On Sun, 10 Dec 2017 08:44:05 -0000 (UTC), gregz
wrote:

for amps, pre-amps, test equipment and lots of other stuff. So I wonder
if they are made for pass filters????

I've built boards to high/low pass, etc. Not much to it. Look around, I
think Marchand was mentioned.

Greg

Marchand has a lot of them, but the cheapest one was well over $600.
Thats out of my price range.

I found some boards on ebay, they look to be complete two channel in,
one out, with all the filtering. They need to be put into a box and a
power supply added, as well as in/out jacks. They cost $10 or less. I'm
thinking about ordering one of them. I can easily build a power supply
or maybe just use a wall wart. They are pretty simple, one op amp IC for
each channel and some passive parts. One model only had 2 pots, (volume
in, volume out). The other model has 3 pots, the third one is to adjust
the cutoff. If I get one, I'll probably choose the 3 pot one.