Is the MXR filter Faint by default??

[chicago_mike]

Is it kinda a low ouput device without the cap mods for the input and output?

I also have a schematic of the Emma Discombobulator and am thinking of making the input and output parts of that guy. Its just one BC549 for in and one for out. I dont know though if it creates any gain rather than just buffering.

But my pedal does filter, it just takes a rediculously strong signal to activate the filter.

Im using this on my basses, wich are all active ( Laklands!!!!!!!!! ) and have LOUD output. Seriously LOUD. And the best Low B on the planet. Enough selling...

[Mark Hammer]

Actually, it is unity gain by default, so you should not be asking yourself "Why is it so quiet?"

More than likely, it is a case of mis-biasing.  There is a resistor pair made up of a 62k and 100k resistor, that divides down the supply voltage to provide a bias voltage that makes the HF clock work.  Some brands of 4069 like whatever bias voltage the 5% resistors you used produce, and some don't.  This has led to all sorts of speculation over the years about which brand to use.  You can drive yourself crazy trying to find the "perfect" brand, or you can simply adjust the bias voltage.

Consider replacing that 100k resistor with an 82k fixed resistor and a 50k trimpot in series.  That will let you adjust the resistance to ground from 82k up to 132k, which will provide a sufficient range of possible bias voltages to work with probably any 4069 out there.

[chicago_mike]

That damned r16/14 again! 

[Mark Hammer]

Yep.  I've owned a few of them (bought my first in 1977 or 78) and built a few.  I've never had to futz around with the biasing myself.  Just plain lucky, I guess.  The photocopy I made of my first MXR one shows RCA chips.  Do they even MAKE them anymore?

[chicago_mike]

I have RCA, Fairchild, ST, Toshiba...etc...

[Mark Hammer]

The one which is more sensitive to the biasing issue is the one used for the clock, which on the Tonepad A-Gua layout is IC2.

[chicago_mike]

IC 2 gotcha.

Ty.

[chicago_mike]

IC2 gives me sine, square and triangle wave forms. So thats good at least.