I've been working on an idea for an inexpensive EQ that would sound good and be worth building (see https://groupdiy.com/index.php?topic=73249.0 for more discussion). I've done most of the design work now and wonder if there might be enough interest to do a run of 100 (minimum necessary for the custom pots needed).
Here's the deal:
-OEP transformer i/o (A187A12C 10k/10k input, A187A13C 600/600 output)
-DOA output stage (you provide the DOA)
-JFET buffers between each stage (adds a little color, keeps the circuit simple)
-Two DIP8 dual opamps for the bands. OPA2134 would be standard, or you can grab a pair of Sparkos Labs SS3602 to make the whole thing discrete.
4 concentric controls:
top big knob: low pass filter, switchable between 6dB/oct or 12 dB/oct (down to 6kHz at 6dB, & 7k5Hz at 12dB)
top small knob: Bax shelf boost/cut (-3dB down point at 6kHz at full cut)
top-middle big knob: frequency for wien-bridge mid-band (650Hz - 8kHz)
top-middle small knob: boost/cut (+/-12dB)
bottom-middle big knob: frequency for wien-bridge mid-band (145Hz - 1K6Hz)
bottom-middle small knob: boost/cut (+/-12dB)
bottom big knob: high pass filter (up to 270Hz), fixed 12dB/oct
bottom small knob: Bax shelf boost/cut (-3dB down point at 250Hz at full cut)
Plus, a bypass switch (bypassing filter stages, but still running through xfrms and output DOA)
Potential front panel attached (WBB = Wien Bridge / Baxandall).
The cost would be somewhere around $280/channel, including everything but the DOA (plenty to choose from out there).
The one thing I could use some help with is the L-bracket. I don't want to machine them myself. Anyone know a good shop that'll do this for a reasonable cost? I estimated ~ $25 per bracket in my price.
Here's the deal:
-OEP transformer i/o (A187A12C 10k/10k input, A187A13C 600/600 output)
-DOA output stage (you provide the DOA)
-JFET buffers between each stage (adds a little color, keeps the circuit simple)
-Two DIP8 dual opamps for the bands. OPA2134 would be standard, or you can grab a pair of Sparkos Labs SS3602 to make the whole thing discrete.
4 concentric controls:
top big knob: low pass filter, switchable between 6dB/oct or 12 dB/oct (down to 6kHz at 6dB, & 7k5Hz at 12dB)
top small knob: Bax shelf boost/cut (-3dB down point at 6kHz at full cut)
top-middle big knob: frequency for wien-bridge mid-band (650Hz - 8kHz)
top-middle small knob: boost/cut (+/-12dB)
bottom-middle big knob: frequency for wien-bridge mid-band (145Hz - 1K6Hz)
bottom-middle small knob: boost/cut (+/-12dB)
bottom big knob: high pass filter (up to 270Hz), fixed 12dB/oct
bottom small knob: Bax shelf boost/cut (-3dB down point at 250Hz at full cut)
Plus, a bypass switch (bypassing filter stages, but still running through xfrms and output DOA)
Potential front panel attached (WBB = Wien Bridge / Baxandall).
The cost would be somewhere around $280/channel, including everything but the DOA (plenty to choose from out there).
The one thing I could use some help with is the L-bracket. I don't want to machine them myself. Anyone know a good shop that'll do this for a reasonable cost? I estimated ~ $25 per bracket in my price.
