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CeeDeePee
(page 1)
A
recycled CD-ROM drive, FM tuner and Sound Processor
Introduction
What do
you do with spare CD-ROM drives ? Over the past few years,
I've collected a large number of spare computer parts - including
cards, cables, and drives; all of them in perfectly working
order. Some items become obsolete (such as ISA cards) and
eventually find their way to the trash. CD-ROM drives are
generally useful - it's usually possible to mount them in
a PC if you have spare 5-1/4 inch bays and available IDE channels.
The older slower drives are not too useful for data access
but can still serve as dedicated audio playback devices.
While rumaging
through my spare parts one day, I noticed that one spare CD-ROM
drive had two buttons on its faceplate. Most CD-ROM drives
have only a single "Eject" button. This drive had
one button with icons for "Eject/Stop" and the other
for "Play/Forward". Looking around, I saw that one
of my DVD drives also had this extra button. What this means
is that this drive can play audio CDs without the aid of a
host CPU. In other words, this drive is also a stand-alone
CD player. Spare CD-ROM drives that collect dust have little
use; but spare CD players are always useful to someone who
has a speaker building hobby ! :)
Another
spare part I have is an old metal case that used to house
an 8mm DAT backup tape drive. This case looked like it would
hold the CD-ROM drive nicely. The unit measures 15-1/2 inches
deep, 7 inches wide and 5-1/2 inches tall. The front has openings
for two 5-1/4 inch devices. Inside are pre-drilled supports
to hold the 2 devices in the bay (these used to hold the SCSI
DAT drives). After accounting for the depth of the CD-ROM
drive (about 8 inches), there is sufficient room in the rear
for a power supply. If I mount the CD-ROM drive in the lower
of the 2 bays, there is plenty of room above it to house some
sort of control and power amplifier. I can then cover the
upper device bay on the spare 5-1/4 inch faceplate.
[This picture shows the 2 devices mounted to the existing
supports in the case. The empty are is where the amplifer
and power supply must sit. There's some existing power wiring
from the EMI filter and fuse.]
Then came
another twist.When I told my brother what I was up to, he
gave me a NewQ
3379 Platinum tuner/preamp unit from his spare parts bin.
Like the CD-ROM drive, the NewQ 3379 is housed in a 5-1/4
inch chassis and is designed to be mounted in a device bay.
By wiring a PC's sound card's output through the NewQ 3379's
preamp stage, the the NewQ 3379 can further process all PC
audio outputs with various surround, hall and reverb effects.
The NewQ 3379 also comes with a remote control.
Parameters
At this
point, I should mention my project parameters. As a DIY hobbiest,
I firmly believe in defining a set of parameters before beginning
any project. If I had infinite resources (time, money, patience,
etc.) I would probably never finish any projects. Feature
creep would guarantee endless cycles of changes. Setting goals
helps control the building process and defines an end state.
The main
characteristics of this project are:
- This
is mainly a recycling effort. I don't need another
CD player and if I did need one, I could just buy one off
the shelf that would give me lots of useful features. But
I do have lots of idle "stuff" so let's use it
up ! This also means it must be low cost.
- It must
be safe to operate. That translates to low heat, electrically
safe, relatively kid-proof.
- I don't
need lots of power.
The JLB
12 Watt Stereo Amplifier from Apex Jr.
With the
NewQ 3379, I no longer had to build a control preamp, but
I still needed a power supply and amplifier. The power supply
was a no-brainer; building it won't be a problem though making
it fit in the case could be a challenge. Building my own amplifier
would have been fun as well, but I didn't have the parts necessary
on hand. Weighing my time, effort and cost, I opted for the
12
Watt JBL stereo amplifier from Apex Jr. At $9.95, it's
almost disposable (in case I decided to ditch it !). This
is a stereo amp on a PCB, complete with wall-wart transformer.
It is fully assembled and ready to use.
[The JBL amplifier comes in two pieces - the amplifier
PCB and the wall-wart transformer. The transformer is labeled
14 VAC @ 850 mA, 18W. The TDA7360 package and a TO-220 package
sit on the top edge and are attached a heatsink that wraps
around to cover the entire back of the PCB.]
It's not
too hard to figure out that this amplifier was originally
used in a multimedia speaker system. The PC board was mounted
in the right channel speaker where it received a stereo signal
from a PC sound card. There is an output to the left channel
speaker. This is a pretty standard design.
There are
5 connectors in the rear edge of the PCB - power supply in,
left speaker out, stereo in and two no-connection jacks. I
don't now what the latter jacks are for, nor did I bother
to trace the PCB layout to see if they have any real use.
On the front are a bass tone control knob, and volume knob
and an on/off push-button switch. The right channel output
is near the bottom of the PCB.
The amplifier
is based on a TDA7360 stereo audio amp "chip". By
itself, it offers a fixed gain of 20 dB with an input supply
range from 8 to 18 VDC. A
PDF spec sheet can be found here. SGS-Thomson calls this
a 22 watt part but this is the sum of both channels. With
a 14.4 V supply, the TDA3760 is rated at 12 watts into 1.6
ohms, 11 watts into 2 ohms, 8 watts into 3.2 ohms and 6.5
watts into 4 ohms; all per channel. This isn't much especially
at "real" impedance levels, but since my goal wasn't
to blow the house down, this would do. The TDA7360 is bridgeable
(though this PCB has no support for it) and I looked briefly
at using two amp boards, each bridged for more output. But
I eventually decided to run with just one board since I didn't
have enough room in the case to mount two.
To interface
the amp board to the rest of the pieces, I made small patch
cables to get to the left and right channel outputs. The amp
PCB is mounted vertically via an L-bracket mounted into the
unit's heat sink. This required that I disassemble the heatsink
from the PCB but that proved to be very simple. The L-bracket
is mounted to a small piece wood which in turn is mounted
to the chassis.
[This picture shows the final mounting of the amplifier.
A metal L-bracket is bolted to the heatsink behind the PCB
(not seen) and to the piece of wood on the case's bottom (the
cream colored piece in the picture). Two sets of red/black
wires go the terminal strip above the 80mm fan - these are
the left and right channel outputs.]
For power,
I ripped apart the wall-wart that came with the amp and strapped
it to the bottom of the case with two plastic cable ties.
[Inside the wall-wart transformer is an EI core. I drilled
four holes into the case and tied the core with two plastic
ties. I used electrical tape to keep the transformer contacts
from accidentally touching the case (or anything else for
that matter).]
05-October-2002
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