Euro Steiner VCF Woes

w4z · Joined: Aug 27, 2009 Posts: 13 Location: Detroit

I finished my build, but I have run into a problem. I am curious if anyone has run into the same problem;
The overall volume of the filter is REALLY low, but the BP IN and LP IN are barely audible. Take into consideration that I have cranked my mixer up to max when testing this. I've looked over all the resistors and they seem to be in the right place. Every polarized component is in correctly.

I did the diode modification for 12v operation and it seemed to help the effect of the actual "filtering" but the volume is still insanely low.

If I replace the "RG" resistor value with one that is higher, wont I still be experiencing the lower BP and LP volumes?

thanks in advance,
-Waz Very Happy

andrewF · Posted: Fri Jan 15, 2010 9:08 am Post subject:

Assuming all else is okay and increasing Rg results in a decent output level, you can always use the input pot to reduce the level of the HP signal so it is on par with BP & LP.

w4z · Joined: Aug 27, 2009 Posts: 13 Location: Detroit

Ok I figured out my problem. I had the final op-amp chip in backwards.

But now its not really "Filtering" that much. No matter how I set the trimpots, the overall filtering is very weak. Do I need to make the trimpot modification?

this one;
On the overlay above two resistors are marked in different colors. If you find you have insufficient resonance, replace the 2k2 marked in red with a trimpot in the range of 2k to 4k7. You should now be able to adjust the resonance to a suitable level. This may be needed to compensate for variations in transistor gains.

What about the second modification? This one;
The resistor marked in blue can be replaced with a trimpot in the range of 2k to 4k7, its purpose being to set the minimum resonance resistance. It's function is not dissimilar to the trimmer mentioned above. It is most likely to be used to offset the range of the pot. It is also best if the trimmer is never adjusted to zero. Perhaps a 470ohm could be wired inline. It is unlikely this modification will be needed.

It says I shouldn't need to make the last modification, but I'm at a loss here.

w4z · Joined: Aug 27, 2009 Posts: 13 Location: Detroit

I did the first trim-pot modification. But it's still not filtering well. It barely filters at all. I replaced the 2k2 resistor with a 5k trim-pot. No matter how I adjust all the pots it just doesn't want to filter.
Sad

Ken Stone's notes are fairly straight forward, except his guide on setting up the trims