I plan to build the JH Varislope Filter in July and have been putting
together a few modifications as well as trying to figure out a panel.
This filter can eat up a lot of panel space, especially with the
onboard morphing LFO, thus I'm leaning towards small knobs in the
hopes of getting everything to fit into 3U. I've posted a few examples
to get some feedback from the group.
The first layout uses 3 switches to select all-pass/low-pass for the 6
filter stages (as JH did with his prototype):
http://www.tellun.com/varislope_panel_1.gif
The second layout uses 6 switches, which makes things quite tight, and
I had to move the AUX input jack (for the LFO) off the grid:
http://www.tellun.com/varislope_panel_2.gif
The Clean/Dirty switch is marked "C/D".
Both layouts are still quite dense and I had a tough time figuring out
where to put the switches. The pot and jack spacing is similar to the
spacing on my JH Scanner panel so I know the pots and jacks aren't too
close. But the 3 switches in the centre of the panel may make
accessing the nearby pots a bit cumbersome. I'll have to cut some
plastic and try it out.
I want this filter to have a similar interface to the standard MOTM
filters (3 audio inputs, one audio output, 2 FM inputs [one with a
reversing attenuator]) and have the following modifications planned:
1. Add a summing amp to support 3 inputs with 100K log pots (for 100K
input impedance).
2. Add an inverter to the MOD1 input so that the FM1 pot is a
reversing attenuator.
3. Skip the MOD3 input (3 external mod inputs is more than I need,
especially with the built-in LFO).
4. Add a driver to the LFO output that will support a bicolour LED
(like MOTM-320).
5. Skip the bypass switch, I've never needed one on a filter.
6. Skip the output pot, I've never needed one on a filter.
7. Change the output driver so that the Mix/Filter switch is not
required to completely silence the Dry signal from the output.
These modifications require 4 op-amps. It'll fit nicely onto a MUUB-4
board, spookily enough.
