FET Mixer

Calculate the gate voltage resulting from the voltages at IP1 and IP2 and then you'll understand. (There is no current into the gate.)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

...and then pickup a copy of the Art of Electronics if you want to calculate what the gain is going to be. (Hint: It's approximately R4/R3)

I'd be quite inclined to capacitively couple into those resistors, then add a third one to a bias source of _my_ choosing, rather than depending on some unknown audio input to have something suitable.

Graham, That's rather rude. Didn't get any last night ?:-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

I wasn't commenting on the mixer, just the "Ppl who are clueless realy (sic) shouldn't post their ignorance on the net".

I have no problem with students who are asking a non-homework question. There are no stupid questions, just stupid answers.

I DO have a lot of problems with rude, pushy, IGNORANT punks, or is it pukes, like that TokaMundo.

...Jim Thompson

I probably already have him permanently kill-filed, just like TokaMundo.

...Jim Thompson

Hello Joel,

...and don't forget that the FET needs a DC bias. Capacitively coupling both audio sources into the resistors would not be a good thing here...

Regards, Joerg

He is right, though. Bad mixer, but maybe OK combiner if he puts some bias on the FET. I am somewhat concerned about one source back driving the other one. Op amp would be better, unless he is going to build 8 million of these.

Tam

You haven't run across Doctor Slick, have you ! .

Tam

I gather you are trying to add/combine the two signals, not mix the frequencies. Your schematic implies the inputs come from current sources; in that case you want to have a buffer with a very low input impedance, like the (-) input of an opamp, not a high input FET.

Tam

Hello Tim,

That is how I would do it as well. Unless the inputs are XLR transformer coupled and the xfmrs are on the circuit.

Regards, Joerg

"redhat" schrieb im Newsbeitrag news: snipped-for-privacy@g44g2000cwa.googlegroups.com...

Hello "redhat",

There is a big misunderstanding about the word "mixer". When people coming from audio talk about a mixer, then they only want an "adder". This means the circuit adds the signals of two sources. It can be done in the most simple way with just two equal resistors as it's done in this circuit.

When we can neglect the source resistance of the audio sources then the result is: Vout=(V1+V2)/2

The FET in this schematics just acts as a buffer to get a low output resistance. It could be replaced by any kind of transistor or an opamp if some small circuit modifications will be done.

Best regards, Helmut

Thank you all for your help. TO GRAHAM MAY BE MY QUESTION DECLARED IGNORANCE BUT YOUR POSTS DECLARED ........ . YOU HAVE SENT 6 POSTS, ONLY ONE OF THEM IS ABOUT THE TOPIC, DO YOU ALWAYS SEND ANYTHING WHITHOUT THINKING OF IT FIRST? TRY TO USE YOUR WIDE KNOWLEDGE TO HELP OTHERS, YOU SHOULD BE ASHAMED OF YOUR BEHAVIOUR WHICH REALLY INCREASES THE IGNORANCE THAT YOU HATE. Thank you all for your help.

Thank you all for your help. TO GRAHAM MAY BE MY QUESTION DECLARED IGNORANCE BUT YOUR POSTS DECLARED ....... . YOU HAVE SENT 6 POSTS, ONLY ONE OF THEM IS ABOUT THE TOPIC, DO YOU ALWAYS SEND ANYTHING WHITHOUT THINKING OF IT FIRST? TRY TO USE YOUR WIDE KNOWLEDGE TO HELP OTHERS, YOU SHOULD BE ASHAMED OF YOUR BEHAVIOUR WHICH REALLY INCREASES THE IGNORANCE THAT YOU HATE.

Quite badly I suspect ! Ppl who are clueless realy shouldn't post their ignorance on the net.

Graham

Please *do* explain how R4 and R3 affect the gain !

Note it's an n-channel fet. R4 is simply a waste of space.

It's basically a source follower Gain =~ 1 with an input attenuation of 6dB ( presume R1 = R2 ) caused by the passive summing.

The output will need to be ac coupled too. I won't even start on the indeterminate input biasing.

Graham

Pfftttt... ! Silly boy - lol . ;-)

Keep them coming.

Graham

It was mean to sound humourous actually, on account of how the question was phrased. Sorry if it missed the spot. We have this rather 'dry' sense of humour in the UK that you guys sometimes find trouble tuning in to it seems. Different culture I suppose.

It *is* a truly awful example of an incomplete and bad circuit though !

Graham

p.s. and no I didn't. :-( Peggy was meant to ring back but got 'diverted' it seems.

doesnt stop me......

martin