Inductor DCR Insanity For SDA's

gimpod

WARNING: If simple math & basic electronic theory gives you a headache you may want to move on.

Let's get on with it. So you've been reading DarqueKnight's threads on replacing the stock board level inductors in his SDA SRS 1.2TL's and SDA CRS+'s and the good results he's gotten from doing so using Jantzen perfect lay inductors from Parts Express (Special order) Link to thread and you've gotten the inductor upgrade bug. Well your in luck if you've got ether the SDA SRS 1.2TL's or the SDA 2B/CRS+'s as DarqueKnight has done all the heavy lifting on doing this mod and was kind enough to supply part numbers and a contact person at Parts Express to order the inductors from.

Now what do the rest of us do who don't have the 1.2TL's or 2B/CRS+'s and want to upgrade there inductors?

First thing we need to do is find out what inductors are being used in our crossovers, here is a list of the different inductors used in the 4th & 5th generation SDA's



All other measurements were made by using a common DMM, a fixed current power supply and Ohm's Law for figuring an unknown resistance, R = V / I. Where R = resistance, V = Volts and I = Current.

So how do you find out what the DCR is, Simply put you measure it. But hold on a minute that may not be as simple as it sounds because you need a multimeter that is accurate to at least 0.01 ohms DCR such as a Fluke 8050A multimeter or something in the range of the Fluke (Big $$$) and no that Radio Shack or run of the mill DMM will not get the job done it just doesn't have the resolution and accuracy needed.

Now some of you may be thinking "No problem I'll use my LCR meter" that most likely wont work ether because most LCR meters don't measure DC Resistance they measure AC Resistance or what's call ESR or "Equivalent Series Resistance" and is typically larger than the actual DC Resistance. Also there is an inherent problem with using any meter to measure very small amounts of resistance and that is call "The parasitic resistance of the test leads" and is usually less than 1 ohm and needs to be subtracted from the reading you get from your meter.

Now if you don't have one of those high end, high dollar meters that can measure DCR down to a hundredth or thousandths of an ohm you can buy one ($$$+) if this is not an option for you, you could take them to a shop or a friend that has such a meter to get them measured.

Now there is a way to measure very small amounts of resistance using any run of the mill DMM, a couple bucks worth of parts, Ohms Law and what's call "4-wire (Kelvin) resistance measurement method" that will give you a very accurate reading with a resolution of better than a millionth of an ohm.

Ohms Law for calculating an unknown resistance states that if you push a known fixed amount of current through the device under test (in this case an inductor) and measure the voltage drop across the device under test you can calculate the resistance using the formula R = V / I, were R = Resistance, V = Volts and I = Current.

Let's use a real world example to illustrate this. If we take a 22 Gauge 0.4mH inductor and push 0.100 amps of current through it and measure a voltage drop of 0.0687 volts across it we can calculate the resistance using Ohms Law like this:

R = V / I
R = 0.0687 / 0.100
R = 0.687 Ohms

If you read DarqueKnight's thread I linked to earlier you will notice that he measured the same inductor with his Fluke 8050A multimeter and got a reading of 0.68 Ohms, How's that for the magic of math.

Here is a link to a tutorial on how to build the power supply and a video explaining the 4-Wire (Kelvin) method for measuring resistance.

Simple Low Resistance Measurement

Now if some of you guys measure the DCR of the stock inductors and post your results here like this,

0.300mH, 22 Gauge, DCR=X.****, Make & Part Number you replaced it with only if you had good results with the replacement.

I will update the above table, Hopefully we'll get the table filled in so we'll all have something to go by when replacing our inductors.

Hopefully I didn't confuse or bore the crap out anyone with this.

Happy Modding. :biggrin:

FTGV

Nice thorough work gimpod.

drumminman

Tony this is a great idea.

PolkieMan

Simple yet accurate.
So as long as you know the exact voltage and the exact current the resistance can be calculated simply by the drop in the voltage.
The kit was just to make it easier by providing a known amount of current divisible by 10.

headrott

Tony, this is an outstanding thing you did in your post! Thank you sir!

VR3

Do you guys want me to add this to the page?

Solid work Tony!

headrott

Yeah Trey, I think adding this to your mods page is a good idea.

VR3

Posted under "Replace Inductors" and "Schematics"

http://vr3mods.com/LCSDAUpgrade.html

vmaxer

I want to do this sometime. Good info!

DarqueKnight

Thanks Tony. Great info. I thought this was going to be a thread calling us insane for changing SDA inductors.:razz:

PolkieMan

Wow this would be cool leaving the old CO board intact and using "all" new parts on the Gimpod boards :cheesygrin:

gimpod

I'm giving this a bump cause I still need the values for the stock inductors for the 2.3TL & 3.1TL. If you want you can send me the inductors if you have no need for them and I'll measure them just PM or e-mail me for my address.

~ Thanks gimpod

drumminman

gimpod wrote: »

I'm giving this a bump cause I still need the values for the stock inductors for the 2.3TL & 3.1TL. If you want you can send me the inductors if you have no need for them and I'll measure them just PM or e-mail me for my address.

~ Thanks gimpod

Tony, I can send you the stock inductors from my 2.3TL's if you still need them. I'll try and get them packed up this weekend.

gimpod

That would be great Fred, PM sent.

PolkieMan

Excellent!

drumminman wrote: »

tony, i can send you the stock inductors from my 2.3tl's if you still need them. I'll try and get them packed up this weekend.

zane77

That's great, would love the values for the 2.3tl's, thanks for all your efforts Tony.

nspindel

Cool thread! Glad I have CRS+'s and the inductors were easily replaced without any calculus!

drumminman

gimpod wrote: »

That would be great Fred, PM sent.

Inductors on the way as of today - check your PM

gmcman

Awesome job! Yes, I would like to give this a try.

For the 2B pin/blade, are the above mentioned inductors all 4 that are used? The .4, 1.250, and 2.500?

Again, excellent write up....thanks for your efforts.

gimpod

gmcman wrote: »

Awesome job! Yes, I would like to give this a try.

For the 2B pin/blade, are the above mentioned inductors all 3 that are used? The .4, 1.250, and 2.500?

Again, excellent write up....thanks for your efforts.

That's correct.

The table has been updated to include the 2.3TL's (Thanks Fred and I'll get those inductors back to you ASAP), Now all I need is the DCR of a stock 18ga 1.25mh inductor or someone to send me one.

drumminman

Man that was fast! Nice work Tony.

gimpod

Updated to include the 18mH 20 Gauge inductor for the early SDA SRS 3.1TL Version A model. NO DCR value for it.

vcwatkins

Excellent. I was about to hit someone up for part #'s since I don't know inductors from, uh..... non-inductor-type-thingies. No reason now to keep putting this off. Thanks, @gimpod!

drumminman

vcwatkins wrote: »

Excellent. I was about to hit someone up for part #'s since I don't know inductors from, uh..... non-inductor-type-thingies. No reason now to keep putting this off. Thanks, @gimpod!

Do it - you'll be glad. I wasn't expecting much difference, but the increased clarity was easy to hear.

gimpod

Nesmith98 wrote: »

So I want to replace the inductors in my 1C's with Jantzen parts. And using the 1.250mH 1.329Ω 22 gauge inductor as an example. I should find the closest one that Jantzen offers which is the; #1137 1,250mH +/-3% 0,800Ω wire 0,80mm=20AWG OD-41 / 15mm. Then solder a Mills .5 resistor on to it. This would give it 1.300Ω.

Then this could be done for each inductor that does not have an exact match with a Jantzen part number.

I think you'll find that this is not a really good idea. The SDA 1C is IMO the least likely candidate for an inductor upgrade as 3 of the 5 board level inductors do not have a direct replacement (0.13mH 22GA 0.370 Ohms, 1.25mh 22GA 1.329 Ohms, and the 2.50mH 22GA 1.953 Ohms). The only real way would be to get a larger inductor in mH's and DCR but same gauge then unwind it. The only problem is inductor unwinding is not for the faint of heart and those on a budget. Getting the DCR right is the easy part just calculate how many inch's or feet of wire needs to be unwound by subtracting target DCR from actual DCR the divied the difference by Ohm's per inch for the wire gauge. Now the hard part getting the inductance to match, you may have to go through several inductors playing with the mH's and DCR to get a match and this can get expensive quick plus there's no guarantee you'll get any to match.

Here's a quote from a well respected member DarqueKnight's thread on this subject,

DarqueKnight wrote: »

Schurkey wrote: »

How 'bout a given inductance and a lower DCR, then add a quality resistor of proper value in series to return the DCR to stock spec?

Two things to consider when adding a resistor in series with an inductor in order to raise the inductors DCR:

1. An inductors DCR changes with temperature. It would be difficult to match a resistor's DCR temperature gradient to that of the associated inductor.

2. An inductors Q (quality factor), which varies with frequency, is decreased by adding external resistance. The higher the Q factor, the greater the ability of the inductor to store energy. Decreasing Q can result in decreased woofer control, which equates to decreased bass weigh and decreased bass detail.

I suggest you read the whole thread as it might give you some idea about how difficult and important inductor matching can be.

Upgrade Low Frequency Inductors For the SDA SRS 1.2TL


Off topic, I HATE THIS FORUM SOFTWARE!!

nspindel

When I did a pair of 1C's all I changed was the 16mH, the ones on the board stayed. I'm with Tony, just use the originals except for the 16.

machone

I just order the parts to build the 4-wire resistance measuring device that gimpod shared in this thread. I plan to measure the tweeter and mid inductors (I will post my measurements) to see if I can find a match from Solen or ?. I already changed the bass inductor to a Solen perfect lay with a dcr less than the original. In my system it is superior to the original with much better transients and more bass output but without any boom. When I get the 4-wire device built I will also measure and post the original and Solen bass inductors for reference.

tonyb

Excellent Tony, fantastic information and thank you for all the work you put into it.

Schurkey

Minor problem with chart in the first post--at least, I think there's an error.

The 1C is listed as having a 16mH SDA inductor. This seems to be correct.

The SDA 2 pin/blade is listed as having a 9.6mH SDA inductor. The pin/blade version of this speaker should be the equivalent of the 1C electrically, therefore the SDA 2 pin/blade should also use the 16mH inductor. The 1B, and SDA 2 blade/blade which are electrically equivalent use the 9.6mH SDA inductor.

gimpod

Schurkey wrote: »

Minor problem with chart in the first post--at least, I think there's an error.

The 1C is listed as having a 16mH SDA inductor. This seems to be correct.

The SDA 2 pin/blade is listed as having a 9.6mH SDA inductor. The pin/blade version of this speaker should be the equivalent of the 1C electrically, therefore the SDA 2 pin/blade should also use the 16mH inductor. The 1B, and SDA 2 blade/blade which are electrically equivalent use the 9.6mH SDA inductor.

@Schurkey The chart was correct, I just changed it to be more clear dropped the SDA from SRS SDA 2 P/B so it now reads “SRS 2 (1987 Pin/Blade)”. What you were reading was in fact SRS SDA 2 P/B not "SDA 2 P/B" also if you had noticed the titles of the chart Stock Inductor Values For 4th & 5th Generation SDA’s and again 4th & 5th Generation SDA’s Stock Inductor Values For The Sub-Bass Drive Circuit (i.e. The Big Inductor) there by indicating that this chart does not cover generations 1, 2, and 3 of the SDA’s i.e. the one with an blade/Blade connector. Also the SRS 2 (1987 Pin/Blade) is the only one to make use of the 9.6mH inductor after the 3rd generation SDA’s.


P.S. Off point, I REALLY HATE THE FORUM SOFTWARE!!!

machone

I finally took the time to build the low resistance measurement circuit.
I believe it is working ok. I measured a know resistor to test. Then I measured a 44" piece of 16 awg solid wire and got .01 ohms.
Now I can measure my tweeter and mid inductors and see if I can come up with a match for upgrading.