AM modulator

E

exxos

Guest
Hi all,

Im trying ot build a very simple AM modulator with a small op-amp, bascially
the carrier is fed into the amp input (as normal audio) then im using a
transistor to alter the other input side in attempt to alter the volume, I
can't however for the life of me get it to work.... I've also tried a
resistor in the carrier line, then pulling the output side of the resistor
down to ground with the modulation wave, this to me should work though no
matter what I do it just dont seem to work at all :(

has anyone got any simple solutions to this ?

thanks
 
exxos posted:

<< Im trying ot build a very simple AM modulator with a small op-amp, bascially

the carrier is fed into the amp input (as normal audio) then im using a
transistor to alter the other input side in attempt to alter the volume, I
can't however for the life of me get it to work.... I've also tried a
resistor in the carrier line, then pulling the output side of the resistor
down to ground with the modulation wave, this to me should work though no
matter what I do it just dont seem to work at all :(
--

I believe something is missing, and the OP may not work at the Carrier
frequency.

What frequency is the carrier? What means are you using to multiply the two
signals. What type Op Amp?

Don
 
Have a look at: http://www.onsemi.com/pub/Collateral/MC1496-D.PDF
 
exxos wrote:
Hi all,

Im trying ot build a very simple AM modulator with a small op-amp, bascially
the carrier is fed into the amp input (as normal audio) then im using a
transistor to alter the other input side in attempt to alter the volume, I
can't however for the life of me get it to work.... I've also tried a
resistor in the carrier line, then pulling the output side of the resistor
down to ground with the modulation wave, this to me should work though no
matter what I do it just dont seem to work at all :(

has anyone got any simple solutions to this ?

thanks
-------------
Click to expand...
Look up "Gilbert Cell" and VCA.

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public
 
thanks everyone, ive got some ideas of more things to try now,

chris
 
"exxos" <exxos@home.co.uk> wrote in message
news:418bc86d$0$2305$cc9e4d1f@news-text.dial.pipex.com...
Hi all,

Im trying ot build a very simple AM modulator with a small op-amp,
bascially
the carrier is fed into the amp input (as normal audio) then im using a
transistor to alter the other input side in attempt to alter the volume, I
can't however for the life of me get it to work.... I've also tried a
resistor in the carrier line, then pulling the output side of the resistor
down to ground with the modulation wave, this to me should work though no
matter what I do it just dont seem to work at all :(

has anyone got any simple solutions to this ?

thanks


This modulator circuit is very simple. As the gain control voltage is varied
Click to expand...
from 10V to 0.5V the gain drops from 100X to nothing. (Pretty much any small
signal transistor will work).

Gain Control
.-----o 0.5 to 10V
|
.-.
| |
2k2| |
'-'
Audio In ___ | ||
(say 10mVpp) .-|___|------o---||----o Audio out
| 470k | || 0 to 1Vpp
|| ___ | |/ 47uF
o-||--|___|----o----------|
|| 1k BC546 |> o
o 47uF | |
| | |
'---------------------------|---------'
===
GND

(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)
 
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