Inductor tests

[alfafalfa]

Just measured it : 8.5 ohms  resistance.

Alf

[Paul Marossy]

That's a pretty low DC resistance. Did you lose that metal screw yet?

[alfafalfa]

Paul,

I measured an earlier attempt to get the ideal inductor and it gave a resistance of 27 ohms but this one 
was only 350 mH , I think thicker wire and not enough turns ?? This was before I found out that the number of turns doesn't behave in a linear fashion and removed too much wire . It was a trial and error situation then.  It has been some time that I worked on this.

I just removed the bolt but the problem is I don't have a ceramic one  and now the pressure is of the ferrite core the inductance has  dropped far too much. It's now about 200 mH varying with the pressure of my fingers. The bolt was holding it together and providing a means to attach it to the board.
Do you know what influence the wire thickness has on the sound , if any ?
I mean does it matter , soundwise , how you get to the 500 mH. I mean with thinner wire will get you there sooner (fewer turns) than with thicker wire ??
And another idea , would with a plastic or ceramic bolt it be possible by applying more or less pressure to the potcore to have a tunable inductor , say from 450 mH to e.g. 550 mH ?

Regards, Alf

[Paul Marossy]

Generally, thicker wire = less resistance, so fewer windings. The actual gage isn't super critical when we're talking about the difference between #36 & #38 wire.

[alfafalfa]

Today I got hold of nylon bolts and put one through the pot core and what I thought  was confirmed the inductor is tunable. I put I on 500 mH roughly ( see my esnips) and put it back on the board.
The only problem now is that the inductor size is getting a bit in the way.
The connected it and I think it sounds very good at least to my ears.
I like it a lot ; much better than with the steel bolt. It didn't make much difference on the meter , only a few mHenries.


http://www.esnips.com/doc/8d126c48-5245-4b8a-b4fa-a504afa7bbde/Tunable-Inductor-wah-fixed.mp3

Thanks for the advice all who helped !!

Alf

[alfafalfa]

Maybe this works :

http://www.esnips.com/doc/8d126c48-5245-4b8a-b4fa-a504afa7bbde/Tunable-Inductor-wah-fixed.mp3

[RedHouse]

I thought the 2nd law was "Everything tends to entropy"
(Einstein?)

[Paul Marossy]

Huh, very interesting. I'm putting this in the Mental Rolodex. 

[alfafalfa]

Well, I had to look that up !!
Thanks for Wikipedia:

the second law of thermodynamics, which deals with physical processes and whether they occur spontaneously. Spontaneous changes occur with an increase in entropy. In simple terms, entropy change is related to either a change to a more ordered or disordered state at a microscopic level, which is an early visualisation of the motional energy of molecules, and to the idea dissipation of energy via intermolecular molecular frictions and collisions. In recent years, entropy, from a non-mathematical perspective, has been interpreted in terms of the "dispersal" of energy.

Alf

[d95err]

Semi-hijack attempt of this thread:

If someone who really likes to do inductor testing would measure the inductance of some wirewound power-resistors, I'd be very happy!

Slightly off stompbox territory, but in tube amps, wirewound resistors are used instead of a choke in some designs (e.g. Trainwrecks). Since the resistor is basically wire wound in a spiral shape it should have some inductance. The question would be if a wirewound resistor would really have enough inductance to make a difference. Would it really decrease power supply ripple significantly, compared to a metal film resistor of the same resistance?

Another question would be if they would have enough inductance to have any effect when used as dummy loads or L-Pads for power attenuation.

[Paul Perry (Frostwave)]

The inductance depends on the number of turns, not the thickness of the wire. Usually, the idea is to use wire as thick as you can, and still get enough turns - because that way, you get minimum resistance. Because, if you want more resistance, you can always put a resistor in series...

[Fret Wire]

I really, really, really, really, really, really need to get something that measures indcutance.

Here's a capacitance/inductance combo meter for $35
http://circuitspecialists.com/prod.itml/icOid/3394

The capacitance range isn't as wide as this dedicated cpacitance model (I have one, it's nice):
http://www.electronickits.com/gold/capacitancemeter.htm
but the combo unit's inductance range covers wah inductors nicely.

[R.G.]

If someone who really likes to do inductor testing would measure the inductance of some wirewound power-resistors, I'd be very happy!
Slightly off stompbox territory, but in tube amps, wirewound resistors are used instead of a choke in some designs (e.g. Trainwrecks). Since the resistor is basically wire wound in a spiral shape it should have some inductance. The question would be if a wirewound resistor would really have enough inductance to make a difference. Would it really decrease power supply ripple significantly, compared to a metal film resistor of the same resistance?

Not significantly, no. It's pretty easy to do the calculations. Power supply ripple is 100 or 120Hz. The resistors you're thinking of are used after the main power supply choke, between sections. They are usually 2.2K to 10K in resistance.

The inductance which has an impedance of, say 4.7K at 100Hz is L = 4.7K/(2*pi*100hz) = 7.48H, or 7480mH. A wah inductor is 500mH and commonly has hundreds of turns of wire. Wirewound resistors have a single layer of resistance wire. Inductance goes up and down by the square of the number of turns, so a wirewound resistor has  a quite small inductance compared to what it needs for audio ripple filtering.  A wirewound resistor will not come close. The principal effect is the resistance.

Another question would be if they would have enough inductance to have any effect when used as dummy loads or L-Pads for power attenuation.

Probably not, but that's a much closer thing. A generic value for speaker coil inductance is 4 to 10mH. That's possibly in the range for a 10K wirewound resistors, at a guess. But for dummy loads, you don't want 10K ohms, you want eight. So many, many less turns of wire are needed. Again inductance goes down as the square of the number of turns reduced. It's far simpler to wind copper wire on a wooden form to make the inductance you want for a dummy load.

[jonathan perez]

thanks for the links, Fret Wire 

[rockgardenlove]

The ArielFX site suggests this:
http://elexp.com/tst_1005.htm
The other suggestion is cheaper though.

[Paul Marossy]

I really, really, really, really, really, really need to get something that measures indcutance.

Here's a capacitance/inductance combo meter for $35
http://circuitspecialists.com/prod.itml/icOid/3394

The capacitance range isn't as wide as this dedicated cpacitance model (I have one, it's nice):
http://www.electronickits.com/gold/capacitancemeter.htm
but the combo unit's inductance range covers wah inductors nicely.

Yeah, I just need to get one. They're certainly very affordable...