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

 

[Ralph Mowery]

In article <ac7quc9ilkhr31uirq4ve2rvla6js04cip@4ax.com>,
oldschool@tubes.com says...

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?)

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.

 

On Sun, 22 Oct 2017 19:12:13 -0400, Ralph Mowery
<rmowery28146@earthlink.net> wrote:

In article <ac7quc9ilkhr31uirq4ve2rvla6js04cip@4ax.com>,
oldschool@tubes.com says...

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?)


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.

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.

 

[rickman]

oldschool@tubes.com wrote on 10/22/2017 7:53 PM:

On Sun, 22 Oct 2017 19:12:13 -0400, Ralph Mowery
rmowery28146@earthlink.net> wrote:

In article <ac7quc9ilkhr31uirq4ve2rvla6js04cip@4ax.com>,
oldschool@tubes.com says...

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?)


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.

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.

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.

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.

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.

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.

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.

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.

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

--

Rick C

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