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1992-11-08
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The Amiga Sound Enhancer Board Project
(c)1992 David Alan Caruana
Revision D., 8th November 1992
Introduction
------------
On this disk you have full instructions so as to make a PCB which
will enhance your Amiga's sound greatly. The effect of the
enhancement is most notable on headphones as the Amiga sounds
MUCh nicer !! As an ulterior benefit, you also get a mixer with
which you can combine the sound of (say) a synth with that of
your Amiga. Any audio source may be input to the AUX input and it
gets mixed with the Amiga's sound so you may ampify both
simultaneosly through one amplifier or record the mixed version
onto tape. The otherfiles on this disk are IFF pictures with
schematics etc.
Theory of Operation of the Circuit
----------------------------------
The circuit is very simple and is based on the op-amp adder
principle i.e. an operation amplifier (op-amp) may be used to add
any number of input voltages (analog) with a specified gain. In
the circuit, the opamp is capacitively coupled to both input and
output circuits so that it may be operated off a single supply
(+12V) instead of the split supply (-12V-0-+12V) normally needed
by opamps. A reference voltage around 6V is generated by the
cirucit (using a voltage divider) so that internally, the
'ground' of the circuit is 6 volts above external grounds. This
difference is blocked by the capacitors.
The circuit includes proportional input gains (set using
potentiometers) and a master-volume control (which is set once
using a preset).
Let's Start !!
--------------
OK then .. leave electonics theory for the electronics buffs ..
let us start off ..
Firstly
-------
Before anything, you will need some components. These may be
bought at any reputable electronics store. You will also need
some hardware and some test-equipment in case the project doesn't
work at once. So ,, here is a list of components :
- Copper clad board , approx 5inches * 5inches
- transfers for straight tracks and pads (these are the type you
rub-on using a pencil)
- A good soldering iron , less than 25W power.
- Solder , 40-60 type is preferable.
Now comes the list of components:
POT1-6 Potentiometers , 220Kohms LOG , 6 off
C1-6 Capacitors , 100nF ceramic , 6 off
C7-10 Capacitors , 100uF electrolytic , 4 off
C11,12 Capacitors , 10uF electrolytic , 2 off
R1-6 Resistors , 220 KOhms , 6 off
R7-10 Resistors , 8.2 KOhms , 4 off
R11,12 Resistors , 470KOhms , 2 off
PR1,2 Presets , horizontal , 5KOhms
IC1,2 Semicondutors : CA3140E op-amps
IC Sockets : 2 * 8-pin
Connectors Female-phono panel-mount sockets 6 off
Components for power-supply
TR1 Miniature transformer 240V -> 12V
D1-4 Diodes, 1N4001, 4 off
Capacitor, 1000uF 16V electrolytic
Capacitors 100nF ceramic , 4 off
IC3 Semiconductor : 7812 regulator
SW1 Switch, SPST or SPDT
NOTE: uF means 'microfarads' throughout.
If you want to add a power-led (to show power on) also buy:
LED1 5mm LED , any color
Res. 1 KOhm
NOTE: All resistors are 1/4 watt.
You will also need a few metres of single-strand wire to make
connections from the board to outside components.
If you are going to case the project, buy a box min. 8 inches by
6 inches.
Lastly, you will need ferric chloride solution to etch the PCB.
Ferric chloride may either be bought ready-mixed as a solution or
in crystal form. In the latter case, mix into a solution as
directed.
MAKING THE PCB
--------------
Now the real work starts ....
The circuit to be built is that in Sheet 1. The circuit is not
complete, as some other modifications are needed to make the full
project. A layout for the PCB is shown in sheet 2. This is
already in mirror-image (you have to this, otherwise the pinout
of the IC's comes out the wrong way round!!) so you may copy it
direcly onto PCB.
Using Transfers:
----------------
If you are using a 'standard' copperclad PCB and transfers work
as follows:
Locate the approximate positions of the IC's and start by laying
out transfers for them (remember, each IC has 8 pins)
Next start copying out the tracks away from the IC's. It is
important to keep to the scale of the layout shown, otherwise the
PCB might not fit in correctly. Remember to rub down transfers
firmly with a blunt pencil.
If you fix a transfer in the wrong place, this may be lifted off
using a sharp craft knife or a scalpel. If the transfer overlaps
other correctly-placed transfers then cut around the good
transfers and then scratch away from them.
When you have placed all the transfers, you may proceed to etch
the PCB. While the PCB is under the ferric chloride, agitate the
solution every now and then. Etching takes between 30 minutes and
1 hour depending on the strength of the solution and how long it
has been used.
Using Optical-PCB
-----------------
If you are lucky enough to have a UV source for PCB exposure, you
may print out the layout and then photocopy-it onto transparency.
It should then by 'burnt' into optical board using the UV source,
fixed and etched.
Drilling the Board
------------------
Using the component layout sheet (sheet 3) as a guide drill 1mm
holes for all the components. For the presets drill 1.5mm as the
1mm holes are not wide enough. If you are going to mount the
potentiometers on the PCB (to save boxing the project!!) drill
1.5 mm holes for them too. Note that the potentiometers must be
PCB-mounting in this case. Always drill from to solder side
(where the tracks are) toward the component side (the other
side!!).
Soldering Components
--------------------
Use sheet 3 (component layout) as a guide while soldering
components. Keep components as close to the board as possible so
as to avoid noise. Capacitors should be of the vertical type as
these fit snugly on the close pads as in PCB. Resistors may be
soldered in a horizontal position. If you are making a box to
house the circuit, don't solder in the variable resistors yet.
Solder in the IC sockets with the notch pointing in the correct
direction ('up' in my diagrams) and then insert the IC's.
Remember to insert them correctly otherwise they will be fried as
soon as you switch on the power. Be very careful to solder the
electrolytic capacitor with correct polarity. In sheet 1, the
capacitors with both plates black are non-electrolytic and may be
soldered in any direction. The electrolytic caps have the
negative plate black and the positive white. The 100 microfarads
on the potential divider (near pin 3 on the IC) is of VITAL
importance so do not leave it out on any account !!
Lastly a note about jumpers J1-4. These are simply wire-links. It
is best to use cut-off component leads to do the job. Any pair of
them may be substituted by a DPDT switch which gives the option
of switching the sound enhancement off and using the circuit as a
two-channel stereo mixer.
External Components
-------------------
When all the components have been soldered in proceed to solder
leads for the external components. The connection diagram in
Sheet 4 should help you in doing this. It is important that the
potentiometers 'open' in a clockwise direction, otherwise
operation of the mixer will be very unlogical.
Note that the six potentiometers have the following functions:
Pot1 : Amiga LEFT channel strength
Pot2 : Amiga right channel thrown onto left output (enhancer)
Pot3 : Auxiliary input LEFT channel strength
Pot4 : Amiga RIGHT channel strength
Pot5 : Amiga left channel thrown onto right output (enhancer)
Pot6 : Auxiliary input RIGHT channel strength
PR1 : Master LEFT volume
PR2 : Master RIGHT volume
Remember to connect together the ground tags of all the inputs
together with the ground of the circuit board. The gound
connections of the potentiometers are taken care of by the PCB.
Putting it all together
-----------------------
All that is left now is to drill holes in the casing so that you
may stick in the potentiometers and input/output jacks. Put the
potentiometers on the front panel and the sockets at the back.
Also make a hole for an SPST switch which will be the power-
switch. If you are using the option to use enhance on/off (see
the 'soldering components' section) make a hole also for the
enhance switch. If you are building a mains power-supply (very
much recommended) leave place within the box where to stick the
transformer and add a mains socket on the back-panel. The
regulator PCB should be very small and is not a problem in
itself.
Making the PowerSupply
----------------------
A good, cheap and easy-to-build regulator circuit is shown on
sheet 5. Making a PCB for it should be very easy and it is easier
still to use a piece of veroboard. Note the connections of the
IC!
Operating the Powersupply
-------------------------
Plug the transformer to the mains via a 400mA fuse. You should
get an accurate 12V output at the output of the regulator and
using a multimeter you can measure about 15V AC at the terminals
of the transformer. Install the power-switch on the low-voltage
side of the system. When the power is 'off' the transformer will
still be connected to the mains but the amount of power it takes
is very minimal. Be careful to disconnect the circuit from the
mains when you are working on it .. remember .. mains can KILL!!
Adding a Power LED
------------------
Take a lead just after the power-switch and connect the LED in
series with a 1kohm resistor to ground. Make a 5mm hole in the
front panel and stick the LED in with some adhesive.
Testing the Mixer
-----------------
Connect the Amiga to the amiga inputs of the mixer.
Set the output presets to full.
Connect the output to a hifi amplifier
Switch on the system.
With the Amiga showing the 'Insert Workbench' prompt, the
amplifier should be silent with at most a slight hum if you crank
up the volume to maximum.
Turn up the channel 1 (Amiga) gain controls slowly and no change
should happen to output. The same applies for channel 2. If
channel 3 is not connected it may produce a hum when turned up.
This will vanish as soon as an input is connected. For the moment
leave channel 1 on max. gain , channels 2 and 3 off.
Load a program on the Amiga with music.
The signal coming from the mixer should be clear (similar to the
normal Amiga sound) but stronger. Adjust the presets until both
the left and right outputs are at the normal Amiga output levels.
Now turn up the channel 2 gain controls to Maximum. The Amiga
should now be heard as MONO. (hear it on a headphones and the
full sound should be heard on both left and right speaker). Using
a VU-Meter display or a headphones and your hearing, adjust the
stereo centering using the output preset potentiometers. Now turn
the channel 2 potentiometers to mid-track. The signal you are
hearing now is stereo but not as separated as the original Amiga
signal so it sounds much better on headphones.
Try connecting an input to channel 3 and turn up the gain
controls. Both the now input and the Amiga should now be heard
simultaneously.
At this point , all should be working 100%
If it doesn't work
------------------
Switch off the mains supply and short the regulator output to
discharge its capacitors. Now pull the IC's out of their sockets
and check the following connections:
Pin 3 - Ground = 8.2K
Pin 3 - Supply = 8.2K
Pin 4 - Ground = Short Circuit
Pin 4 - Supply = Open Circuit
Pin 7 - Supply = Short Circuit
Pin 7 - Ground = Open Circuit
Pin 2 - Pin 6 = 470K
Connect the powersupply and measure the following voltages
relative to ground ...
Pin 3 - 6 Volts (or very near)
Pin 4 - 0 Volts
Pin 7 - 12 Volts
All other pins : 0 Volts
If these are not OK recheck the circuit thoroughly,
If there ARE OK then you have either a burnt component or a cut
track on the PCB .. Some patience is in order here !! Check each
track with a multimeter and then compare values in the tow
circuits (left and right). Check that power is coming.
Try calculating resistance values off the circuit diagram and
measuring them in practice until you locate the fault.
Contact Me
----------
I would like contacts interested in the Amiga, Electronics,
Engineering, Programming, KCS Power PC Board and Music.
I am a second-year engineering student at University.
Addresses:
Snail Mail-
"Blossom",
Acacia Str,
San Gwann SGN03
M A L T A
EMail (internet)
dac%panther@carla.dist.unige.it
Licence
-------
You may use this circuit freely provided :
- if you build it and you like it PLEASE send me a note. I am not
asking for any money so a few pence spent on a stamp should be
enough.
- If you would like to send me something, PD software will do
fine!!
------------- THE --- END -------------------------------------
This doc. typed on 9-11-1992 , time now is 0037 hrs.
I am using Wordworth 1.0 on the following system :
- Amiga A500 with v2.04 ROM
- 1 Meg chip + 2 Megs fast
- 105 Meg Quantum harddisk with Commodore controller
- KCS Power PC-Board
- Star LC10 Color printer
- Ext. floppy drive
- Trilogic Midi Interface
- Yamaha PSS795 MIDI synthesizer
Also connected to the system are
- An Atari 520STFM
- Sansui A1000 40W * 2 hifi amplifier
- Pair of home-built speakers with Eunex 7" woofers and Motorola
3.5" piezo tweeters.
- Fisher AD-9020 CD-Player
- TEC 2377PP 3-in-1 hifi system with TEC speakers and 2*50W PMPO
output.
- Hitachi B/W television (13")
- a pair of Philips headphones ..,.
that should be about all of my system ..
If you write, state yours !!
My Amiga is now 3 years old and the Atari ST is 7 years old (!!)
OK then .. bye and goodnight from David Alan Caruana ...