Tic Tac Transistor Amp

Hi folks - I'm back already, with my promised Tic Tac transistor Amp - a one transistor amplifier, built in much the same way as the previous project - the Tic Tac crystal radio.

It is built on the same kind of matrix board, is powered by a 1.5 volt AAA cell, and fits inside the smaller Tic Tac box. It will allow you to connect your Tic Tac radio into the second Tic Tac amplifier box, and use a standard pair of low impedence earbuds to hear your favourite AM radio programs with!

This means that you will have a louder sound in your ears, and will be able to hear faint radio signals or low powered AM radio stations near to where you live, and look really 'cool' with your earbuds on.

I tried the prototype down at the local park a couple of days ago with several Tic Tac crystal radios I had built and it worked just fine. With the minimum antenna and ground wires installed, and the polyvaricon tuning capacitor wired in between the Antenna and the crystal set, most of the local AM stations in Brisbane came booming in.

So, let's get to work and sort out what parts we will need for this project - once again, you can source all the parts for this amplifier from Jaycar Electronics, either at your local store, or online via the Internet.

OK - well, it IS a transistor amplifier, so let's talk about transistors first up. The transistor was first invented back in 1947, by three scientists working at Bell Labs in America. Since that time, literally hundreds of millions of them have been made! Maybe even billions...

So what's so special about the humble transistor? Well it has two basic functions. One is to amplify small signals fed into its input lead, known as the "base" lead. The output signal which has been amplified by the transistor usually appears on its "collector" lead, while the third lead, known as the "emitter" lead, is usually the ground lead, common to both base and collector leads.

The other job it does for us, is to act as an electronic switch. This happens inside computers - inside the main processing chips as well as in any memory chips or add on chips that perform special tasks inside the computer.

There are many different types of transistors that are made for many different purposes, but today, we'll be using a simple BJT (bipolar junction transistor,) as the centre of our amplifier circuit. The BC547 is a very common BJT device. It is used in many different applications, but is simple enough and rugged enough for us to make our transistor amp with only one transistor, a resistor and a capacitor. Powered by a small battery, we can plug our earbuds in and hear the sounds coming from our basic Tic Tac Radio, through our earbuds!

We need two other components to make our simple one transistor amplifier work - a resistor and a capacitor. We'll also need a 1.5 volt AAA battery and holder to go with it and a 3.5mm diameter stereo earphone jack - and that's it!

So here's the parts list, with Jaycar Electronics catalogue numbers along with them, so you can order online if you want to;

Resistor R1 - 150k - RR 0624 (1/2 watt through hole resistor)

Capacitor C1 - 0.1uF - RG 5125 (a "green cap" capacitor)

Transistor Q1 - BC547 - ZT 2152* (NPN BJT transistor)

3.5mm earphone jack socket - PS 0132

AAA battery holder - PH 9260 (with flying leads)

* If you live in America or Canada, the 2N3904 will do as a substitute for the BC547.

* If you live in England or other parts of the UK, a ZTX300 will do as a substitute for the BC547.

* If you can't get any of those three transistors mentioned above, then a 2N2222 will be OK too!

Looking at the circuit diagram above, we can see the symbols for the BC547 transistor (Q1) the resistor (R1) and the capacitor (C1). A BJT transistor needs a 'DC bias' for it to turn 'on' and without that bias (which comes from the 1.5 volt AAA cell,) it will stay 'off'! So we need to connect it to the battery, but we also need to do this in such a way so that the transistor won't overheat and go "pop" and then be no use to us...

In other words, we need the energy from the battery to make it work, but we need to limit that energy (in the form of a DC 'current',) from the battery, so the transistor can turn on and stay in the 'safe zone' of its operating parameters. Hey - such big words. "Parameters" is a list of things that describe how much voltage, current, heat etc., you can apply to an electronic component, before you will damage it. If you go outside the 'parameters', you may damage it beyond any future usage.

This is where the resistor comes in - the 150k (remember - 'K' means 1,000) will allow us to 'bias' the transistor on, but at the same time 'limit' the 'current' flowing from the battery. A transistor needs between +0.5 and +0.7 volts DC between its base and emitter leads (emitter lead is -ve), before it can turn on and allow a current to pass through it.

This large DC current flows from the battery negative (-) terminal, up through the emitter, through the silicon material of the transistor, and out the collector lead (via the earbuds) and back into the positive (+) terminal of the battery. This is known as the emitter/collector current. Another smaller current flows from the battery - up through the emitter and through the base lead, via the 150k resistor, and back to the battery + terminal. this is known as 'base current'. Small amounts of base current, allow the larger collector/emitter current to be controlled by certain circuit conditions.

The job of capacitor C1 is to allow any AC (alternating current) or pulsed DC signal from the Tic Tac Radio's output, through to the transistor, so that when that signal comes through the capacitor (C1) the transistor can then allow that signal to pass through it and come out of the collector lead, as an amplified signal. The capacitor will block any DC from the battery that might upset the output signal coming from the Radio.

When the transistor has amplified the signal fed in from the crystal radio, our earbuds will then 'hear' that amplified signal and then change (transduce) that amplified signal into sound waves that our ears can hear it's that simple! Signal in - amplify - then signal out!

The earbuds have tiny miniature coils made of very thin copper wire wound around a magnet. The coil moves in and out of its suspended position, and is connected to a large disc shaped diaphragm. when the amplified signal current comes down the wires and into the earbuds, they respond by converting the electrical impulses int sound waves that we can hear

This part should be fairly easy by now, as you have already built one project on matrix board, but just to be sure, I've included a diagram and a photo, so that you will have a clear guide as to where the parts and wires will go.

The lead out wires from the body of the transistor are fairly short, in most cases, so if you need to go any distance away from the transistor itself, wrap the transistor leads (carefully) around a longer wire or component lead, and let the longer leads and wires do the 'distance' running - OK?

Point To Point Wiring Guide

1. First, splay the three leads of the transistor so that when you insert it, there is one hole between each lead, in the matrix board. Push it down gently until the splayed leads prevent it from going down any further.

2. Then take the resistor and mount its leads in such a way that they are close to the base and emitter leads of the transistor. Make sure that the body of the resistor is flat against the matrix board, and that the lead wires are inserted down the holes closest to each end of the resistor body.

3. Gently twist the base and collector leads around the wire leads of the resistor, so that each join is secure. You may need to use a basic tool, such as small pointed pliers to do this effectively - see photo above for good 'under the matrix board' joins..

4. Then take the 0.1uF 'green cap' capacitor and insert it so that on end is inserted close to the join of the transistor's base lead and R1's lead. The other 'free' end goes to the top edge of the matrix board, and will have the input wire connected to it later on.

5. Take a short piece of insulated wire 3 cm long, strip 1 cm of insulation off both ends and then wrap one end around the collector/R1 join and fold the wires over, so the join is secure. Take the other end of the wire and connect it through the eye of the 'R' terminal of the 3.5mm earphone jack, as shown in the pictures/diagram above. Note that dotted lines, indicates wires or component leads run underneath the matrix board.

6. Take the 1.5 volt AAA battery holder - RED lead, and connect it through the other eye of the other Jack terminal marked 'L' in the diagram. Take the BLACK lead on the other end of the battery holder and connect it to the emitter lead of the transistor. If the wires coming from the battery holder don't have enough bare wire exposed, use your side cutters to strip another 1 cm from both ends.

7. Take another short piece of insulated wire 5 cm long, strip both ends, and wrap one end around the black wire/emitter lead connection, and secure the join using the same technique as before.

8. Take a different coloured piece of insulated wire, strip both ends and connect one end to the free lead wire of capacitor C1 - and you are all done!

You are now ready to test out your newly constructed Tia Tac Transistor Amp!

Well, now that you've completed the construction of the Tic Tac Transistor Amp, it's time to hook up the amp up to the Tic Tac crystal set, set up your antenna/ground wire system and see just how much louder it really is. Here in Brisbane, 612 khz ABC radio is the strongest AM radio transmitter, pumping out 50 kW (kiloWatts) of power and covering a rather large part of South East Queensland.

You can experiment with the amp first up by disconnecting the crystal earphone and connecting it up to the to the input of the amplifier (free end of C1 and the ground wire). You will hear some 'rustling' type noises, as most crystal earphones (of either type) are very sensitive - so now just gently blow down the front hole - and then say something (with your earbuds in, of course!) You should be able to hear your own voice, and some of the sounds in your immediate area.

To do this, use the following guide:

1. Disconnect your earphone from the Tic Tac radio.

2. Pop the radio board from out of the Tic Tac box, and then join the wire from C1 (on the amplifier board) to the output lead of the crystal set - the 'colour bar' end of the diode/resistor join.

3. Connect the two ground wires from the amp and the crystal set together,and place a 1.5 volt AAA cell i the holder, noting that the RED lead is the positive (+) end and the negative end (-) is the black lead.

4. Plug your earbuds into the open hole of the earphone jack and turn the tuning knob of you radio, and see if your amp and radio set work together...

5. If it checks out OK (and you can hear radio stations loudly in your earbuds,) then disconnect the amp from the radio set, and proceed to place the Tic Tac Transistor Amp neatly in the second Tic Tac box. drill a hole in the bottom of the box, and mount the board, so that the earphone jack hole is accessible to the outside of the box.

That's it folks - we are done...

You may be having lots of fun building these projects, but you can end up with a right old mess, if you're not careful. School teachers, who may be reading this Instructable with a view to doing it in a classroom setting, please consider the following:

The best way to keep control of your electronics hobby stuff, is to use a medium sized fishing tackle box with a dozen or so compartments and place your parts in each section. You can mark the lid over each compartment with the name of each part and its value. This method will help to keep your valuable class set of parts safe and accounted for.

Wire can be kept in a 'wire bag' or box, and all hand tools kept safely out of harm's way when not in use. I know I don't have to tell teachers these things, but just in case mums and dads are considering a weekly neighbourhood hobby class, I have to say it for reasons of safety. mk484

One last thing - these breadboards are a great way to experiment, using your stock of electronic components. They consist of two sections of 5 holes down by many holes across, so you can plug your parts for the Tic Tac radio or amplifier into the holes, making connections a lot easier, and using less wire for each project.

"Well mk484, why didn't you tell us all about this on page one?" someone may ask... Well, that's because I had to assume that you didn't have one - not yet, anyway. I also take the view that it is good to struggle a little bit, and develop the hand skills necessary to build these projects, from scratch and without soldering irons or wire wrap tools. Your best friends are going to be your pliers, side cutters, small screwdrivers and hobby knives. They are the tools you will use the most, so it is good to understand how to use them fully, before embarking on "easier" ways of doing things. OK? Good.

So now that you know about them, you can get mum or dad to buy you one (schools - inquire about a class set of five or ten,) and really get into this exciting area of electronics.

Jaycar catalog numbers:

Mini Breadboard - PB8832

Medium Breadboard - PB8814

Large Breadboard - PB8816

Breadboard Jumper Kit - PB8850

Here's a link to another 'Instructable' that explains basic breadboards and how they work:

https://www.instructables.com/id/Breadboard-Basics-...

Just for the record - I'm not promoting Jaycar Electronics because I get some kind of benefit from it ($$$) because I don't. It's just that they have around 80 company owned stores, with an additional 150 stockists around Australia, and 12 stores in New Zealand. They also offer an online mail order service for both local and overseas customers.

When purchasing parts in bulk (5 or 10 of everything for a class set,) through a local store, it may be wise to phone them and make sure that everything you want (EVERYTHING :) ) is in stock, in order to avoid any disappointment...

mk484

Project number 3 in the tic Tac series will be an audio signal generator - it uses 2 transistors, is built on a large piece of matrix board and is powered by a 1.5 volt AAA battery - stay tuned!!!

mk484