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Post by svart on Jun 21, 2018 9:38:09 GMT -6
Looks expensive.. LOL
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Post by matt@IAA on Jun 21, 2018 9:44:34 GMT -6
Not too bad, to be honest. Biggest cost is the rack unit itself, of course the four audio transformers, and the Grayhill switches for the frequency selection.
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Post by matt@IAA on Jul 2, 2018 21:22:35 GMT -6
All systems are go. I’ve got some weirdness in a switch in the EQ but all the gain staging is right on.
Also picking up some radio stations since it’s sitting on my workbench.
I pushed +24 dBm cleanly with the board running at +/-28V. Headroom for days.
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Post by Cyrus Melchor on Jul 3, 2018 6:42:03 GMT -6
Looking good! And a very anti-IC project you got going on here. HAA.
I do dig them 1280B EQ's. They kill on aggressive drums.
Looking forward to seeing more.
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Post by matt@IAA on Jul 3, 2018 20:04:01 GMT -6
The HF grayhill switch had exploded itself inside, the tiny contacts had gotten cross-wise with the rotor and then destroyed the plastic rotor. Like a box of pinball parts. I had another multideck Grayhill so I rebuilt it, and realized that the molded portion that carries the pin was twisted, so the knob could only be turned clockwise. Two or the counter clockwise clicks and it bound up again. Never seen that before!  Anyway, with that off I confirmed that the first op amp in the EQ was oscillating when both the high and low filter circuits were switched "off". Added a feedback cap to the op amp which cleaned it up, then I chased my tail for about two hours trying to eliminate phantom pulsation caused by the interaction between my signal generator and the cable going into the scope. Happy 4th! |
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Post by matt@IAA on Jul 7, 2018 20:35:51 GMT -6
-83.5 dB noise A weighted sitting on a plywood board.
-0.71 to +0.21 frequency response referenced to 1k.
Rock and roll.
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Post by matt@IAA on Jul 26, 2018 17:46:42 GMT -6
All the EQs work as intended. Here's the LF at about half boost. Each is +/-15 dB.  |
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Post by johneppstein on Jul 26, 2018 21:00:51 GMT -6
oops.
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Post by matt@IAA on Jul 26, 2018 21:04:51 GMT -6
You mean in the frequencies? The low and mid overlap (200 low, 250 mid, 400 low, 500 mid) and the high and mid both have a 4.8k. What would you expect?
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Post by johneppstein on Jul 27, 2018 0:29:18 GMT -6
You mean in the frequencies? The low and mid overlap (200 low, 250 mid, 400 low, 500 mid) and the high and mid both have a 4.8k. What would you expect? Never mind, I misread the chart. Dunno how I missed that... |
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Post by matt@IAA on Jul 27, 2018 0:59:17 GMT -6
No worries, I really do appreciate the feedback.
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