Salvaging Audio Amplifiers From Vintage Volvos

The common automotive scrap yard is a land of plenty for the enterprising hacker., where many items that would be prohibitively expensive elsewhere can often be had for a song. This isn’t just limited to strictly automotive parts either, as the modern vehicle is full of all kinds of hardware. [Nikita] managed to salvage a pair of audio amplifiers from an old Volvo, and put them to good use. It’s a great idea if you’re looking for cheap audio hardware!

The amplifiers are from a Volvo 760 made in 1984. There’s one rated at 40 watts per channel, and a smaller device rated at 25 watts per channel – likely to drive the front and rear speakers from separate amps. The amplifiers take 12 volts nominally, as one would expect. After some initial testing with a car battery and unsticking old relays, things began to crackle into life.

With the hardware now functioning, it was simply a case of bolting the amplifiers into a frame, hooking them up to a converted ATX power supply, and wiring up some connectors for speakers and audio input. With a few bits and pieces invested, [Nikita] now has a good quality amplifier to run audio in the workshop.

There’s plenty of useful hardware you can score down at the wreckers, and we see these parts used in hacks all the time – from peculiar milling machines to automated watering systems.

30 thoughts on “Salvaging Audio Amplifiers From Vintage Volvos

  1. I can not speak about the Volvo amps but I own a Corvette with the Bose sound system in it, you have to be careful as the way they managed to get as many watts as they did is they used ridiculously low impedance (2 ohm) speakers. I doubt using an 8 ohm speaker would harm the amplifier, but it would greatly reduce the amount of output power.

    One of my other cars, a Plymouth Aztek has the premium pioneer system in it. Both the head unit and the amp were dead, and I was away from home when I bought it. It was an interesting adventure installing an aftermarket stereo with nothing but an AA cell and a ring light. Installing the head unit was child’s play. Bypassing the amp with no pinouts, that took some doing.

  2. quoting:

    “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.”

    uhm, no.

    car amps use dc/dc converters to boost the internal voltage rails. and yes, they almost always create a bipolar rail structure, so the fact that 12v is the input, that’s not at all a limiting factor.

    its still a bad idea to send noisy atx-grade psu power to an AUDIO AMP.

    and you likely want LOWER impedance spkrs. 8 is standard for home. 4 is more standard for car.

    1. WHY lower impedance? That’s the fault I see all the time with HAD: saying stuff without explaining it. Not every reader is a guru in every subject. Help a fellow or fellowette, won’t you?

        1. No no no. It is all ohms law. If you have 12V available as the power supply to an amplifier that does not have a DC to DC converter in it, the most you could possibly get out is 12V and given transistors have voltage drops, realistically more like 11 volts. But lets look at the best case and assume 12.

          So we have 12V across a 8 ohm speaker. 12/8= 1.5A (remember ohms law, E/R=I) and power is E*I so 12*1.5=18W. If you go to a 4 ohm speaker, you have 12V/4 ohms or 3A, and the power is 3A *12V=36W.

          You can see that the lower the impedance of the speaker, the more power you get out for any given supply voltage.

          Once you kind of get the hang of doing the calculation the long way you can use P=E squared over R so you don’t need to figure out the current, but that at least to me does not show the path as clearly.

          So if you have an amp rated for 4 ohms and you put 8 ohms on it, it will result in less power and the amp will actually run cooler as it will be dissipating less power in the amp itself.

          Note also as impedance goes down, currents and power goes up. Some amps can not drive low impedance loads such as 2 ohms, some actually advertise being 2 ohm stable. Also as current goes up, the resistance in both the power supply leads and the speaker leads becomes more critical, so shorter leads are better if possible, or heavier gauge wire to the speakers.

          1. Also consider that an amplifier with a simple push/pull setup could run a full 24v swing, providing 72W at +/-12v. This can be done by not grounding either line to the speaker and running two amplifiers in opposite input polarity to each other. As one amp pushes to 12v, its sibling will push to -12v. The total relative voltage between the speaker terminals results in a 24v rail.

            This is without even considering boost conversion to get a base rail of greater than 12v to start with, but that’s somewhat covered in another thread.

        2. You need to go to the mountain and meditate about Ohm’s Law until you actually understand it. Current varies inversely with changes in load, so if the voltage is fixed the transistors will run cooler with higher impedance loads

      1. Let me try this. The impedance of the load (speakers) should match the impedance of the output. If the impedance of the load is too low it will draw too much power (watts) from the source ( amp) and could (will) damage (overheat, fry ) the amp. If the impedance is too high the load will draw less current . Safer but less efficient. (less sound)
        Hope that helps

        1. No, not really, in general the driving source has a much lower impedance than then speaker does. An amp may be rated to drive an impedance but it’s actual output impedance is generally much, much lower than that. The lower the amps impedance, the greater the damping factor on the speaker.

      1. Right. What’s really wrong with an ATX? These days, any quality of ATX can be found, not bought, found. And after a year you have four lying around, and you can get really spoilt about which ones to use where. ATX is perfect for this.

  3. Still a notch or two above most mobile audio stereo amps. Volvo used flac back in the hard disc playing days of more packed formats of compressed audio. My Chrysler has a ugly box behind the trunk liner with 7 or more power channels and gobs of unlabeled wiring, the radio source as 7 out plus 5 going back up to the doors and dash. 2 ohm woofers in the doors. It was the deluxe package audio.

    My try at home running with an ATX is a 4 channel rat shack amp. The only noise is a subsonic pumping from the ATX supply, I have point 2Farad on the 12volt line and a 5 watt load on the 5volt line to make the ATX behave.

  4. FYI the HA-3141 is a rebadged Alpine 3506.

    Larger car amps can draw 20+ amps @ 12vdc so an ATX supply will only go so far. Large bench power supplies used to be linear but modern SMPS units are much better.

    This barely qualifies as a hack in my book. He found a commercially made amplifier and hooked up power/speakers/input to the harness. There are countless inexpensive ($20 or less) ebay class D amp modules that run on 12v and deliver even more than 40W/8R.

      1. Lots of people on forums ask stupid question that a quick google search would have been better, so online shopping especially requires searching/dealing with foreign shipping is above that. :P
        On some websites, case mods or ‘art’ are considered as hacks. :P

    1. Found a Mercedes, I think R129, deck and CD changer player that looked like those were rebadged Alpine CM1910 & MC3198 at the Goodwill for about $9 total. Couldn’t resist. Was thinking the CD changer can go in the Dodge Ram with the JVC deck or I can just use the fiber optic and maybe other components. Last left off reviewing the fiber optic connection which is proprietary… though the chipsets on each end seem either removable to be replaced, hackable to use different connections and/or make a RCA to fiberoptic 3D printed/hacked connector. Didn’t come with the cable though. Was just at the salvage yard yesterday hoping to score some 2010 Prius parts and thinking might if any are left on the next holiday sale event.

      1. Wish our yards had stuff that new, I have an 04 Prius and normally when I find a Gen2 in the yards it’s demolished, and usually pretty clear that someone bought it from Copart to hastily harvest the hybrid battery and sell the hulk to Pick N Pull as normally all the rear trim is missing.

        1. Was a complete surprise to me seeing the 2010 Prius when I was searching the Row52 inventory. I literally made the trip specifically for that car and to see about some other parts for the Ram while I was at it.

          I spoke with the workers and they don’t even let the batteries into the yard and I’m not sure if they even sell them to customers. I did see a 2007 prius with the engine, motor and transmission still there though has ~250K miles on it. For the price… seems like a neat project car drivetrain to experiment with as long as only the battery is missing… though not sure with that many miles and in the yard.

          The 2010 looked like was ~65K though was pretty much stripped in the front and unfortunately the front quarter panels were peeled back and beat up. The only item I think worth it might be the front drivers side quarter panel to have another to practice metal forming with and to place a 120V outlet if a 700W inverter is wired into the stock alternator, and the rear brakes and wheel bearings. That puppy was stripped down.

  5. Many (higher-power) car amps have a converter/inverter to make +-V at higher than input. So running these at home with a 12V supply is kind of like crossing the river to get water.
    And the lower power (25W RMS is what you can get with 12V into 4 ohm) are already BTL connected.

    1. It’s more like using what you have to hand vs going and spending money.
      Thanks to a car hobby I have many amps lying around ,many subs and car speakers.
      I have many ATX power supplies doing duty as “high amp” 12V supplies.
      I dont have many mains powered amps “spare”.

      The sounds in my garage are a car stereo and 4x speakers from same stuffed into the front of some capped PVC tubing to make boxes. Sounds fine over the noise of grinding and the air compressor.

      The sub for my home cinema system is a dual voice coil 4ohm in a 1.5cu ft box, coupled to a 4 channel bridged car amp, connected to a 13.8V 50 amp toroidal (this bitch is super heavy) power supply which got aquired from an old car stereo display/demo case.

      Make do with what you have.

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