Wharfedale Dovedale 3-way crossover

[hfivefour]

Firstly I have to confess I haven’t got a clue what I’m talking about (I’m not an electronic engineer and don't understand the symbols) but I wondered if someone could provide or point me at an idiot guide to what the various numbers mean on the 3-way crossover units I have on my son Wharfedale Dovedale 3. I suume its to do with the frquency filtering,

One speaker has died with only a faint sound out of the tweeter. The mid and bass are dead. On removing the back I see three coils and what I assume two capacitors and another thingy. I think my son who is back o to vinyl shorted the two L/R speaker wires when he reconnected them after moving it for a NYE party.

The coils are marked 403.05 4.0mH, 403.10 0.5mH and 403.11 0.3mH.
The two Elcap capacitors +25mfd and +5mfd and the ‘thingy’ 3.3ohm.
They are all mounted on a Pressac 40/232 board.

I have seen another Pressac 40/232 3-way crossover unit but the markings are different. The circuit board is marked 'Pressac 40/232' and '2036-4' like mine but with the coils marked 403.09 2.0mH and 402.06 0.2mH with one unmarked. On these there are three ELCAP capacitors are marked 50V and 25mFd, 12mFd and 4mFd.

I assume this is from a different speaker set with different wattage.

May not be the crossover but drivers/speakers but all three to have gone!

Trying to understand if fixable and way forward cos nice classic speakers.

Any guidance gratefully received.

There should be photo of mine here.

[paulsherwin]

I assume that you've swapped the speakers to eliminate an amplifier fault?

[RojDW48]

I can't think why your son would have disturbed the x-over connections to move the speakers. You could test the individual drivers with an AA battery - hold one end on one terminal, hold a bit of wire to the other end and wipe it across the other terminal - if you get a crackle, the driver is probably OK.

[hfivefour]

Thanks for prompt replies.
I had swapped speakers around, changed leads and outputs from the amp. The other speaker is fine, the dodgy one fails whatever output, lead etc. combination.

Did the swipe test on bass and tweeter, both crackled. Have not tested the mid as it is sealed internally in a cardboard cone, and I would only want to break the seal as a last resort.

Totally unqualified to say, and only based on advice, but all have gone which would suggest crossover to me.
Which brings me back to what the numbers mean, if I want to look for replacement. If only to use as a test.

I could use the other crossover from the other speaker, but I don't want to knacker that one aswell.

['LIVEWIRE?']

The numbers 403.05, 403.10, & 403.11 may only be part numbers(others may know better), however 4.0, 0.5, & 0.3mH (millihenries) are inductance values. These devices are unlikely to be faulty, but the Capacitors (25uf & 5uf -uf = microfarads, btw. may be faulty. Note tht capacitors in crossovers are usually of thnon-polarized type, so I'm puzzled by the +25uf marking. The 'thingy' is a 3.3ohm resistor which could be faulty. A multimeter set to a low ohms range is needed to check this component. The other Pressasc crossover boards you have are obviously made for different drive unit (i.e. speaker) combinations, as you rightly say. Individual speakers (disconnected from the crossovers) can be checked with a multimeter on a low ohms range. If their speech coils have continuity, they should read between about 4 and 8 ohms, anfd, if the speakers are in a working condition, you should hear a 'click' in them when the meter probes are applied.

[RojDW48]

It probably is the x-over at fault. You could do the 'swipe test' on the wires to the mid range driver if you pull them off the x-over. The capacitors are probably non polarised electrolytics and it wouldn't hurt to change them anyway on such an old speaker. I did that recently on a pair of old Radfords - I got the caps from The Hi-Fi Collective. You just need to read the values off the existing caps - in uF (microfarads) - how's your soldering?

[hfivefour]

Again many thanks for comments. Slowly some of its starting to make sense.

After doing the 'crackle' test with the battery I am thinking of changing the capacitors and maybe the resistor. Assuming coils ok.

Through web searches I can easily find what appears to be like for like capacitors at 50v 25ufd and 6ufd specifications. Although ALCAP seems to have superceded ELCAP.

The 3.3ohm resistor is a bit confusing as not sure how many flavours the come in i.e. what wattage I should be looking at.

I have a friend who does domestic electrics pat testing etc. some maybe able to test item but this is an exercise in understanding and rescuing older audio. seems a shame to bin it.

All I need to do now is figure out how to de-solder as my soldering iron has little impact on what is probably 40 year old soldered components.

Anyhow photos of resistor cos not sure what the 39 followed by splodge means, if anything. Also if anyone interested actual speaker I'm guessing from early 70's. I understand the purple tweeters are well regarded.

[paulsherwin]

I have to say that it's very unusual for a crossover to fail in this way. Given that the speakers have just been used for a party, are you sure the woofer hasn't blown? Speakers of this era don't have great power handling, and can easily be damaged by a cranked up modern amp. You should be able to move the woofer cone in by pressing it gently with your outstretched fingers. There should be no roughness or sticking.

[Hartley118]

Many years ago I built up a couple of the Wharfedale 'Unit 3' kits, which were essentially Dovedales in a build-your-own-cabinets kit form. Rather good they were too, and I used and abused them at home and in halls. What I found was that the mid-range units were rather quick to fail. I replaced them with KEF B110 units which, along with the Wharfedale 12-inch woofers, still survive to this day.

So my first diagnostic test on your speakers would be the battery 'click' test on the mid-range units. Although as you say, the units are inaccessible, you should be able to trace the wiring to them and get access to the connections on the crossover board.

Best of luck!

Martin

['LIVEWIRE?']

Those wirewound resistors, at an educated guess, are either 3 or 5watt typles. The symbol to thr right of the value (omega)is the standard way to indicate 'ohms'. If they measure 3.3 & 3.9 Ohms repectively, they don't need changing, but, if they do, replace them with 5 watt types of the same resistance as the originals. Desoldering components is easier using either a solder sucker or 'solder wick' desoldering braid.

[Phil Pearce]

Hi FiveFour.....Try resoldering all of the connections in the Xover. You might get lucky!! If you have a radio where you can access the speaker connections, use clip leads to connect to the suspect Dovedales, one at a time. This will most likely confirm whether or not they are functional. Good luck...Phil

[hfivefour]

Once again thanks for replies. I am new to all this so I am thrashing around a bit.

For completeness I read elsewhere that a Dovedale III differs from the Dovedale 3. Mine or should I say my sons is a Dovedale III with the Rank logo which suggests not a very early Dovedale but earlier than the 3

I finally decided to disconnect the woofer and mid range from the x-over board.

I had someone check the main 12"/300mm woofer resistance with their multimeter which read 5.7-5.9ohm which together with the crackle test suggests speaker is ok. I still intend to do the suggested "radio speaker" test when I find the bits and bobs to use.

I also removed the mid-range and had that tested. This is dead. Pulled it apart (unscrewed it) and assuming I didn't knacker the coil it was falling apart.

As an exercise I thought I would drop in another mid range. However as I am on a learning curve I don't want to spend silly money. Here I mean ideally pounds as opposed to tens of pounds. Once I understand and get things working I would then consider upgrade.

Heres the rub. Finding a 6ohm 5.25"/130mm mid range speaker is nigh on impossible let alone cheap.

Anyone happy to suggest what to use. Alternatively could I drop in a 8ohm mid to run alongside the main and, yet to be fully tested, tweeter, or is this a bit dodgy.

As I say I am using this problem speaker as a sort of testbed in understanding these things. OK I could go out and buy a cheap speaker set but whats the fun in that.

TIA

[Hartley118]

Interesting that your experience of failure of the mid-range unit tallies with mine. I guess that the rather flimsy mid-range unit has to take most of the power.

The B110s I used to replace the mid- range units is nominally 8 ohms, but seems to work well. The Dovedale was made at a time when there was a move to follow a DIN speaker impedance standard of 6 ohms rather than 8 ohms. In theory, the lower end of the mid-range pass-band will be extended a bit with the 8 ohm speaker, but I haven't noticed any audible difference.

I don't believe there was anything very special about the Wharfedale mid range unit, so If you can't readily get hold of the B110s, I'd be inclined to try a decent 5 inch 8 ohm car speaker instead

[paulsherwin]

Agreed, just drop in the best 4 or 8 ohm speaker you have to hand that will fit. The sound of the speaker will be modified somewhat but it will get you going while you think of a long term solution. Some of these bodges don't sound bad at all - I ran a pair of Omar CR251s for about a decade with a car stereo woofer in one of them and it wasn't obviously substandard.

Check the phasing is correct for any replacement you fit - there should be + and - or red and black markings.

Your local scrapper or car dismantler may well have something suitable for a couple of quid.

[crackle]

I dont understand, you said there was NO sound coming from the woofer. Yet the woofer speech coil is OK when measured with a resistance meter. Did you do the test, gently pushing evenly on the woofer diaphragm to test if it is rubbing, it should push in and out smoothly and make no scratching sound. If it does not move or makes a scraping/scratching sound it is knackered.
You can do a final test of the woofer with the speaker disconnected from the cross over, by connecting the output of the amp direct to the speaker.
You can do the same test on the mid speaker but keep the amp turned right down with the bass also turned right down. But if it measures open circuit there is not much point in doing this test.

If if the speakers are all OK then there is a fault in the cross over.

If you fit an alternative mid range speaker you will need to ensure it is fitted in a closed off section of the speaker cabinet or have a closed back to the speaker itself. The back of the mid range must not be exposed to the sound vibrations in the cabinet caused by the woofer.

Mike

[Hartley118]

Worth noting that the mid-range unit is apparently connected out of phase with the other units. I recall querying this with Ken Russell, then Wharfedale Technical Director, and he said it gave a flatter response due to phase shifts in the crossover.

Martin

[paulsherwin]

You should wire any replacement in the same way as the original, though it will do no harm to experiment of course.

[hfivefour]

Crackles' point about the woofer is a fair one.

So far it (the woofer that is) has passed all tests off the cabinet, i.e. battery and ohm test. The movement appears ok but time will tell.

I have been side tracked by checking the individual speaker components and so my original thoughts on the x-over may be wrong but until I have had a chance to check the individual components and then hooking them back on the x-over I don't know.

I have a cheapo mid range on order, if only to prove the x-over works.

Being a novice I may have come at this from completely the wrong direction making assumptions but am trying to learn through experience via the invaluable advice provided here.

As an addendum I hooked up the woofer direct to the speaker leads and sound came out.

Not powerfully a lot weaker than from the other working unit. I'm sure I wired it the right way around. Is it a function of the x-over to improve on this.

Any way I know it works......sort of.

[RojDW48]

Was the woofer in the cabinet when you connected it direct? If so, it should not have been significantly weaker as you describe. If it you had removed it from the cab it would sound very feeble...simply put - it is the cabinet that makes the speaker project the sound forward into the listening area. Wiring one way or the other wouldn't make any difference in the context of that test.

[hfivefour]

I was going to go quiet for a while whilst I waited for the cheap speaker to use for testing. But interestingly I fell across what appears to be a pukka Wharfedale mid-range from a Dovedale, so risking a few extra pennies bought it.

Accepting a little knowledge is a dangerous thing some of what I have read elsewhere suggest changing the capacitors can 'improve' the sound quality.

It may well be I could bring this speaker back to life without further intervention. But ignoring the rule 'if it ain't broke dont't fix it' and as an exercise in futility would it worth considering, only considering mind, what I beleive is called recapping the board with some replacement capacitors.

I may have to do so anyway but thought I would ask.

This is done in the context of using the speaker issue as a vehicle in understanding how to do these things.