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.

Update! Based on reader feedback, I’ve added more info about passive subwoofer use. The diagram is also updated and improved.

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. Mini amplifier option for passive (non-powered) subwoofers

Example of a 2.1 stereo mini amplifier with sub output

When wanting to add a single voice coil (SVC) non-powered subwoofer, several issues come up. Hands-down, the simplest solution is using a mini amplifier with a mono low pass subwoofer speaker output.

For this setup, you’ll do the following:

  • Use a line-level RCA converter to get an RCA signal to the amplifier.
  • Connect the passive sub to the subwoofer output.
  • Use the AC-DC power supply to power it.

That’s pretty much it! Having a built-in sub crossover means the sound will be nice, clear bass without vocals much like a self-powered subwoofer provides.

Today’s small amplifiers are typically very compact in size as many use an efficient class D amplifier design. They’re sometimes called a 2.1 amplifier as they usually have both stereo speaker outputs and a dedicated subwoofer channel.

Facmogu ST-838 2.1 Mini Amplifier With Subwoofer Output
20Wx2 stereo + 40Wx1 subwoofer output. RCA and 3.5mm input jacks. Easy to use speaker terminals. Bass, treble, and volume controls. Includes power supply.

Cost and other notes

They cost around $35 to $50 or so depending on the model. The downside is that if you want a ton of power, they’re not the first choice as many offer about 34W to 68W sub power. If that’s not enough you’re better off getting a more expensive amplifier.

Note: Mini amplifiers may or may not include the power supply so be sure to check when shopping.

4. Connecting speaker outputs to a passive sub

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 helpful speaker info & diagrams

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

Your comments are welcome!

  1. Does hooking the speakers up to the same terminal as the line level converter change the ohms going into the receiver from 4 to 8 on some older receivers / vintage does cause the receiver to work harder ??

    Reply
    • Hi Eric. No, in 90%+ of cases the input impedance (resistance) to a line level converter will be extremely high, meaning it will not cause a lower load at the amp or stereo. For example, the amp will still “see” an 8 ohm speaker if a line level converter is connected to the same speaker terminals.

      There are some el-cheapo converters that might drop the total speaker load, but that’s rather unusual so there shouldn’t be a problem if you’re using a decent quality one.

      Reply
  2. Marty, Thank you for this excellent article. My question involves connecting two powered subwoofers to an older amplifier ( amplifier: Dynaco ST-120, preamp: Dynaco PAT-4). I have two powered sub woofers. Both subs have line level inputs, speaker outputs, and dual RCA input jacks. From your article I understand how to connect a powered sub to my system using the line level speaker inputs. Can I “daisy chain” the second sub to the connected one? Do you advise doing that? What’s the best way? Thank you again very much.

    Reply
    • Hi Donn. Sorry, I recall writing a reply but I cannot find it now fo some reason. Anyway, yes you should be able to daisy chain the speaker level inputs from the 1st sub to the second if that’s what you meant.

      The impedance (resistance) on the speaker inputs of the subwoofers is very high so it won’t have any real impact on each other or the amplifier. Best regards!

      Reply
  3. Hi Marty

    I have a power amp with loop connections. Can I connect a powered sub with these. They are RCA. The manual says it is to connect another amp for bi-amping.
    Regards,
    Les

    Reply
    • Hi Les. Generally speaking you can, yes. But it’ll depend on your equipment so you’ll need to try it out and see. Some preamps or receivers don’t have a constant output on the RCA output jacks but you don’t always know until you try unfortunately.

      Best regards.

      Reply
  4. Thank you for a well chosen and extensive review. Just hooked my Monitor Audio RS w12 sub to a vintage Revox B750 MkII amplifier via RCA from preamp out to sub RCA in.
    How important is quality of cable for this connection?
    Thanks again and greetings from Belgrade, Serbia.

    But with a “thump” of the sub when amp switches on and off. Comment please.

    Reply
    • Hello Branco. The quality of the cable isn’t very important. Just a basic quality cable/cables will be fine.

      If you’re getting a thump it can be due to a number of things, especially possibly the preamp generating that noise when it works. Some people use a time-delay relay board to keep the amplifier (subwoofer in this case) turn off for a moment until after the thump would happen to eliminate it.

      You can try narrowing it down to what is causing it as that’s the first step, then go from there. Best regards.

      Reply
  5. Thank you Marty. I went to 2 different sites for help prior to finding you. Adding a sub can be very basic but I wanted to be sure first. I watched 2 videos and they both made this event something akin to rocket science. Your explanations and diagrams are very clear and confirmed my suspicions of a very basic function. Thank you again.

    Reply
    • Hi Tommy that’s interesting to hear the videos weren’t good. Yeah, it shouldn’t feel like rocket science, ha ha.

      Thanks for the feedback and I’m happy to hear you found it helpful! :)

      Reply
  6. Marty, I have a McIntosh mc250 with a Cambridge AXR85. The speaker volume is only controlled by the amp. Speakers are older JBL studio monitors. Sounds fantastic. I have a klipsch sub connected to the sub out on the Cambridge but get no signal to it. Where have I gone wrong?

    Reply
    • Hi Charles. I went through the manual for the AXR85 and didn’t find anything obvious. I would normally suspect the subwoofer output isn’t active for some reason (a setting or no output due to the receiver mode) but in this case I’m not sure.

      If you’re 100% sure the Klipsch is working right I would look into those above I mentioned. But I’d be sure the subwoofer is working right with a signal by running a separate signal input into it and see if you have sound. If so, also try Bluetooth mode on the Cambridge and see if the receiver’s subwoofer output is active then.

      It’s a bit odd as from what I see the subwoofer output should work regardless (appears to be derived from the RCA inputs you’re using). Best regards.

      Reply

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