output is then sent back via another long screened lead to our Studio 100. Bassman Sid then gets his over-driven bass sound, rich in harmonics and sustain, desired for Electric Cheese Trolley music.

Interstage Decoupling: On the diagram's left side is a 2.2k resistor and 100mfd capacitor. These filter out any voltage fluctuations caused by Tr2 and Tr3s operation that would affect transistor 1. Missing these components out may lead to 'motorboating', manifesting as an unpleasant noise from the speaker. The right hand 100mfd capacitor helps extend a battery's useful life.

As a continuation of the ‘designing simple transistor amplifiers’ section on this hoofbags Website, we have three of the above circuit (at the start of this section) strapped together on one bit of 5" long wood. This stuff is sold as baton for boxes and is 3/8ths thick, 1‘n half inch wide.  In mm, to be Euro friendly: 127 mm long X 44 mm wide and 7 mm thick. If you used thinner stuff the drawing pins might cause splits, but just about any lump of wood would do. Balsa is unsuitable. One amplifier stage feeds into the next (cascade) and provides enough volume for a transistor guitar amp that is loud enough for practice purposes, and more. It can form the basis of a fuzz pedal, and a means of connecting to a bigger amp, in which case this would be the pre-amp, will be investigated and described in an update. This amp as used here with it's speaker is about as loud as a small transistor radio and will work from a battery such as an Ever Ready PP3 or PP9.

 

 Wire

So much of the telephone stuff is discarded by telecomm engineers or sold off cheap that it's probably worth the effort in stripping it back, or used in its insulated form when wires cross. In the event of drawing-pin interconnects, the insulation is more-often-than-not, removed. I mostly do this with my thumbnail but if you're not used to it, side-cutters or a wire stripper may be employed.Maplins, and Radio Shac type shops do sell reels of tinned bare copper wire. I should mention that four single conductors are inside an outer sheath that will have to be removed first, easier to do in 15cm lengths.

Here at hoofbags, and coz we're skint, we like doing stuff on a budget, and it’s also why we still use an old but functioning Amstrad Studio 100 'what Sid rescued from a skip'. If you attempt this ultra-budget design a beginner will understand fundamentals of audio electronic amplification. This may lead to a reader eventually being able to design their own circuits and enable self-repair of amps such as Pignose and effects pedals.There’s another issue: if you go to Maplins you'll see 0.1 matrix board for soldering chips and other parts to, for a self-build. You can use one of the excellent Antex miniature solder-irons but these are hardly hot enough to melt this modern lead-free stuff we’ve all got to buy. When it eventually melts, it's supplied in too-thick a gauge to be used with 0.1” and the chances of causing adjacent track shorts makes the entire endeavour anything but an enjoyable craft hobby. I've lost my camera USB lead. When I find it or get a replacement I will present powerful LM383 and LM386 designs that can be built in this way.

For these projects I've used a Black Spur 30W at £2.00 from ESK. They’ve got a fat bit that's hot enough for unleaded solder. If you’re new to soldering, a temptation is to try conveying molten solder on the iron tip to the joint, using 'melted solder as glue’, plonking it onto a joint. This is incorrect! You must, in the case of a drawing-pin, heat one up already in the base-board, to the point that it will melt the solder upon contact. This is to be done on component leads, too. Don't worry too much about solder damage to transistors or other components: it’s difficult to even deliberately cause component damage when soldering lead-outs. This caution was propagated because early germanium types were more fragile and a budget transistor would cost about a day’s wage.

 

 

 Take a bit of 1.5" X 3/8ths" softwood baton and saw it to 5" long. Using a pen, mark it out with 4 vertical divisions, as in the photo with 1" sections. Draw a centre-line horizontally. After that, draw another two that are a quarter of an inch from the top and bottom edges. The line inter-sections are drawing-pin insertion guides.

With drawing pins inserted into the baton: our baseboard, it should look like the right-hand photo. We need to add more pins and should look a bit like the rather out of focus photo below. (appologies!)

Wood can withstand solder-iron tempratures for some time; resulting heat damage is minimal.

It's entirely possible to build the amp from careful examination of the large-view photo avaialble from clicking on the hyperlink picture: right.

Component List:

A high impedance minature loudspeaker: of any value between 65 - 100 ohms. lyn3009 eBay Item number: 360026730614

Three of  BC 337-16 transistors. auntyant2 eBay. Any BC 337 will work but not sound as good. Alternatively: adjust base-bias resistor values.

18 of the smaller size drawing-pins, aka: thumbtacks.

Two of 100 micro-farad capacitors.

A 47 micro-farad capacitor

A 1 micro-farad capacitor (both  can be substituted with 10 mfd but almost any value would work)

1N 914 or 1N 4148 diode (almost any similar type would work)

Resistors: 15k, 3.3k, 270k, 2.2k, 5.6k, 560k.

Other Bits: bit of wood, ball point pen, ruler, 1metre of screened cable with a guitar type jack plug on the end, thin tinned copper wire of about 26 swg or similar, about 1 metre of single flex to wire up the speaker and battery, 9 a volt battery or mains adaptor set to the appropriate voltage.

 

An essential item: a means of powering up and testing projects in development. Maplin part No: JK09K with crockadile clips attatched. It enables a £3.99 Uniross AD100061 multi-voltage power plug to be used. PSU polarity is determined by the co-axial/two pin pluggie bit's direction. If project don't work upon competion, reverse crock-clips.

Power supply socket connection details (+ pin)

This amp specifies 9 volts. Budget power adaptors are poorly regulated, giving higher voltages than on the selected rating switch. In which case, it's kinder to the transistors if 6 or 7.5 volt setting is chosen. The amp might be louder at higher voltages but be prepared to replace T 3 regularly. Under such circumstance, T 3 gets hot enough to cause injurious burns, if touched. Always included, is a 1N 914 or similar rectifier diode, in the circuit's top-right corner power line, preventing reverse supply damage. To establish correct PSU unit's polarity, in event of project initial non-working, simply reverse the 2-pin/co-axial plug into the lead-end.

A Dead Town Cat Playing Guitar Through a Homemade Stainamp

If you have any trouble viewing this, please right-click and download.

 

If you're any good at carpentry a wooden case would be ideal. For a quickly finished project however, an old VHS storage shell can be used and you even get see through type iMac styling! I used hole saw attatched to drill for the speaker hole but if you ain't got one, make hole with soldeing iron. If so, be sure to clean the tip off immediately afterwards with damp cloth and do the melting in a well ventilated area: melted plastic fumes is nasty! It may also be possible to make the hole with a craft knife or copying saw. Another smaller hole can be drilled to accept the co-axial power connector. To stick the parts in, superglue won't work: you must use Evo Stick. Unfortunately, this is exactly the type of glue that some folk get high on: If your local store won't sell it to you, tell them to shove it and go elsewhere. I got problems with this scenario: I often needed to buy the stuff and, being an ancient hippy, I got accused. In truth, just using the stuff is enough to give me a headache and deliberately sniff it, I should coco!

Get your anoraks on, we've some  points to consider: Although this is a simple circuit, there's a surprising amount of stuff going on. For example, if using ohm's law, we were to work out a speaker impedance at 25 - 30 mA it would resolve at around the 160 ohm range instead of 65. However, using this order of collector load would limit output power and cause the circuit to function incorrectly. When the circuit is making a sound, there is an AC (alternating current) content superimposed upon the DC, (direct current) flowing through our BC 337. This AC frequency, determined by which note your guitar is producing, will cause the collector current to fluctuate. Viewed on a suitably configured oscilloscope, it'll be seen that the current will increase to perhaps 41 mA on the peaks and decrease down to, say, 19 mA on the troughs. When reproducing a guitar signal, an overdrive is often accidentally or deliberately opted for so, these fluctuations may be much more. It is therefore appropriate that a speaker load impedance is specified that will more accurately represent a correct load during these transitory peaks. There are other issues occurring: those of thermal runaway. It is a fact that the hotter a transistor gets, the more current flows between its collector and emitter. Unless kept in check, the resulting increase of current causes a further increase in temperature. This cycle will continue, assuming the presence of an uninterruppted supply current of course, until the transistor reaches saturation or the bias conditions render it un-useable. Here, the problem is eliminated because we take our base bias at the junction of the

transistor’s collector, and its load. Now, as the transistor warms up, conductivity increases, and has the effect of a reduced voltage at the collector junction. This causes a matched reduction in the base bias current. It behaves in the same fashion as a speed governor on a steam engine. This arrangement is commonly known as ‘collector-base’ biasing, because the base bias resistor is strapped between the collector and base. In older electronic hobby books, one may encounter simple bias arrangements where the base resistor goes directly to the supply rail. Probably, these circuits were designed at a time before the complicated scientific principles behind thermal runaway were fully understood. I’ve noticed an improvement in eBay available 65 ohm 3” speakers recently. No bad thing at all! It is often considered that, in place of a suitably high impedance speaker, an audio coupling transformer and 8 ohm speaker may be substituted: This may work, or perhaps problems could be encountered. A suitable transformer, especially if it’s large, may not have a sufficiently high primary winding resistance to the DC, which will disable the installed thermal stability measures. If a transformer is opted for, a good choice would be a commonly available Eagle Electronics LT 700, which has a primary resistance of about 72 ohms. However, comparable output results might not be achieved. There is a commonly used transistor biassing arrangement where the collector load matters a lot less. It's called the voltage divider type and uses about twice as many resistors and an extra capacitor. It will be explored in an update. Watch this space! :o)      

Stain's Busker Amp

 

Wood is just over 2.5" x 5.5" x 3/8" thick (picture is near actual size) 24 drawing pins are inserted. Make sure none of the pin heads are touching. This spacing allowes for easy connection of the specified components' leads when new.

 

The 3 transistor design above is only capable of between 10 - 30mW. That's enough volume for practice purposes but if the guitarist needs an amp for busking, it would need to be louder. Another problem with the 3 transistor design is that it uses up the battery at the same rate irrespective of the volume setting: being of 'class A' biasing configuration. The 5 transistor design suggested here is volume verses battery life inversely proportional because of it's 'class B' biasing. It's capable of 300mW RMS with a 9 volt supply and about 600mW with 12v. It may be possible to get more at higher voltage: up to 14 although higher than this may cause component damage. I'm using 2 mini transformers: LT44 and LT700. These are stocked by Maplin's occasionally, and other sources such as through an eBay search. T1 and T2 should be BC337-16. T3, T4 and T5 can be almost any NPN TO92 plastic general purpose audio, however, for best performance they should be 3 of the same type number and specification. Needless, BC337-16 is ideal. The LED, blue in this instance, serves three purposes in this circuit: it drops 2 volts for intersatge decoupling, lets the user know that it's on and it looks nice. Naturally, in the finsihed project, LED may be front panel mounted and interconnected via wire.

This amplifier's design has been around for long enough: it can be found in every transistor radio up until the late 70s and the legendary Pignose 5 watt is reasonably similar.

Current flow: under 2mA, through LT44's primary is limited via the 2.2k resistor. Without this (via direct wire connection) current woud be about 6mA and the poor little LT44 doesn't like it very much. It will over-heat and go open circuit. The LT700 data sheet recommends a 3.2 ohm speaker, 3 ideal. 3 ohm speakers are a bit rare so 4 ohm will do. An 8 ohm is useable but there will be a reduction in much needed volume. a good size for this would be about 4 - 5". Any size would do. Note also that transistor T4 has its flat side facing the opposite way from the others:  For T4 the flat side must face to the right. Also important is the correct LED connection. In this example the flat denotes the cathode and negative, which faces left. If the light don't come on the amp won't work: try re-soldeing the LED the other way 'round.

There're transistor interstage transformers in existence smaller than LT44s  / LT700s but all are still referred to as minature. One issue about these components' size is that, in order to get enough turn's winding within transformer coils, the wire must be very thin: the wire of an LT44's primary, at about 650 ohms, is as thin as hair! Thinner wire means higher resistance and that reduces the maximum current that can flow  through it. Consequently, in combination with the limited mass of the transformer's iron core, the output power is limited. Larger transformers can be used in this circuit without modification of any other components, with exception of the 2.2K which can be lowered for bigger transformers if necessary and T3, T4 may need heatsinking. These transformers must be of the type specified for transistor driver and output and can occasionally be salvaged form very old transistor radios. 2 or more watts RMS is easily feasable.

Stain’s glissades: easy to build simple audio VFOs

'Glissade' means 'slide' in another language and they seem to be making a comeback in some Drum 'n Bass music. Additionally, Elis uses one in the Electric Cheese Trolley music tracks: see INDEX above. A similar type of tone generator is the Theramin. However, Theramins are rather complex bits of kit working at radio frequencies. I've a design from a 1960's book 'Having Fun With Transistors by Len Buckwalter. It's a very simple circuit consisting of two transistors but some other components are no longer available. I'm gonna work on it ! Whereas Theramins need no physical contact, with a glissade the pitch is varied by rotating a potentiometer. There will also be a means of volume adjustment, later. Glissades are Variable  

This means we can upset the base bias setting to an extent that wouldn't allow a linear audio signal to pass through. The bias is controlled by the dual potentiometer. (Below) The output frequency is determined by the time constant of whatever the 100k potentiometer is set to, multiplied by the 0.1 micro-farad capacitors: The resistance value is multiplied by the capacitor value to derive T.  Then divide 1 by the result to get ' f ' = frequency. Many glissade designs have only a single potentiometer, and may be presented here later. However, I've found that a dual pot seems to give a much needed wider frequency range.

Frequency Oscillators working in the audio range. Examining the circuit diagram, it can be seen that it's based on another amplifier presented in this section, and, with the addition of an extra drawin-pin or two, the same arrangement can be used as in the three-transistor amp above. The amplifier output is fed back into the input and we get positive feedback. It's a similar action to when someone sticks a microphone too near its amp; called 'howl-round'. Another description of this circuit is 'astable multivibrator', where the amplifier gain is said to be infinite. Because we aren't dealing with a linear audio signal, as in a conventional amplifier circuit, distortion isn't an issue.

 

 

 

A Budget LM383 Amplifier

The LM 383, or its equivalent the TDA2003, is a common IC found in amps sold as 'guitar packages' from catalogues: you get the guitar, amp & lead in one box: Typically the Park-Marshall 10 watt ones. These amps don’t seem to last very long, though: I’ve often been asked to repair these and the usual fault is the output amp chip is burnt out. Aother problem is the potentiometers fitted into these are rubbish: they get noisy in no time at all and replacement isn’t an option, being non-standard. If you manage to get them, the printed circuit is hardly robust enough to withstand the de-soldering & re-soldering of any faulty parts. Pretty much, these are ‘throw away post warranty’ units....  

 

...The failings aren't down to the LM383 chip, though: I’ve built loads of circuits with these and they don’t go wrong. It only happens if the supply voltage is maxed out to get a higher output. I always prefer to keep supply voltage lower than 15, ideal for a 9 – 12 volt battery busker-amp, and use a low-impedance speaker. This may be achieved by connecting two 4 ohm speakers in parallel to get 2 ohms. However, the LM383 will drive loads down to 1.6 ohms.

 

In the photo a bit of veroboard interfacing is used as a means of extending the LM383 lead-outs; a bit pointless because one might as well just build the entire thing with Vero. I did a batch of these in the event of a quick amp being needed, that could be chucked together in a short time. Here, I'll describe an LM383 amp that can be constructed using the drawing-pin on wood method, without Vero. Unfortunately, they don't make these chips with long lead-outs so if a 'pintronics' version is going to be attempted we need to extend the lead-out connections..

 In my photo: above right, an M.T. baked-bean, or any other consumable supplied tin, is used as a heat-sink, although hardy adequate. Improvements here can be made by an interfacing washer between chip tab and tin, and using heat-sink silicon grease. Painting the tin matt black and packing it with aluminum cooking foil will help greatly. Tins have sharp edges: I always run a knife on inside rim and rub down using abrasive paper to prevent painful cuts.

LM383 as it comes out of the packet and ready to be inserted into a printed circuit board, if you have one.

 The chip will come to no harm provided some precautions are taken during adaptation. All the legs can be flattened out on the same plane and then need to be spaced apart so that they fan out. As with every electronic component, the leadouts must never be bent against the epoxy body but at least one eigth away along it. The LM383 lends itself conveniently here because the legs become narrower a short way down their length so providing a definable bending point. Bending component leads flush with the body is chancy: there will be times when we may get away with it. Only an infinitessimally small crack need appear before the device won't work. mercifully the chips are cheap but some effort will be dispensed in the building of a project only to dissapoint.

 

Thinner stuff is best for chips because it's fits more easily between the legs/lead-outs. It may be a bit fiddly but by no means impossible. Ideal, is the stuff taken from a length of flex: It's probably about 30swg. We need to line it up with the leg that's being extended, held with a thumbnail and then wrapped around the leg. It should look a bit like the one I did in the next photo. Next, we repeat with the remaining four legs: Photo on right.

 I originally tried using the type of solid core wire that telephone engineers often throw away. It's great stuff for making interconnects within a pintronics board although not great for an LM383 being too thick. Next comes the soldering. To do this it might be easier to mount your iron in a vice and position the leg to be soldered onto the tip end applying solder to the joint.

 

You may also have access to a Helping Hands craft tool.

Wisker!!!! Wisker issues: Although the above photos look similar, one has a 'wisker' on leg No: 2. This is an easily overlooked unwanted thin wire that could result in short-circuit, ultimately resulting in chip destruction and project failure.  In the next picture...

No Wisker! :o)

 ..it has been removed! This is typical of a mistake that deters many beginner electronics hobbyists, but learned through experience: Closely examin the components employing a manifying glass if necessary! It should also be mentioned that the thin extending wires can easily break off at this stage so handling care in essential to prevent constructional setbacks.

An LM 386 amplifier. When the original 386 audio amp chip was introduced, it's output was limited to 250mW. This is adequate for such applications as an audio stage for a walkie talkie for example but not ideal for guitar purposes. The manufacturers re-vamped the circuit, increasing it's output to 940 mW (1W). All the connections were the same so, the LM 386 N-1 became the direct replacement for the earlier chip. The more powerful LM 383

(above) is a perfect choice for general audio purposes but I've found it doesn't perform well in an overload scenario. This may be because of the LM383's overload protection which seems to shut it down when reaching it's peaks: It really doesn't sound at all nice! The smaller 8-pin DIL 386 addresses this issue and it actually sounds really great with an overloading guitar shuved up it's chuff. This device sounds so great that if you wanted to build a fuzz-box with only a 3 volt supply; most guitarists would be impressed. Almost all battery powered guitar amplifiers I've encountered recently, including the reputable Pignose amplified guitar, has  

 

one. My circuit in the above pane is a drawing pin-on-wood version. You may not wish to bother with this because the LM 386 N-1 has a number of small PCB's available for it, it's usually available as a kit containing all the necessary components and all you have to do is get soldering. It is worth building this project if, for example, you're an electronics student who's been asked to build a small amp, although you're not allowed to buy a kit for this purpose. This drawing pin version is also useful as a break-out-box for taking measurements such as voltage levels  and similar. One

 educational experiment would be to temporarily disconnect the 47 mfd capacitor between pins 8 and 1. It will demonstrate a considerable reduction in gain. Another would be to see what difference the 0.1 & 10R HF filter components removal would make: If you were to hear the same noises on an amplifier brought to you for repair, you'd immediately know what the problem is likely to be. An amp project containing a battery, potentiometer and speaker would certainly have sufficient space available to accommodate this stretched-out LM 386 N-1 circuit.

 One cannot fault the printed circuit as a general concept: every electronic device sold has one. However, if you wish to put together a 'one of' bit of gear in a short time, to use a printed circuit board is always an involved process : you need to draw at least 3 layers of etch-resist pattern using a suitable felt tip pen. It then needs to be placed in a ferric chloride solution and, as I've found, it sometimes goes wrong. For production runs of more than one of the same device, where the printed circuit is essential,

  a light-box will also be needed. Radio circuits working at frequencies of above about 30 MHz will need a printed circuit because of the criticality of component position. If you look inside most guitar amplifiers there's unused space. It is there for acoustic purposes. Hoever, some of it can be used to spread the components out  

 a bit, enabling ease of both construction and repair. An additional time consuming issue with repairs on printed circuits is that conductors/components are on both sides and you have to keep flipping the thing over. I've found that using a strong light shining through the board and a continuity tester helps in this process and is also useful in the endeavour of reverse engineering. In case the reader is unfamiliar with this concept, it's where you draw  a circuit diagram using a bit of manufactured equipment as a guide: this can be useful in figuring out how a manufacturer gets 'round arkward design issues.

Fuzz Circuit. Fuzz is a guitar effect that has been stated as "the most dramatic guitar effect possible". Originally, guitar amps were pushed into overload to get a similar effect but many were damaged by doing this: in particular, the amp's speaker would suffer and output transformers in valve gear would internally short, destroying the equipment. Some clever engineer designed a add-on pedal that would safely create a similar effect and protect the amp. The fuzz effect is derived from clipping the peaks off a guitar signal. Because the signal clipping produces a limiting effect, you get sustain. Additionally, there are harmonics produced that were not in the original guitar signal output. The signal distortion sounds great for single note runs and major chords but doesn’t really work for most 7th chords or minors. Here is a fuzz circuit that was found in an old book called Electronic Projects in Music by AJ Flind. When I originally built this circuit in the 80’s I thought it sounded really good. I’ve built it on occasions since, and for some reason, I was disappointed with the results. This may be because the original metal canned BC109Cs are difficult to obtain. The modern replacement: BC549c appears to have a higher gain and, in this circuit at least, doesn’t seem to sound as good. Upon high potentiometer settings for max effect, the circuit temporarily shuts down and ceases to output. My (humble) theory is that, the excessive drive from transistor TR1 gradually charges up the inter-stage coupling capacitor C3 and during this charging, DC flows through it, upsetting the bias for TR2, pushing it into saturation: turning it off. The problem is solved by substituting C3, R4, R5 and C4 with an inter-stage coupling capacitor of 5600pf. It is of a critical value. In this instance, it would connect directly to TR1 collector and TR2 base. It certainly performs better than the original circuit although is not strictly speaking a fuzz effect, more of a clipping sustain. The lowered capacitor value has a ‘differentiating’ action and it results in a much reduced bass content of the guitar sound.

I use a Hohner G3T headless. (LOVE IT! Only wish I could play it properly.) The Select EMG humbucker pick up has a higher output than any cheaper guitars I owned previously and this will also make a difference to the way this circuit functions. In my opinion, it’s a perfect example of refinements in design. Any amplifier, including the one in this circuit, will distort at high input settings but it is the quality and nature of this distortion that distinguishes a great fuzz box from a poor one. The two transistors are intended not to distort a great deal by themselves: they are just meant to increase the output voltage of the guitar. Although they do get overdriven and pushed into distortion, the main fuzzing content is supposed to generate from the 1N914 diodes, where they induce their much desired clipping action. In practice, practically any general purpose silicon rectifier diode will do the same job. 1N 914s are specified because they’re very cheap, easily available and small. You could use a BA127 and it will work but it would seem a waste of a higher spec component that can rectify at higher than mains potential in a mains valve amp. In the finished board, below right, there is an omition: the diodes aren't connected! there is meant to be a joining wire that connects the diodes. This joins R8 1K, R9 39K junction to the diodes. It's a good idea to temporarily disconnect these diodes during testing so that the clipping action can be heard. The finished item should be mounted inside a metal box which will also house the battery. I've often seen these built into M.T. tobacco tins.

 

 

 

Similar Fuzz with Stain alterations

As stated previously, I don't much like the sound of the one in the photos above. Here is a modified circuit that, in my opinion, sounds a lot better. In the next pane is the finished board, ready for installation into a metal case which will also house the connectors, switches and battery.

 

 

 Arranged, are 18 drawing pins on the wood: size 5/16ths X 1.5 X 3 inch.

The first 6 components are soldered...

..and then the second transistor.

 << At this stage, the 'amplifier' component arragement may be tested by connecting a set of high impedance headphones between ground/negative and output capacitor. Supply is a 9 volt supply or battery, type PP3.

 << A guitar test lead with a pair of crockadile clips soldered onto the end instead of the usual jack output connector plug. As shown above, it connects between the 0.01 mfd input capacitor and ground-line.

 

Simple AM Transmitter - Broadcaster.

I once played a practical joke on some friends, yes, believe it or not I do have them! I connected this to an aerial and an mp3 player with hoofbags music on it and took a radio: "Guess what, they're only playing The Electric Cheese Trolley on radio, we're famous! My scam was soon revealed when I introduced them to this simple AM transmitter.

Go to any decent radio club, such as our local HERC and you will meet restoration enthusiasts: they get ancient valve radios that are all beaten up, broken and restore them to showroom quality. It's absolutely amazing what standard of restoration can be achived. One problem is, though, that the music played through their amazing restorations doesn't quite suit the vintage set's aura, so I built this simple low-power TX to help bridge the gap. It could more accurately be described as a modulator. You could even claim, if you're so inclined, to tell your friends that it is a vintage radio and therefore plays radio programmes from the era of which is originated. Well, it's the kind of thing this sad act would attempt! :o)

 

When I first built it, it didn't work. However, I tweeked it a bit, changed a few components and it sprang into life. One problem with RF oscillators is that they're very fussy about component type. In this, my first attempt, I used a standard potentiometer for the 50k. These have a metal back cover and the capacitance between it's internals and surrounding components reduced the circuit 'Q' so the oscillations wouldn't start. Using a skeleton pre-set did the trick. Another issue with a radio transmitters is it's not actually very obvious if it has started working or not: you have to twiddle the pre-set potentiometer at the same time as adjusting your radio's tuning. Not the easiest of tasks! The initial finished article is shown in the pane to the right. It is built on a paxoline board with 'Stick On Wiring from :

It should be remembered that using a transmitter of this type in your part of the world may be subject to strict prohibitions: it's up to you to research this before attempting to buid this.

In the UK, AM transmittion is definitely not allowed. We only get away with it here because the power output from this device is so low that it can't adversely affect any other radio or electronic equipment that is being used at a safe distance: it will only transmit up to about ten feet away using a good receiver and aerial.

The supply must not exceed 3 volts and you must not attatch an aerial to the collector of Tr 2, where it connects to the 4700pf capacitor to extend transmittion range. In fact exceeding the 3 volt power supply limit will prevent it from working, so it is pointless to do this unless you make careful adjustments to the resistance values, which you also certainly mustn't do!

There are a few errors in the schematic/circuit diagram: the 150 ohm emitter resistor should be 100 ohms and an audio input, say from an mp3 player must be connected to the left hand side of the 0.1 mfd input capacitor (far left of this diagram).

For garuanteed results it's best to carefully examine the finished board because this is the one that was actually tested as working so ya can't go wrong!

If you're at a college, school or know someone who works with electronics, you probably wouldn't buy solder in small quantities like this. On the plus side, small solder bottles like these can be bought from local hardware shops if you're out 'n about. Another is that the packaging materials can be recycled. The M. T. tube can be used as a coil former for this transmitter. A coil made this way will also work in a radio receiver. Coil winding is a learned skill, just like most

Beginners sometimes find it difficult to wind coils. They get to the end of a winding endeavour only to accidentally let it go at the finish and the whole thing becomes unwound. A way of preventing this mishap is to wrap adheasive tape around the former, sticky side outwards: this will hold the windings in place until it can be terminated by threading through holes at the ends of the former. This coil is made from two four feet lengths of solid core telephone wire. These are tightly twisted together before winding onto the former so that a centre-tap is provided. Enamel coated wire will work just as well but care must be taken to remove the enamel at the coil ends.

The M.T. solder tube is fastened into a vice. Care should be taken to avoid over-tightening to prevent breakage. Next, a 1.5mm hole is drilled at one end. Another one is drilled 10mm down. These holes are used to tie the coil wire ends.

For this transmitter we need a centre-tapped inductor that constitutes the 'tank' coil. In combination with a 470 pf capacitor, it 'rings' or ocsillates at our desired radio frequency in the middle of the MW AM band and is powered by our second 2N2222 transistor. An 8 foot length must be divided into two 4' ones. Each end of the two lengths must be stripped and then re-attached by tightly twisting.

Our coil's Q or sharpness is determined by the neatness of its windings. How close the windings are to each other and the material from which the former is made all have an influence. For ease and chepaness we use telephone wire. It appears that the coil wire length is more critical that the wire thickness. Most types of insulated solid core wire will do.

Another means of obtaining a tank-coil inductor is to use a section of expired felt tip pen. These pens are very cheap, sold in packs of about 50 for a few quid. The coil wire is 26 swg enamel insulated, again two 4' lengths joined at the centre-tap.

   

Below is the Stylophone circuit diagram as printed in the book that I got with my Stylophone.

Above is the Stylophone circuit diagram. Please note that T1 is not a conventional transistor but a unijunction device. These devices have two bases, B1 and B2 and Emitter. Stylophones are useful as a tone generator in electronic music, not just a toy. Every model of Stylophone has an audio output socket for output to an amplifier or recording device.

Liz Costa. 2E1 FQN

  < more of this sort of stuff!

 

Newham General Hospital, NE London

John (Cap'm) once worked as a private mobile radio (PMR) engineer: For those who don't know, it's the network of radio receivers and transmitters used by cab companies, motorcycle dispatch firms and similar. We were on 24 hour emergency call-out. The transmitters are often located on top floors of high buildings and Newham General Hospital's top floor is one such location. When visiting it for the purposes of transitter adjustment, I (Stain) accompanied John, usually as the toolbox carrying sidekick/misfit. I took a camera up there on one occasion and took these: click on thumbnail for bigger picture. It is quite a big area: an entire floor, the size of the hospital's footprint, devoted to electric fans for ventillation purposes, and other instruments labled 'Autoclave 1, 2 and 3': unusual, I thought because this equipment's usually installed in the operating theatres. The radio transeiver that John was working on had a slight fault although not adversely affecting the equipment's functioning: a volume control had a tendency to not allow the radio 'through' conversations that were emitted from a loudspeaker, to be effectively muted. It's quite spooky when you consider that what all of the cabbies were talking about was audiable throughout this floor, at night and in the dark! I was concerned that this may be a problem and was informed by a security guard that, it once had them all on a wild goosechase because the transeiver was near a ventillation duct going directly down to the morgue: could  the dead had re-animated?  The radio could occasionally and clearly be heard from within there also!

 

Stain's Pictures - Canary Wharf 50th Floor late 80s

     

 

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