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I want to build a voice changer that takes its input from a line out? Answered

Hi
I want to build an "in-line" voice changer. There are loads of kits and devices to build one that takes input from a microphone but I cannot find an inline one at a sensible price.
I bought a Vellman kit - but this too has an on board mini microphone.

https://www.velleman.eu/downloads/0/minikits/manuals/manual_mk171.pdf

 
I was considering just replacing the mic with a line-in socket.
I will also attach a line out socket to the speaker output pins.

I have done some reading and it appears as if:
The mic output will be a few millivolts.
The line input will be 1-1.5v
So looks like something will go phut.
Can I just put a resistor in line with the line-in socket - and if so what size?

Any other thoughts on how I can do this with hardware (not software).

Many thanks
Steve


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user
SteveM290 (author)2018-02-11

Thanks for the advice.
I have finally made up the circuit. Tested OK with Microphone.
I then replaced the mic with the circuit :
C1
+Line level in --||----R1----+-- +Mic level output
+ |
|
+----R2----+
|
Ground (input)----+--------------- Ground (output)


R2=1 kohm
R1=10 kohm
C1=10 uF

It kind of works.
I get sound and can moderate it using the mic sensitivity trimmer and the output controls - but I get a lot of noise.
Its fine until activated - a bit of hum but thats all - but as soon as sound goes through it has a really loud electrical noise.
I am a complete novice and just copying what I am told.
What can I try?
Do I increase resistance in +ve side? Double it?
Or is the -ve side.
If I reduce the mic sensitivity (now line input) it gets better but then I can't get any volume out - so then I think, reduce resistance.

Note - when I had the mic attached it did similar when I had a bad solder on the mic case earth.
Any thoughts most welcome....

Thanks
Steve

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steveastrouk (author)2018-01-10

It means don't connect the line in directly to the pin after your resistance network, keep the capacitor shown in the circuit

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Downunder35m (author)2018-01-09

What you need is called impedance matching.
But that can be quite tricky in modern days when an elecrete microphone is used instead of an old school magnetic type.
Modern mics provide a change like an adjustable capacitor, old ones produce an actual voltage signal.
IMHO the best way would be to check where the mic signal goes and is amplified.
At the point where it turns into a real signal you can use a matching connection to your line input.
In case that is too much you can check this website for a more direct approch using just resistors.

http://www.epanorama.net/circuits/line_to_mic.html

Just too lazy to paste all the stuff here ;)

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SteveM421 (author)Downunder35m2018-01-09

Thanks for this.
2 resistors and bit of wire.... ;-)

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Downunder35m (author)SteveM4212018-01-09

Keep in mind that just because it looks it easy does not mean it is ;)
Best to check the levels with an oscilloscope before soldering it all together.
And as always: Start with the lowest volume to prevent damage.

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SteveM290 (author)Downunder35m2018-01-10

I'll use the largest resistor sizes and keep volume down to start.
I don't have a scope and wouldn't know what to do with it.
I have multimeter - a decent one.

Thanks

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user

And the input is AC coupled.

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iceng (author)SteveM4212018-01-09

If you are skilled the resistor end wire will do it easily :)

Unless you are using SMT devices..

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