Home > Members' Area > Projects > SW+ Project Build > The Audio Amplifier

SW+ Project Build - Stage 3 The Audio Amplifier

Build instructions by Paul M0BMN

< Previous  Next >

Stage 3 The Audio Amplifier

in this section we will be building the audio amplifier part of our radio, there are a number of parts used for this stage and I would suggest that you find out all the parts ready first, I have made a list to help.

you may want to print this page off and cross of each part as you fit it.

Parts for the Amplifier (Resistors)

R2 10 K Ohm Brown Black Orange
R3 10 K Ohm as above
R4 510 K Ohm Green Brown Yellow
R6 10 Ohm Brown Black Black
R7 510 K Ohm Green Brown Yellow
R8 1 M Ohm Brown Black Green
R9 4.7 M Ohm Yellow Violet Green
R10 22 K Ohm Red Red Orange
R11 510 K Ohm Green Brown Yellow
R12 1 M Ohm Brown Black Green
R13 1 M Ohm Brown Black Green
R14 10 Ohm Brown Black Black

Now the Capacitors note the Markings are in the 3rd column

C19 0.033uF '333J' large brown pillow type
C20 0.1uF '104' small yellow pillow type
C21 0.01uF Ceramic disk marked '103M'
C22 150pf Ceramic disk marked '151' or '151J'
C23 150pf as above
C24 0.1uF '104' small yellow pillow type
C25 820pf Ceramic disk marked '821K' or Brown Pillow type
C26 0.0022uF '222J' small yellow pillow type
C27 47uF 16V or 25V Can Type marked as 47uF 16v/25v, watch which way round you fit this!!!!
C106 47uF 16V or 25V as above
C107 0.1uF '104' small yellow pillow type

Now the semiconductors

D3 1N4148 Small Glass diode with brown body, black band at one end
D4 1N4148 Small Glass diode with brown body, black band at one end
D5 1N4148 Small Glass diode with brown body, black band at one end
Q1 2N5485 Field Effect Transistor (FET) layout calls it a MPF102 which is wrong!
U4 NE5532 8 pin audio chip IC, fit a 8 pin socket as first before the chip (Supplied)

Now we have all the parts sorted we can start to build this stage, please pay attention to the instructions, they show where each part is to be located, i would fit the parts in the order of the list above, take care when fitting the electrolytic capacitors c27 and c106, these must be fitted the correct way round, the instruction sheet tells you this too, then be careful with the diodes D3-D5,

they are made from glass and can be broken, also make sure that you fit them the right way round (see the pictures below if unsure)

Note that the layout picture in the instructions shows a MFP102 transistor for Q1, this is a old picture, the MFP102 as been replaced by a new device '2N5485' again make sure you fit this the right way round, make sure that the flat on the body of the transistor is in line with the flat on the outline on the PCB and push the device down so it has about 4-5mm of leads above the board (see photo below) . Be careful with the semiconductors they can be easily damaged by heat and static.

Part1 of Stage 3 The Resistors

These are a easy to fit part, my advice would be to try and make sure that you put them the same way round so the first colour band indicating the value is on top (look at the photos below). you don't need to do that at all and it will work just the same but...if you do have a problem later its easier to read the values if all the resistors are the same way round, and it looks better!, we do want a kit to be proud of don't we.

Photograph of resistors fitted to the PCB with the exception of R13 and R14You may notice this picture does not have R13 or R14 fitted, I ended up fitting them after the capcitors , thats because I write the instructions before I build the stage and then follow them myself to make sure that there right, they are now!

Now more advice, if you haven't got one go and buy a multi meter, you can get them for much less than £5 or you can pay as much as you like, if this is likely to be the first of many projects i would say go and spend a bit more , around £20-£30 will get you a very nice unit that should last you years.

Photograph of all resistors fitted to the PCB

if you have a meter PLEASE check each resistor with it before you fit it, I nearly fitted a 1K resistor Brown Black Red, where i was intending to fit a 10K one (Brown Black Orange) and if I had not checked each one at fitting stage i would have made a mistake for sure.

If you do make a mistake first thing don't panic, check and double check that you have got it wrong for sure, if you have the main concern must be to protect the PCB, we can get most parts from Maplins but we cant get PCB's. If you have to remove parts you will need a solder sucker or solder wick,

Photograph of desoldering pump and wick

Desoldering Pump and Wick

That's part one done, now part 2 the Capacitors

Fit these parts has you did the resistors one by one, check each one before you fit it . with C27 and C106 be extra careful, these devices need to fitted the correct way round, if you look at the case of these you will see that one side is marked - and has a thick black line on it, it also as a shorter leg, this is the negative lead the long lead is the positive, make sure you understand the difference, look at the photo of the board below, that may help too.

Photograph of capacitors fitted to PCB just before I fitted R14! see i make mistooks too!

if you look at your board you will see that one hole for both C26 and C106 have a small + mark by them, the longer lead of these two devices needs to go in this hole, also this is shown in the instructions too that come with the kit.

One more word about fitting these capacitors is like the resistors try and fit the other ones (Not C26/C106) so that the value is readable after the part is fitted (if possible).

Ok Now the Diodes

These are glass be careful not to break them, they are not expensive parts just a few pence each but im sure you dont want to haveto wait a week to get replacments.

Photograph of diodes before fitting to PCB Photograph of a diode with wire bent into hook

bend the diode leads as shown on the picture on the right above, note the black band is near the bend

Photograph of PCB with diodes fitted Close up photograph of diodes showing their polarity

here are the diodes fitted and a closeup showing which way round to fit them

Now onto Q1 and U4 Fitting

Note that the layout drawing in the instructions shows a MPF102 in the location of Q1 , well this is a old part and has
been replaced by the newer 2N5485 device. make sure you fit it the right way, look at the outline on the PCB and the picture below, also fit a 8 pin socket for the audio chip, make sure you fit that the right way with the small cut out as per the layout on the PCB again,

When fitting this socket push it in from the top of th eboard and bend over the two outer pins so it doesnt fall out when you solder it in

Photograph of bottom of PCB showing two corner IC socket pins bent to hold it in place See the bent pins that stop it from falling out when soldering.

Photograph of IC socket for Q1 mounted on PCB Photograph of Q1 fitted in IC socket

The first picture shows Q1 and the socket fitted, the second shows which way round to fit the audio chip.

Now turn the board over and inspect all the soldering, make sure you have not shorted out any tracks, makes sure all pins are soldered and nice and no dull looking joints, if any do look dry re-solder that joint.

Now take a break, before moving onto the next stage which will be the Crystal Filter/Product Detector/BFO

< Previous  Next >     Back to SW+ Project Build page