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fum

fum

Well-known member
Joined
Jun 3, 2004
Messages
861
Location
Seattle
Hey there.

Am shopping for some inductors, and am having a rough time finding proper values. Most of the catalogs are carrying things in the uH ranges, but not much in the mH range. ( I thought I was doing pretty good until I noticed the mH vs. uH)

Is this truly something I should be winding myself, or does anyone have a secret hidden company that stocks everything =)

I'm looking at the circuit on the gyraf site for the MEQ5, values are:

120mH
280
420
520

24
61
100
145
277
420

477
625

Regards

ju
 
To become a senior member of GroupDIY, you must wind your own! :razz:


meq1.jpg


Try sampling some torroids from Fair-Rite.

Like a 59-77-001701,002701, 003801, or if your really crazy, 011101.

Then, start winding. I split the mid into two coils for better response.
cj
:guinness:
 
It's on my list to try winding my own inductors, like Steffen did with his Pultec, but how in the world do you wind your own torroids? I have'nt found anything on the web about home-brew torroid winding.

Cheers,

elco
 
Now hold on here, I think there are a couple people looking for inductors and I could have sworn on the last forum someone pointed out some cheap inductors from mouser or digi key or farnell or somewhere... I think it was NYDave...were they called teky or tyke hmmm can't remember... :?
 
Yep, but TOKO only goes as far at 120mH. It seems that no one actually manufactures inductors larger than that these days.

You could wire a 2x47mH current-compensated power filter inductor in series to get some 190mH, mut that is as high as you can go with off-the-shelf components.

Jakob E.
 
[quote author="gyraf"]Yep, but TOKO only goes as far at 120mH. It seems that no one actually manufactures inductors larger than that these days.

You could wire a 2x47mH current-compensated power filter inductor in series to get some 190mH, mut that is as high as you can go with off-the-shelf components.

Jakob E.[/quote]


Is it possible to get decent behaviour from inductors with their
inductance increased by a transformer?

It seems strange to use a transformer *plus* an inductor for this,
but if you can get these cheaper / easier, it might be worth
a try.

I want to try this soon, to get 2H from a 120mH TOKO (and
the smaller values accordingly):
Please note that this is *untested* yet. Will this work ??
http://www.oldcrows.net/~jhaible/neve/jh_neve_presence_inductor_idea.pdf

(I don't need high Q - in the 2H inductor has a 2k7 resistor in series
in the original circuit.)

Sorry for asking this twice (tried it yesterday in another thread).

JH.
 
Fum: Winding your own inductor is not that hard as you might think. My first pultec inductors was handwound. On Steffens page everything is explained very well.
 
Ju,
Magnetic Circuit Elements Inc. http://www.mcemagnetics.com/ have a good range of inductors if you're Stateside. I wanted to get some stuff from them to build the Scott Dorsey EQ, but they wanted $60 to send 10 small inductors to the UK..!! That doubled the price..!!

peter
 
JH,

I'm not sure your transformation scheme will work without sideeffects.

Why not simply use the OEP transformer as an inductor by itself?

Connect pri and sec in series, and you'll have more than enough inductance. Somewhere inbetween you'll find the value you need...

I often use transformers as inductors for testing circuits before ordering specially-wound inductors..

Jakob E.
 
[quote author="gyraf"]JH,

I'm not sure your transformation scheme will work without sideeffects.

Why not simply use the OEP transformer as an inductor by itself?

[/quote]

Hi Jakob,

that was my first idea as well. But when I connected the transformer to an impedance analyser (I have access to a HP 4192A analyser - I just start to learn to make use of this) I found that this stops to be inductive at a few kHz! I still consider myself a beginner in understanding audio transformers, but apparently these are optimised for entierly different goals than an inductor. I think the transformer will be able to have a good frequency response way beyond the audio range when properly terminated (!), but still be a lousy inductor with low resonance frequency when I just use it unterminated. I don't undersand this completely, but my gut feeling is that all the (unused) extra windings will still add a lot of parasitic capacitance even when they are not used.

My *hope* is that the transformer in my crazy circuit is closer to its original task, and thus might work better. Probably not good enough either, though. I'm really curious about the results.

Connect pri and sec in series, and you'll have more than enough inductance. Somewhere inbetween you'll find the value you need...
Click to expand...

How does "somewhere in between" work?

I often use transformers as inductors for testing circuits before ordering specially-wound inductors..
Jakob E.
Click to expand...

How do you measure their inductance?
(I'm asking because of this: My multimeter measures at a single frequency, a few hundred Hz.
I was really shocked when I measured the same devices with that
HP analyser afterwards.)

JH.
 
Wilco (here in the US) manufactures low-DCR inductors up to 2H. They're not into selling small quantities, but sometimes you can get samples. The trick is to not get greedy and try to order too many samples; that sends up a red flag and they'll ask a bunch of questions before they consent to send them.

If you can get a quantity order together, it would certainly be much cheaper to go with discrete inductors from Wilco as opposed to costly custom-made multitap inductors.

Sure, you can wind your own, too, but who has that kind of free time?

As Jakob mentioned, small audio transformers can sometimes be applied successfully as filter inductors, with values of up to a few Henries. You can use small, inexpensive telephone or transistor coupling transformers. Inductance values are rarely published for these, though, so you have to buy a few and measure them.
 
Howzabout gettin a defintive inductor value list for NYD's passive eq (like that supercharged beasty blue done), then gettin em from the place NYD mentioned? Make it into a diy project for ready to go passive eq box :thumb:
 
I posted them before, but here's the chart again:
passive-eq2.gif


Inexpensive Toko or Mouser inductors, as used in some Pultec clones, are fine for the values from 47mH and lower. But for the higher-valued inductors, you'll have to go to someone like Wilco. You can use two 360mH inductors in series for the low shelving. Wilco doesn't offer 360mH as a standard item, but it might be available in quantity. Alternatively, you could use 390mH and 330mH together.

The inductors you use must not exceed the maximum DCR figure on the chart if you want the EQ to work properly.
 
JH,

To measure inductance, make a series resonator with a capacitor and a resistor. Find resonance frequency, and calculate inductance. Or use a nomograph readout:

http://www.testecvw.com/carl/images/ImpedanceNomograph.pdf

This is the only "real" way of measuring inductors for audio - very often you will have trouble measuring audio inductors because inductance changes with the current used to measure it..

What I mean with series coupling both pri and sec of an OEP line transformer, is that you will end up having multiple taps on that "inductor"

Jakob E.
 
[quote author="gyraf"]JH,

To measure inductance, make a series resonator with a capacitor and a resistor. Find resonance frequency, and calculate inductance. Jakob E.[/quote]


Ok, by that way you find the resonance peak where XL = -XC.
This is the resonance you want to have.

But any parasitic capacitance across the L will create an additional
parallel resonance, and bejond that resonance the whole
config will start to conduct again.

With an optimised inductor (let's call it "ideal"), when you look at the
current thru the series connection, you get the BPF response that is used in equalizers.
With a lot of parasitic capacitance, starting from low frequencies, you first get the desired BPF response, then a deep notch, and then an additional HPF response.

So a transformer like th eOEP, which has its _parallel_ resonance at a few kHz, can't be used to make an audio BPF, unless you can tolerate an additional treble boost as well.

I've made some quick measurements to show the difference; see my next posting.

JH.
 
Ok, this measurement was done with a cheap talema mains transformer, *not* with an audio transformer. But the principle is the same (the resonance frequencies are just much lower).

Mesuring the primary inductance of a Talema 1.6VA transformer at 50Hz gives an inductance of 380H.
At 88Hz it goes into parallel resonance (!) - the OEP audio transformer does this at a few kHz for comparison - at higher frequencies (above 88Hz), the primary is a capacitor, not an inductance.

Now use the same transformer, but connect a good 15mH inductor across its secondaries. (44V secondaries).
The inductance is transformed upwards. I measured a value of 0.8H, which is much higher than expected. I guess that's the stray inductance in series with the external 15mH inductor. But let's put this aside for a moment. I measured at higher frequencies to find the resonance point.
This configuration has a resonance frequency of ca. 3.3kHz !

Conclusion: this was "bad stuff", not audio, but it's clearly visible that the usable frequency range is 37 times higher when the transformer is used to "transform" an external inductance rather than using it as a mere inductor by itself.

More to come when I have the "real stuff" in my hands.

JH.
 

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