<HTML><FONT FACE=arial,helvetica><HTML><FONT SIZE=2 PTSIZE=10 FAMILY="SANSSERIF" FACE="Arial" LANG="0">Before changing pots I would ask: "What problem exists for which a change in potentiometer is the solution?"<BR>
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Alpha pots (Mouser 31VJ401) cost $0.96 if you buy 10<BR>
Spectrol 248-series (Mouser 594-248-7104) cost $5.50 each, $4.82 (25)<BR>
Spectrol 249-series (Mouser 594-249-7104) cost $5.50 each, $4.82 (25)<BR>
Spectrol 148-series (Mouser 594-148-7104) cost $7.88 each, $6.30 (25)<BR>
Spectrol 149-series (Mouser 594-149-7104) cost $7.88 each, $6.30 (25)<BR>
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Alpha pots are carbon composition, 1,000PPM/degree C, 15,000 turns rotation life<BR>
Spectrol 248 pots are conductive plastic, 1,000PPM/degree C, 50,000 turns rotation life<BR>
Spectrol 249 pots are cermet, 100PPM/degree C, 25,000 turns rotation life<BR>
Spectrol 148 pots are conductive plastic, 1,000PPM/degree C, 50,000 turns rotation life<BR>
Spectrol 149 pots are cermet, 150PPM/degree C, 25,000 turns rotation life<BR>
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Now for the kicker... Mouser does not stock 148/248 series Spectrol pots in anything but linear taper. You want audio taper? T.S. Mr. Eliot. You will get linear taper and you will like linear taper! But those "deer nuts" Alpha pots are linear, audio, single, dual, and about any flavor you want. (I liked that ... "deer nuts". Hit my funny bone.)<BR>
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For controls that adjust "frequency" (VCO, filter cutoff, LFO, etc.) a nice stable cermet pot would be better due to lower temperature coefficient. Best would be a 10-turn wirewound pot with a temperature coefficient 1/5 that of cermet (20 PPM).<BR>
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Now the great debate... should level controls be linear taper or audio taper? For example, should a mixer have linear pots (and possibly reversing attenuators) or audio taper like most any other volume control on the planet? Which do you prefer? The MOTM-830 mixer has 6 inputs. 3 of those inputs use linear pots and are more suited to mixing of control voltages. The other 3 inputs use audio taper pots and are more suited for audio inputs. Do you tweak by sound or knob position? A linear pot sitting in the middle of its range is easy to determine what voltage levels you'd see if you scoped it out. Great for not overloading subsequent stages. But audio taper pots give a finer adjustment at the lower ranges of signal levels (more pot travel for less change in perceived signal level). But audio taper pots make it harder to figure out if you'll overload subsequent stages.<BR>
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If I had the money to stock up, I would go with Spectrol 248/249 series pots and special order a boatload of audio taper pots at the values I anticipate that I would want. That's a risky proposition, obviously. Maybe you buy some 1M audio taper conductive plastic pots for use in planned ADSR modules. After you order them and they arrive 8 months later, you figure out that you really wanted a voltage-controlled ADSR generator and those panel controls must be linear taper because the taper change is the result of an exponential convertor. Arrggh. That is one of the problems one faces with special orders.<BR>
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Going the other way, I started using the Alpha pots from Mouser because I can layout PCBs to accommodate 248-series pots, but use Alpha 24mm pots to do things on the cheap. I can still change my mind if I pop the lottery! Besides, the "deer nuts" 24mm Alpha pots work very well with Stooge brackets for MOTM-format modules. That was important to me.<BR>
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YMMV<BR>
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Peace.<BR>
Tom Farrand<BR>
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