Understanding Audio Levels

A basic understanding of the general audio levels mentioned in this article will help you avoid the common mistakes often made when connecting audio devices together. We are going to talk about three different general levels of audio signals.  The names of the three general audio levels are speaker level, line level and microphone level. For simplicity, the different audio levels are described in volts. For an understanding of decibel levels used in audio, see the articles on decibels starting here.

Speaker Level

A speaker needs a few volts of electrical audio signal to make enough movement in the speaker to create a sound wave that we can hear. Small speakers need only a few volts, but large speakers need 50-100 volts to make a loud sound.

Line Level

A speaker is connected to an amplifier. Think of your HiFi amplifier at home. What plugs into your amplifier? DVD player, CD player, radio/tuner, video camera. All these devices plug into the “line in” or “Aux in” of your amplifier.  “Line IN”, “Aux IN” and “Line OUT” all have an electrical audio signal at line level. You are probably aware of the standard red and white leads used in HiFi equipment, these all use line level. Other plugs are also used for line level. Line level is about half a volt to one (½ – 1) volt. It is the job of the amplifier to amplify the half to one volt of line level, up to the 10 volts or more of speaker level.

Note: A common error is to connect plugs and sockets together just because they fit. Don’t assume audio level based just on the type of plug being used. The same type of  plug can be used for different purposes (and different audio levels).

Microphone Level

Ok , so we have line level (about ½ – 1 volt) which goes into an amplifier to make it up to speaker level (about 10 volts or above).  What audio level do you think Mic level is? How much voltage do you think comes out of a microphone, as a result of you speaking into it? Answer: Stuff all!

The output voltage of a microphone is very low. It is measured in milli-volts, that is 1/1000th of a volt. A mic can give as little as 1 mV, or upto 100 mV, depending on how loud you speak into it. That is not very much. So what do you think is going to happen if you plug a mic directly into the line in of an amplifier? Answer: A very low level of muffled sound if anything.

Mic Pre-amps

The amplifier is wanting line level, ½ – 1 volt to produce enough signal to make the speaker work properly. But the mic is only producing milli-volts. So what is needed is a small microphone amplifier that amplifies the audio level from mic level to line level. This should go between the microphone and the amplifier. Because it is for the microphone and it is before the main amp, it is called a mic pre-amp. A mic pre-amp amplifies the milli-volts from a microphone up to line level.

Mic pre-amps are normally built into devices designed for connecting to a microphone. Equipment like an audio mixer, a digital recorder, a video camera or a computer – all these may have mic level inputs as well as line level input, or just a mic level input. .

Audio level microphone level, line levelThe picture on the right shows for each input on this mixer there is a line level input (labelled Line 3 and Line 4), as well as a microphone pre-amp (labelled MIC PRE).

Obviously a microphone plugs into the mic input, as the mic inputs are connected to the in-built mic pre-amps.

A line level device would obviously plug into the line in socket.

But what if your mixer (or camera/recorder) only has a microphone input, and you need to connect a line level source to it? This would result in the line level (½ – 1 volt) being connected to the input of the mic pre-amp. The trouble is, the mic preamp is expecting only a few milli-volts. The resulting sound will be very distorted as the mic pre-amp is completely overloaded.


So how can we do this? How do we connect a line level to a mic level input? We have to reduce the line level down to mic level.  The technical word for this is to attenuate the signal. As an amplifier amplifies, or boosts the signal; an attenuator attenuates, or reduces the signal.

You can buy attenuators at a music shop, they are called DI boxes. DI stands for Direct Injection, meaning you can directly inject a line level into the mic input without any problems. It is also possible to make an attenuator, possibly with variable attenuation, to cope with different levels. It is also possible to buy or build a fixed attenuator in a cable. This is a cable with resistors built-in to the plugs to attenuate the line level down to mic level – this is very useful for a video camera or portable digital recorder.

Audio Level Summary

There are three main audio signal levels: mic level (millivolts), line level (around 1 volt) and speaker level (around 10 volts or more). The rule is, only plug speakers into the speaker socket of an amplifier; only line level into the line in of any equipment; and only mic level in the mic input of your mixer, camera or laptop.  The most common cause of  audio distortion comes from not understanding the different levels, and how to connect them all together.

Practical Example 1

Scenario: A keyboard (electric piano) located on the stage needs to connect to a mixer located at the back of the hall, with a microphone multi-core cable connecting between the two.

Issue: The output of the keyboard is at line level, and the microphone input at the mixer requires mic level. (There is also the issue of different plugs and balanced/unbalanced inputs but these are the topics of other articles).

Solution: Use a basic DI box available from most music or electronic stores. A DI box acts as an attenuator which reduces the line level of the keyboard to mic level for direct connection to the mixer (via the multi-core cable). The DI box also overcomes the issues of matching plugs and going from unbalanced to balanced  – so this is a perfect solution. This solution also works for connecting electric guitars, electronic drums and DVD players.

Practical Example 2

Scenario: The output (line level) of an audio mixer needs to connect to a digital camera or digital recorder which only has a microphone input.

Issue: The output of the mixer is at line level, and the microphone input of the camera/recorder requires mic level.

Solution: A basic DI box could be used, but this would require an input lead, and output lead and the DI box  – a lot to carry in your camera bag. A neater solution is to have a lead with a 40dB attenuator built into it. This will reduce the line level from the mixer by a factor of 100, which will bring the line level down to a reasonable mic level to connect directly to the microphone socket of the camera/recorder.

This article is based on one I originally wrote for my friends at CamcorderUser.net, and has been refined by their helpful comments.


  1. I have a DAC with a RCA output and a aux output. When I connect my earbuds to these two, the output volume are very different. The RCA offers very low volume. Can you pls tell me why and how to solve this issue?

    • Hi Phoebe,

      The RCA output is probably at consumer line level which is not very high. For headphones you need a low speaker level.

      If you want to use the RCA out, you will need a headphone amplifier to bring the level up to a low speaker level.


  2. Thanks for the great article — but it doesn’t appear to apply to my install. I have 1/4 jack aux outputs on my PreSonus StudioLive 16.0.2 mixer. I want to feed one output into my Sony camcorder 1/8 mic input, and the other output into my IP camera for live video/audio streaming.
    When I plug in the Sony camera has no audio
    When I pug in the IP camera I have to increase the gain inside the camera software and I get very low volume and distorted.

    Please advise.!

    • Hi,

      I don’t know what IP camera you are using, but for the Sony camcorder will almost certainly want mic level, not the line level the Presonus puts out.

      I suggest treating each input separately. Try using a DI box or attenuator as discussed in Understanding Decibels. This should solve the camcorder issue, and may will help with the Ip camera also.


  3. Hi Geoff,

    I have a question about relatively high line level output, as in 8 volts. As an example of this, I have a car stereo head unit capable of 8 volts at line level. This is a competition type deck designed for external amps and to optimize their overall performance. My question has to do with line level limitations for other small amplifiers like those that would normally expect to see around a volt or so. Would 8 volts of line level damage these smaller amplifiers? I would like to re-purpose this car stereo head unit for a portable project involving one these smaller external amplifier boards. I could achieve my goal in a different way, but wanted to know if this was a viable option, and if damage would occur to the input stage of the external amp with 8 volts coming in at line.

    • Hi PB,

      It will depend on the design on the input stages of your external amp as to what they can cope with. However, the head unit is only going to produce a 8 volt output when turned up full, I suggest. Therefore if you only turn it up a little bit then you will only get a little out, which is what the amp would be expecting.

      I don’t think it should normally cause any physical damage, but it will distort the sound if the input levels are exceeded. So as long as you don’t hear distortion all should be OK.

      You could though have the problem that you have very little control of the output. That is, the volume on the head unit only goes up to (say) 2, before it causes distortion. If this is the case, you could make a 8:1 attenuator with two resistors (1000 ohms and 7200 ohm). Some guidelines for this are at the bottom of my Decibel Calculator for Audio (use 18dB as the input, and 0db as the outout).

      hope this helps some.


      • Good help indeed, thanks. It’s validating that your advice isn’t surprising. I’m not as dumb as I thought, but that too is relative. So the other thought that I have here is using the rear speaker level outputs to wire a very small 4ohm single driver subwoofer that used to be an old Altec Lansing speaker system whose controller card is toast. Do you have any advice, for or against, wiring that sub with the rear channels, assuming that the sub is appropriately low-passed of course?

        • Hi again,

          my main thought is I wonder how much sub signal might be on the rear speakers. Mostly the rear speakers are for effects, not the dialogue or the main action, so there may not be much audio for the sub to work with.


  4. Hi Geoff,

    Good information. Thanks for clarifying. I have a couple questions.

    First, the service manual for my car says the radio and audio amplifier have a DC bias voltage that is about 1/2 the battery voltage. The audio is produced by varying AC centered around the DC bias voltage. Is this normal for car stereos? Can I just change the speakers with aftermarket brands, or do I need special speakers for this?

    Second, the radio in my car only has 4 speaker outputs, but the amplifier has 9 outputs. I found out that they used the same radio on cars with and without the amplifier. A friend told me that they probably send a speaker-level signal to the amplifier. How can I tell if the output of the radio is speaker level or line level? Can I just measure the voltage with a voltmeter? How will the DC bias voltage affect this? If it is line level, can I just plug that into a new amp with line level inputs, given the DC bias voltage?

    • Hi David,

      Yes I would have thought all car amps need to run with a bias at half input voltage. That is the only way the output can swing. For example, lets say the input voltage is 12 volts. Half voltage will be 6 volts. Therefore the output can swing from 0 to 12 volts, centered around 6 volts. Normally a capacitor is used on the output (within the amp) so you or the speakers would never know what the bias voltage is.

      Given that I believe this is normal, then you should be able to use any after market speaker – but I guess the car audio shops will know more than I do about this.

      Normally the line out of a radio will be on RCA sockets. But you can check it easily by connecting a speaker to each output. If it works pretty loudly, then it is speaker level, If it is a line level signal, then the speaker will not be very load at all.


  5. Hi Geoff,

    If I connect the headphone output to a line input of my amplifier, the sound is quite weak. Can I connect it to the phono input of the amplifier instead?

    • Hi Ctaya,

      Your situation is not normally the case.The headphone output is normally quite adequate to drive an amplifier, although not recommended (mainly because the headphone amp is often quite noisy), and the level will change with the master volume). Is there a (headphone) volume control you can turn up?

      Whatever, you can’t use the Phono input either. Yes it is is designed for a much lower level, but it also needs the boost the bass a lot to compensate for the way recorded are made. So the sound will be very bassy.

      What is the source you are trying to use?


      • Dear Geoff,

        Thank you for your reply.
        I have found a way to adjust the level of the headphone output of the TV. Now my problem is solved.

  6. Sir,I’m very greatfull for this article…
    You have helped me a lot explaining the levels and resolving the problems.
    I have a keyboard and camera mic input,and I had no clue what to do,and now You’ve saved me my friend.

    Thank You a lot for Your time writting this article,and thank You to share this information with us.

    Wish You all the best in the future my friend!

  7. hello,
    I loved this article. it is very informative;
    I have a project I am working on and I have been scouring the internet all day and night trying to research possible problems I might encounter.
    I have a late 40’s Wurlitzer jukebox that is missing the amp and record guts. I plan on hooking up a car cd receiver and running the line out, or as it states in the description: 2 Pre-Output Terminals (Front + Rear / Subwoofer Selectable)4.8v Line and Subwoofer Pre-Output LevelMOS-FET 50W x 4 (20W RMS x 4) ,
    I will be running this into the input of a tube amplifier which will be installed in the top dome of the jukebox.
    the tube amp is stereo, 10w/channel and has 2rca input.
    do you think I have to cut the voltage down to run it into the input? am I going to fry my amp?
    also if I do need to cut the voltage, how can I build a lead with a 40dB attenuator in it?
    one more question, I have an older akai reel to reel tube amplifier 6w mono and I am wondering if running an mp3 player into the mic input will ruin the preamp? what about a usb/mp3 amplifier with a 20w/channel output? the akai also has a line in input which is a lot quieter with the mp3 player going through.

    • Hi Sandy,

      The line out from the CD player should work OK into the line in of the tube amp.

      Your MP3 into the Akai is an interesting one. MP3 players often output a level in between mic level and line level. Normally with the MP3 volume flat out, it will drive the line input at a reasonable level. Otherwise you may need to reduce the level a bit to feed the mic in. Probably a 20 or 30dB attenuator would work. There is some help in designing your own at the bottom of my Decibel calculator, and a way to build one at the end of Understanding decibels.

      hope this helps,


  8. Your information is great but I hope you can assist me I finding,maybe making a device that I or anyone can add to TV’s that allows the viewer to adjust background sound/music ETC. in programming.
    Example I am watching a action show and the background music is louder than the actors speaking thus my ability to clearly understand the full conversation is hindered. I have found this increasing since transmissions became digital. My thought is that I am sure there are many others that must have these same issues.
    So it seems like a device that is put inline with the sound could easily allow users to control all levels of the output sound thus providing users the ability to better hear the voices or what portion they prefer.
    That you for you quick response to my ongoing listening concern.

    • Hi Paul,

      I understand what you are trying to fix. unfortunately it is not that easy, as the sound as mixed, so to separate them and then remix them to make them sound better to you is difficult. Also the sound on most modern TVs is quite poor, which doesn’t help matters.

      To try to compensate for this, have you tried the different sound settings on your TV? On some they have an option for “clear voice” which can help. Also try to decrease the dynamic range if you have that option.

      Apart from that, there is not a simple solution



  9. Hi Geoff,

    I’m Wawan from Indonesia. I’m a newbie in this audio video stuff.
    I have radio with no ‘line out’ jack. it just have built in speaker and headphone jack.

    I have an amplifier. it has ‘line in’ socket.
    I want to connect from radio to amplifier. how can I do it.

    is it ok to direct connect from headphone socket to line in of amp?
    or I need some stuff ( maybe DI box ) before connect.
    ie : headphone jack –> DI box –> line in ?

    terima kasih / thank you ^^

    • Hi Wawan,

      You should be able to connected from the headphone out socket directly to the line in of your amp. You can then adjust the volume of the radio to get the best sound from your amp.

      hope this helps


        • Hi again Wawan,

          Line level is the level that goes between the a radio, CD player or DVD player and an amplifier. An amplifier will then amplify the line level to speaker level. A headphone amp also amplifies, but not by very much.

          Another issue with headphone level is it normally changes when you adjust the volume, whereas line level is normally at a set level independent of the volume control.

          However line level and headphone level can both be used to feed another amp.


  10. Geoff (or anyone): I am looking for Audio Electronics instructors in my area. Anyone available?

  11. Very informative and easy to understand! Thank you very much, Geoff. I have been searching for a solution to my problem that I have been facing, and I think I may have found it here. I have been attempting to plug a digital mp3 playing device into my stereo receiver via its “CD in” port by using an RCA to 3.5 mm jack. The receiver is an Onkyo tx860, and it is attached to two 4 ohm NAD towers. At first I thought that the mp3 player was causing clipping in the speakers, even at barely audible levels. I found, however, that the problem is the 3.5 mm jack: even a slight touch or adjustment to the 3.5 mm jack entering the mp3 player causes crackling in the speakers. When I plug the jack into the mp3 player I can get one speaker or the other playing properly, while the second speaker plays softly and with crackling in the tweeter. It is almost impossible to get both speakers playing well. This made me think that the mp3 player jack had an issue, but it plays through headphones without a problem.

    After reading your article, specifically about mic level and line level, I tried flipping to “CD direct” instead of the “CD in”, and this did improve the sound. The jack does not seem as sensitive as it had before.

    While Im glad it worked, I am still a bit perplexed as to how it worked. Why is it that my jack appears to be very a sensitive using “CD in”, but not with “CD direct”? It is as if the line itself is more “live” when using “cd in” instead of “cd direct”. Any ideas?



    • Hi Chris,

      There are a couple of things that could causing you grief.

      Firstly, the input to your amp is quite sensitive at 150mV, where most domestic amps these days are around 360mV. So you could be overloading the input, but that is not likely to be the case when the volume of the MP3 player is low. I also suggest the difference in “liveliness” when connecting to CD in compared to CD direct, is that when using CD direct, the tone controls are bypassed. With the tone controls in play, the bass and treble would boost some frequencies to make it sound brighter.

      I’m wondering if your problem is the connecting lead. I have seen this a few times. If the lead is wired out of phase, it means that most of the sound is cancelling each other out when both channels are connected. When only one channel is connected the sound is fine. Hence when you were playing with the connection in the headphone jack, any one channel would work fine but not both together. Humor me, can you try using a new lead to connect to the amp?

      let me know if that changes things


      • Hi Geoff,

        Thank you very much for your response, and I apologize for not getting back to you sooner. I think that when you mention the “connecting lead” you mean the 3.5 mm jack that is connecting the mp3 device? The first approach I took for this problem was actually replacing the RCA to 3.5 mm jack, as I read online that these cables can be notoriously easy to damage in daily use. I ordered a slightly better cable than I had previously but the problem still persists. Sometimes one (or the other) speaker is playing a bit too soft, sometimes one (or the other) sounds “gritty” regardless of the set volume of the mp3 player or receiver. One quirk of note is that everytime I push a button on the connecting and playing mp3 device I get a soft “pop” sound. I also get this “pop…pop…pop…pop…” ( about 1x per second) sound sometimes if I withdraw the 3.5 mm jack about 0.5 mm from the mp3 device.

        While I said previously that switching to the “cd direct” was an improvement over simply the “cd” setting on my receiver, I think that it may have simply been happenstance that the connection was better at that time.

        I appreciate your listening and trying to understand these problems, but I understand that they are very specific and likely unique to the setup I have. I suspect that the problem is related to the relatively small device I am using and attempting to use to drive a relatively older system that wasnt designed to do what I am attempting to do with it. Haha. If that makes sense.

        Thank you again for your time. Do let me know if you have any other thoughts or recommendations. I think I will give my local stereo dealer a visit to see if they may be able to pinpoint the issue.



        • Hi Again,

          Thanks for getting back to me.

          It could be a bad connection issue as you say. It would be interesting to test it with another phone or MP3 player.


  12. Hi Geoff. Great article.
    I’m coming from the video world but audio plays a big role. Please bear with me. I record live performances on stage and take a direct line feed out from the mixer (which I assume that’s all there is) and it’s always hit or miss in getting a decent level ie: too soft or over modulated. My video camera does have the ability to accept Line, Mic or Mic +48v. The camera audio reference level set to -20db. I also have the option to adjust the MIC input reference level to -62db,-56,-50,-44,-33. I also have an attenuator adjustable from -10db,-20db,-30db. All connections are XLR. What would be a good setting to get great audio? Thank you.

    • Hi Mike,

      The great thing about standards is that there are so many to choose from. I say that as a introduction because every mixer/operator could be at different levels.

      It is also going to depend on where you get the feed from the mixer. Normally the left and right out should be around +4dB, so your 20db or 30db attenuator feeding your -20db line in should be fine. That is if the operator is running the mixer at full levels, which often isn’t the case. If the operator is at lower than full output, then you will need less (like 10db) attenuation or none. Then again, the main left and right out are normally used to feed the amplifiers, so they might not be an option anyhow.

      So what other feeds are you likely to have access to. A common one could be tape out. This is normally via RCA plugs. The level here is often -10db, so connecting that directly to your line in should be OK.

      Other feeds could be a separate mix out through one of the AUX sends. This is normally closer to 0db, so your 10db or 20 db attenuator should work here. Also if you get on weel withthe operator, they can adjust the the level for you, as it should only be your mix.

      Personally, I would not always rely on the mixer, as they are mixing for a live mix, which includes all the ambient sounds coming from the stage. It is useful, but not always the best. I would use a digital recorder to record the mixer, and use a good stereo mic connected to the camera(s). Then in post I mix them as I think best.

      does this help any?


      • Yes that helps, thanks Geoff. I try to get on a separate aux out so we can set the level just for me during rehearsal. I need to hear everything that comes out of the speakers. I put my own wireless mic on stage which feeds channel 2. Problem is sometimes I’m at a state theatre a College or High School auditorium so the equipment/ crew quality varies.

  13. Hi Geoff, I have just recently discovered my old Sony turntable in the loft. I have a BOSE CD/Radio (The smaller one). Recently I bought a Two Phono to 3.5mm Stereo Adapter from Maplin and linked it up to the Aux socket in the BOSE. The result? Very ,very faint sound . I also have a portable CD player which also uses a 3.5 mm stero plug and this works perfectly. Why won’t my old LP’s play?

    • Hi Baz,

      The “line in” of most amps is designed for line level. The output from the cartridge in your turntable is called Phono level, which is almost as low as microphone level. It also has specific tone characteristics which need to be applied before going to an amp.

      Older amps have an input called Phono. These phono inputs have a phono pre-amp, which amplifies the level (up to line level) and sorts out the tone issues. Most modern amps don’t have this, although they are starting to become more popular again.

      Your Bose system seems not to have a phono input. However all is not lost. It is possible to buy a separate phono preamp, for situations like yours. Here is a sample from Amazon. YOur turntable would plug into one of these, and then the output of the preamp would plug into the line in of your amp.

      hope this helps


  14. Hi sir,
    I need help. My lg tv had no 3.5 mm headphone jack. So i purchased dual rca male to 3.5 mm female jack from amazon. But when I plug in my headphone to tv via this cable the sound out is extremely low. I connected 5.1 speakers and they work fine with full audio. But while connecting headphone sound is too low and cant increase as well from tv remote. Please help me as i need full sound from headphones. What else i need to connect to my tv?

    • Hi Gurdeep,

      As I think you realise, the problem is with the levels.

      The level from the line out is too low to drive your headphones, but perfect to feed your 5.1 amp.

      The only real solution is to use a small amplifier to amplify the line out to a higher level. Most amps should have a headphone socket built in.


  15. Hi Geoff. Thanks for giving voltage ranges of the levels – that’s what I was particularly after. I’ve got an unusual situation involving a phone being used to page (announcements) and connecting it to a public address system. I’ve hijacked the speaker output of the phone – which is a small, mono 4 ohm 1W affair – and at mid volume level it will directly connect to a cheap line level input ipod speaker. Trouble is that it has to go into a mic input on the PA. I’ve ordered a car speaker to line level convertor for when I thought it would need to be line level. Would that work or do I need to wire a resistor in the cable? If so, how do I work out what resistance please?
    Many thanks,

    • Hi Gareth,

      You may be able to use the converter you ordered. While it isn’t designed for what you want to do, it may well work.

      Otherwise you will need an attenuator, like described at the end of Understanding Decibels. I would start with a 40dB as described. If you need a different value, you can use the bottom calculators here.

      In many countries there is a requirement to use an isolation transformer when connecting anything to the phone system. You might want to check this out.

      • Thanks Geoff. It’s an IP system (VoIP) so isolation is taken care of. Measuring the output with a (cheap) oscilloscope at full volume it peaks at just under 3V. Turning the volume down a little quickly brings that down to peaking at 1V – which I understand from your articles to be line level. So it does look like 40dB attenuation is good place to start and hopefully the phone’s volume control should be able to take up the slack either way if necessary. Your resistor calculator suggests 100 and 10k ohm resistors but do I need the load to roughly match the 4 ohm speaker it’s replacing? In which case, presumably 4 ohm and 400 ohm would be suitable? Am I worrying about nothing or getting it mixed up here? Also, do my resistors need to handle 1W power?
        Many thanks,

        • Hi Gareth,

          There are different definitions of line level. A common one is 0dBu, which is normally .707 volts RMS, or 2 volts peak to peak when viewed on an oscilloscope. I’m not sure if your measurements are p-p or RMS, but this might help you with your calculations.

          The 100 ohm resistor determines the output impedance of the attenuator not the input impedance, so changing it to 4 ohms will not help. As you saw when looking at the oscilloscope (which is a very high impedance load), the voltage is there. So having a high impedance input is not a problem. And because it is high, the current is low, so you only need 1/4 watt or 1/2 watt resistors.

          does this help?


  16. Hello Geof,
    The website is informative. Thanks. Recently I picked up a Panasonic 5.1 AV reciever. I was not happy with the front left and right satellite speakers. So I got a used Panasonic stereo CD changer system which has a pair of 3 way speakers(Panasonc CD changer + Left 3 way speakers + Right 3 way speaker). Unfortunately, the crossover circuit for the 3 way speakers are inside the CD changer centre console instead of inside the speakers. So if I decide to use the speakers, I have to send the audio through the center console which has a aux input. Now, I want to connect the left and right speaker wires from the 5.1 Panasonic AV receiver to the RCA aux input of the Panasonic CD changer system to use the 3 way speaker. Should I use line output converter in this case? If yes, most of the ones I find online are for cars. Is it safe to use for home theatre? Please let me know.


    • Hi Karthik,

      If you wan to use the better speakers, then yes, you will need a speaker to line converter. As you say, most of these are advertised in the car section of catalogues. However they should be fine to use in your situation.

      I wold start with the volume of the 2nd amp at about halfway, and then first amp at zero, then slowly increase the the volume of the first amp, and all should be fine.


  17. Hi Geoff

    I’m grateful indeed for the illuminating article and all your time spent replying to people, much appreciated.

    I have a question too, if I may… On most cheap domestic IA’s like the Cambridge Audio Topaz AM5, one’s likely to find a set of ‘rec out’ sockets, but seldom ‘line out’ or ‘sub/pre’ sockets. I understand these are all vastly different levels, and I’m looking to connect a ‘line in’-only active subwoofer (no high-level speaker in/through) to said amplifier. I would like to know what sort of device (an attenuator/resistor perhaps) I’d need in-between the two components, in order to connect the sub to the ‘rec out’ sockets as if they were line-level.

    Thanks heaps!

    • Hi Jacques,

      On most domestic amps, line out and rec out are the same thing, and the same level. Domestic line level is normally -10dbU. This is what most domestic subs would cope with also.

      The home theater amps which have a “sub out” would also be at this level – but they are normally filtered to send only the “sub” frequencies to the sub. If your sub has a built in cross-over, then all should be fine.


  18. Hi Geoff,
    I would like to connect the output of my Fishman Platinum Pro Eq bass preamp (used with a piezo pickup on my double bass) to a Bose Soundlink iii speaker.
    Can I connect the 1/4″ amp output of the preamp to the 1/8″ aux input of the Bose speaker ?
    Can I connect the XLR D.I. output of the preamp to the 1/8″ aux input of the Bose speaker ?
    Is any of the 2 above scheme preferable ?
    What kind of cable should I use?
    Many thanks in advance for your advises.

    • Hi Pat,
      The easiest and best way to connect the pre-amp to the Bose would be from the 1/4″ output of the Pre-amp. This should be the correct level, and over short distances will work fine. The XLR output is more for connecting to a mixer (microphone input) over longer distances.

      You would need a cable with a mono 1/4″ plug on one end, and a stereo 1/8″ plug on the other.

      Hope this helps


  19. Hi Geoff

    I need to take a better look at your website when I have the time – right now I’m frantically catching up with spring yard cleanup and maintenance.

    One quick question for you. I’ve just retired from the military and living out of a duffel bag for a bunch of years. Dusted off my old Harmon Kardon stereo system to once again have quality sound now that I have a permanent residence again. Of course, the audio scene has changed just a tiny bit during the intervening years, and there are new audio toys out there.

    So, quick question: the RCA cable inputs on my old receiver are phono, aux, Tape 1, and Tape 2. The first three are already occupied. Do all these circuits work at the same input levels? i.e. can I run an RCA cable from my TV audio out into “Tape 2”? If not, I guess it is time for an RCA male to female splitter cable for the “aux” input?

    • Hi Rick,
      In your case, the answer is yes. You can connect your TV to tape 2. Aux, Tape 1 and Tape 2 are all designed for line level. The phono input is the exception, it is designed for a much lower level, and if you plug a line level into that it will be very distorted.

      If you still need more inputs, you are better off getting a AV switch, like one of these.

      hope this helps


  20. Can I ask a question not sure how this works but in reading this article I think I know the answer but I want to know if I am putting my stereo at risk. I have a factory radio that has an input for a video dvd aftermarket player installed in the roof it has an option for an additional line in(rca)with red and white as well as a video (yellow) line level inputs. My son got a cable that converts the earphones out of his iphone to the rca inputs on the dvd player so he can play music from his iphone through the stereo. Is the voltage coming out of the iphone headphone jack going to burn out or up my stereo/dvd player if he plays music this way.

    • Hi Brent,

      I think you are right, it should work fine. An issue with using the headphone socket is the level out will be dependent on the volume level of his phone. Mostly phones aren’t capable of sufficient level to overload the line level input. The easy way to tell is if you hear any distortion. If you do, then turn the phone down and the radio volume up to compensate.

      I like to try to use the phone volume to adjust the output level so that the volume is the same from the phone as from the radio or CD. This way there are no loud surprises when changing from one source to another. Once you have a good level from the phone, always set its volume at that level and all should be good.



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