Question on Inductors

drumminman

If you have an inductor made with the same wire gauge and inductance as the original factory inductor, does it follow that the DCR will be the same? If not what would cause it to be different?

For all you 2.3TL owners I've found someone who I think will wind inductors, at least the low frequency ones. The problem is Polk no longer has the DCR values in their files.

skrol

Not necessarily. There can be differences in the way that they are wound, shape, diameter of the core and type of core (air or iron). You can measure the DCR of your old inductor and find a match.

quadzilla

From DK's thread on inductor replacement "The stock 16 mH SDA inductors are comprised of 18 gauge wire and have a DC resistance of 2.8 ohms."

DarqueKnight

drumminman wrote: »

If you have an inductor made with the same wire gauge and inductance as the original factory inductor, does it follow that the DCR will be the same? If not what would cause it to be different?

For all you 2.3TL owners I've found someone who I think will wind inductors, at least the low frequency ones. The problem is Polk no longer has the DCR values in their files.

skrol wrote: »

Not necessarily. There can be differences in the way that they are wound, shape, diameter of the core and type of core (air or iron). You can measure the DCR of your old inductor and find a match.

Other important differences may be the dielectric properties of the insulation and the degree of mechanical vibration damping.

With regard to replacing the other inductors, it does not make sense to replace them unless you have some reasonable expectation that the replacements will offer higher performance.

quadzilla wrote: »

From DK's thread on inductor replacement "The stock 16 mH SDA inductors are comprised of 18 gauge wire and have a DC resistance of 2.8 ohms."

The 16 mH inductor DCR was actually 2.56 ohms. In my initial post I forgot to account for the 0.24 ohm resistance of the meter leads. A corrected measurement chart was posted.

FTGV

skrol wrote: »

Not necessarily. There can be differences in the way that they are wound, shape, diameter of the core and type of core (air or iron).

Correct since DCR is a function of wire gauge and length.

drumminman

Thanks for the responses! These would be air core, Solen perfect lay hexagonal wound.

As far as measuring the DCR of the inductor, can I touch the leads from a VOM on the inductor wires to get that? Would I measure the resistance of the VOM leads by touching the ends together and taking that reading?

DarqueKnight

drumminman wrote: »

For all you 2.3TL owners I've found someone who I think will wind inductors, at least the low frequency ones. The problem is Polk no longer has the DCR values in their files.

drumminman wrote: »

Thanks for the responses! These would be air core, Solen perfect lay hexagonal wound.

Are you saying that Solen has agreed to make custom inductors?

drumminman wrote: »

As far as measuring the DCR of the inductor, can I touch the leads from a VOM on the inductor wires to get that?

Yes, just like measuring a resistor.

drumminman wrote: »

Would I measure the resistance of the VOM leads by touching the ends together and taking that reading?

Yes.

In measuring inductor DCR and VOM lead resistance, you will need a meter that measures at least in hundreths of an ohm (two decimal places).

evhudsons

Is there an online course anyone is aware of or could recommend so I can learn some of this? Great stuff!

drumminman

Are you saying that Solen has agreed to make custom inductors?


My question to them was about matching inductance values for air core inductors in wire gauges that they stock (don't know about other wire gauges). They said they would. I would presume they would batch DCR as well, if I can work out the values.

My VOM's lowest setting is 200 ohms. That's not gonna work, is it?

thejck

measure the DCR of the multimeter by shorting out the probes. then measure the dcr of the coil by probing each end of the coil. then subtract the first value from the second and that should give you the DCR of the coil

DarqueKnight

drumminman wrote: »

Are you saying that Solen has agreed to make custom inductors?


My question to them was about matching inductance values for air core inductors in wire gauges that they stock (don't know about other wire gauges). They said they would. I would presume they would match DCR as well, if I can work out the values.

The person who answered my inquiry, Chris, said they would not do custom values for inductance and DCR for the small inductors in the high frequency circuit of my 1.2TL's.

drumminman wrote: »

My VOM's lowest setting is 200 ohms. That's not gonna work, is it?

The 200 ohm setting refers to range. What I was referring to was the measurement resolution of the meter. If your meter displays measurements this way:

2.3
1.7
5.6

then the resolution is in tenths of an ohm (one decimal place). If your meter displays measurements this way:

2.35
1.73
5.62

then the resolution is in hundreths of an ohm (two decimal places).

This is important because a meter which displays only one decimal place will show 5.3 ohms if the reading is actually 5.25, 5.28, or 5.34. VOM lead resistance is typically in the range of 0.2 to 0.4 ohm.

If you have an inductor with a nominal DCR of 0.56 ohm and the meter can only display 0.5 or 0.6, then that is a problem. If the VOM lead resistance is actually 0.24 ohm and the meter can only display 0.2 or 0.3, that is a problem.

drumminman

DarqueKnight wrote: »

The person who answered my inquiry, Chris, said they would not do custom values for inductance and DCR for the small inductors in the high frequency circuit of my 1.2TL's.







The 200 ohm setting refers to range. What I was referring to was the measurement resolution of the meter. If your meter displays measurements this way:

2.3
1.7
5.6

then the resolution is in tenths of an ohm (one decimal place). If your meter displays measurements this way:

2.35
1.73
5.62

then the resolution is in hundreths of an ohm (two decimal places).

This is important because a meter which displays only one decimal place will show 5.3 ohms if the reading is actually 5.25, 5.28, or 5.34. VOM lead resistance is typically in the range of 0.2 to 0.4 ohm.

If you have an inductor with a nominal DCR of 0.56 ohm and the meter can only display 0.5 or 0.6, then that is a problem. If the VOM lead resistance is actually 0.24 ohm and the meter can only display 0.2 or 0.3, that is a problem.

Interesting - a Chris also replied to mine. What wire gauge do your small inductors use? Here's what I asked him:

"I'm rebuilding the xovers in an older set of Polk SDA speakers and I'm looking for replacement inductors.

I need exact values in the following:

1.75 mH 20 awg

0.875 mH 18 awg

I need two of each (4 total). Would you unwind larger values of the Perfect Lay Hexagonal Winding Air Cored Inductors for me to meet these specs?"

DCR wasn't mentioned - wouldn't think that'd be the deal breaker

DarqueKnight

drumminman wrote: »

Interesting - a Chris also replied to mine. What wire gauge do your small inductors use? Here's what I asked him:

"I'm rebuilding the xovers in an older set of Polk SDA speakers and I'm looking for replacement inductors.

I need exact values in the following:

1.75 mH 20 awg

0.875 mH 18 awg

I need two of each (4 total). Would you unwind larger values of the Perfect Lay Hexagonal Winding Air Cored Inductors for me to meet these specs?"

DCR wasn't mentioned - wouldn't think that'd be the deal breaker

The Solen inductors used to replace my 1.2TL's low frequency inductors were exact matches in inductance and DCR. If Solen agrees to unwind their 1.8 mH 20 AWG and 0.91 mH 18 AWG inductors you are in luck.

In my case, I needed 0.4 mH 22 AWG (0.66 ohm DCR) and 0.7 mH 25 AWG (0.57 ohm DCR) inductors. The smallest wire gauge solen makes is 20 AWG. The closest they had to what I needed was 0.39 mH 20 AWG (0.42 ohm DCR) and 0.68 mH 20 AWG (0.57 ohm DCR).

drumminman

DarqueKnight wrote: »

The Solen inductors used to replace my 1.2TL's low frequency inductors were exact matches in inductance and DCR. If Solen agrees to unwind their 1.8 mH 20 AWG and 0.91 mH 18 AWG inductors you are in luck.

In my case, I needed 0.4 mH 22 AWG (0.66 ohm DCR) and 0.7 mH 25 AWG (0.57 ohm DCR) inductors. The smallest wire gauge solen makes is 20 AWG. The closest they had to what I needed was 0.39 mH 20 AWG (0.42 ohm DCR) and 0.68 mH 20 AWG (0.57 ohm DCR).

I thought the wire gauge might be the problem. They don't have inductors with wire gauges that match the ones in my high pass section either: 0.3 mH and 0.4 mH, both in 22 awg.

In your opinion should I get them to unwind them and, based on your experience, assume that the DCR will match?

thejck

If you know what the guage, exact DCR and mH of the coil is you can use this calculator
http://www.diyaudioandvideo.com/Calculator/Inductor/
Play with the dimensions of the inductor so that you get it to spit out the exact DCR you are looking for.
I tried to get this to give me dimensions of the LF coils in the 1.2TL using DK's numbers for the DCR and was successful. I was considering winding my own coils. However I got luck with the stock solens.

skrol

drumminman wrote: »

... My VOM's lowest setting is 200 ohms. That's not gonna work, is it?

Unfortunately, no. I have a nice Fluke 187 that can measure resistance: Accuracy ? (0.05%+2) and Max. Resolution 0.01 Ohms and a $3 Harbor Freight DMM with unknown specs. When I measured the new Mills 1.5 ohms 1% resistors in my XO's they measured 1.48 ohms using the Fluke and 3.6 ohms using the Harbor Freight special.
Stan

DarqueKnight

drumminman wrote: »

In your opinion should I get them to unwind them and, based on your experience, assume that the DCR will match?

There may be other factors involved and I might have gotten lucky. You should tell Solen that it is important to meet your DCR target and if unwinding their inductors will get you to the desired inductance value and DCR.

drumminman

I think I'm attempting to take a short cut here and it's not a good idea :redface:

I checked my VOM again, and if I set the Ohms to 2K I get a reading of 1-2 whole numbers + 3 decimal places, so I should be good to go for checking dcr on the original inductors. Now I just have to find the time to pull the Xovers, desolder the inductors and measure 'em.

Thanks for your help everyone, especially you DK.

DarqueKnight

drumminman wrote: »

...if I set the Ohms to 2K I get a reading of 1-2 whole numbers + 3 decimal places, so I should be good to go for checking dcr on the original inductors.

No.

If you are tying to measure single digit ohms or fractions of one ohm, why would you expect a meter setting in thousands of ohms to give accurate results? The lead resistance should be well below 0.5 ohm. Set the meter on 2K, connect the leads together and see what the meter reads. Repeat for a small value resistor like 2.7 ohms.

drumminman wrote: »

Now I just have to find the time to pull the Xovers, desolder the inductors and measure 'em.

No.

You also have to find a meter that measures low ohms. Here's a link with more information:

Low Ohm Measurements

drumminman

DarqueKnight wrote: »

No.

If you are tying to measure single digit ohms or fractions of one ohm, why would you expect a meter setting in thousands of ohms to give accurate results? The lead resistance should be well below 0.5 ohm. Set the meter on 2K, connect the leads together and see what the meter reads. Repeat for a small value resistor like 2.7 ohms.



No.

You also have to find a meter that measures low ohms. Here's a link with more information:

Low Ohm Measurements

Thanks for the link - and helping me not to screw up my speaks! Looks like I need two things: a bit more knowledge, and a better DMM. Man those Flukes are high dollar.

DarqueKnight

drumminman wrote: »

Man those Flukes are high dollar.

But they're worth it!!!

You don't have to pay high dollars to get an accurate low ohm meter.

I have a variety of hand-held VOMs, but I wanted a bench meter and didn't want to spend four figures. I recently bought an old Fluke 8050A off eBay for $150...and that is on the high side because I wanted one that was calibrated and came from a test lab with a certificate of calibration. 8050A's in excellent condition can be purchased from between $50 and $75.

After reading the 8050A's manual, I realized I could have taken my 8050A to work and calibrated it myself.

skrol

Ebay can be a great source at times. I paid about $150 for my calibrated Fluke 178. It still had the shipping plastic film over the display and a very nice leather case.
Stan

drumminman

How often do the Flukes need calibration?

I'm guessing that the average hobbyist won't have the equipment to do this, so it would have to be sent somewhere. Where would one send it?

DarqueKnight

Like any tool or machine, the maintenance interval of a precision laboratory instrument depends on the amount of use, type of use and level of measuring precision that must be maintained. The manual for my Fluke 8050A states:

"Under normal operating conditions the 8050A requires calibration once every year."

For a laboratory grade instrument such as the 8050A, "normal operating conditions" would consist of several hours of daily use during a five day work week. Of course, if the multi-meter is used infrequently at home in pursuit of a hobby, the maintenance interval would be longer.

drumminman wrote: »

I'm guessing that the average hobbyist won't have the equipment to do this, so it would have to be sent somewhere. Where would one send it?

Do a web search on "multimeter calibration services".

The required calibration tools are a digital multi-meter calibrator and digital multi-meter calibration leads. A used Fluke 5700A multi-meter calibrator will cost between $24,000-$36,000.

RickTfromAZ

DarqueKnight,

Have you checked out Jantzen Audio?
They have some air-core coils that are pretty close to the OEM Polk coils.
They have two listed as being 0.4mH/0.64 Ohms. One is 21 awg and the other is 22 awg.
They also have a 0.7mH/0.710 Ohms that is 21 awg.

http://jantzen-audio.com/download/coils/Wire%20Coils%20List%20%2004%2006%202008.pdf

RickTfromAZ

Correction on that last post. The DCR of the 0.7mH air-core is wrong. The closest that Jantzen gets for the DCR on the 0.7mH is a 1.25 Ohm DCR. So the 0.7mH is not likely a candidate.

The closest air-core that I found to 0.7mH on Jantzen's list is a 0.65mH/1.68 Ohms 26awg.

Toolfan66

I like to be calibrated now and then:cheesygrin:















Now where is my wife?

DarqueKnight

RickTfromAZ wrote: »

Have you checked out Jantzen Audio?

I have not. What performance advantages might the Jantzen inductors offer over the stock inductors?

RickTfromAZ

DarqueKnight wrote: »

I have not. What performance advantages might the Jantzen inductors offer over the stock inductors?

Very simliar to the Solen inductors. Perfect layer construction. As I understand it, the biggest drawback to the bobbin-type inductors is that they are more susceptible to vibration and ringing. The dielectric (bobbin material) may also play a role in the degredation of sound.

DarqueKnight

RickTfromAZ wrote: »

They have two listed as being 0.4mH/0.64 Ohms. One is 21 awg and the other is 22 awg.

RickTfromAZ wrote: »

The closest air-core that I found to 0.7mH on Jantzen's list is a 0.65mH/1.68 Ohms 26awg.

These should work.

The nominal DCR of the 0.4 mH Jantzen inductor is only 0.02 ohm less than the measured DCR of the Polk OEM part. The 0.65 mH inductor is within the 5% tolerance range of the 0.7 mH OEM part, plus the nominal DCR is only 0.02 ohm more than the OEM part.

I didn't find them on the Parts Express website, so I assume they are special order items. I'm waiting for PE to get back to me with prices and delivery times.

RickTfromAZ

http://www.audio-components.co.uk/store/wirecoils.asp

This place is in the U.K., but they have both inductors listed on their website.