How To Hook up/Install An Amp Without RCA Jacks
By Robert Jones · 2020-08-22
Got an amp but your head unit's missing RCA outputs? Don't despair! I've spent decades wiring car audio, and there are solid ways to get that amp working, even with an old-school stereo. I'll show you how.
Right then, let's talk car audio. You've got a shiny new amp, eager to give your motor some proper oomph, but your head unit – bless its cotton socks – is a bit, well, old-school. No RCA outputs. It's a tale as old as time, or at least as old as my twenty-odd years fiddling with speakers and amps. Don't you fret, though; not having RCAs isn't the end of the world. We can absolutely get that amplifier singing without them. It just takes a slightly different approach. **Quick Verdict: You can definitely wire an amp without RCA jacks using a Line Output Converter or an amp with high-level inputs.** I've seen countless setups like this over the years, from souped-up boy racer Civics back in the day to more sedate family cars where someone just wants a bit more bass. The principles are the same. It's about getting a signal from your head unit to your amplifier in a way it understands. ### Why the Blazes are There No RCAs Anyway? Most decent aftermarket head units these days, the ones you'd pick up from Halfords or online for a couple of hundred quid, will have RCA pre-outs. These are brilliant because they send a nice, clean, low-level signal – usually around 2-5 volts – straight to your amplifier. It's the ideal scenario, designed for clarity and minimal fuss. But here's the rub: many factory stereos, the ones that came with the car, often lack these. They're built to a budget, for a specific purpose, and usually only have speaker-level outputs. Same goes for some older aftermarket units or the really cheap ones you might find on Amazon. They just don't bother with RCAs, figuring most users won't be adding external amps. It saves a few quid on manufacturing, I suppose. ### So, What's the Plan, Guv'nor? Basically, you've got two main routes when your head unit is devoid of RCA outputs: 1. **Use a Line Output Converter (LOC):** This is a small device that takes the speaker-level signal from your head unit and converts it into a low-level RCA signal that your amp can use. Think of it as a translator. 2. **Use an amplifier with high-level inputs:** Some amps, especially those designed for factory system integration, come with built-in high-level inputs. This means they can directly accept the speaker-level signal from your head unit without needing a separate LOC. Let's break down both options, because each has its own quirks and considerations.  *How To Hook up/Install An Amp Without RCA Jacks — tested in the SpeakersMag workshop.* ## Option 1: The Trusty Line Output Converter (LOC) This is probably the most common method, and for good reason. LOCs are relatively inexpensive, widely available, and generally pretty effective. They come in various flavours, from basic passive units to more advanced active ones. ### How a LOC Works In simple terms, a LOC does the opposite of what an amplifier does with its main outputs. Your head unit sends a strong, amplified signal to your speakers. This "speaker-level" signal is much higher voltage than an amp's RCA input is designed for. A LOC steps this voltage down, turning it into a nice, clean, low-level signal that your amplifier can happily digest. It also provides RCA outputs, so you can just plug your standard RCA cables into the LOC and then into your amp. Easy peasy. ### Types of LOCs #### Passive LOCs * **What they are:** These are the most basic and cheapest. They use resistors to drop the voltage. No external power needed. * **Pros:** Dirt cheap (you can get one for under a tenner), simple to install, no extra wiring for power. * **Cons:** Can sometimes introduce a bit of noise, might not provide a strong enough signal for some amps, and don't usually offer remote turn-on for your amp (more on that later). * **When to use:** If you're on a super tight budget and just want a subwoofer, and your amp has a decent input sensitivity. Don't expect miracles. #### Active LOCs * **What they are:** These are more sophisticated. They contain circuitry that requires a small 12V power supply (usually from your car's electrical system). They often include features like gain control, bass boost, and, crucially, a remote turn-on output. * **Pros:** Better sound quality, stronger and cleaner signal, often include a remote turn-on feature, adjustable output levels. * **Cons:** More expensive (think £30-£100+), requires a power wire, ground wire, and sometimes a remote wire. * **When to use:** If you want the best possible sound without changing your head unit, especially if you're running multiple amps or a full-range system. Worth the extra few quid for the convenience and performance. ### Installing a LOC: A Step-by-Step Guide This isn't rocket science, but it does require a bit of patience and some basic wiring knowledge. Safety first, as always – disconnect your car battery before you start messing with wires! 1. **Locate Your Speaker Wires:** You'll need to tap into the speaker wires coming out of your head unit. The easiest place is often behind the head unit itself, but sometimes you can find them in the kick panels or even at the factory amp if your car has one. You'll need to identify which wires go to which speaker (e.g., front left positive, front left negative). Your car's wiring diagram is your best friend here, or a quick Google search for "[your car make/model] stereo wiring diagram". *A quick tip from my years of experience: always test with a multimeter if you're unsure. Polarity matters! Positive to positive, negative to negative.* If you're only adding a subwoofer, you can usually tap into the rear speaker wires. For a full-range amp, you'll need to tap into all four speaker channels. 2. **Connect Speaker Wires to the LOC:** Most LOCs will have clearly labelled inputs for speaker wires (e.g., "Left +" "Left -" "Right +" "Right -"). Splice into your chosen speaker wires and connect them to the corresponding inputs on the LOC. Solder and heat shrink are always my preference for a solid, long-lasting connection. Crimp connectors work too, but make sure they're good quality. 3. **Power the LOC (if active):** If you've gone for an active LOC, you'll need to run a 12V power wire (fused, of course, near the battery!), a ground wire, and sometimes a remote turn-on wire. The remote wire usually comes from an accessory circuit that's only live when the ignition is on, or some active LOCs can sense the speaker signal and generate their own remote output. This remote output then goes to your amplifier's remote turn-on terminal. 4. **Connect RCAs:** Plug your RCA cables into the output of the LOC and run them to the RCA inputs on your amplifier. 5. **Grounding:** Always ensure your LOC has a good, solid ground connection. A bad ground can lead to all sorts of nasty humming and buzzing. Find a bare metal spot on the car chassis, sand off any paint, and secure it with a screw. 6. **Test and Tune:** Reconnect your battery, fire up your stereo, and test it out. Adjust the gain settings on the LOC (if it has them) and your amplifier to get a clean, undistorted sound. Start with both gains low and slowly increase until you get the desired volume without any distortion. ## Option 2: Amplifiers with High-Level Inputs This is often the cleaner solution if you're buying a new amplifier and know you'll be keeping your factory head unit. Many modern amps, especially those geared towards OEM integration, come with high-level inputs built right in. No separate LOC needed. Happy days. ### How They Work These amps have internal circuitry that performs the same voltage reduction and signal conditioning that an external LOC does. You simply run your speaker wires directly from the head unit to a dedicated input on the amplifier. Many also feature signal-sensing turn-on, meaning the amp detects when a signal is present and switches itself on, removing the need for a separate remote turn-on wire. ### Pros & Cons of High-Level Input Amps #### Pros * **Simpler Wiring:** Fewer components, fewer wires. Just connect speaker wires directly. * **Cleaner Install:** No extra box to hide. * **Often Better Sound:** The circuitry is designed to work perfectly with the amplifier, often resulting in less noise and better signal integrity than a cheap external LOC. * **Signal Sensing Turn-On:** A huge convenience, especially if you can't easily find a remote wire in your car. #### Cons * **More Expensive Amps:** Amps with good high-level inputs generally cost a bit more than entry-level amps that only have RCA inputs. * **Limited Choice:** Not every amp has them, so your selection might be narrower. * **Still Need to Tap Wires:** You're still splicing into speaker wires, just like with an LOC. ### Wiring an Amp with High-Level Inputs This is even more straightforward than using an LOC: 1. **Locate Speaker Wires:** Same as with the LOC – find those speaker wires coming from your head unit. 2. **Connect to Amp:** Your amplifier will have a special multi-pin connector or screw terminals labelled "High Level Input" or "Speaker Level Input". Connect the corresponding speaker wires directly to these inputs. Again, mind your polarity! If you're only running a subwoofer, tap into the rear speakers. For a full-range amp, you'll connect all four speaker channels (front left, front right, rear left, rear right). 3. **Power and Ground:** Run your main power wire (fused at the battery!) and ground wire to the amp as usual. If your amp has signal-sensing turn-on, you might not need a separate remote wire. If it doesn't, you'll need to find an accessory power source for the remote turn-on terminal. 4. **Test and Tune:** Reconnect battery, turn on the stereo, and adjust the amp's gain. Listen carefully for any distortion and back off the gain if you hear it. ## Where to Tap into Speaker Wires: A Detailed Look Getting this bit right is crucial. You want a clean signal, and you want to do it safely. ### Behind the Head Unit * **Pros:** Usually the cleanest signal, as it's closest to the source. All speaker wires are usually bundled together. * **Cons:** Can be a cramped space, sometimes difficult to access the wiring harness. ### At the Factory Amplifier (if present) * **Pros:** Wires are often clearly labelled or identifiable in a larger harness. Can be easier to access than behind the head unit. * **Cons:** The factory amp might apply processing (EQ, crossover) that you don't want to send to your new amp, potentially affecting sound quality. You'll need a wiring diagram specific to your car's factory audio system. ### In the Kick Panels / Door Sills * **Pros:** Can be easier to route wires to your amp from here. Wires are often thicker and easier to work with than right behind the head unit. * **Cons:** You might only find wires for the front or rear speakers, not all four. More disassembly required. *Robert's Golden Rule: Always, always, always check your specific car's wiring diagram. Don't just guess. I've seen too many botched jobs because someone assumed the blue wire was always positive.* Also, use proper wire connectors, whether it's soldering, Posi-Taps, or good quality crimps. Don't just twist wires together and tape them up – that's asking for trouble and potential fire hazards. ## Important Considerations & Niggles Even with these methods, there are a few things to keep in mind to avoid headaches. ### Remote Turn-On Your amplifier needs a signal to tell it to turn on and off with your car. This is usually a 12V "remote" wire. If your head unit has no RCAs, it's unlikely to have a dedicated remote output either. Here's how to get around it: * **Active LOC with Remote Output:** Many active LOCs will generate a remote signal for your amp when they detect a signal from your head unit. This is ideal. * **Signal-Sensing Amp:** As mentioned, many amps with high-level inputs will turn on automatically. * **Accessory Power:** You can tap into a 12V accessory wire in your fuse box that only gets power when the ignition is on. Use an "add-a-fuse" tap for a safe connection. Be careful not to tap into something critical like airbags! * **Ignition Wire:** You can usually find a wire at the back of your head unit that provides 12V when the ignition is on. Use this as a last resort and ensure it's properly fused. ### Ground Loops and Noise Connecting external components can sometimes introduce ground loops, which manifest as an annoying whine or hum through your speakers. This often happens if the ground points for your head unit, LOC, and amp aren't all at the same electrical potential. * **Best Practice:** Try to ground all your audio components to the same point on the chassis if possible. Make sure all ground connections are clean, bare metal, and tight. * **Ground Loop Isolators:** If you still get noise, a ground loop isolator (a small device you put on the RCA lines) can sometimes help, but they can occasionally degrade sound quality. They're a band-aid, not a cure. ### Signal Quality and Processing Factory head units, especially in newer cars, often apply a lot of digital signal processing (DSP) to the audio. This might include factory equalisation (EQ), bass roll-off at higher volumes, or time alignment. When you tap into the speaker wires after this processing, you're getting a signal that's already been messed with. * **Impact:** This can make it harder to get a truly flat and accurate sound from your new amp and speakers. A good active LOC or a DSP unit can help correct some of these issues, but it's something to be aware of. * **Solutions:** Some high-end active LOCs (like those from AudioControl) have "summing" capabilities (to combine signals if the factory system uses separate highs/lows) and "de-equalization" features to flatten out the factory EQ curve. ### Output Impedance Mismatch Less of a concern with modern LOCs and amps, but historically, tapping into speaker outputs could sometimes cause issues with the head unit's internal amplifier if the impedance wasn't right. Good quality LOCs are designed to present a suitable load, so don't skimp on a super cheap one here. ## Who it's for: * Someone who wants to upgrade their car's sound system without changing the factory head unit (e.g., to retain factory features, steering wheel controls, or aesthetics). * Anyone with an older or budget aftermarket head unit that lacks RCA pre-outs. * DIY enthusiasts looking for a cost-effective way to add an amp or subwoofer. ## Who should skip it: * Those seeking the absolute pinnacle of sound quality – a dedicated aftermarket head unit with RCA pre-outs will almost always provide a cleaner signal path. * Anyone uncomfortable with basic wiring or splicing into their car's electrical system – hire a professional installer instead. * If your factory head unit has really aggressive DSP that you can't bypass or correct; it might be better to replace the head unit entirely. *** ## Comparison Table: LOC vs. High-Level Input Amp | Feature | Line Output Converter (LOC) | Amplifier with High-Level Inputs | | :------------------ | :-------------------------------------------------------- | :---------------------------------------------------------- | | **Cost** | £10 (passive) - £100+ (active) | Amp itself generally costs more than RCA-only alternatives | | **Complexity** | Adds an extra component and wiring | Integrated, simpler wiring for signal | | **Sound Quality** | Varies; good active LOCs can be excellent; passive can be noisy | Often very good, designed to integrate seamlessly | | **Remote Turn-On** | Passive: no; Active: often included | Frequently has signal-sensing auto turn-on | | **Footprint** | Small, extra box to hide | No extra box, cleaner install | | **Flexibility** | Use with any amp with RCA inputs | Limited to amps with this specific feature | | **Ideal For** | Adding an amp to existing setup, budget sub upgrade | New amp installation with factory head unit, cleaner look | *** ## FAQ: Your Burning Questions Answered ### Q: Can I just cut off the RCA ends from my amp wiring kit and connect the speaker wires directly? A: Absolutely not! Please don't do this. Speaker wires carry a much higher voltage than RCA inputs are designed for. You'll likely damage your amplifier's input section, your head unit, or both. RCAs are a low-level signal; speaker wires are high-level. They need converting, not just chopping and joining. ### Q: Do I need a separate LOC for each channel of my amplifier? A: It depends on the LOC and your amplifier. Most LOCs are 2-channel (stereo). If you're running a 2-channel amp, you'll usually need one 2-channel LOC. If you're running a 4-channel amp, you'd typically use two 2-channel LOCs, or a single 4-channel LOC if you can find one. However, if your amp has high-level inputs, it will usually accept all channels directly into one unit. ### Q: Will using an LOC or high-level inputs affect my car's original speakers? A: No, it shouldn't. You're simply tapping into the speaker wires in parallel. Your car's original speakers will continue to work as normal, playing audio from the head unit. The new amplifier will power its own set of speakers (or subwoofer) independently. ### Q: How do I know if my amp has high-level inputs? A: Check the amplifier's specifications and the input panel. Look for terminals labelled "High Level Input", "Speaker Level Input", or sometimes "SPK IN". The manual will also clearly state if it has this feature and how to wire it. ### Q: My factory stereo has weird wiring colours. How do I know which is positive and negative? A: This is where a digital multimeter (DMM) comes in handy. With the stereo on and playing music at a low volume, set your DMM to measure DC voltage. Touch one probe to what you suspect is the positive wire and the other to the negative. The DMM should show a fluctuating positive voltage. If it shows a fluctuating negative voltage, you've got your probes reversed. If you don't have a DMM, a 9V battery test can work: quickly tap the wires to the battery terminals; if the speaker cone pushes out, the wire connected to the positive terminal of the battery is the positive speaker wire. *** ## Final Word from Robert So there you have it. Don't let the lack of RCA outputs put you off upgrading your car audio. Whether you go down the Line Output Converter route or choose an amplifier with built-in high-level inputs, getting that extra punch or clarity is perfectly achievable. I've wired hundreds of these setups over the years, and with a bit of care, the right tools, and a good wiring diagram for your specific motor, you'll have your new amp singing along in no time. Just take your time, double-check your connections, and for goodness sake, disconnect that battery! Nothing ruins a weekend like a short circuit. Enjoy the improved tunes – you've earned 'em.