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How To Make Your Own Audio Signal Injector

By Jestine Yong on June 23, 2017

Recently I had some extra time thus I had built one Signal Injector which can make troubleshooting easier for Audio System and Amplifier Devices.

By googling on the net I found one handy circuit diagram which works on 1.5V only.

See the diagram:-

I have arranged required parts from my storage box

And now time for assembling. Components arranged one by one and soldered accordingly, now it is time to cut the PCB to the size.

Now it is time to connect power source hence I have arranged one broken Calculator from my junk box and cut the battery holder from it.

And here is the finished the job:

Now Signal Injector is ready to use. Just add the 1.5V battery and connect the earthing wire to the grounding circuit under test. And start detecting the signals one by one from speakers towards volume control section as you touch the test probe on the components it will gives beep sound from the speaker that means up to that stage everything is OK.

This article was prepared for you by Yogesh Panchal who works as a Computer Hardware Engineer in Mumbai India.

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30 Comments

Albert van Bemmelen

June 23, 2017 at 4:40 pm

Thank you Yogesh but I already made one exactly like yours about 25 years ago.
It is hardly been used eversince because Audio is not my field of interest anymore. And other test devices had taken its place. It still will be interesting for beginning electronic engineers like we were.
I however placed the multivibrator circuit in a defect electrical toothbrush housing. That originally also has space for a NiCD/NMiH 1.2 V battery. And the metal 'rotor' where the brush normally would be placed on serves as probe. And by adding a little external charger connector you also easily can recharge it. Or just use the original Toothbrush charger station. I even believe it produces harmonics upto about 30 MHz. But do not take my word for it if it doesn't.

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- Yogesh Panchal
  
  July 3, 2017 at 4:07 pm
  
  Albert,
  
  Thanks for your comment.
  
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  - Albert van Bemmelen
    
    July 8, 2017 at 9:53 pm
    
    If you have a Philips model HP735/A electronic toothbrush (200-240VAC charger model) at home with a worn out motor it is ideal for making a recheargable audio-signal-injector with it.
    
    The electronic controller board that drives the motor even can be used to switch on/off the signal injector board. Just remove the bad useless motor and use the injector board in its place! You only have to add a ground connector pin on the outside to connect it to the gnd pin of your audio device under test. But that is easy because the ground bolt with screwnut fits just fine when you drill a hole on the sides where the inside plastic leaves the most space. And it works great. (I know because I made one!).
    
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    - Albert van Bemmelen
      
      July 9, 2017 at 2:11 am
      
      But for putting a led to work on the mentioned Philips ex electrical-toothbrush as indicator you'll probably need a little Joule-thief circuit in order to pep up the low 1.2V NiMH/NiCAD voltage to about 1.8V before the Led will work. Or a small voltage step-up converter chip.
      
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      - Albert van Bemmelen
        
        July 10, 2017 at 12:23 am
        
        And if you have a Philips HP510/A electric toothbrush it probably is exactly the same useable device for a signal injector. Mine works fine with the original 1.2V Toothbrush battery and charger. No need for 3V DC supply.
        
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        Reply
stanley

June 23, 2017 at 4:46 pm

how does this work

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- Yogesh Panchal
  
  July 3, 2017 at 4:08 pm
  
  Dear Stanley,
  
  Just read the article once again.
  
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S Ramachandran

June 23, 2017 at 7:08 pm

good one and handy while trouble shooting channel issues ..

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- Yogesh Panchal
  
  July 3, 2017 at 4:09 pm
  
  Thank you sir.
  
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Mike Zook

June 23, 2017 at 7:19 pm

Good job Yogesh. Simple and easy. Cool. Thanks

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- Yogesh Panchal
  
  July 3, 2017 at 4:19 pm
  
  Mike,
  Thanks for the comment.
  
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JimKo

June 23, 2017 at 11:33 pm

This is a Multivibrator, square wave output. One thing I would insist on is placing a 1mF bipolar or disk capacitor in line with the probe, otherwise any voltage coming in through there will blow your device.

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- Yogesh Panchal
  
  July 3, 2017 at 4:19 pm
  
  Jimko,
  
  Thanks for your feedback.
  
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Parasuraman S

June 23, 2017 at 11:49 pm

Good job and time pass!

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- Yogesh Panchal
  
  July 3, 2017 at 4:20 pm
  
  Thank you sir.
  
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  - Romeo
    
    July 16, 2017 at 6:31 pm
    
    Good day.Mr Yogesh this article is great for newbies like me.I built it but don't know how to use it,can you kindly explain to a level that I can I stand please.
    
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    Reply
Mihai

June 24, 2017 at 12:58 am

Thanks for sharing Mr. Yoghes !

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- Yogesh Panchal
  
  July 3, 2017 at 4:21 pm
  
  Mihai,
  
  Thanks for your comment.
  
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mahmoud_tajpour

June 24, 2017 at 3:17 am

Hi Panchal I made one of this and I am using thank you Sir.

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- Yogesh Panchal
  
  July 3, 2017 at 4:22 pm
  
  Mahmoud Tajpour,
  
  Congratulations!
  
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  Reply
romeo

June 24, 2017 at 3:57 pm

IN CONNECTION WITH ARTICLE How To Make Your Own Audio Signal Injector.

WHEN I'M DOING IT HOW WOULD I TELL THERE IS A SIGNAL COMING OUT? NO LED OR SPEAKER TO PEAK SIGNAL?

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- Yogesh Panchal
  
  July 3, 2017 at 4:28 pm
  
  Romeo,
  No need additional LED. if you have in build speaker in audio system then you will get the buzz sound from the same speaker because you are injecting the signal through this device.
  
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Robert Calk

June 25, 2017 at 2:23 pm

Good job, Yogesh. Thanks for sharing.

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- Yogesh Panchal
  
  July 3, 2017 at 4:28 pm
  
  Thank you sir.
  
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Matsuokai

June 25, 2017 at 11:57 pm

Dear Mr. Yogesh, sincerely I made those signal injectors in 1972, using germanium transistors 2SA75 or similar, simply because they could work at low voltage of 1.5V. Later, about 1980s onwards, I made a lot of those from music chips taken out from greeting cards and broken Chinese toys, to gift my pupils. They cost mostly 0$ and so easy to build w/o much effort, and with coin battery they were very thin and compact, providing real sound/song rather than buzzing tone. Anyway thank you for waking up my memories with your share. Cheers.

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- Yogesh Panchal
  
  July 3, 2017 at 4:30 pm
  
  Matsuokai,
  
  Thanks for sharing your experience.
  
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ramli

June 27, 2017 at 10:33 am

good job sir...tq.

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- Yogesh Panchal
  
  July 3, 2017 at 4:30 pm
  
  Ramli,
  
  Thanks for the comment.
  
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Humberto

June 27, 2017 at 12:56 pm

Good tool Yogesh.

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- Yogesh Panchal
  
  July 3, 2017 at 4:31 pm
  
  Thanks Humberto.
  
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