A couple weeks ago I was cleaning my garage and came across these Volvo amplifiers from my 86 Volvo 760 (wonderful car worth every penny!) I was about to trash them but I decided to build a portable desktop power amplifier.
The smaller amplifier is HA-3121 and rated at 25 Watts per channel, the rear amplifier HA-3141 is rated 40 watts per channel. Ok, a 130 watts desktop power amplifier!
Since I was in the recycling mood I salvage an assortment of RCA inputs, speaker connectors, switches, LEDs, from my garage cleanup. I also used rails and nuts and bolts left over from my flat panel TV mount.
I temporarily hook up all the wires to a 12 volt wall transformer and was disappointed that nothing works (very low current). I then quickly connect a 12 automotive battery and only the HA-3141 came alive, the HA-3121 did not. The problem was traced to a faulty relay, probably the reason the amps were out of the car in the first place. A few taps on the relay and a few minutes of activating deactivating it and now the relay works trouble free.
Bolted the rails to the main power amp.
Bolted the secondary amp to the main amp. The main amp had a mounting plate allows for a 1/4 inch air gap.
A piece of Plexiglas foundation for the input, power and output connectors.
The 12 automotive battery provided plenty clean current which the wall transformer could not. I hooked up my bench top power supply recycled from a computer power supply. The plans are here http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply
*** Of course be very careful when working with electricity, line voltage can and will kill! ***
The computer power supply yields approximately 11.7 volts plenty of oomph as I take the amplifier to max. There is a limited amount of voltage available in an automobile (approximately 13.5 volts). This means that the amplifiers have fewer than 12 volts to apply to the speaker leads after factoring internal system resistance. If we have only 12 volts to drive into a speaker, there may not be sufficient volume output if the speaker has high impedance; therefore I wire my 8 ohms speakers in parallel for 4 ohms to maximize the output power to the speakers. (Ohm’s law)
Wiring for the HA-3121
Speaker wires
left output: green/yellow -
left output: green/white +
Right output: gray/yellow -
Right output: gray/white +
Power
Yellow constant 12 Volt
Black (thick) Negative ground
black (small) not connected
Input (shielded bundle)
Orange 12 volt remote on
left input: Blue (contains 2 wire, unshielded is negative)
Right Input: Green (contains 2 wire, unshielded is negative)
Ignore all other wires ( red, black etc)
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Wiring for the HA-3141
Speaker wires
left output: Black -
left output: Yellow +
Right output: black -
Right output: white +
Power
Yellow constant 12 Volt
Black (thick) Negative ground
black (small) not connected
Input (shielded bundle)
Orange 12 volt remote on
left input: Blue (contains 2 wires, unshielded is negative)
Right Input: Green (contains 2 wires, unshielded is negative)
Ignore all other wires ( red, black etc)
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Posts
Hi, I have this exact stereo that I was going to install in a older volvo. D you by chance have a wring schematic for all the wires involved with the hook up of this unit? Any help would be greatly appreciated! the stereo came from a 740 wagon and I am going to attempt installing it into a 242.
ReplyDeleteUpdated with wiring
ReplyDeleteThank-you for the decode. Great build by the way, a creative use for equipment that would have unfortunately landed in a recycling center. GReat save!
ReplyDeleteAwesome, I'll have to try this myself as soon as I can get a car amplifier to fool around with. I've already got a couple of power supplies lying around...
ReplyDelete