To those who've made CGS30 BPFs...?

Bodega · Joined: Nov 02, 2008 Posts: 75 Location: Montreal

Where does one put the 100n 1206 SMD caps? It's such a small pcb - am I looking right at it without seeing it?

Also, I'm assuming that this is the type of thing I should be using:

http://www.epcos.com/inf/20/10/db/cc_07/X7R_CC.pdf

thanks!

Dave Kendall · Posted: Sat Oct 03, 2009 10:21 am Post subject:

Hi.

Sounds like you have a REV2 board.

Bridging the square pads on the solder side, under both TL072/1458s is where they should go. They're bypass caps for the opamps. Each pair of caps goes from +v to Gnd, and -V to Gnd respectively.

You could use tiny regular 100nF ceramic caps if you don't have SMD components. Just cut the leads down and solder on to the pads.
I don't believe the type of cap is critical for use as a bypass cap - use what you have...

Incidentally, Ken's suggestion on the CGS30 page for increasing the maximium resonance by tweaking the value of the 4K7 resistor to GND is a very good one. I did this in my build.

cheers,
Dave

lanxe · Posted: Sat Oct 03, 2009 10:46 am Post subject:

Bodega · Joined: Nov 02, 2008 Posts: 75 Location: Montreal

I think I have a 2k or 2.5k trimmer - maybe I'll stick that in where the 4.7k is marked. I do like a bit of resonance....

Thanks for the tip re: the caps! I never would have figured that one out.

Bodega · Joined: Nov 02, 2008 Posts: 75 Location: Montreal

Actually, using a trimmer there is overkill - I'll stick a socket in.

Bodega · Joined: Nov 02, 2008 Posts: 75 Location: Montreal

Just finished putting one of these together and it sounds great but wow, the resonance is pretty subtle. Like, the difference between 6dB/oct and, maybe, 9dB/oct, max.

I stuck in some box caps in the spots where I figured they should go. Does this looks very wrong to anybody? Specifically it's the bottom left one.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

and for comparison:

I haven't trimmed the wires connecting the jacks and pot, obv. Consequently, it looks like there might be a bridge on the lower right, but that's just the angle I took the picture from.

thanks!
Matthew

otherunicorn · Joined: May 11, 2008 Posts: 136 Location: Australia

And a month after you asked... The caps are in the right place Smile

Bodega · Joined: Nov 02, 2008 Posts: 75 Location: Montreal

Great - thanks!

They're good sounding units. There's something really satisfying about having two and continuously riding the freq and res as you record.