Mixing circuitry especially with spring reverb - diyAudio
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Old 27th July 2009, 09:29 PM   #1
akis is offline akis  United Kingdom
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Join Date: Jul 2008
Default Mixing circuitry especially with spring reverb

I had thought that mixing two signals together was dead easy, simply merge them through R resistors at least times ten then input source impedance and then follow them with a buffer stage stage of at least R times 10. That means the buffer stage sees 50% of each signal (assuming two sources) and additionally as R is times 10 the input source's impedance, the voltage drop across it will almost eliminate any back feed from one source into another.

That is how I understand it in my amateurish thinking.

Looking at a few reverb schematics (one from my Fender princeton chorus amp), it appears there are more issues at play than how I described it above. It seems there is some play with "ground level" and I am not going to try and describe it because I will surely mess up.

Could someone please explain it to me in simple terms and big pictures?
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Old 29th July 2009, 02:55 PM   #2
akis is offline akis  United Kingdom
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/bump in case someone can help
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Old 30th July 2009, 12:20 PM   #3
teemuk is offline teemuk  Finland
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Join Date: Nov 2004
Location: Suomi, Finland
If I'm looking at the right schematic(s), I see just a simple inverting opamp stage using two inputs, hence becoming a "mixer". e.g.
Click the image to open in full size.
Roughly, the ratio of the input resistor and feedback resistor defines the gain per each input. I suppose the signal can't bleed to the other inputs either since the inverting terminal is effectively a virtual ground.
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