Polk SDA 1a Is This Wire Wound Part Of The X-over Smoked?

Benjisan

Is This Wire Wound Part Of The X-over Smoked?

Started working on these in order to replace the capacitors and noticed the upper portion of the interconnect crossover board with copper wound wire appears to look suspicious.

Any thoughts?

pitdogg2

It's been real hot. I'd suspect the enamel that coats the wire to keep from shorting out on itself may be gone.
Good news is you can replace it with a new pair Jantzen air-core inductors. Your schematic is in the link below


https://forum.polkaudio.com/discussion/55888/polk-audio-speaker-wiring-schematics-amp-more-stereo-dimensional-array-sda#latest

audioluvr

SMOKED!

Gardenstater

I bet if you do the resistance checks in the SDA Handbook for your model, it will reveal that there is at least a partial short in that inductor. I vote SMOKED.

Benjisan

Thanks guys.

In the photograph below you can see that the other one in the right speaker looks suspect too.

I'm pretty sure those being faulty along with the 35 year old capacitors are why these speakers sound like shite.

Somebody school me as to how well these inductor parts need to be matched to their 1.82 mh oem specs.

Say would a 1.5 mh inductor work okay.

By the way I just picked up a very decent looking pair of Polk Monitor 10a for $50 off of guy selling them about 45 minutes away from me.

I just grabbed for the MW thinking they might be good spares to have for these SDA's but they are in such good shape I'm wondering if it would be worth it to refurbish the crossovers in them. All the drivers wires are soldered on. When I tested them they were both muffled and no sound was coming from either tweeter.

Gardenstater

I would say +/-5% would be OK and they should be matched to each other within 1%. But if 1.82mH is correct, 1.5mH is outside that range.

I think your speakers use the MW6501 or MW6600x. I do not know what MW drivers your Monitor 10s have. They aren't the favorite among the monitors because of the lobing issue. It was fixed in later speakers like the RTA12 and the Monitor 11 and they had different frequency ranges going to each MW driver. Lots of people enjoy listening to their Monitor 10s however! A really cool thing to do is to turn them into SDAs and several members have done that. You need the XO from a SDA CRS+ IIRC. I think tennman has done this?

pitdogg2

Make me wonder if someone tried to use mono amps or non-common ground amp and the interconnect cable?
IIRC you also need more than just the mH value, doesn't ohm value and wire gauge also come into play?

Benjisan

Gardenstater wrote: »

I would say +/-5% would be OK and they should be matched to each other within 1%. But if 1.82mH is correct, 1.5mH is outside that range.

I think your speakers use the MW6501 or MW6600x. I do not know what MW drivers your Monitor 10s have. They aren't the favorite among the monitors because of the lobing issue. It was fixed in later speakers like the RTA12 and the Monitor 11 and they had different frequency ranges going to each MW driver. Lots of people enjoy listening to their Monitor 10s however! A really cool thing to do is to turn them into SDAs and several members have done that. You need the XO from a SDA CRS+ IIRC. I think tennman has done this?

Hey guys,

What's your opinion on this inductor as a suitable replacement.


https://www.parts-express.com/Jantzen-1131-1.8mH-18-AWG-Air-Core-Inductor-255-264

Gardenstater

Hard to say without knowing the DCR of your Polk OEM inductors. You can measure the wire diameter and try to get the same awg in the replacement coil, but there are lots of factors besides awg that determine the inductance. So you really need to know what the DCR is supposed to be, but yours may be partially shorted making measurement impossible. I would start by trying to check the DCR of both inductors with a meter. That Jantzen one you're considering is 0.74 Ohms. In the SDA Handbook they speak of lower DCR SDA inductors being a modification that has merits in better bass response. So maybe having a wee bit lower DCR wouldn't be so bad.

From Pin#1 to Pin#2 you're supposed to have 10.5Ohms +/-5%. That includes the SDA MW and the inductor in question. The MW6501 is supposed to have a DCR of 7.75Ohms, which you can calculate the Inductor DCR to be 2.75Ohms. At the very least probably 2.25Ohms. I'm guessing your OEM inductor is smaller than 18awg of the Jantzen. 0.74Ohms would be quite a bit lower DCR.

Benjisan

pitdogg2 wrote: »

Make me wonder if someone tried to use mono amps or non-common ground amp and the interconnect cable?
IIRC you also need more than just the mH value, doesn't ohm value and wire gauge also come into play?

Pitdogg,

These were my deceased brothers speakers from day one. He never had any mono amps as far as I can recall. He used these originaly with a Pioneer 1980 which was shelved and sold after the tuner failed and one channel gave up the ghost. He was then using them with a Nakamichi Pa-5, which is currently in my possession.

Perhaps it was the Pioneer that damaged the speaker.

invalid

I don't think the Nakamichi pa5 is common ground. It's a nelson pass designed amp, it was designed like the threshold stasis amps which are not common ground.

Benjisan

Gardenstater wrote: »

Hard to say without knowing the DCR of your Polk OEM inductors. You can measure the wire diameter and try to get the same awg in the replacement coil, but there are lots of factors besides awg that determine the inductance. So you really need to know what the DCR is supposed to be, but yours may be partially shorted making measurement impossible. I would start by trying to check the DCR of both inductors with a meter. That Jantzen one you're considering is 0.74 Ohms. In the SDA Handbook they speak of lower DCR SDA inductors being a modification that has merits in better bass response. So maybe having a wee bit lower DCR wouldn't be so bad.

From Pin#1 to Pin#2 you're supposed to have 10.5Ohms +/-5%. That includes the SDA MW and the inductor in question. The MW6501 is supposed to have a DCR of 7.75Ohms, which you can calculate the Inductor DCR to be 2.75Ohms. At the very least probably 2.25Ohms. I'm guessing your OEM inductor is smaller than 18awg of the Jantzen. 0.74Ohms would be quite a bit lower DCR.

George,

I'm going to take ohm readings tomorrow and see what the numbers are.

This inductor has a DCR of 0.97Ω but it's a 1.75mH with 20 AWG

https://www.parts-express.com/Jantzen-0819-1.75mH-20-AWG-Air-Core-Inductor-255-053

Would it be worth contacting Polk directly in order to see it they have the proper replacement inductors?

Benjisan

invalid wrote: »

I don't think the Nakamichi pa5 is common ground. It's a nelson pass designed amp, it was designed like the threshold stasis amps which are not common ground.

I can't be sure that he ever used that amp with these speakers, but I do know that these SDA's were stored in his basement for the past 20 years.

He was using his M & K S-100b and the Mx-125 sub woofer for the longest time until he sold them to one of his coworkers.

invalid

https://meniscusaudio.com


If you find out what inductors you need. They unwound some inductors for my sda2a's.

Benjisan

invalid wrote: »

https://meniscusaudio.com


If you find out what inductors you need. They unwound some inductors for my sda2a's.

Thanks Invalid,

That's a great source since they can customize the values for you.

Now if I can somehow determine the correct inductor values for these speakers.

Benjisan

Okay fellows,

I took some ohm readings going through the interconnect cable and the left speaker measured 11.8 ohms and the right measured 11.5 ohms.

Definitely not the ideal specification the SDA handbook lists.

What do you guys think?

Gardenstater

So it's high, which is unexpected if there were shorts from enamel melt in the inductors. Hmmm. I'd measure the inductor DCRs outright, in isolation next. What does your meter read when the probes are touched together? Any reading above zero should be subtracted from all resistance measurements.

Benjisan

Gardenstater wrote: »

So it's high, which is unexpected if there were shorts from enamel melt in the inductors. Hmmm. I'd measure the inductor DCRs outright, in isolation next. What does your meter read when the probes are touched together? Any reading above zero should be subtracted from all resistance measurements.

Yes George, it doesn't seem to be fried.

I just removed the top x-over network that uses the bolt with the Allen head and have the top half of the x-over on my desk.

I took my meter and measured across the + and - probes and it bounces between 00.2 & 00.3 ohms.

I didn't truly isolate the 1.82 mh inductor completely from the circuit board as I just probed the under side for a quick reading and my meter reads 00.9 ohms.

Would it be safe to ****ume that the inductor is still functioning okay?

Gardenstater

So 0.9 - ~0.25 = approx. 0.65 Ohms? What do you get for the DC resistance of the SDA MW drivers? Something isn't adding up. The other thing you need to check and do is to clean all the connections on the XO and to the XO. Some crocus cloth or ~1500 grit sandpaper would work well, followed by some alcohol on a cotton swab or the like.

What is the awg of the SDA inductors? If you have a caliper you can measure dia. and look up awg in an online chart.

Too soon to say the inductors are OK yet.

SeleniumFalcon

If you want to send the inductors to me I'll measure inductance and return quickly, no charge.

Benjisan

Gardenstater wrote: »

So 0.9 - ~0.25 = approx. 0.65 Ohms? What do you get for the DC resistance of the SDA MW drivers? Something isn't adding up. The other thing you need to check and do is to clean all the connections on the XO and to the XO. Some crocus cloth or ~1500 grit sandpaper would work well, followed by some alcohol on a cotton swab or the like.

What is the awg of the SDA inductors? If you have a caliper you can measure dia. and look up awg in an online chart.

Too soon to say the inductors are OK yet.

Hi George,

Well to be quite honest I can't vouch for the accuracy of my meter since I'm using a Radio Shack Micronta 22-188 DVM from the 1970's.
As far as the DCR of the MW drivers I posted them in a previous thread here. If I remember correctly I was seeing high 7's and very low 8's.

The 1.82 inductor wire measures 0.48 mm or 0.018"

My guess is that this is most likely aircraft grade wire and the corresponding numbers with the addition of the lacquer coating make these inductor windings right around 18 gauge wire.

SeleniumFalcon wrote: »

If you want to send the inductors to me I'll measure inductance and return quickly, no charge.

Selenium thats a nice offer.

Where about do you live?

Benjisan

By the way unless my eyes are deceiving me, I don't see the 5.6 mh inductor on my stereo module pc board.

Can someone verify that I'm either going blind or the said component is there and I'm overlooking it.

Gardenstater

Probably 25awg or 26awg then. https://www.powerstream.com/Wire_Size.htm

Must be high contact resistance connections (need cleaning) if 0.9 + ~8 = 11 or so. The missing 2 Ohms must be bad connections.

But it still looks like the inductors might be bad, unless I'm missing something. Should be around 2.25Ohms but you get 0.65Ohms or 0.9 Ohms or so.

The 5.6mH inductor would be too big to be on the board. Must be wrapped on the binding post plastic bobbin

Benjisan

Gardenstater wrote: »

Probably 25awg or 26awg then. https://www.powerstream.com/Wire_Size.htm

Must be high contact resistance connections (need cleaning) if 0.9 + ~8 = 11 or so. The missing 2 Ohms must be bad connections.

But it still looks like the inductors might be bad, unless I'm missing something. Should be around 2.25Ohms but you get 0.65Ohms or 0.9 Ohms or so.

The 5.6mH inductor would be too big to be on the board. Must be wrapped on the binding post plastic bobbin

Lol, yes George as that would be the big winding that has the bolt going through it to secure the board to the speaker cabinet.

There’s no published values for the 1.82 mh inductor, but I was looking at similar value inductors and none of them are above 1.00 DCR measurements. I was thinking the 1.82 mh inductor in the SDA has a value of 0.72 DCR?

Or am I wrong?

So my speakers are about 8 ohms and the interconnect pins 1 and 2 are suppose to be around 10.5 and mine measured 11.5 as the difference would be about 1 ohm, no?

Gardenstater

From Pin#1 to Pin#2 is *supposed* to be 10.5 Ohms +/- 10%. Another table in the SDA Handbook says 10.0 Ohms. Whatever. You are getting a slightly high of a reading of 11.5 Ohms although it is right at the upper end if +10%. Also, if you look at the schematic the only way DC current can pass from Pin#1 to Pin#2 is to go through some wires and associated connections AND MW6501 and 1.82mH inductor. However you are reading 0.9Ohms for the inductor and around 8 ohms for the MW6501. 8 + 0.9 is approx. 9 ohms. You are reading 11.5 Ohms. The missing resistance must be in bad wiring/connections. Also, since the wires and connectors should be approx. 0 Ohms, the Inductor *should* be around 2.25 - 2.75 Ohms by calculation. 10.5 (or 10) - 7.75 Ohms = 2.75

So things don't add up is all I can say. You need to check those wires and connections.

Gardenstater

"There’s no published values for the 1.82 mh inductor, but I was looking at similar value inductors and none of them are above 1.00 DCR measurements. I was thinking the 1.82 mh inductor in the SDA has a value of 0.72 DCR?"

Is that for a 25 or 26awg inductor? According to the chart (posted link) a 0.018" dia. wire is 25awg. Maybe 26awg depending upon enamel thickness.

Gardenstater

Here ya go! Jantzen makes a 26awg 1.82mH air core that might be pretty much a direct replacement for what you have. It has a DCR of 3.087 Ohms.

https://www.hificollective.co.uk/catalog/000-0159-1820mh-jantzen-air-core-wire-coil.html

There is also a 24awg one that is 1.8mH that has a DCR of 2.2 Ohms

https://www.hificollective.co.uk/catalog/000-1868-1-8mh-jantzen-air-core-wire-coil.html

Benjisan

Gardenstater wrote: »

From Pin#1 to Pin#2 is *supposed* to be 10.5 Ohms +/- 10%. Another table in the SDA Handbook says 10.0 Ohms. Whatever. You are getting a slightly high of a reading of 11.5 Ohms although it is right at the upper end if +10%. Also, if you look at the schematic the only way DC current can pass from Pin#1 to Pin#2 is to go through some wires and associated connections AND MW6501 and 1.82mH inductor. However you are reading 0.9Ohms for the inductor and around 8 ohms for the MW6501. 8 + 0.9 is approx. 9 ohms. You are reading 11.5 Ohms. The missing resistance must be in bad wiring/connections. Also, since the wires and connectors should be approx. 0 Ohms, the Inductor *should* be around 2.25 - 2.75 Ohms by calculation. 10.5 (or 10) - 7.75 Ohms = 2.75

So things don't add up is all I can say. You need to check those wires and connections.

Okay I tested all the speaker lead wires from the female ends back to their circuit board solder joints and all of them test fine with nothing being open in the wiring.

DMM with both leads - and + connected to each other have 00.7 reading.

I measured the 1.82 mh inductor across the solder spots and 01.2 ohms and subtracting 00.7 from the inductor value measure = 0.5 ohms.

That obviously means that I have a very low a DCR reading for that inductor if it's suppose to be reading around 2 ohms or more.

I agree George, there's a lot of missing resistance.

My guess the 1.82 mh inductor is compromised.

If I were going to replace them with the Jantzen inductors from the two links you provided I'm thinking the 1.8mH 24 gauge one with slightly lower DCR. would be a better choice since most of my amps are pretty solid in the 200 watt range. I plan to use these SDA's with my a Anthem MCA 20 that can handle 2 ohm dips without any issues.

Gardenstater

Another option for you then is the Mundorf 0.5mm 1.8mH 2,26 Ohm

https://www.hificollective.co.uk/catalog/l50160-180mh-inductor-p-2867.html

SeleniumFalcon

Western Maryland

Benjisan

Gardenstater wrote: »

Another option for you then is the Mundorf 0.5mm 1.8mH 2,26 Ohm

https://www.hificollective.co.uk/catalog/l50160-180mh-inductor-p-2867.html

Thanks for another excellent link and all your help George.

What I'm going to do next is measure the other 1.82 mh inductor from the other crossover board to get a direct DCR comparison as it looks to be in excellent shape before I order any replacement parts.




Thanks Selenium, but I'm pretty sure that the inductors in question are damaged.


This quote below is from this link here on testing inductors.

http://www.learningaboutelectronics.com/Articles/How-to-test-an-inductor

"The inductor should read a very low resistance across its terminals, only a few ohms. If an inductor reads a high resistance, it is defective and should be replaced in the circuit.

If an inductor is reading very, very small resistance, less than an ohm (very close to 0Ω), this may be a sign that it's shorted. Functional inductors normally read a few ohms, greater than 1Ω and normally less than 10Ω. This is a healthy range for an inductance value. Outside this range and this is normally a sign the inductor is bad.

So a resistance check is a simple but effective method for finding out if an inductor is defective or not."