Amp with high level input: How to Install an Amp with High Level Input

High-Level Input Vs Low-Level Input (RCA)

At first glance, high-level inputs, and low-level inputs, also famously known as RCA inputs, may appear identical, especially for a first-time user. Ideally, the two sets of inputs are found at the back panel of a subwoofer, and they are used to add an aftermarket amplifier to any sound setup.

When looking to add a new amplifier to your stock stereo system, finding a way to integrate the amp is often a big consideration. So, what’s the difference between high-level input vs low-level input? In this article, we’ll highlight primary differences between the two inputs and show which set to use for what application.

In a nutshell, the primary difference between high-level and low-level inputs is the type of audio signal transmitted through each input. The high-level input, or simply speaker level input, helps to transmit audio signals using speaker connections from the amplifier to your subwoofer.

On the other hand, low-level (RCA) input facilitates the transmission of low-level audio from your amplifier to the LFE (subwoofer) unit. That said, let’s dig deeper into these audio terms to keep you informed on their noteworthy features and the differences between the amp high-level input vs RCA.

What is high-level input on amp?

The primary role of high-level inputs is to allow the user to add an amplifier to either a stock or aftermarket stereo that does not include RCA (low-level) connectors. Ideally, high-level inputs are characterized by several speaker wires that plug into a multi-pin wiring harness.

In other words, the speaker level inputs allow you to connect almost any amplifier to your sound system without the need to use an additional level-matching device. Such amplifiers will often come with a special adapter featuring bare wires that you’ll use to connect to the speaker wires. That way, the amplifier is able to utilize the speaker output signal as its input source.

Overview of low-level input (RCA)

Low-level inputs, or simply RCA/line-level inputs, are a type of connectors used to integrate an amplifier that is not compatible with high-level inputs or when the inputs are unavailable. In such applications, you’ll need to utilize the designated RCA interconnect cable to connect the amplifier to your source device.

The best thing about aftermarket stereos is that they are equipped with several RCA inputs that you can use to add multiple amplifiers. However, it is important to highlight that RCA inputs are often used with aftermarket setups that mostly lack speaker-level inputs.

High-level input vs RCA- The Key Differences

Perhaps the most notable difference between subwoofer high-level input and RCA input is the kind of connectors they use. As we mentioned earlier, the high-level inputs come in a series of identical speaker wires that plugs into a multi-pin wiring harness.

On the other hand, low-level inputs are color-coded, with each color representing each channel of your stereo system. In addition, the inputs feature a color-coded opening coupled with a metallic lining on the inside part of the hole.

Typical scenarios that require one to use low level inputs in place of the speaker level inputs include;

  1. Applications that do not permit the user to use speaker outputs. For example, the RCA inputs are your to-go option when connecting to a computer or TV directly.
  2. Using the low-level inputs is the most preferred method when connecting Monoblock amplifiers with a single REL. Such applications require you to use a pair of stereo connectors for both the left and right channels,

When it comes to functionality, the high-level inputs are responsible for the transfer of signal from your amp or even receiver to the subwoofer unit. Typically, the transmission of signals is facilitated by speaker-level connectors found at the back panel of your subwoofer.

Similarly, low-level inputs help to transmit audio signals between your amp/receiver and the sub but instead of using speaker outputs, the latter uses the RCA connectors. Generally, most AV receivers and aftermarket amplifiers use the RCA inputs to transmit audio signals via preamps outputs.

Another notable difference between low-level vs high-level amp input is the level of voltage. Ideally, the low-level, inputs just as the name suggests, accommodate low-voltage signals to the amp/receive, where the signal is amplified.

During transmission, the audio signal may not be powerful enough to push your subwoofer/speakers. Once in the amplifier, the signal is amplified, hence allowing you to enjoy the audible sound. On the flip side, the signal transmitted by the high-level input is often powerful enough to run the subwoofer.

In terms of the sound produced, there seems to be no noticeable difference in sound quality, especially when using an aftermarket stereo system. However, the high-level signal tends to suffer a bit when using a stock stereo system as opposed to when running the signal through low-level inputs.

This is because the user is required to tap into existing vehicle wiring, and in the process, it might cause signal degradation. Other than that, both input methods are highly flexible, and you can use either to install your new system depending on your application needs.

Older receiver models without high-level inputs may also use low-level inputs in place of the speaker-level inputs. As such, when looking to add a subwoofer or amplifier to your setup, you may want to counter-check the available set of inputs and outputs. This will help you avoid incurring additional repair costs or the need to buy new wires/adapters to go with your new setup.

The good thing is that most, if not all modern subs, are equipped with both sets of inputs. In the past, RCA inputs were quite rare, but today it is not uncommon to find most subwoofers with several RCA inputs. This helps ensure you won’t run into a problem, especially when you want to use both types of inputs.

Parting Shot!

Using the right inputs allows you to get the most out of your audio system. However, the type of cable and inputs you use can make or break the sound you get from your system. The subwoofer only constitutes half of your sound experience, but to get the most from your entertainment setup, you’ll need to get it right when it comes to plugging the cables into the correct inputs. Furthermore using the right connectors and inputs allows your music and movie sound effects to come to life.

Necessary to use all high level speaker input wires?

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Last post by 
Mellowperch, 

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Mellowperch
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Aftermarket amp input wire has 4 pairs total for the fronts and the rears. Am I required to tap into all 4 speakers to add a sub or can I pick and choose a single speaker to tap into and ignore the rest?

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You need to know if that channel has sub information or if it’s cut out by the factory headunit. What kind of vehicle and trim level? Regardless I’d take both left and right to sum together into a mono bass signal.

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Its a 1st gen tlx. It does have a factory subwoofer. So do I tee off of the rear left and right speaker? Or use the single pair coming off the sub? Or all 3 speakers?

I’m also curious why there’s a whole set of input wires but unnecessary to use them all. Is the purpose just for signal if 1 or 2 pairs isn’t enough signal or how does that work?

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Note, I am not experienced with that car. But if you have a factory sub that seems like the first place to check. Do you have any measurement tools that can check the signal into the amp?

Am amp has multiple inputs for separate channels. You could run:

Left and right for both front and rear
Left and right tweeter and mids
Left and right front passive set plus bridged channels to a sub

Many combinations are possible. What’s your goal and what equipment do you already have?

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I only have the basics: sub, amp, and wires. Only tool I have that might be useful is a DMM.

All I want is to add a sub that isn’t 8″ and 40 watts like the factory.

There are a handful people reporting running a passive LOC and only wired to the factory sub with good results. On paper there should be some bass drop which I’ve only read 1 person come across so I think it exists to an extent.

I’m going straight to an amp so I don’t know what my results would be and whether I should make use of all the input wires or only the ones I need. Says “4 channel speaker level inputs” so 4 Lefts and 4 Rights.

Since I have access to the rear sub and 2 speakers beside it, could I connect those to the input wires? Use RL RR and FL wire coming from the input maybe? Let me know your thoughts thanks. Also sorry for the wall of text.

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What model are the amp and subwoofer?

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Amp: Alpine MRV-M500
Sub: 12″ Skar SDR 600rms

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Guess it’s my turn for the wall of text.

Regarding the sub wiring, did you buy the dual 4 Ohm version of that Skar sub? If so then you can parallel the voicecoils into a 2 Ohm mono load which will maximize the power from that amp. You can parallel either at the amp or subs speaker terminals. The larger amp terminals are likely easier. If you bought the dual 2 Ohm version then you’ll need to series connect into a 4 Ohm final load.

As for the amp input, your amp’s manual states, “MRV-M500/MRV-F300 accepts input from high power or standard power head units.”

There is a note for using both L&R channels of an input, “Low output will result if only one channel input is used. The Y-adapter is not required if a stereo/mono pair line output is used to drive both inputs of the bridged amp. ” Also,

“Only left/right channel speaker level input is required. However, all speaker input leads (FL/FR/RL/RR) may be connected to prevent zero output when the head unit fader is adjusted”

You could tap into the factory sub before the amp, if possible. This is possibly already crossed over by the factory system. Someone else might know this vehicle but, as stated above, I do not. You can find out if it is crossed over or not with your DMM. Disconnect the factory sub where you are looking to tap. Set the DMM to read AC Voltage and connect to that tap point. Play bass tones and watch/record the voltage level. If they are all the same voltage level between 20-100 Hz then you have a flat output signal from your headunit. You will use your new Alpine amp’s crossover feature to control the low-pass frequency. If the voltage readings fluctuate (drop off at high or low frequencies in the sub range) then your headunit is already filtering the signal (more likely). You can use that signal as-is and open up the crossover setting on the amp or look for a full-range signal in the car for more control of the subwoofer crossover frequency. You would repeat this experiment on your other speaker leads and look for a full-range signal. I would prefer to have more control but the extra work is up to you since it’s your system. Regardless, set the gains correctly. Do not just wing it or guess.

Do note for future reference, “Use either RCA line level or speaker level inputs. Do not connect both at the same time.”

FYI regarding the remote turn-on, your amp’s manual has this note: “If using speaker input level signal from the head unit, remote turn-on lead connection is not necessary due to automatic signal detection.” Also,

“For the “Speaker Level Input System” setting, connecting the Remote Turn-On Lead is not required due to the “REMOTE SENSING” function of this product. However, the “REMOTE SENSING” function may not work depending on the signal source connected. In such a case, connect the Remote Turn-On Lead to an incoming power supply cord (accessory power) in the ACC position.” And lastly,

“Remote Turn-On Lead
a. The head unit does not have a remote turn-on or power antenna lead.
b. The head unit’s power antenna lead is activated only when the radio is on (turns off in the tape or CD Mode).
c. The head unit’s power antenna lead is logic level output (+) 5V, negative trigger (grounding type), or cannot sustain (+) 12V when connected to other equipment in addition to the vehicle’s power antenna.

If any of the above conditions exist, the remote turn-on lead of your MRV-M500/MRV-F300 must be connected to a switched power source (ignition) in the vehicle. Be sure to use a 3A fuse as close as possible to this ignition tap. Using this connection method, the MRV-M500/MRV-F300 will turn on and stay on as long as the ignition switch is on.”

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So I spent the weekend rigging quick temp setup and the bass does seem to get flat once I really turn up the volume yet the other speakers get louder. Line output only wired to sub only so I wonder if wiring another pair to one of the regular speakers would help with this. Or my only option is lc2i?

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