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Potentiometer question

I acquired a Peavey commercial rack mount equalizer from the mid to late

80s. It appears to work well, aside from two problems. First, the AC power switch was bad. I temporarily just jumped it, till I can find something to fit the hole. Second, one of the slide potentiometers is broken off, and it happens to be the main (GAIN) one for the left channel. I was able to lift it with a thin tool, to it's max position, but I want to replace it.

I found an online schematic. It's a 50K pot, and it says "all pots are linear". But on the schematic it says 50K "s". I'm assuming the "s" means SLIDE. Is that correct? (If not, what does it mean?)

I have never replaced a slider pot. To obtain a replacement, are they all the same size and pinout? Or do I need to go by any specs? Since it solders directly to the PC board, it has to pretty much be identical.

I plan to first contact Peavey and see if they have this part, along with it's knob, but considering the age of this device, I suspect they wont. So, if they dont have it, how do I match it up? (I'll be buying this online, so I have to make sure I get the right part).

If it matters, this is a Peavey EQ 215 equalizer.

Thanks

Reply to
oldschool
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When a pot is "linear" it means the resistance goes up in porportion to the movement of the adjustment be it a slider or a round shaft, not that it is a slider type control. There are others such a log and audio taper. The resistance will not be in direct porpottion to the movement of the shaft.

Most volume controls have an audio taper. That is so the sound comming from the speraker will seem to increase in porportion to the rotation of the shaft. I forget which end it is, but as the shaft is turned ( or the slider moved) the resistance will not go up smooth, but will change a lot at one end and not much at the other for the same ammount of movement of the shaft.

Reply to
Ralph Mowery

Thanks Ralph. I am familiar with audio taper pots. I am not sure which end it is either, but I think the sound level rises faster on the low end (quiet end), and increases more gradually on the loud end. However I could be wrong. I know a lot of the old tube radios had 500K pots for volume and they were all audio taper. In fact back in those days, I had a whole coffee can full of them, wbich I salvaged from old radios. Many, if not most had power switches on the back of them too.

Anyhow, this application says the pots are all linear taper, which for an equalizer makes sense. Since it says "ALL", that includes this GAIN pot, which is the one I need to replace.

So, I know I need a 50K linear taper slide pot. But I still do not know about size and pinout on these slide pots. This is a pretty simple repair, but getting the correct pot may be a challenge. -OR- are all slide pots the same pinout and size? Thats what I am not sure about. And since I have to order online, I cant just match up the pins. I am only hoping that Peavey has an exact replacement, that would insure it will fit and work, but I am not counting on that, since this is a 1980's era device. If they still have the parts, I'll just order it from them along with the knob, and probably that power switch too. Then I know it will be the right parts.

The schematic I found online, lacks a parts list, so there are no part numbers. Just the drawing with the part values listed. One thing I have noted, is that this equalizer has 32 slide pots total. ALL of them are

50K linear sliders. (15 sliders for equalization, plus the GAIN slider, PER CHANNEL).

In all the years I have tinkered with this stuff, this is the first time I ever had to replace a slider pot. That's why I am not sure about them.

Reply to
oldschool

snipped-for-privacy@tubes.com wrote on 10/22/2017 7:53 PM:

I believe audio taper is the same as log taper. That's because the ear's sensitivity to sound volume is logarithmic. That means at the low end a small increase in volume will result in a large increase in perceived volume. As the volume gets louder it takes more power to make the sound appear to increase the same way. So the taper is actually anti-logarithmic or exponential with the larger change in resistance at the high end.

You would not need an audio taper for a pot that isn't directly in the path of the signal. If the pots are controls to a signal processor, they simply provide a voltage to the device that is controlling the sound. In older gear they are equivalent to volume controls in the audio path but each one is controlling the output of a band filter. Then they should be audio taper.

If you are going to replace the pot, you should be able to measure the pin spacing and the case dimensions. Go to sites like Digikey and find a match.

Live and learn. There's nothing magical about them.

--

Rick C 

Viewed the eclipse at Wintercrest Farms, 
on the centerline of totality since 1998
Reply to
rickman

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