How To Connect A Subwoofer To An Old Amplifier Or Vintage Receiver

Got a vintage amplifier or receiver? When it comes time to add some great low-end bass you might be scratching your head wondering how – and if – you can add a subwoofer. 

The great news is that there are several ways to connect a subwoofer to an old amplifier or vintage receiver.

Even better, it won’t cost a lot, either! Read on and I’ll share with you 3 ways to connect a subwoofer along with clear subwoofer diagrams anyone can understand.

Home stereo subwoofers explained

Passive vs active home subwoofers diagram

Comparing passive (non-powered) vs active (powered) home stereo subwoofers. Powered subwoofers have an internal amplifier and one or more signal input options: speaker inputs, RCA input(s), and in some cases, digital audio inputs.

There are two kinds of home stereo subwoofers: powered (“active”) and non-powered (“passive”).

  • Powered subwoofers use a low-signal signal which is boosted greatly using the built-in speaker amplifier, power supply, and crossover. These types are one of the most common and in many cases use an RCA type input jack to connect to the receiver for sound.
  • Passive (non-powered) subwoofers are simply a subwoofer speaker inside the bass enclosure which is directly wired to the speaker terminals or a passive bass crossover inside. These types are less common.

How does a subwoofer work?

An amplifier boosts the low-level input signal in order to drive the subwoofer’s voice coil with sufficient power and move the speaker cone, producing sound. As the cone moves the air inside of a specially designed enclosure (speaker box) deep bass, contained in the musical input signal, is produced.

They’re designed for only low-end bass and not voice or other musical instrument frequencies.

A powered subwoofer includes an amplifier already inside the subwoofer enclosure. It also has a built-in low-pass crossover to block higher sound frequencies in order to produce clear and great-sounding bass only.

For non-powered subwoofers the problem comes when you connect one to an amplifier or receiver’s outputs without a crossover – it sounds terrible!

Old amplifiers and vintage receivers vs new receivers

Unlike older amplifiers, more modern home stereos and especially home theater receivers have a subwoofer output jack (or pair of jacks) dedicated to this bass signal a subwoofer uses to create sound. This is usually from stereo music signals or the subwoofer (“.1”) channel sound in multi-channel surround sound material such as Dolby Digital or DTS.

For example, you may see terms like “5.1” or “2.1” speaker systems or surround sound audio listed for movies. In this case, the first number represents the number of main speakers. The “.1” is used to represent a sound channel limited to only bass for subwoofer use.

Older amplifiers and receivers don’t provide a subwoofer output so we’ll need to connect a subwoofer using some other ideas.

Powered subwoofer inputs & controls to know

Powered subwoofer example with inputs and controls labeled

Shown is an example of a powered subwoofer’s rear panel with 2 kinds of inputs: speaker inputs and RCA (low level) input jacks. Note that not all subwoofers offer speaker level inputs, meaning if yours doesn’t have them it’s a bit harder to connect the bass signal input.

Powered subwoofers usually have a few different inputs and controls. It always depends on the particular brand and model you buy.

Here’s what you’ll usually find on most:

  • Power input (AC outlet power)
  • On/off switch
  • RCA input jack or a pair of jacks
  • Subwoofer crossover adjustment
  • Subwoofer level adjustment know (the amplifier’s signal boost level)

In most cases, a subwoofer input jack, if you had one on a receiver, is a “mono” (monaural, 2 stereo channels combined into one) signal you connect with a single RCA cable.

Receiver subwoofer output jack example

Shown: What a receiver with a subwoofer output jack looks like as found on many newer receivers. These connect to the RCA input jack on the subwoofer, if present.

Of course, if you’re reading this it’s because you don’t have a receiver with a subwoofer output. In fact, some of the information you’ll find right now on the internet says that you have to buy another subwoofer if you don’t have a receiver with an output jack. That’s simply not true.

Subwoofers with speaker level inputs are great to have for exactly this reason as you can connect them directly to an older amplifier or vintage receiver’s speaker outputs.

Even if you buy (or already own) a subwoofer without speaker level inputs, it’s ok – there’s another way to basically connect it essentially the same way!

Below you’ll find a diagram showing how to connect an old amplifier or receiver without a subwoofer output easily.

Diagram & examples: Connecting a subwoofer to an old amplifier or vintage receiver

Diagram showing how to connect a subwoofer to an old amplifier or vintage receiver

1. Connecting an old amplifier or receiver to a subwoofer with RCA input jacks

Example of a powered subwoofer RCA jacks & RCA Y adapter cable

Left: Example of a powered subwoofer with 2, instead of the typical 1, RCA input jacks. Right: An RCA Y adapter that can be used with a line level converter to connect to a subwoofer with a single RCA input jack.

If you’ve got a subwoofer with 1 or 2 RCA input jacks and no speaker level inputs, here’s a simple and high-quality way to connect it: by using a line level converter.

What is a line level converter and how do they work?

Line level converters (also called RCA speaker level adapters) are small electronic devices that connect to speaker outputs from an amp or receiver and scale down the higher-voltage signal to a low level (“line level”). The outputs are RCA jacks which can then be connected to any amplifier or subwoofer with RCA jacks.

 While you almost never see them used for home stereo systems, they’re extremely handy in the car stereo world because they make it possible to connect a stereo without RCA outputs to any amplifier or powered subwoofer.

Likewise, they can be used for home stereo amps and receivers, too!

Image showing examples of line level RCA converters

Shown here are two examples of line level/RCA speaker level converters that work well for home receiver/amp to subwoofer use.

How much do line level converters cost?

Line level converters vary in price a bit depending on the quality and features, selling around $15-$25 or so in many retail stores and online stores.

How to use a line level converter

To convert speaker level outputs from your amplifier or receiver to RCA jack subwoofer outputs, you’ll connect the provided speaker wire connections (marked by colors and striped) just like you would regular speakers. You then connect RCA cables (or a single cable, depending on your particular one) to your powered subwoofer.

The internal electronics not only scale down the speaker output voltage from a receiver but also help prevent noise from the audio path, too. Most, but not all, speaker level adapters do not need a power source.

If your subwoofer has a single RCA subwoofer input jack, you may want to pick up a “Y” RCA adapter to combine both receiver channels on the output side into a single mono RCA plug.

Subwoofers with 2 (stereo) RCA jack inputs will need a standard stereo male-male RCA cable.

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2. Connecting a subwoofer with speaker level inputs

Example of subwoofer speaker level inputs

A subwoofer with speaker-level inputs is especially easy to connect to your older amplifier or receiver! To do so, just connect to the speaker outputs on the source unit using speaker wire and then to the matching inputs on the subwoofer. You can even power speakers from the amp or receiver at the same time.

If your subwoofer has speaker level inputs built-in you’re in great shape! Just connect them directly to your amplifier or receiver’s speaker outputs, either to unused speaker terminals or at the same time (in parallel) with speakers connected to the receiver.

Just like an off-the-shelf line level RCA converter I mentioned earlier, the subwoofer’s internal electronics will scale down the speaker signals to a much lower line level signal the internal amp can use.

You can still expect very nice sound quality as the signal used is just divided down and isn’t changed. Because speaker level inputs have a very high input impedance (total input resistance), in most cases it won’t hurt to connect them to your receiver or amp at the same speaker wire terminals where speakers are already connected.

To do so, you’ll just connect them in parallel: positive speaker inputs to positive speaker outputs and negative speaker inputs to negative speaker outputs.

Additionally, there’s a low-pass crossover built-in as well to produce great-sounding bass and no unpleasant parts of the music – just pure, low-end bass.

Note: Subwoofers with speaker level inputs and outputs provide a way to easily connect both at the same time. The outputs are internally connected to the input connectors, making it easier to add speakers and the subwoofer to a receiver simultaneously.

3. Connecting an amplifier’s speaker outputs to a passive (non-powered) subwoofer

Example of a passive subwoofer low pass crossover

A passive subwoofer low-pass crossover, unlike an electronic crossover, works using capacitors and inductor coils instead of electronic components to filter out the unwanted higher-frequency sound that would otherwise go to the subwoofer. This lets you power the subwoofer with only a lower bass sound similar to how a powered subwoofer works.

Using a passive (non-powered) subwoofer is definitely not as easy as a powered one. The good news is that it can be done, and relatively easily, too. In fact, it you don’t have to worry about going broke, either, although you will need to do a bit of shopping.

To connect your amplifier or receiver to a non-powered subwoofer as is shown in the diagram above, you’ll need to pick up a low pass crossover that you’ll connect between the amp or receiver and the subwoofer.

These will filter out sounds above the crossover frequency and provide only a nice bass sound to it.

How to choose a subwoofer crossover

Speaker crossovers like the one shown are sold both in a single (one speaker) or dual (2-speaker) models depending on the brand & supplier. They also have to be matched correctly to the impedance (Ohms rating) of the sub.

For example, for an 8 ohm subwoofer, you’ll need to use a crossover designed for 8 ohm speakers. Otherwise, the sound filtering is radically different and won’t sound right since the speaker load will change how the crossover filters the sound quite a lot.

Normally you’d choose one with a low-pass frequency of close to 100Hz or close to that. You may need to shop around to do so.

Where to shop for passive subwoofer crossovers

Speaker crossovers are sold where speaker parts & related components are sold as well as marketplaces like Amazon or Parts Express. Other speaker specialty stores where replacement speaker parts are sold may have them, too.

Stereo vs surround sound receiver subwoofer output comparison

Stereo vs surround sound receiver differences diagram

Unlike older or standard stereo receivers, surround sound receivers have a unique output that comes from the surround sound movie or music source. However, in regular stereo listening mode, they act the same as regular receivers.

Just as a side note, one thing to be aware of is that when you connect a subwoofer to an old amplifier or receiver you won’t be able to get the separate dedicated bass sound channel (.1 channel) like you can with a surround sound receiver. 

Those are able to extract the dedicated bass sound from a DVD or other media and route it to the subwoofer output jack. On the other hand, it might not even be a problem.

Did you know? The surround sound receiver “LFE” (low-frequency) output is considered optional – hence the “.1” name. 

Surround sound receivers and amplifiers are designed so that you can play nearly all the sound through the main speakers if needed.

In some cases, for example, some movies and music use the bass channel to really draw you into the experience. Using a receiver without that output means you can’t get the same effect, but that’s only for surround sound mode.

The good news is that in stereo mode, both new and old receivers & amps have very similar subwoofer behavior when connected as you’ve seen here. In other words, you probably won’t really miss it if you’re using an older receiver or amp.

That’s just something to be aware of in case you’ve considered upgrading at some point.

More articles with speakers, speaker wiring, and diagrams to help

I’ve got some other great info to help you learn more and get your system going:

Questions, comments, or etc?

Please feel free to leave a comment or question below – I’d love to help, and it’s appreciated. Note: please provide specific information like brand & model numbers, speaker ohms, and so forth so I can best help you.

Need direct help? Feel free to contact me here via my Contact page.

Your comments are welcome!

  1. Hi Marty, Your article was most informative.

    I have a vintage sony pre amp which i want to connect to modern 2.1 system. The speaker output has Speaker Wire. So in order to connect it to my 2.1 (which has RCA) should i use a Speaker Wire to RCA Adaptor or a RCA Line Level Converter?

    Reply
    • Hi there my friend. Yes, you’d have to use an RCA line-level converter if you only have access to speaker level outputs. Do be aware that it’s not quite the same fidelity you’d get with a direct line-level (RCA to RCA) connection. But it’ll get the job done.

      But a preamp unit normally only has line level outputs so it’s interesting to hear it has speaker outputs.

      Reply
  2. Very handy article! I want to follow example 3 with an unpowered sub, but what if the source does not have separate rear channels, only L and R? Is there any way to piggyback on either of the 2 channels with a separate amp or something?

    Reply
    • Hi Steve. In that case yes, you’ll connect a line level converter to your existing speaker channels alongside the current speakers, then you can go out to a separate amp of your choice. Parts Express has a nice little one with a subwoofer output that’s affordable. I need to update this article to show an example.

      Thanks!

      Reply
          • Not the greatest reviews for the sub output of that amp, but it seems like it would be sufficient for my purposes and would avoid the need for the external crossover. Last question, I promise: for this application, is the 12V in required for the line level converter? I can provide that (since I need it for the amp anyway), but it would be handy if I didn’t need to.

          • Yes, it’s a lower-cost alternative to having to replace the subwoofer altogether or use a plate amplifier. Line level converters don’t normally need +12V power so it’s not an issue unless you buy one that requires it.

      • I’m thinking my reply somehow never published.

        Anyway, so the wiring would be source L/R -> line-level converter (speaker wire to RCA) -> amp L or R channel (RCA back to speaker wire) -> crossover -> unpowered sub.

        Is that accurate?

        Reply
          • So I started doing this and I replaced the L/R speakers at the same time. The source amp is evidently not that great. I now hear more noise in the background with these better speakers and there are pops as it powers on. Would it make any sense to take the L/R speakers off of the direct connection from the source and connect them to the amp after the LLC so they’d be coming from the same amp (which includes a crossover) as the sub? So instead of piggybacking (source connected to both speakers and LLC), source only connects to LLC. Or do I need some type of grounding or shielding somewhere perhaps?

          • Hi Steve. Since in this case there’s a line level converter coming from the speaker outputs that have the pop, I strongly suspect the pop will get carried through the amp as well. However, it’s worth a shot.

            The good news is that either way there’s another solution. You can buy a basic on-off delay board that will avoid the pops and is made for this problem. They work (usually) by opening the circuit to the speakers until a small amount of time has passed to prevent it. I’ve seen them online before, quite possibly on eBay and other sites.

  3. My audio literacy is zero. I have two old system pioneer amplifiers. One has a LFD-14 connector from Amplifier to Subwoofer. I am trying to buy another connector to connect my old Amplifier to Subwoofer. Cannot find one available. Do you have one I am able to purchase? If not explain how to connect a old Amplifier to Subwoofer. My audio helper doesn’t have a clue. Please help. Thank you.

    Reply
  4. Is there a recommended speaker port to wire the sub woofer on multi channel system. I have scenario number 2. Should I use front, rear, center?

    Reply
    • Hi Rob. Front should work unless rear is also the same (full range) as the front channels in which case it would work also. Center or dedicated surround sound channels don’t have the bass signal you’d want.

      Reply
  5. Hi
    Just want to get this straight before i connect this up.
    I have a 35w valve amp with only 2 speaker outputs going to some old 70s wharfedale e50s.
    Theres not alot of bass, so after reading this it seems i can connect wires to the same speaker outputs on the amp that the speakers are on and run those into the speaker level inputs on my powered sub, both left and right.
    Does this not change the ohms? i dont wanna blow my amp, it likes 8 ohms only.
    Appreciate any reply

    Reply
    • Hello, Dan. No, the amp won’t see a change in the speaker load Ohms value. That’s because although the speaker level inputs will be in parallel with the speakers, their input resistance is so high (in the thousands of Ohms) that it’ll still be right at 8Ω at the amp’s speaker outputs.

      If you were to measure resistance on the speaker level inputs (with it off, power removed, and no wiring connected) you should see at least several thousand Ohms.

      You can also check it across the amp’s speaker terminals with everything connected but powered off. It should measure close to 8 ohms (the speakers are normally a bit below 8Ω).

      Best regards.

      Reply
  6. Forgive if this question is buried away in the past.

    If I have a Rotel RA-920-BX3 with standard A and B speaker outputs, how would I connect these to a Panasonic SB-HW480 passive subwoofer that only has a ‘bell wire’ coming out from the unit, ie one negative and one positive wire.

    Do I connect the amplifier LEFT and RIGHT B negatives to the single negative subwoofer INPUT (and likewise for the positives), or do I just use the LEFT OR RIGHT speaker outputs and accept that it is in effect a mono feed?

    Thank you.

    Reply
    • Hello Giles. Yes, that’s always kind of a tough one when the original subwoofer doesn’t have dual voice coils. You could try using one of these stereo to mono speaker transformers, although it’s limited to 30W/channel and you’ll need to add an 8Ω resistor in series with the inputs, one per input. You’d still need a passive subwoofer crossover.

      For that reason you may find it easier, cheaper, and even better-sounding to use a mini amp with built-in low-pass crossover output like this one and a line level converter to get the RCA input signal. The total cost would be less plus you could use the little amp for other things later.

      Reply
      • Thank you for coming back to me. I’ll give it a whirl (the transformer). The amp is 30W so that’s not a problem but I’m not sure the pre-amp option will fly as the Rotel doesn’t have a pre-amp output (it is an old, but beautiful sounding relic from the 90s).

        Appreciate the help.

        Giles

        Reply

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