mfos mono mixer

synthesist

hey,

arent all these stages of the opamp in the schematics inverting?
I`ve always thought if the input signal is postive, the output is a negative voltage.(if it is an inverting opamp)

Since there is a second inverting stage, the headphone-out should change to positive again. But what about the line-out?

I must be totally wrong. Can someone explain me, before all my beliefs turn out to be wrong and all of my doubts are turning out to be true...

Sorry the direct link is not working.
At the MFOS site click/ MFOS oldies but goodies/mono mixer 1

http://www.musicfromouterspace.com/mfosweb/navigate.action?MAINTAB=SYNTHDIY&TOOLSURI=ELECTRONICS/WEBSCHEMATIC/index.html&PROJARG=SOUNDLABMINISYNTH/page2.html&CATPARTNO=DELAYMOD2011

blue hell

synthesist · Posted: Mon Oct 17, 2011 11:47 am Post subject:

thanks for the answer. I think I want to build this one next.

But just for my comprehension:
there is no positive AC flowing into my speaker-amp. It is reversed now?
the speaker-amp is feeding the mixer-circuit with pos. AC and gets back the "ground" from the mix. circuit?
This works?

I`d really like to learn more about electronics, but I have to wait till next year when a class starts.

diablojoy · Posted: Mon Oct 17, 2011 2:31 pm Post subject:

The AC signal is ideally centered around 0 volts
if there are no gains through the mixer
when the input signal is at say +5 volts the output
signal will be -5 volts and vice versa
the output signal is the same as the input just 180 degress out of phase
to it, overall the signal is still centered around 0 volts and over time the AC
signal can be considered to be neither positive or negative
The statement a positive AC signal would imply there is a positive DC offset to the AC signal which would be inverted to a negative offset at the output. this can occur but is in audio terms not desirable as in the case of an amplifier driving a speaker any DC offset component in the signal will
have a detrimental effect on the speakers coil, at a high enough level this will effectively turn the speaker coil in to a heater which they dont like being at all this is why audio mixers should be AC coupled so that any DC
component is effectively blocked , a CV mixer on the other hand will allow both DC and AC signals through as there is no blocking capacitor involved and in this case it is generally preferable not to have an inverted output.
hope this helps