Do Bartolini buffers invert polarity?

[edwinhurwitz]

I have an ACG preamp and I wanted to blend the filter output with the straight pickup. So, I found a Bartolini quad buffer and ran the pickups directly into it. I then took the outputs of both buffers (after a volume pot for each one) and the ACG and brought them all the output jack. So far, the ACG is working great, but the outputs from the Bart is very very low and inverted in polarity from the ACG. Any ideas? Am I doing something wrong? I figured the Bart pres would isolate the pickup direct outs from the ACG out, but apparently it's not quite happening like that.

TIA
Edwin

[edwinhurwitz]

OK, I routed the summed outputs of the Bart pres into another channel of the Bart and the polarity reversed again, giving me the correct polarity so that there isn't a dead spot when interacting with the output of the ACG. However, the gain is still really, really, really low. I am using Dark Star pickups which aren't the wimpiest pickups in the world.

Edwin

[DavidRavenMoon]

The problem might be the output impedance of the Bart preamp and the input impedance of the filter. Doing it that way needs a summing amp.

But do it this way instead. Use the Bart buffer as a splitter. If the Bart has two channels, run the pickup into both channel inputs. Take one channel and feed it to the filter, and take one straight. Put something like a 2.2K resistor on the outputs of each and then to the volume pots.

[edwinhurwitz]

Originally Posted by DavidRavenMoon

The problem might be the output impedance of the Bart preamp and the input impedance of the filter. Doing it that way needs a summing amp.

But do it this way instead. Use the Bart buffer as a splitter. If the Bart has two channels, run the pickup into both channel inputs. Take one channel and feed it to the filter, and take one straight. Put something like a 2.2K resistor on the outputs of each and then to the volume pots.

Thanks! I think that's a great idea. The ACG has buffered inputs, but I bet it wouldn't be bothered by pre buffering the pickups. However, then I run into the phase problem since I only have 4 channels in the buffer. I wonder if somehow the Bart isn't getting power properly. I need to test that.


Edwin

[DavidRavenMoon]

You can also try buffering each pickup, and then split that signal, one half to the filter, and the other half straight. The filters might also be inverting the signal.