ARP 1047 Multimode Filter

[elmegil]

I'm looking for anyone who knows any details about the calibration of, and hopefully the resistor selection process for the ARP 1047 Multimode Filter....

Several resistors have no value except "SEL"; they appear obviously there for fine tuning resistance values at various points, I'm looking to figure out what it is they're selecting FOR. I can find schematics, but so far no luck finding actual service notes (and the one thing I found that claimed to be service notes for the ARP 2500 was only schematics).

[brock]

I don't have any experience with this filter but I'm pretty sure you can leave the SEL resistors off and it will work fine.

There is a DIY board that a few people have built that does not have those resistors included. Do a search for "Is There Anything Like An ARP 2500 Filter In SDIY Land?" and you should be able to find some pictures of it.

As for what the SEL resistors do, I think I can answer that. They are all parallel resistors with another 1% value so they can only adjust values in one direction. Therefor R22 and R15 will increase the ranges of the coarse and fine frequency pots, R38 and R40 will increase the range of the peak resonance pots, and R73 will increase the bias of the frequency control voltage to the gain cell.

Have you read Dennis Colin's paper about what he set out to do with this filter?
http://www.guitarfool.com/ARP2500/DennisCollinPaper.pdf
He doesn't talk about it at the component level but he does discuss the performance of the filter and you should be able to prove to yourself that the ranges he expects are available with the components specified.

Brock

[elmegil]

Yes, Dennis' paper which was posted recently on another list in discussion after he passed away is the reason I'm interested in this filter.

Thanks for the pointer!