100KB sliders

[rabiticide]

I'm repairing a (music) keyboard because the 100 KB sliders are shot.
What does the "B" mean? It's a 100 k ohm pot. Does anyone know where I
could buy such a thing? It looks to have a strip of resistant paint
and I was wondering if I could repair mine with the stuff. Does anyone
sell resistive paint? Anyway, I'm going to go google, but I thought
I'd check here first.

rK

 

[Eeyore]

I'm repairing a (music) keyboard because the 100 KB sliders are shot.
What does the "B" mean? It's a 100 k ohm pot.

The delightful thing is that if it's a slide fader made in Japan or Asia
generally, B means linear and if it's European, B means 'log' or audio
taper.

Fun isn't it ?

What's its function ?

Does anyone know where I
could buy such a thing?

Electronics hobby shop ? Or electronics distributor.


You don't say where you are of course, so I can't suggest a possible but
unfortunately both faders and opts generally are often customised to suit
the manufacturer and exact replacemnents are often very difficult to find.

It looks to have a strip of resistant paint
and I was wondering if I could repair mine with the stuff.

No. Forget it. It wouldn't last long anyway.

Does anyone sell resistive paint?

No. Not in the quantities you need anyway.

Graham

 

[rabiticide]

It's a fader on the synthesizer section. There're four octaves 16', 8'
4' and 2' and a white noise generator. The keyboard itself is really
cool; it's all analog so the adjustments are all made with faders,
switches, and turnpots. Inside, ther are 49 clusters of components
corresponding to the 49 keys. Each key has its own sine wave
generator (I guess). You can get pretty cool sounds out of it but you
can't 'save' anything. The closest you can get is a template they give
you in the owner's manual. They tell you to copy it and write in any
interesting timbres that you might want to remember. It is ca. 1980.

I live in Felton, CA. I was thinking: instead of resistant paint, is
there something like a blank PCB but with resistant instead of
conductant? I could etch it and cut it myself then. In the mean time,
I'm looking for linear slide pots that will fit. I think I'm going to
have to build it myself though...

rK

 

[BobG]

If its audio, it has 10% resistance at 50% travel, so set it in the
middle and measure from the wiper to both ends. I'll assume one half
wont work... If the other half reads 50K, its linear. If it reads 10K
or 90K, it audio.

 

[Bob Masta]

It's a fader on the synthesizer section. There're four octaves 16', 8'
4' and 2' and a white noise generator. The keyboard itself is really
cool; it's all analog so the adjustments are all made with faders,
switches, and turnpots. Inside, ther are 49 clusters of components
corresponding to the 49 keys. Each key has its own sine wave
generator (I guess). You can get pretty cool sounds out of it but you
can't 'save' anything. The closest you can get is a template they give
you in the owner's manual. They tell you to copy it and write in any
interesting timbres that you might want to remember. It is ca. 1980.

I live in Felton, CA. I was thinking: instead of resistant paint, is
there something like a blank PCB but with resistant instead of
conductant? I could etch it and cut it myself then. In the mean time,
I'm looking for linear slide pots that will fit. I think I'm going to
have to build it myself though...

Just out of curiosity, what is the make and model?

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

 

[BobG]

Make and model of the fader or the synthesizer? (I'm betting on a
polymoog?)

 

[rabiticide]

Just out of curiosity, what is the make and model?

Best regards,

Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

korg delta ca. 1979 to 1984


rK

 

[BobG]

Just post a link to a photo of the sliders against some size
reference... there's a bunch of misc sliders at Skycraft... did we
determine if they were linear or audio?

 

[rabiticide]

Just post a link to a photo of the sliders against some size
reference... there's a bunch of misc sliders at Skycraft... did we
determine if they were linear or audio?

It's linear. But now I have another problem: The attack slider works
but is a little scratchy, so I'd like to replace it now that I've got
it pulled off the board. It is designated as "2MA" Nothing I can find
has such high resistance. I don't know why they would design it this
way.

BTW, It's a lesson I learned that the resistance of a component is
best measured when disconnected from the circuit. Is this correct?

rK

 

[BobG]

Measure the resistance! If its 100k, a 20k or a 1meg might work just
fine if it is being used a a voltage divider. The value isnt the most
important feature in that case.

 

[Michael Black]

Measure the resistance! If its 100k, a 20k or a 1meg might work just
fine if it is being used a a voltage divider. The value isnt the most
important feature in that case.

Of course, like everything else, it depends.

You're right, as a voltage divider it doesn't matter in itself what the
value of the pot is, since putting the slider at the halfway point will
mean the slider contact is at half the voltage across the pot.

But the value may matter a lot, depending on the circuit it is in. If
the previous circuit is expecting a high value load on it (admittedly
less likely these days when that driver is likely an op-amp and doesn't
care), then a lower value pot may load that output too much.

Michael

 

[rabiticide]

Just a guess, without seeing the circuit, but since it's controlling
attack they probably use it directly in conjunction with a cap.
In fact, I would expect they may even be using it as a variable
resistance rather than a voltage divider. The R and C together
provide the time constant of the attack; by using a bigger R they
can use a smaller (cheaper) C.

Okay - that rings some dusty bells... I am lucky enough to have the
circuit diagram. I really appreciate your help on this. I posted the
diagram on my blog at:

http://rabbitshead.blogspot.com

You can see four dashed-line boxes around four resistors with the
little arrows through them. These controls comprise the envelope
generator:

A = Attack
D = Delay
S = Sustain
R = Release

Like I said, the 2MA attack pot is flaky and I would like to replace
it. But I've searched high and low and can find, at most, a 1MA
slider. Will this work?

rK

 

[Eeyore]

First of all, I assume that "MA" is Korg-speak for "Megohm".
(Normally just abbreviated "M".)

I think it probably means 2 Megohms, A taper (logarithmic).

Graham

 

[Eeyore]

Okay - that rings some dusty bells... I am lucky enough to have the
circuit diagram. I really appreciate your help on this. I posted the
diagram on my blog at:

http://rabbitshead.blogspot.com

You can see four dashed-line boxes around four resistors with the
little arrows through them. These controls comprise the envelope
generator:

A = Attack
D = Delay
S = Sustain
R = Release

Like I said, the 2MA attack pot is flaky and I would like to replace
it. But I've searched high and low and can find, at most, a 1MA
slider. Will this work?

It will certainly work but you will get reduced range of the control
Possibly this won't matter too much and it's crtainly an improvement over a
flaky control.

Graham

 

[BobG]

I've tried lots of Home Remedies to cure scratchy tube guitar amp
pots.. I've heard WD40.... others say nooooo... thats a solvent and
will eat the conductive plastic... How about Amway or some similar
silicon slippery stuff (wow 5 Ss in a row)? Just need to knock the
dust off the wiper area.

 

[Eeyore]

I've tried lots of Home Remedies to cure scratchy tube guitar amp
pots.. I've heard WD40.... others say nooooo... thats a solvent and
will eat the conductive plastic... How about Amway or some similar
silicon slippery stuff (wow 5 Ss in a row)? Just need to knock the
dust off the wiper area.

When they're badly worn the carbon track is worn away. No solvents going
to help that.

Graham

 

[rabiticide]

First of all, I assume that "MA" is Korg-speak for "Megohm".
(Normally just abbreviated "M".) Whatever, if your replacement pots
are half the value of the originals, all the time constants will be
halved as well (envelopes speeded up x2) for the same relative
settings. If you rarely use the half of the sliders that give the
longest envelopes, you might be happy with a simple replacement.
However, if you want to restore the original range, you can also
replace capacitor C6 with one of twice its value. Note that this is
an electrolytic, so be sure to observe polarities.

Best regards,

Bob Masta

okay, last question (I hope!). Can I do 100KA for the pot (1/20th the
value) and replace the cap with 200uF (20 X the value) for an
equivalent circuit? I was mistaken about the 1 MA, it's only
available if I order 200 at $2 a piece!

Yes, the "A" stands for audio taper.
Yes, the coating is worn off so no amount of cleaning will help

rK

 

[Allen Bong]

okay, last question (I hope!).  Can I do 100KA for the pot (1/20th the
value) and replace the cap with 200uF (20 X the value) for an
equivalent circuit?  I was mistaken about the 1 MA, it's only
available if I order 200 at $2 a piece!

Yes, the "A" stands for audio taper.
Yes, the coating is worn off so no amount of cleaning will help

rK

Hi Ribiticide,

Take a look at the pots and sliders that I have. Do they match the
sliders of yours that went bad?
I am a part time Yamaha and Kawai organ technician and I can get the
old parts if I try.

http://www.flickr.com/photos/11236051@N08/sets/72157601399254969/


Allen

 

[Rich Grise]

It's linear. But now I have another problem: The attack slider works
but is a little scratchy, so I'd like to replace it now that I've got
it pulled off the board. It is designated as "2MA" Nothing I can find
has such high resistance. I don't know why they would design it this
way.

Sorry, but is is not very helpful. Is it possible at all for you to post
a picture somewhere? Either on your ISP's "personal webspace" (every ISP
I've had has provide a personal page of maybe 10 MB.) or one of those
free photo hosts.

And also, for some reason I don't trust those numbers - they could be
house numbers and I don't know if _anybody_ has ever heard of a 2M
slider. Would you ohm them out? Or are they blown already? Is the
company still in business? Could you ask them for a parts list, or
even order replacements? Is there a Sams PhotoFact for it?

BTW, It's a lesson I learned that the resistance of a component is
best measured when disconnected from the circuit. Is this correct?

Yes; there are always sneak paths somewhere when it's in-circuit. Of
course, you know to NEVER EVER use an ohmmeter on an energized circuit.
Voltmeters are fine, of course - that's how we troubleshoot stuff.

Cheers!
Rich

 

[Rich Grise]

I've tried lots of Home Remedies to cure scratchy tube guitar amp
pots.. I've heard WD40.... others say nooooo... thats a solvent and
will eat the conductive plastic... How about Amway or some similar
silicon slippery stuff (wow 5 Ss in a row)? Just need to knock the
dust off the wiper area.

The problem with WD-40 is that it gums up whatever it touches. If
you think you've got a scratchy pot, a little WD-40 will not only
silence the scratchiness, but the whole shebang - it will coat the
element, and the slider won't make contact again until you use proper
control cleaner stuff. And, of course, when you spray the control
cleaner on the part, be sure and work the wiper back and forth to,
well, wipe it.

I once got an old teletype unit donated to me because the guy was
tired of hauling it around with him. It was very dusty, so I figured
I'd clean it, so I sprayed it with WD-40. It gummed up the unit so
bad it wouldn't even operate. I spent about a week dismantling the
thing and cleaning the individual parts in isopropyl alcohol, with
a typewriter brush.

WD-40 is for squeaky car front ends, door hinges, and keeping your
garden tools from rusting. ;-)

Cheers!
Rich