Installing an Auxiliary input on any Stereo

Maybe you have an old boombox, cassette tape player or old car stereo lying around, and would like to connect your portable music player or another modern device. We will implement an auxiliary input to do that.

This project requires basic electronics knowledge. If you don’t have practice with electronics, ask a friend with experience to help you.

Required Materials

  1. Old Stereo, car cassette deck, or car cd player.
  2. iPod, mp3 player or whatever source you use to listen music.
  3. Stereo cable with 3.5 mm plug
  4. Double Gang potentiometer (on some cases you can scrap it from the same stereo).
  5. Two ceramic capacitors, start with 0.1 uF
  6. Soldering Iron, screwdrivers, etc.


My example device is this Sony boombox. I like it because sound quality is decent, construction quality is greater than average (It was made in Japan) and can operate with batteries, which is a very nice feature for camping or pool parties.

First unplug the device and take the cover off.

This is how the main board looks.

On devices designed to operate with 110/220 VAC you will see a separate circuit board that steps down and rectify the voltage coming from the wall. Ir’s very easy to spot due the big transformer. We don’t need to touch it.

Going back to our main board, let’s take a quick look to the theory. The signal generated by either the Radio Tuner or Tape player is sent through a volume and tone control. Then the signal reaches a Power Amplifier that (as the name suggest) amplifies, “boosts” or “magnifies” the signal enough to make a speaker vibrate and produce sound.

We will inject the signal coming from our mp3 player directly on the amplifier input, and disable the other parts of the system. As the existing volume control will be removed, we will need to include a new one.

In theory we could keep the other functions, but that would require an isolation transformer and not all people may have access to them. So, let’s keep the guide at the bare minimum.

Finding the amplifier

Now we need to locate the amplifier chip. It’s easy to spot because it’s (normally) under a metal heat sink. Each chip is labelled with a code. Click on any picture to enlarge.

Getting the amplifier Datasheet

Google the code printed on the chip to make sure about its identity. We are looking for the “amplifier” or “power amplifier”, not “pre-amplifier”.

Don’t forget to put word “datasheet” after the name. A datasheet is a document that describes all the functions and usage of an electronic component.

Once you located the datasheet, take note of each pin number and its function. Some old datasheets are harder to understand, like the following  (TA7282)

Newer datasheets are far cleaner and self-explanatory for the beginner. The following example belongs to a modern integrated circuit.

Determining the necessary pins

Using the information from your datasheet, locate the required pins on the amplifier circuit board. The following pins are required for our project:

  • [NON INVERTING INPUT A] (corresponds to the left channel input)
  • [NON INVERTING INPUT B] (corresponds to the right channel input)
  • [GROUND]

At the same time please be careful with the following pins, find and mark them. Do not connect anything to them or your music player will be severely damaged!

  •  [V+]
  • [V-]
  • [OUTPUT A]
  • [OUTPUT B]

Coupling the new Signal

Take your stereo cable with 3.5 mm plug and peel the end exposing the wires. You will find tree smaller wires, they correspond to the left channel, right channel, and ground.


Before soldering the cable on their corresponding amplifier pin place a small value ceramic disc capacitor (like 0.1 uF or 0.22 uF). Repeat the same on the other channel.

If this sounds confusing the following picture explains it graphically.


After soldering the respective cable on its amplifier input pin, notice that the pin is still connected to the other original components on the circuit board. We need to scrap both the right and the left channel tracks. You can scratch the track using an x-acto knife or box cutter.

Remember not to scratch the track going to the Ground Pin, the amplifier needs it to work.


The volume Control

The volume control it’s very easy to implement, you only need a dual gang potentiometer (two potentiometers will also work, but controlling the volume would be messier).

On the following drawing both are the same circuit. The first drawing shows how the right channel is wired to the “top” potentiometer, and the second drawing shows the left channel and the “bottom” potentiometer.


This is how the whole circuit looks. Hell yeah!

If everything works as desired (I’m sure it will do!) install the new potentiometer and any cosmetic features.

13/08/2012 errata

I (incorrectly) stated that connecting the input signal to the tape player head was a good alternate method. Is not. Sound volume will be hard to control, requires an isolation transformer, cassette deck switches must be bypassed, and overall results may be frustrating.

Below is a picture of a car stereo where I employed the tape deck method.

The switch on the top is to “simulate” the presence of a cassette on the deck. An air fan was also installed.

As I said, using an isolation transformer (sold in stores as “noise suppressor”) will be necessary.

Spare you the annoyances, the main method is better.


92 thoughts on “Installing an Auxiliary input on any Stereo

  1. Would you have any advice for attempting this on a car radio cassette player (circa 1985)?

    I have disassembled it and found that its amplifier chip as a NEC uPC1185H2. I can not find any normal datasheets for it, only a rough schematic:

    It looks like the noninverting inputs are connected to Vcc (which doesnt seem correct to me).

    I also found another schematic which has different information:

    • Hello Ben!

      I had more look googling by the term “uPC1185H2”

      According to this diagram your input pins are 5 and 7 for left and right channel respectively.

      Ground would be Pin 12

      I recommend you to use a ceramic capacitor between each music player channel and its respective amplifier input, but I’m not sure about the value, some experimenting will be needed.

      Here is a picture of your amplifier to make sure we are talking about the same one

      If you have more questions I’ll be glad to help!

      PS: The inputs are not connected to Vcc, is just the square delimiting the amplifier package

  2. Hi felipe,

    From an old sony radio I would like to make a mp3 speaker, and I’ve got a question.
    Is it already clear what kind of capacitor is needed between de mp3-player and the amplifier? I really have no idea where to start searching and what value is needed.. the amplifier is a TA8207K from toshiba.
    Should the capacitor be placed Mp3player-Capacitor-volumecontrol-amplifier or after the volume control?

    Thanks a lot!

    • Hello Freek!

      I’m sorry, I’m not sure about the value because I found it via trial and error. A .1 uF may work, you can identify it by its label “104”. A 103 OR 102 may also work, listen to the sound.

      Remember that two identical capacitors are required, each one for a channel.

      The capacitor is installed just before the amplifier input pin, as physically close as you can.

      • All a “tiny” 0.1uF capacitor will do – is SURE “stop the dc from entering the circuit
        (via DC blocking action).

        However it will “never stop any ac signal (or up to “mains” current, if either device faults) from freely flowing between your “connected” devices.

        What a 0.1uF capacitor WILL DO though, is ensure that you NEVER get any “bass frequencies, passing through your “incorrectly modified” circuit either.
        As a CAPACITOR of that size, is normally used to bypass AC Ripple, in a DC power line, so that voltage peaks and dips are avoided, thus allowing MORE SENISTIVE (to ac ripple) dc devices to be supplied, from mains power supplies and voltage adaptors, by removing mains HUM (ac ripple) from the rectified pulsing DC.

        THAT – is what 0.1uF “caps” are (normally) used for.
        THEY ARE NOT USED: For “allowing full frequency audio signals to travel “unimpeded”, between two devices. (as they will seriously impeded bass tone signals).

  3. So I’ve been thinking about doing something like this to my 1990 accord with a factory tape deck.I’m pretty cheap and kind of nerdy. I would love to see a write up on how to use the tape inputs and use a switch to do that part of it instead of using a blank tape.

    • Sorry, that was an awful errata! Is corrected by now.

      I don’t recommend using the tape inputs. I have used that method on the past but it requires isolation transformers and tweaking. Give the method I described a try.

      • Felipe thanks so much for your help and…. input(bahahah). What do you think about using a double pole duoble throw switch so the device would be either on the aux function(that we are wiring in) or factory function? That way there would be no chance of feed back causing problems, you know as a safety measure, especialy if somebody else uses the car. I have also toyed with the idea of using small ( not really sure how small) diodes and turning the factory volume all the way down to kill signal from the factory unit and using the secondary volume(double gang potentiometer) for the aux jack as already disscussed. Do you think the forward bias required to get things moving through the diodes would effect sound control or quality in a negative manner? Any way,still
        need get the device out of the car. BTW I love this website. The home made laptop is probably one of the most ingenis things I have seen in a while.

      • Hahaha good Pun TheDude

        Your Double Pole Double Throw suggestion is actually a much better idea, because the naked 3.5 mm plug may touch a bare metallic surface inside the car (never though about that!). I will correct the guide.

        I understand your idea with the diodes (analogically to a water check valve) but unfortunately it cannot be done. Audio signals are alternating current (that’s why the speakers pop outwards and inwards while playing music) and rectifying them will “destroy” the information that is converted into sound. Keep also in mind that feeding D.C. to the audio circuit or speakers may burn them.

        As you already know the volume control works by simply shorting (in more or less degree) the audio signal to the ground. Unfortunately some knob settings may also create a low impedance path to the eyes of the mp3 player, burning it. In conclusion, although I made a couple of units where the original circuits where left untouched (and the mp3 player just overpowered them, like a charm), today I prefer to physically separate them after the bad experience.

        Hey, thank you very much by your comments! Since I started writing very few people actually asked for advice or gave feedback, and I was somewhat demotivated by that. I’m very glad I served you with my limited knowledge.

        Good luck man!

  4. Great website Felipe! I was trying to do this on my own when I came across your site and it gave me some good insites.

    I am trying to modify a Pioneer DEH-1300 CD/AM/FM player in my boat to accept my droid phone output. I would like to use the rear speakers which means I have to inject my input to the input side of the preamp which controls the fader controls for the rear speakers. I was going to use the radio left channel and right channel output lines as my injection point but saw your notes on needing an isolation transformer for a CD injection point and thought it would be similar for the radio output lines. I have access to an oscilloscope and was thinking I would use the dual gange potentiometers to match levels but wondered what the isolation transformer was needed for.

    I was also going to use a jack that will disconnect the radio lines when I plug in my phone so as to keep the radio functionality.

    Thank you!

    • What the “H&($” are you doing?
      YOU HAVE A HEAD UNIT, which is “already fitted”..
      CD Receiver with MP3 Playback
      ??? AS = WHAT IS THIS = HEY ???
      MP3/WMA Playback
      Bluetooth®/iPod®/Apps/SD Card/USB
      AUX Input: Front

      JUST USE A 3.5mm plug (here)
      And whatever plug your “droid phone output” uses>
      It’s called a MALE TO MALE cord-set.

      TRY THIS —
      (or any other brand) suitable plug/to/plug connection cord.
      THAT IS IT.!!!

    • Hello Tom!

      I’m sorry if I took a lot of time answering, I didn’t worked on the blog for a while. Maybe you already have completed your modification, but if you don’t here’s the answer.

      The isolation transformer is used to match the impedance between the cassete player circuit and your music player. The method is not very predicatble, and you may accidentally overpower the cassette player circuitry causing distorted bass and awful sound quality.

      In the other hand, injecting the signal on the amplifier pins is easier, Care must be taken to avoid overloading the music player with the stereo volume / tone control circuitity. It would be better to leave the rear speaker amplifier pins isolated from the rest of the circuit, and connecting them to the music player as described.

      Again, excuse me for taking so long. If I can help you in any way please let me know

  5. Would this still work if I stripped everything except for the main circuit board and the transformer? I would like to get rid of the cd player and tape deck, and make a little box to just house the bare minimum components so that I can hook up the speakers to my computer. Thanks!

  6. There’s already the 120 coming into the transformer. I’m messing around with a stereo very similar to the one in your tutorial–the amplifier chip has the heat sink on it already like in yours. The thing is, I will never use the tape player or the cd player again, so I will like to get rid of them completely. I was able to locate the input pins on the circuit board, and things are going pretty good. One thing I am really unsure of is whether or not it will mess things up if I pull off the circuit board that the cd player controls, input buttons, volume, etc. go to. I’m thinking it would be ok since I’m by passing the old input anyway. Thanks.

    • Oh, I’m sorry, for some reason I thought you were working with a car stereo, my bad. I’m 99% sure that there is no problem removing the cd player and the tape deck. However be careful when removing components, try it with each one at a time until all of them are gone. Some amplifiers have something called “Mute” or “Standby” function and the missing circuitiry may be required to take the amplifier out of that state.

  7. Thanks for this post. This is what I am trying to do as I am not an electronics guy.
    Sony CFD-S28, trying to disconnect the audio left and right of the CD player. I was able to find the ones for the tape deck, but the ones from the CD player I’m only getting a ribbons. I guess I could simply use the tape deck left and right and then solder to headphone speakers, but that means I loose the tape deck and I much rather not. The CD player can go as I don’t need it.
    Again, I am not an electronics guy and finding someone who is has proven difficult. I should have taken a shop class in high school! :( Anyways, you tube is great. There is even a kid that did this and others as well, but it seems that the CD player in their unit is just a regular wire that looks like my tape deck wire.
    Any thoughts might help if you have time. I even contacted a local electronic shop and they said they had no idea how to do it and it was difficult. What I was trying to do was not easy according to them.

    Thanks again


    • Hello Tracor

      I suggest you to take another look to the post. Messing with the tape deck is very problematic, never tried the CD player lines THO. Why you don’t try the amplifier approach that is described?

      • Hello
        I took a closer look at your approach. It does make more sense. Questions that I have are:
        1. The only amplifier chip I found was in the pre-amp –

        I am confused since as you said it needed to be in the amplifier and not the pre-amp? From the diagram, if it’s the correct diagram, are you able to locate the pins for the right/left/ground inputs?
        Thanks again!

      • Don’t worry, I’ll do my best to guide you!

        Yes, indeed, the chip that you found is not the one we need. The power amplifier may be hidden under a piece of metal, don’t give up until you find it.

        Tell me as soon as you find it

      • I think I found the chip, however it is inside a metal casing that if I try to remove will just destroy the circuit board. I will try to email you some pictures…

      • Do you have an email address where I can email you the pictures and the the datasheet manual I found online? Or is there a way to post pictures on this blog?
        Thank you…

      • Haha you will never believe it! but I have exactly the same model of boombox, if you see my post “fixing a hard to read LCD display” you will see it. I’ve used a different method for this unit because that damn heat sink was too hard to remove. If you give me a day or two I can take apart my boombox and tell you exactly here you need to connect everything.
        You can fill the e-mail field on the comment section, so I can find you on FB

      • Exactly Pyleck!! that was exactly what I did!! I also attached a switch to the radio board power line, to shut it down while the aux input was being used, but from your schematic I guess that step was completely unnecessary. I’m so sorry Christian, the university didn’t gave me time to take the pictures as I promised. Pyleck explanation is good enough, but I will take the pictures of the finished thing tomorrow to make it more clear. Thank you very much by your comment Pyleck!

  8. hi i have ben trying the same with a car casete unit i foun a chip where tape in1 and tapein 2 pins i atachtd ground to one and right to the other
    but my car plays only with back speakers when i change sound to driver it plays front speaker
    Can any sombady help me please

    • Hello! You must connect the IN 1 pin to one channel of your music player, and IN 2 pin to the other channel. The ground pin indicated on the datasheet goes to the ground of your music player plug. Don’t forget the coupling capacitor as mentioned on the post. Can you provide the chip name or a link to the datasheet?

  9. Hello, you have made a very nice post, but I am trying it on a 2000 ford taurus, it has 2 parts to the radio, one unit in the trunk, then a cd player and controls in the front deck. It is my fiancees car and im trying to do this for her birthday. Any info would help. So far ive bin able to identify the 4 wires that run from the front cd player to the tuner and amp in the trunk, could I just throw a dpdt switch on the lines to the trunk and connect the aux input and cd player to the switch?

  10. ….Also, could i wire a relay instead of a switch that gets activated when i plug in a aux cable? again any info will help greatly and I’m sorry for posting so late in the thread.

  11. Hello Samer!! Quite the opposite, I’m glad when people comments on the posts.

    I’m working on a small diagram for you right now. What type of wires are running to the trunk? 4 RCA cables?

  12. Here it is Samer, sorry by the low-budget graphics! You can get all the components on radioshack. I don’t know the english name for some of them, but using the picture you will easily figure out.

    To use it she just has to turn on the car stereo and set its volume to zero, then plug the iPod. Remember to reduce the iPod volume to a very low setting before connecting it, to avoid scaring her with a sudden loud music blast.

    PS: The “traditional way” would be adding a switch to independently turn on the amplifier to the trunk. But that approach requires more installation steps and she may forgot to turn off the switch when leaving the car, draining the battery dead.

    I personally tested the car stereo on a zero volume setting and works very well.

    • No it is a 20 pin plug, it is the stock radio. Ford set it up with the controls and cd player in the front, but with the radio tuner and amplifier in the trunk. Sorry for not getting to your reply sooner.

    • I have bin able to identify the 4 wires that come from that cd player in the head unit to the rest of the stereo in the trunk (left positive, right positive, left negative, and right negative) i was wondering if i can just cut those wires, put a switch on it to toggle between the cd and aux input. then just put a cd in the player hit play and then flip the switch to aux and “inject” my own music from the aux input. and if so, would i need any fuses or capacitors on the new lines.

      thank you very much for your diagram and for your time.

      i think what i am trying to do is what you posted in the top, except since her stereo is in 2 parts, i have wires instead of having to work with the board. and also im trying to put a switch on it so she can still use her stock cd player

    • I connected the 4 wires from a aux jack against those 4 wires from the 20 pin plug and it worked but played both the cd and the aux input, so I gave her a cd with a track that was silent to play. Everything is working fine for now, but I am concerned that it might mess up something, am I missing any fuses or capacitors? And is it possible to put a relay on it to disconect the line to only play aux or cd instead of both. Thank you very much for your diagram it wasnt exactly the same for her car, but it was close enough that it helped me out greatly.

      • wait wait wait! hold on, 20 pin plug? you didn’t described anything like that! now I’m lost. Can you make a small diagram of what you have?

  13. i tried making a diagram of what my system is like, but here is the best i can do,
    (ive never used tiny pic before so i hope the link works)

    i have put a aux in line against those 4 wires so it plays both cd and aux, but gave her a silent track on a cd to use till i can figure it out better.

    i cant just turn down the cd player since they are connected turning down the cd player also turns down the amp.

    thank you for your diagram, i was able to implement it into my system and it worked.

  14. I just don’t know much about this, so if there is a way to put a switch on it, id love to, and i don’t know if im missing any fuses or capacitors or any other type of safety so it wont kill the rcu and amp.

      • I can, but not till tomorrow, she took it to Texas and will be back tomorrow. Which is why I rushed and put it in temporarily the way I did. I’m sorry about all the confusion, I tried making a diagram, just to show the set-up.

  15. I figured it all out, i made a small preamp to make it as loud as the regular cd player, plus a small transistor to swap between cd and aux input when power from the aux in line was put into the base line of the transistor. but all of that would not of mattered if it wasn’t for your diagram to plug it into. thank you very much for all your help Felipe La Rotta.

  16. Pingback: Installing a rear auxiliary input | Cocodrilabs

  17. Hello, i have an old turntable which spins too fast, i tried to mend the problem several times without succes, so i’m turning it into an amp with an aux input for my ipod. I followed your first post but my amp circuit board only has four big transistors and no chips. It’s a fairly old turntable and i wasnt able to find any schematics for it. one more thing, it has two VU meters for the right and left channel and i would really like to see them work, is there any possibility that they wont work if i bypass the tone control and the other stuff according to your tutorial? VU meters are a kind of eye candy to me and i would really like to see them worki. I will gladly accept any help.

    • Hello Luka!

      I’m not an expert on turntables, but the ones I know require an external amplifier hooked to the speakers to work. The transistors you saw indicate that the turntable includes some amplification means (a pre-amplifier) intended to increase the signal coming from the needle. But that amplifier is not designed to drive spealers on its own.

      Regarding the UV meters, you can remove them and connect them on the speaker output of another stereo (in parallel with the existing speakers). I did the same thing on my stereo and work well. They will not give an acurate VU level, but they are still pretty neat to look. If you need further help for that step just ask



      • Hey, thanks for the advice.
        My turntable has an inbuilt amp, i can tell that from the output at the back, as i only need to connect a pair of passive speakers and it does play fairly loud. I’ve heard that Vu meters need a rectifier circuit to even move as the signal on the speakers is supposed to be low-voltage AC, and the VUs need DC or something like that. I’ve also stepped in contact with another person who told me to just attach the aux cable to a socket at the back which is an input for an external radio unit, and it is supposed to have two chanells and a ground. Its a five-pin input jack-something. I can get you a picture if you need. There is also a button which switches between the two devices and he said that i should test the pins with a screwdriver for noise and simply attach the aux wires to the pins that make noise. Is this also an option? i think you mentioned something about non-matching impendance possibly burning out the iPod and i don’t want to risk destroying a 200€ device with a 10€ one that doesn’t even serve its purpose :D

      • You are correct in all what you said. Recapitulating: the VU meter is connected in parallel with the speakers. If your VU meter doesn’t move, then put a 1N4148 diode in series with it (that should convert the AC signal into DC). A series resistor is also useful to avoid sending the VU meter out of scale everytime you crank the volume up. The value is found via experimentation, I don’t remember the value I’ve used, avoid using anything lower than the impedance of your speakers (I guess >8 or >16 ohm).

        As you already know you will need a diode and resistor for each VU.

        Now, if your turntable already have an auxiliary input don’t bother dismantling it! You can try the method your friend say, but I would do this instead:

        First, with a multimeter check that there is no voltage (either AC or DC) coming out from the connection to avoid nasty surprises.

        Then pick a couple of random leads from the input, one will be ground, the other will (hopefully) be the desired input. Don’t forget to ´put a small ceramic capacitor (0.1 uF) between the unknown input lead and your music source. If the sound works, keep the ground lead were it is and go searching the input lead for the other channel. If there’s no sound at all, pick other combination of leads and try again.

  18. I’ve done it, can’t thank you enough and the VUmeters also work, I also managed to calibrate them quite accurately. The sound is great and also all the tone controls and the balancer work fine.
    Thank you again :D

      • Hello, me again.
        I’ve encountered a problem and sorry because I keep bothering you.
        I’ve stripped the amp circuit of the turntable housing because it was quite damaged and bad looking, i was planning to move the entire assembly into another housing. The only thing i did apart form removing the circuits form the housing was extend the wiring of the potentiometers so they would be more flexible for the new housing. I turned the thing on while it was still on the table with some music playing by the aux. It was playing fine for a few seconds, i tested the tone controls and the balancer a bit, volume etc…. until the led diode, which indicates power ON went out and the sound disappeared. All i can get out of it now is some brum on the left channel if i touch the trebble potentiometer housing. What could have gone wrong?

      • Hello Luka! don’t worry man, is totally the opposite, I’m very glad when people comment on my blog. It’s kinda sad when you write about something and nobody discuss it (Imagine a “foreveralone” face next to my comment hahaha)

        Without personally seeing your turntable or having a schematic is very hard to tell what went wrong.

        I had exactly the same problem as you with a reel to reel recorder, Later I found that the original metal chassis served as a ground connection for all the components, and without it the circuit boards refused to work.

        If you are telling me that the turntable actually turned on before going dead, maybe it was a short circuit or a loose connection. Check all your wiring!

        You need to get a good multimeter. To discard the obvious failure points, test every stage of the system following their logical order. Let’s say, for example, on the power supply, start with the transformer, then the diodes, then the capacitors, then the voltage regulator, and so on. If you need to know how to test these components I can send you some Afrotech’s Videos, his tutorials are the best.

        If the problem is not your wiring or the power supply then things are more serious. To get a better advice, sign in on and ask on the “Repairing Electronics” section. Don’t forget to take good pictures of your turntable and the modifications that you made. These dudes are real experts and I’m pretty sure they will help. I have an account there too, so I’ll keep an eye on the discusion, maybe I’ll learn too!

  19. Hey,
    i’ve examined the circuits a bit, i also attached some pics. There is also one thing i noticed before the entire thing went out, which is that one of the chanels on the vu meter was pointing about -3 dB while the other chanel was always around -20 dB. Upon examination i found that two fuses were burnt out, both low amp fuses, i think, because their marks were 250/0,315, i think that stands for 0,315 amps?

    In the first picture the preamp is on the left, the pcb with the metal frame. On the top is the pcb with the balancers and the tone controls, it also powers the vu meters, which are visible below. The pontentiometers are in the middle with the extended wiring and the powerboard is on the right along with the transformer. Just above the transformer were five fuses of which 2 were fried. I also noticed one other thing, the bulb that illuminates the vu meters still works when i turn it on, and it is the only thing that actually works so I dont think that any components on the pcbs got fried beacuse the fuses actually saved them, so i reckon i won’t need any multimeter testing. so what could’ve caused the surge? i admit that i didn’t attach the grounding wire to the frame of the turntable, but i was testing it one more in the past with the gnd wire off the frame and nothing went out, so, what causes the low-amp fuses to burn out? the picture

  20. I’ve posted on the forum you suggested and i’ve been told that the power amp has probably burnt out the fuses, so something on the poweramp is porbably burnt already. Is there any hope left?

  21. Hi Felipe!
    so glad I found this forum, I tried to do this project on an old sony boombox with a sanyo LA 4597 amp card. I am only getting really quiet sound though, when I turn it up it just gets really distorted. What could I be doing wrong? I have the ground going to pin #4. and the inputs to #2 and #6 .

      • ok, I did what you suggested, but it is no different. when I play music very quietly (I have this connected to my pc at the moment), the sound is alright, but when I turn it up, it becomes distorted and does not really get very loud. I am trying to do this on a sony CFD-510, and I have disconnected the whole main board and the power supply. I also took off the potentiometer off the board, could that be a problem. at the moment I am sure that the amplifier is not really amplifying the signal. also, is it possible that maybe the right ground pin is #11 and not #4?
        thanks, Karsten

      • According to your previous comment your input pin selection was good, also ground.
        Taking the pot out of the board is not a problem since you are not using that circuitry.

        Ohhh! wait, I understood that you had disconnected the power supply pins on the amplifier. Please confirm me that. These pins are crucial for the amplifier to work since they deliver the current that the amplifier needs to operate.

      • I meant that I took the transformer and the main board with the power amp on it out of the stereo housing, the power supply is still plugged into the main board and the light for selection of cd/radio/tape lights up, only it doesn’t seem like the amp is getting power.
        is it possible that I hear something coming out of the speakers without the amp getting power?, like I am now? it is just a weak signal.

      • Do you have a multimeter? please take a read of how many DC volts are between pin 8 and ground. Also try temporarily shorting Pin 5 and pin 8 to make sure the amp is not in standby mode

  22. I meant that I took the transformer and the main board with the power amp on it out of the stereo housing, the power supply is still plugged into the main board and the light for selection of cd/radio/tape lights up, only it doesn’t seem like the amp is getting power.
    is it possible that I hear something coming out of the speakers without the amp getting power?, like I am now? it is just a weak signal.

  23. Hi I have a Philips rc 624 car stereo. I have found the amp, but the thing that confuses me is how should I wire it, it has four inputs and four outputs (Front Right, Front Left, Rear Right, Rear Left). How should I wire that? The amp is a “TDA7384”, datasheet: Also as other people already discussed I want to keep the radio and CD usable.

    I’m a newbie so please be detailed.

    • Hi..
      I hope you NEVER attempted to use that op-amp (TDA 7384)
      With this person’s incorrect “aux input modification
      As sadly :(
      There is no way your device (or THAT TYPE of bridge-mode IC itself),
      could to be used, via grounded RCA stereo inputs, from those outputs.
      Because IC TDA7384, is a MODERN DIGITAL (cheap and nasty)
      Being a 4ch at 35 watt “per (isolated) channel”
      (INTERNAL) BRIDGE MODE = 4x isolated outputs
      Digital IFGRS amplifier.
      (my short-form-term, for that: NASTY, & thus cheaply made, SYSTEM)


      That op-amp uses “internally bridged output amps, where the internal “bridge mode’ is already connected to ground earth>
      Any “attempt” to force any of those EIGHT “high potential outputs, to become low potential 0v chassis/ground bonded “returns”
      will blow the internal op-amps, AS IT WILL SET UP massive CIRCULATING CURRENTS, INSIDE THAT IC.
      There is no way to stop the run-away circulating current at that instant of time, until the bridge-mode “open circuits”, by blowing the IC apart.

      If all you GET when that happens is a shut-down IC & destroyed amp?
      Consider yourself lucky.
      If it explodes and goes on fire, (a burnt house is a distinct possibility).

      Only a “common grounded earth return” output stage amp
      Can be GROUNDED to a common return point by “connecting it to”
      Common “signal return” (earth/grounded) CHASIS MOUNT R/W RCA.

    • There IS only one way, to “connect” ANY of the internally grounded (bridge-mode-isolated) Floating Ground Return System’s isolated speaker output-circuit “device”, to any other aux input device.
      BUT — it involves the uses of TWO VERY CHEAP, signal isolating transformers.
      Easily obtained from electronic supply stores.

      Unlike what this “page operator” thinks.
      In fact, if NOT sure what “type” of output stage, your device is.?
      At least 3 k_ohm : 3 k_ohm CT “signal” isolation transformers.
      Or – (at worst case scenario) even the much more “common attainable” 600 ohm: 600 ohm (telephone line) isolation transformers will suffice.

      And if the input / output reactive impedance values need increasing (if needs be), these can quickly be added, by the simple addition of series resistors in the primary input leads, or in the three output leads of the centre-tapped (CT) transformer outputs.

      Using two 3K : 3K isolation transformers, instead of “speakers” (normally connected to any “floating ground return system’s speaker circuits) will normally suffice to KEEP the amps outputs WELL above ground potential (eliminating circulating currents in the internally bridged bridge mode IC amp, and also provide approximately the correct “input values” (for your modified aux input RCA’s – which you will use as the “internally selectable” switch function values, if swapping such as the radio signals with your “new” aux input signal wires.

      Also .. for THOSE with the ability to do this modification,
      Simply either “install” an additional “switch”, in ANY of the selector feeds, OR simply replace the selector switch itself, with one having ONE more selection?

      • Hi Tripello! It’s Felipe here (or blog’s operator, as you call it). Somehow your comment notification accidentally arrived at my e-mail. Sorry for not using my blog account, I don’t remember the login credentials right now. As you may have figured out, I had abandoned blogging some years ago. But I’m amused to see how much time, passion and effort you had invested on correcting this post. I must note that sadly my electronics knowledge wasn’t as great and almighty as yours when I wrote originally this (circa 2011), but please, don’t loose your calm. if you have some free time you could write your own corrected post. I can put a link to your article as soon as I recover my credetials. Let me know. Best regards, Felipe.

      • That’s OK ..
        I lose and find (many of) mine all the time.?

        Some I haven’t FOUND since starting them (blogs &/or entire websites even) back in 2002 to 2006 (ish)..
        Until I “trip over them” in a google search result (sometimes years later?)
        & With a..!
        Now when did I MAKE that one = THOUGHT – before a “where’s it’s passwords and ? Email address” even…)

        But somewhere an old “archived” email pops up.!
        Or if not, then there’s always a “password reset function somewhere”, and on a password reset, that simply “triggers an email (look an email from?) that I can “link back in through” & bingo, a logged-in “login”, that I promptly forget even as soon as a couple of days “after re-logging out”..?

        To not recover (some) for many years later again .. (or as soon as I need back in).

        Thus I’m sure you will find a way, or others will just have to google around some more too, (as I was doing – that day).?

        If not.. then simply go look at my other 14 TLD URL’s and some 250+ websites, blog posts chat room forum “inserts” – by my two usernames I now frequently use (as well as TRIPELLO and others ? I have way too many usernames to remember myself now.?

        So I won’t be trying to find your post to correct it, as that’s your page.

        Actually — IF.?
        If my “comment on your posr, arrived at YOUR current email address, THEN YOU ARE SWEET.

        It’s your “blog’s login administrator’s email address”
        Where wordpress notifies you of all new posts to that blog.

        All you need do – is CHECK YOUR DASHBOARD (for your current wordpress “blog” (or if you don’t wordpress any more, simply go to your “blog” select admin log-in and resend a password reset.

        It should arrive at the same email address, you got this notification on.

        Then simply “click the link in the email”, make a new password and WRITE IT DOWN (on the back of your hand, or o a notepad beside your PC, or in your kid’s playroom toy-box..
        I don’t care where you write it down .. just don’t forget it and your username/ email address.! ;-).

  24. It’s pretty amazing your tutorial but I have a problem I have a Matsushita AN214Q Amplifier and I have only one Input and two GND I give you the datasheet, I’ll wait your help ;___; please.

  25. Very helpful and exactly what i was looking for. In fact, i have the same sony boombox that i picked up from a thrift store for $5. Have you considered adding a switch for the scratched off leads from the amplifier so that using the radio function would still be possible?

  26. Thank you Luis for this post.

    I have the same Sony box that Karsten reported on, a Sony CFD-510. (Sanyo LA4597) Did you find out his problem? I would like to know before I begin the modification. Do you believe it to have been a stand-by problem? What precautions should I take before proceeding with the modifications, based on Karsten’s reporting? I am making the modification to go from a computer sound-card into the Sony. Any additional help you could give me would be appreciated. Thanks

  27. Thank you a lot, it works!
    P.S. I didn’t want to lose radio function, so i didn’t scratch left/right channel from circuit, but my stereo has got only Radio/Tape switch, no On/Off. So it only enable the signal (3,5mm jack) when is pressed play button on tape. So I removed whole tape part and find out that there is two wires that needs to be connected to turn on amplifier. I connected these two wires to a new switch, so when i turn this switch on, it playes aux and when i turn it off and turn original switch to Radio position, it playes radio.
    Hope it helps for people which have got only Radio/Tape switch too. :)

  28. I have a couple of thoughts. For the volume control, use a potentiometer with a logarithmic taper. dB is a logarithmic scale, so the volume knob will behave as you expect. If you use a linear taper pot, then it will be really hard to hit the volume that you want.

    It’s more work, but you don’t have to completely disable whichever source you’re hijacking. Instead, you can get a switched stereo jack that gives you the best of both worlds. What you do is identify the right/left signals and scratch the traces as usual. But then, you solder on jumper wires from the source, through the NC contacts of the jack, and back down to the amp. This creates new path that runs parallel to the old traces and has the jack sitting in the middle. Then, when you insert your stereo plug, internal switches are thrown and your AUX signal gets fed to the amplifier.


  29. Hello, first i thank you for the great article. I wanted to ask if by any chance do you know how can i locate the mainboard or the amplifier on a jvc ux-rc7? i can send pics if you want, just cant find the wiring online and the layout is a bit more complicated than i thought.Thanks.

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