This must be the separate coil shown in my first photograph of the crossover board.
The resistance of a coil is only fractions of an ohm so you have not subtracted the resistance of the multimeter leads. Short the leads together to measure the resistance of the multimeter leads themselves then subtract that value from your total readings..
The inductance of a coil is measured in mH (millihenries) and you need an inductance meter to measure that.
The thickness or gauge (AWG) of the inductor wire determines the resistance of the inductor. The smaller the AWG number, the thicker the wire and the smaller the resistance for a given inductance.
All tests on the components of a crossover network must be performed with at least one leg of the component desoldered from the board.
Iron (or ferrite) core inductors have a low DC resistance for their inductance value. You should endeavour to obtain a substitute air cored inductor of equivalent DC resistance value as well as the same inductance value. Look at the manufacturers' specifications for these values.
Allow me to reiterate my previous statement that choosing the wrong types of replacement inductors could actually make your speakers sound worse. I see no good reason for changing the ones you have as they are commensurate with the overall quality of the speakers.
P.S. Short the Positecs with a short length of thin wire (same order of thickness as the legs on the Positecs themselves).
P.P.S. The inductance of wire wound resistors is so small that it is only of relevance at radio frequencies. Changing your present resistors will make no audible difference at audio frequencies. The only components worth changing in my opinion are the bipolar (non-polar or NP) electrolytic capacitors.
I should add that an air cored inductor, having the same inductance and dc resistance as the ferrite cored one you wish to replace, is likely to be physically larger.
And the choice can be bewildering! Audio Inductors - Air Core - Willys-Hifi Ltd
Check the downloadable files on the above site if you want to get technical!
And the choice can be bewildering! Audio Inductors - Air Core - Willys-Hifi Ltd
Check the downloadable files on the above site if you want to get technical!
Thanks G
I've measured the multi meter resistance at 0.5 ohm.
I'll need to cut away a coil from the circuit board to measure its resistance.
Are inductance meters expensive?
I'm very mindful of your warning and advice regarding replacement of the Inductors. If I do replace them I'll consider this very carefully in terms of making sure replacements have the same values.
An experienced Loudspeaker engineer advises that iron core inductors remain charged after the signal has passed resulting in possible smudging of the sound.
Do you think the HiFi set up I have isn't up to discerning any improvement to the signal path?
Why do speaker enthusiasts go on about getting rid of the cheap sandcast resistors often found in enclosures?
Can these cheap resisters either fail to meet their values or deteriorate, or contribute to sound deterioration due to their poor build, or other, to cause a difference?
You need to match the inductance and resistance of each coil for the crossover design to stay the same. The inductors you have are fine. The metal cores only really cause distortion at very high power levels if the core starts to saturate. That is very unlikely to happen with any competently designed speaker as the design engineer would have known to size the core correctly to avoid saturation. You can use any PC with a sound card and two resistors to measure impedance and determine the coil size. Look at the Arta software impedance program called Limp. The Limp user manual shows how to built the two resistor circuit required. I think other software like REW will do it as well. You can test the saturation distortion of a coil using Arta software, your power amp a 100W load resistor and an attenuator. So you don't have to listen to audiophile guru's that claim to hear things. It's just too easy to measure coil saturation.
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Your aim is to improve the sound quality of your speakers. I suggest you modify one of the pair of speakers in the ways you suggest, then compare it with the unmodified one. You will then be in a position to gauge which changes most improve sound quality for yourself.
You would need to do this in stages - change capacitors first then compare the sound, then change inductors and compare and finally resistors. It would be interesting to see which component or components make the greatest difference to the sound quality.
It's diyAudio so go ahead and experiment!
Google 'multimeter with inductance scale'. They cost very little. Example shown below.
Digital LCR Meter Capacitance Inductance Resistance Self-discharge Meter Multimeter | Wish
You would need to do this in stages - change capacitors first then compare the sound, then change inductors and compare and finally resistors. It would be interesting to see which component or components make the greatest difference to the sound quality.
It's diyAudio so go ahead and experiment!
Google 'multimeter with inductance scale'. They cost very little. Example shown below.
Digital LCR Meter Capacitance Inductance Resistance Self-discharge Meter Multimeter | Wish
Hi G.
I'm discovering that I'm having memory issues and forgot about our Mordaunt Short discussion on this thread regarding the overload protection devices.
Hope it's temporary and not the beginning of Alz!!!
I've done the recapping and replaced the resistors with like.
I'm following your advice and at this stage I'm leaving the inductors as they are.
I'd like to replace the overload protection devices ("MEXICO -35 805D" & "MEXICO -070 802C"), but can't find a source.
Digikey was suggested, but these particular devices don't show up on a search in their website.
You referred me to element14 from which I'll order the PTC 955's for the Jamo upgrade.
https://au.element14.com/epcos/b599...&ddkey=https:en-AU/Element14_Australia/search
It would be ideal if element14 had something suitable for the MD device replacements.
trobbins feels that the 802C -070 is likely 700mA hold and the 805D -35 may be 3.5A hold.
Sorry for the previous doubling up and memory issues.
Too many things on my plate.
cheers
Cliff
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Hi G.
I ended up replacing the 4 mm speaker sockets with non ferrous variants which allow bare wire connection as well as via banana plug.
Someone had replaced one of these plugs with a non standard connector which looked wrong and was ill fitting.
The new terminals have nice knurled knobs allowing a tight fit using spades or bare wire.
I understand less parts make a cleaner circuit, and most of the bargain banana connectors I had previously bought online ended up being magnetic.
cheers
Cliff
It's cool G.
I've written to element14 to find out if they stock the Positec overload protection devices.
I've also found a source of almost identical MEXICO devices on EBay, but it's a Chinese supplier.
I prefer to avoid a Chinese order, as my experience has been either 8 - 12 weeks delay or lost in the mail.
You did advise to cut them out of the circuit.
With new replacements do you think that the unreliability of these devises shouldn't be a problem for a considerable period?
Not knowing the Loudspeakers history I think it's worthwhile either eliminating or replacing them as they must be 30 or more years old.
thanks
Cliff
FYI: Yes, that's the most common definition. But there are exceptions as well: JBL, for instance, used to mark their professional drivers exactly the other way round. I still remember how puzzled I got when I bought and examined my 1st JBL woofer, a K130, in 1978 when I didn't know of this fact yet.
Best regards!
That remains my advice.
Without knowing the exact specifications of the original positecs, you will not be able to source replacements.
I removed the positecs from my Mordaunt Shorts years ago and I still haven't managed to blow the darned drivers up!
That makes it clear cut, quicker and cheaper.
I'll junk the positecs and replace by soldering in wires clipped from the PP caps.
element14 regrets they don't keep the original positecs.
The Chinese EBay examples display different part numbers, and as you say, might have different specifications.
I might go the same with the Jamos.
Always love saving on expenses.
Thanks
On a side note, the previous owner indicated the Mordaunt Shorts had poor bass reproduction.
I'll get them going with the cap/res replacements and generous internal insulation and review the bass situation.
Do you have any clues regarding bass?
I've heard it said that English speakers are good at mid to high range detail at the expense of bass. Don't know if this is a factor?
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Bass quality is a subjective thing and greatly dependent on room placement.
A differentiated 'British Sound' is pretty much a thing of the past. While the 'American Sound' was associated with a fullsome bass reproduction, the 'British Sound' was associated with a leaner, tighter bass.
We still hear of American speakers being 'tweaked' to suit British or European tastes, but I believe the differences are small (if not just marketing hype!) - see review below.
Polk Audio Signature S15e | Hi-Fi Choice
Hi.
I'll be working towards finishing the crossovers this weekend.
Do you recommend I test, on removal, the resistance of the positecs and match them with resistors in their place on the circuit board?
thanks.
I didn't do what you suggest, although Mordaunt Short claimed they took the small resistance of the positecs into account when designing the loudspeaker.
So you may like to replace them with their equivalent resistances, it's really up to you. Personally, I didn't detect an audible difference after simply removing the devices.
However, what if the positecs have gone high resistance over time? You would then be adding too much resistance to the circuit by replacing them with their measured resistance!
At the end of the day, if the positecs are measuring any more than a fraction of an ohm then they are suspect and I would simply remove (bypass) them.
I hope we have now exhausted all avenues, Cliff!
So you may like to replace them with their equivalent resistances, it's really up to you. Personally, I didn't detect an audible difference after simply removing the devices.
However, what if the positecs have gone high resistance over time? You would then be adding too much resistance to the circuit by replacing them with their measured resistance!
At the end of the day, if the positecs are measuring any more than a fraction of an ohm then they are suspect and I would simply remove (bypass) them.
I hope we have now exhausted all avenues, Cliff!
Thanks G.
I clipped the polytecs from the circuit board.
Before soldering pieces of wire to restore the circuit paths I measured the resistance.
After subtracting the resistance of the meter I measured the following:
The polytec (Mexico XD-070) measures 0.3Ω.
The polytec (Mexico XD-135) measures 0.1Ω.
So I decided, based on your experience and the very low resistances involved to go without adding resistors.
I can revisit this if I find the sound to be overly bright.
Once again thanks for your input.
Although war and peace, I learned a lot from your input.
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