OneRoomStudios

Feeler: A 500 Series EQ (The People's EQ)
« on: May 22, 2020, 12:10:20 PM »
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.


OneRoomStudios

Re: Feeler: A 500 Series EQ (The People's EQ)
« Reply #1 on: May 22, 2020, 12:25:26 PM »
First swipe at the board.

Ricardus

Re: Feeler: A 500 Series EQ (The People's EQ)
« Reply #2 on: May 23, 2020, 12:08:24 AM »
Where is the L Bracket going?
Audio mastering for hire..

Ricardus

Re: Feeler: A 500 Series EQ (The People's EQ)
« Reply #3 on: May 23, 2020, 12:09:57 AM »
First swipe at the board.

Board layout is very logical. Love it.
Audio mastering for hire..

OneRoomStudios

Re: Feeler: A 500 Series EQ (The People's EQ)
« Reply #4 on: May 23, 2020, 11:43:49 AM »
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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