TL084 to???

[Mooly]

To replace any of the pots you need to keep the total resistance of the two fixed resistors the same or very close to the value of the original pot.

You connect the two resistors in series in place of the pot (it's outer pins).

The junction of the two resistors goes to where the middle wiper pin connected.

Set the pot in the position you want to fix first, then carefully isolate it and measure the resistance from the middle pin to each outer pin to determine the value of fixed resistors to use.

 

[troystg]

Thank you. I was hoping to figure it out without uninstalling it. First world problems...

 

[troystg]

And we have liftoff..

The new circuit does work and I am in the process of integrating it with the amplifier modules.

But a quick question on the "shelf filter" circuit.

Attached is what I think is the shelf filter to give the circuit it's 12db/oct boost below XO frequency.

If I open/remove the capacitor will it be just a gain stage? I need to defeat the boost/shelf function for a test but want to be sure first.

Thank you in advance. View attachment 835663 View attachment 835665 View attachment 835666

Yes, just a variable gain stage.

I took out the capacitor and the shelf filter is gone. Fixed the low boost condition but apparently it needs SOME low boost, just not as much.

I will put the capacitor back in but I will change the resistor in this circuit with a variable resistor to adjust the level of the shelf filter.

If I put a pot in the place of the resistor and tie the wiper (output) and ground together it should be just a variable resistor going from zero Ohms to 10K Ohms correct?

That will make it a variable LEVEL shelf filter and then I can change the +15-20db of boost at 20HZ to something more manageable like +3-6db...

 

[Mooly]

To replace the resistor with a pot only needs two connections, wiper and one end one but don't forget to connect the opamp input correctly.

I can't just visualise how a pot wired like that will affect the response but it will change the turnover point. As you reduce the gain by reducing the resistance then the turnover frequency will rise.

 

[troystg]

Thanks again mooly!