Feeler: A 500 Series EQ (The People's EQ)

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OneRoomStudio

Well-known member
GDIY Supporter
Joined
Jul 8, 2004
Messages
590
Location
Minneapolis, MN, USA
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.
 

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Ricardus said:
Where is the L Bracket going?

The idea is that the board and the front panel will mount to the L-bracket, for better rigidity. The board will mount via the six 4-40 screw holes (the yellow circles on the pcb), and the front panel will mount via the pots. If that's not strong enough, I might add a pair of screws to the front panel too.
 

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