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General Category => Your projects => Topic started by: trutrusisw on February 06, 2011, 21:26:28 PM

Title: Something like Frequency mixer
Post by: trutrusisw on February 06, 2011, 21:26:28 PM
I'm new here so Hello to everybody! :)
I'm a student and I'm working on a project- I have to make something like a frequency mixer to change the frequency of an audio signal with 5Hz, for example if we have a frequency of 160Hz I could change it to 165Hz. My idea is to mix it with a sine wave signal with frequency of 5Hz(I will make a sine wave generator) and to get on the output an audio signal with 165Hz. I have been searching for a frequency mixer scheme and I found some: http://electroschematics.com/393/fet-audio-mixer/   http://electroschematics.com/327/one-transistor-audio-mixer/  I wanted to try them but I didn't find the transistors at any store. I will appreciate it, if you can help me with a scheme of the mixer, of the generator or just with an advice.
Thank you for your answers!
Title: Re: Something like Frequency mixer
Post by: kam on February 07, 2011, 13:31:19 PM
unfortunately i have no experience in audio systems. maybe someone else from the forum could help?
Title: Re: Something like Frequency mixer
Post by: bob on February 08, 2011, 13:06:20 PM
Hi there friend,
take a look at the link below, your best bet is to implement an OP Amp and there are millions of them for all sorts of purposes.http://homepages.which.net/~paul.hills/Circuits/Adder/Adder.html (http://homepages.which.net/~paul.hills/Circuits/Adder/Adder.html)
From your question I think you want to add two different frequencies, is that right? If so, this neat example will get you started in understanding of adding and subtracting different frequencies. A mixer does something else.(In radio and TV communications a mixer at the transmitter end mixes "program" frequency ie; speech, music or picture , with a carrier frequency. At the receiver end detector "strips" and discards the  carrier and we can hear speech or music and see the picture.) I hope this helps.
Cheers. Bob

Title: Re: Something like Frequency mixer
Post by: trutrusisw on February 08, 2011, 18:41:39 PM
Thank you two kam and bob.
Bob I want to make an audio frequency larger with 5/10Hz. I thought that the mixer produces a total of two frequencies and my idea was to sum the audio signal with a sine wave signal generated from a generator with frequency of 5Hz and therefore to get a totaled signal from the audio frequency and the sine wave, but I understand that the mixer won't be useful. I looked at the link that you gave me and I think that I haven't understood something because the OP Amp adds or substracts voltage not frequencies.
Title: Re: Something like Frequency mixer
Post by: bob on February 10, 2011, 07:19:01 AM
Hi there friend,
you have found the solution yourself. Link below is your ticket. In fact, you can try any NPN transistor if you do not have BC109. Working with FETs requires great care, because they are easily destroyed by static charge. An oscilloscope is a must in experiments like these, preferably two chanal.

http://electroschematics.com/327/one-transistor-audio-mixer/ (http://electroschematics.com/327/one-transistor-audio-mixer/)

On the other hand, I think you should put together the OP Amp circuit I suggested, because it is quick to do, cheep, low component count and very easy to understand. Also, read again  your theory book to understand amplitude, voltage and frequency.
Cheers. Bob