Electronics > Beginners
Building a sound mixer within my guitar amp with line IN & mic input
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dazz:
Thanks for the info on the LTSpice pot simulation. I'll take a look now.
I modified an existing component to create my own pot with a parameter to pick the taper (1=linear, 2=logarithmic, 3=reverse log)
But it seems to be rather inefficient and transient runs sometimes get stuck when I have one in circuit.

Files attached
Zero999:

--- Quote from: dazz on June 15, 2019, 04:03:26 pm ---Thanks for the info on the LTSpice pot simulation. I'll take a look now.
I modified an existing component to create my own pot with a parameter to pick the taper (1=linear, 2=logarithmic, 3=reverse log)
But it seems to be rather inefficient and transient runs sometimes get stuck when I have one in circuit.

Files attached

--- End quote ---
I'll have a look later.

Did you look at the tutorial I linked to? Modelling a potentiometer from discrete resistors seems to result in a faster simulation and is more flexible, although the schematic doesn't look as nice with a symbol and it's a bit more clumsy to use.
https://www.eevblog.com/forum/beginners/simulating-potentiometers-using-ltspice/
Audioguru:
Your "Mic output" is a very low impedance from the output of a preamp opamp. When you connect it directly to the (-) input of the mixer opamp then the mixer opamp will have a gain of almost infinity for its high frequencies. You MUST include a series resistance to set its gain low.
dazz:

--- Quote from: Zero999 on June 15, 2019, 04:51:21 pm ---Did you look at the tutorial I linked to? Modelling a potentiometer from discrete resistors seems to result in a faster simulation and is more flexible, although the schematic doesn't look as nice with a symbol and it's a bit more clumsy to use.
https://www.eevblog.com/forum/beginners/simulating-potentiometers-using-ltspice/

--- End quote ---

I had a quick look, will test all those later today. The only reason I went with a custom pot is that it allows me to test different tapers simply by changing a parameter.


--- Quote from: Audioguru on June 15, 2019, 05:30:07 pm ---Your "Mic output" is a very low impedance from the output of a preamp opamp. When you connect it directly to the (-) input of the mixer opamp then the mixer opamp will have a gain of almost infinity for its high frequencies. You MUST include a series resistance to set its gain low.

--- End quote ---

Yes, that was an incomplete schematic. The resistor is at the output of the mic preamp. It's of the same value Rin as in the other inputs
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