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Old 20th March 2011, 09:46 PM   #1
C04pl is offline C04pl  France
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Default Moog parametric EQ - proper pots?

Hi
I have build this parametric moog which you can find almost everywhere in internet (schematic). I modified signal path by adding balanced ins and outs. Also i added one filter section. Now there are 4 (in original 3 freq sections). The problem is that boosting/cutting potentiometers doesnt work properly - i mean only 15 clock minutes makes dramatic changes. These positions are: 9:00 to maybe 7:00 which is cutting frequency, 3:00 to 5:00 and its adding/boosting freq. The space between - 9:00 to 3:00 almost do not make any changes or they just tiny. How to improve the whole scale? I want that in middle (12:00) will be neutral point and other parts will make differences linearly. How to do that?
At schematics these pots are just linear and i used this type but it doesnt work.
Someone has build this before?
Regards and thanks for advance.
P.S. I may send my schematics and pcb designs in EAGLE. All this project is modular: Mainboard + PSU + 4xfilter sections.
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Old 22nd March 2011, 01:06 PM   #2
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Maybee someone would help you if you post the schematic aor a link to it! E
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Old 23rd March 2011, 02:18 AM   #3
C04pl is offline C04pl  France
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Ok here it is. Problematic potentiometers on this schematic are: R211, R212, R213. I used 4580 opamps.
Its nice sounding eq at all but this regulation makes me crazy. I tryied different connections and always the same results. Even two pots log + antilog.
Second schematic is my. Its only filter section and the same pot here is VR1 22kA (linear).
Regards
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Old 23rd March 2011, 02:00 PM   #4
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Schematics like these make my eyes and brain hurt!
The dual pot should be 100k, the RA propably means "reverse A taper" (good luck finding that). I can not make out the value of your C2 which with C18 sets the (not stated) centre frequency. E
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Old 23rd March 2011, 03:40 PM   #5
C04pl is offline C04pl  France
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As i told previously i made some changes in my schematics but this doesnt matter because filters works excellent. The problem is with cutting/boosting and originly there were 25k lin pots. Right now i have about 20k lin - it doesnt make any changes if i put there 10k, 47k or 1k still the same problem. Only in right and left horizontal positions i can hear incrasing or decrasing levels of frequency ive set. I mean if left horizontal to max left and right horizontal to max right. There center where adding and cutting are in balance is from left to right. Its hard to explain - half of turn makes nothing but there at 12-clock (at center) should be signal flat and turning this knob should make some linear characteristic changing by cutting or boosting depend which position i move this pot. So im asking maybe there just not linear potentiometers were used and that the problem. Maybe there best idea would be M+N pot... otherwise i have no idea.
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Old 23rd March 2011, 10:41 PM   #6
C04pl is offline C04pl  France
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Ah... these 2x100k antilog/reversed taper o already have, also these 47k log+470R lin. It wasnt so hard to get them.
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