Crossover nightmare!!!!!!!

[Inductor]

Originally Posted by dandoee

yes i like both, i am lucky enough to have saved £, then unlucky because i spent all that on pair pmc2b mk 11 so enjoy active in those immensely i every time i think i cant afford these without having a working studio i put some vinyl on bam!! they are worth every penny .

Do you mean the "PMC TB2S-A II" monitors?
PMC Ltd

[dandoee]

alan hi i have sent all (unused caps back) keeping the ones ive used .
its the F&T 68uf
thank-you for explaining capacitor pulse rise time , and how it applies to caps
i have taken readings as follows
( speaker 1) base 3.7 mid 0.9 trb=3.9
(speaker 2) base 3.9 mid 4.7 trb=3.7
i have checked this reading a lot it is correct . i have a problem dam now a new mid is needed

on the 9 v speaker test they all seemed as suggested some extra crackle in the low ohm mid
shop in USA any suggestions ??
all best dan

[dandoee]

yes its the "PMC TB2S-A II" quite right

[dandoee]

alan MY MISREADING my speaker ohm readings have one adjustment the one i first thought faulty 0.9ohm
is now 4.9 i checked it so many times getting correct contact ,
what is a mystery to me is when you meter past the soldered contact points on a small pcb
kinda lip and go straight to speaker braiding that goes to cone the readings are haywire
why is that ?? there is no separation components this side of contact?
dan

[alan-1-b]

Hi Daniel,

Often what happens when one trys to measure from the Braid is that the meter-probe does not maintain constant stable contact with the metal of the braid,
and sometimes the exterior of that metal is too much oxidised.
I recommend that you do not try to measure from on the braid,
because it is fragile - both itself, and where it connects at each end.
Better is to measure at the terminals -{the pcb you described}-on the back of the driver chassis,
and press the ends of the probes in firmly whilst rotating them a little so that they slightly penetrate through the surface oxidation,
or you may not get a stable reading.

For the mid with the 0.9 <--> 4.9 ohm reading, and because it gave "extra crackle" with the battery test,
it may be partially faulty, as these aging cones do become such,
but can still be used if continous reliable electrical circuit through,
so carefully check that one as follows:
if you can see where each end of each braid connects with both the cone and the back of the terminals' pcbs then look at each connection and very gently move the braid to see if the connection is still strong.
Pull it very softly only, and especially so if you cannot see it well.
Hopefully it will still be connected OK at each point on the cone, because that is delicate to repair.
If it is not firmly connected onto each input terminal's pcb, then heat the existing solder to melt it, and resolder with a bit more solder added,
but if the old solder is missing you will have to gently scrape-clean the surface of the braid AND the hole through the terminal to get all the surface oxide off so that a good electrical contact can be made.
Scrape-clean with a sharp blade - gently on the braid.
Do not rely on the Flux in the solder to sufficiently clean the old surfaces.

If still the occasional low ohms reading after all that, then the voice-coil may have too much of its insulation worn off - that does happen,
because the voice-coils will have expanded with age as result of the heat generated during playing,
and when expanded they rub on the magnet and the insulation wears away.
If that has happened you will have to find a specialist to remove and repair the voice-coil -{there is at least one repairer in the UK}
or search ebay until a 44 cone becomes available,
and then there are 2 different cones for the 44 - read earlier in this thread to find where LucasAdamson describes each so that you know which yours is.

---

I am still not clear on which caps you have kept - is it the 68uF F&T, and 2 or 4 of ?
or is it any PAIR of the Icel ?

If you have pairs you can use them,
but if its the F&T electros, well they were cheap thus not much lost if you decide to use the better poly caps for the bass/low mids' filter.

For prices, it is cheaper to buy the 250 volt size poly caps for mids and treble in the UK than from overseas, because they are made in the UK,
and cheaper to buy the 250 volt poly caps for bass filter from overseas because moderate priced ones are not made in the UK,
and the resistors will be cheaper from the o'seas sellers for the best type to use, but low price fairly OK resistors can be bought in UK.

If you don't mind buying from 2 different sellers ... and that is what I would do.

---

As you have those Active PMC loudspeakers you will be used to good quality sound when high volume level.
The old Celestion 44 cannot be safely played as loud as the recent PMCs , unless you are listening in a small room,
because the heat generated by pushing the Celestions hard will damage the voice-coils of the old drivers,
but at moderate driving force you can get a clearer sound from them if you replace the 3 ferrite cored inductors - the small ones on the boards -
2 in the bass and 1 in the mid filter.
Those saturate when pushed to highish current through, and the sound goes a bit muddy in the bass and low mids.
The 2 air-core inductors do not saturate, thus those can be kept - 1 in the mids' filter and 1 in the tweeter filter.
I mention this because if you are replacing ALL the caps with polypropylene types it is worth replacing the 3 cored inductors also,
unless you intend playing only at low volume levels.
You will not get PMC performance from the 44s , but you can approach it with air-core inductors,
and those can be bought in the UK ... but if you decide to, then post about that here before you buy, because there are matters to consider when choosing optimum inductors ...
and you can wind you own if you want to ... a discussion about that was started in this thread, but not finished however I will if you are interested to.

[alan-1-b]

I should have included in my last post:

For drivers where the voice-coil's electrical continuity seems suspect,
and particually if there may be rubbing of the voice-coil on the inside of the magnet, test as follows:

Choose music that has no bass - eg: solo violin recordings - I use Bach's Sonatas and Partitas for solo violin.
- or at least music that has no low bass and little upper bass, such as Bach's suites for solo Cello.
Solo Flute may be suitable also, but I have not tried such.
I have tried Acoustic guitar - both Nylon/Gut string and Steel string, and also acoustic guitar + vocal, for which female is the most suitable,
as may be unaccompanied female singing.

Connect the suspect driver directly to the amplifier - no crossover nor any other drivers.
Start at low volume and increase volume if sound is OK.
Listen carefully for any distortion, and it may be low level.
If you are not sure if distortion, then try the other driver of a pair
- in your case Daniel, compare to your OK measuring mid-cone -
to hear if sound is clearer through it.
A tiny amount of distortion may be acceptable, and there may still be some life-span left in the driver,
but if clearly annoying distortion, then it is not worth spending money on new capacitors, etc ... until a replacement driver is obtained.

Electric instruments often are distorted by intent, thus less useful for this test,
and Drums and some types of Piano recordings are less suitable, as they can render small degrees of distortion less audible.

For testing bass drivers, one can use lower bass music signals,
though here I find the Bach Cello suites to be suitable.
Again do not use any crossover between amp and driver.
Simple music signals, such as single instrument or singing voice, or duos, usually display any distortion more readily than multi-instrument recordings, but I have not tried Choral - I only thought of such now - however the various intermodulations in large choral can cause less clear sound through the amplifier -{regardless of its Technical distortion specification}- unless it is a very good quality amplifier,
and some Choral recordings are distorted in themselves - the fault of the engineers !
Spoken voice-{speech}- for test makes it less easy to hear the distortion at low levels than singing voice.

The distortion initially becomes evident as if something extra is playing along with the music, and varying in level,
and sometimes it is only there during some parts of the music and not in other parts.
This is the reason I think Choral music may not be suitable for this test - we need to hear if something is added to a simple signal.

Tweeters are the most difficult to test for the above.
First one MUST NOT drive them at or below their Fs, and not hard even an octave above their Fs,
thus if your crossover is known to not be faulty, then test them connected to the crossover,
but with the lower filters' arms of the crossover disconnected from the amp or with resistors connected in place of the lower drivers for dummy loads.
Do NOT drive any crossover filter that has no load connected, because it may cause your amp to draw excess current and burn-out its output stage.

If you tweeter filter is likely to be faulty, then find or estimate the Fs of the tweeter.
Connect a 5 watt resistor of equal or slightly higher resistance than the tweeter's DC resistance in Parallel with the tweeter.
Calculate the - 3dB point for a single capacitor filter into that resultant half-resistance as follows:
C = 160/ohms x kilohertz = uF, using kilohertz an octave or more higher than Fs.
Obtain the nearest size capacitance - any low price plastic film cap is OK for this test
and connect it in Series with the driver//resistor coupling.
The reason for the Parallel connected resistor is that it reduces the high Impedance magnitude of the tweeter's Fs.
It is necessary to reduce this impedance so that the voltage drop at that frequency will be mostly across the capacitor and not across the tweeter.
If most of the signal voltage is across the tweeter, then it will distort at its Fs even if no distortion in its higher frequencies,
and distortion at its Fs will mask whatever distortion that may occur at higher frequencies.
Test with solo violin or female singing, and listen for excess sibilence,
preferably in comparison to a known non-faulty tweeter.

[dandoee]

alan had the hell of busyness to deal with outside of this arena diy audio so appolagies for delay in response to your informative guidance in these matters , i am going to make time later to complete all superb tests you suggested and am vry interested in air core inductor replacements indeed ive had these 44 and project on the desktop for sometime now and am keen to complete ,or i could arrange to claim some space back as it seems with help from diy audo yourself included i can really tackle this .
testing later post follows
dan

[dandoee]

Alan hi i have completed testing as suggested , i also used bach solo sontana, played by viktoria mullova , perfect for the task. anyway both ohm and audio test seems good ,i suppose if i felt i had time i would like to have spl read , the response of all drivers individual im not set up for that now and must get on .

1,my past posts regarding AUDIO CAPS supply ,is now null and void lets just rub them of the board ,,starting from scratch ,
2, i have taken onboard your suggestion in regards to sourcing 250 polys for mid & top ,in uk & base + resistors overseas , do you suggest USA ?
3.ferrite core inductors are being replaced with air core from uk
i am going to start looking tonight for the inductors
look forward to hearing from you
dan

[alan-1-b]

Hi Daniel,

if I've understood your post correctly, it seems you intend to buy inductors rather than wind them yourself - yes ?
If so, for the two inductors in the bass filter section, these need to have the lowest DC resistance possible if you want tight and punchy bass,
and the maximum possible from the woofers, thus have to be made from thick wire, and with DC resistance significantly less than 1 ohm each.

For the 2.2mH inductor in the low-mid section of the midrange filter, this does NOT have to be extremely low DC resistance, and is better not,
but is better with a resistance between about 1 ohm <---> 1.5 ohm.
Thus thinner wire is OK there, and thus that inductor will be much smaller physical size than the 2.2mH in the bass filter.

What have you found so far ?

I'll post a UK seller who can wind suitable inductors for you at no greater cost than the other two UK sellers I know of, and I'll specify for you what to ask for there,
but do post here what you have found in case it is one I do not know about, and which may be better.

I'll post about the capacitors next time, as I'm out of time now.

[dandoee]

alan arfter carfull concideration , i have decieded to re install caps for now and see how it sounds .
thankyou for the advice on inductors if i decide later to replace i can refe to this post cheers.
i have left the two sets of bundled caps at the back of board on 44s as they are good ,
rplacement from FALCON AUDIO im not having a lot of luck here ordering caps , the tolerance ordere listed below , is not whats arrived, !! again im fed up with this i have +_5 tolerance on the solens and +_10 on the all cap ,i orded and payed for 2 and 3 tolerance what a cheek these people have do they think i wouldent notice ???,, this is what i ordered Solen 6.00uF 400V DC Polypropylene Capacitor
Capacitor Tolerance
2%
PB600-+2%
2
Solen 25.00uF 400V DC Polypropylene Capacitor
Capacitor Tolerance
2%
PB2500-+2%
2
Alcap 72.00uF High Power 100VDC Electrolytic Capacitor
Capacitor Tolerance
5%
72U00 V100KHV-+5%
4
Seas 19TFF 1 H0737-08 Tweeter - Prestige Series
Seas 19TFF 1 H0737-08
will be ringing jerry bloomfield at falcon audio tommorow
all best dan