Stir Plate

[Banjo-guy]

I've gathered most of the parts for a DIY stir plate. I got everything from an old Apple tower that's been lying around doing nothing.

Most of the instructions use a 12 volt power supply and a potentiometer to vary the fan speed.
There are a couple of instructions that call for LM371 voltage regulator.
If anyone's built a stir plate...do I need to use a Voltage regulator ? (LM371).

[mashani]

You don't *need* it, but the voltage regulator is used to reduce the load that the potentiometer has to deal with. Without it, the potentiometer will potentially fail much sooner.

[monsteroyd]

Jeez Mashani, do we add electrical engineer to your list of knowledge too? Damn man, you are a walking encyclopedia.

Monty

[Banjo-guy]

You don't *need* it, but the voltage regulator is used to reduce the load that the potentiometer has to deal with. Without it, the potentiometer will potentially fail much sooner.

Thanks. I thought that would be the case. I was just thinking that the life span of the pot might be long enough and easy enough to replace that it might not be worth the effort to use the LM371.

I'll use the voltage regulator circuit. It just calls for a capacitor and resistor in addition to the other parts. The hardest part is getting the parts without spending a lot on shipping. Radio Shack hardly has any parts anymore and they charge too much. The pots from there are really low quality.

When I build musical effects I use a site called Small Bear that lets you order small quantities. The shipping is 5 dollars and the parts are probably 4 dollars.
It looks like they have the LM371.

[Dawg LB Steve]

What Monty said!!!

[Banjo-guy]

Mashani has deep knowledge!

Does it matter if the potentiometer is audio or linear taper?

[BigPapaG]

Here's a pretty good article that explains more than most will want to know about potentiometers:

Pot Secrets

All pots are minimum voltage at position zero and maximum voltage at position 10.

In the case of a linear pot, with the stem at mid rotation (position 5), the voltage should approximate 50% of the available maximum.

However, for an audio/log pot, the value at position 5 will most certainly not be 50% of maximum as audio pots traverse the change in resistance more slowly during the first half (approximately) than the last half of rotation.

The most important part that impacts how your stir plate speed ramps up is:

"If you used an audio/log taper pot for the control of the power supply we mentioned, the output voltage would increase very slowly at first, creeping up to maybe 10% of the final output at 50% of the pot rotation. It would then blast the other 90% in the last half of the rotation - very hard to control. Likewise, if we used a linear pot for volume control, the volume would come up dramatically in the first half of pot rotation, and then do very little change in the last half."

With that in mind, my choice would be linear.

Also note, while the most common designations for pots are linear and left hand logarithmic, you might also run into a reverse log pot or right hand logarithmic, so be aware.

[monsteroyd]

Oh no, not you too BigPapaG! Dang encyclopedias everywhere.

Monty

[BigPapaG]

Good times... Good times !

[Banjo-guy]

Thanks BigPapaG. The link is really helpful. I've read other material from Keen. I think I tweaked a Tube Screamer distortion unit using his mods.( I haven't built an effect in a few years and am a little rusty with my electrical knowledge.)

It looks like linear is the way to go.

[mashani]

Jeez Mashani, do we add electrical engineer to your list of knowledge too? Damn man, you are a walking encyclopedia.

Monty

I was into electronics before I turned into a hardware/software geek, and long before I brewed. Built me a quadrophonic stereo back in the day using real transistors.... none of those silly integrated circuits. Hey at least it wasn't vacuum tubes LOL. But yeah in general I know enough about anything to be dangerous, but not necessarily "proficient". My friends used to call me the "Tome of Useless Knowledge". That came back to bite them one day when I DM'd a D&D campaign for them. LOL.

[monsteroyd]

OMG, I did the quadraphonic thing too. Too Funny.

Monty

[RickS]

I was a electronic tech, while in the USMC, I repaired the boxes that were taken off the RADAR package on the F-4 Phantom. When I got out of the Service I worked for a company building RADAR systems in Fl. I went from that to driving a truck, I hurt my back doing that and went back to work as a tech working on circuit borads that went into medical equipment. I have always been into electronics.

I like that things have gotten more compact, but I still think that the old Tube type amplifiers had and still have the best sound.

[BigPapaG]

I have alway been into electronics.

I like that things have gotten more compact, but I still think that the old Tube type amplifiers had and still have the best sound.

+1

[Banjo-guy]

I have alway been into electronics.

I like that things have gotten more compact, but I still think that the old Tube type amplifiers had and still have the best sound.

+1

Tubes still sound the best!