View Full Version : Are these speakers worth refurbing?
I have a pair of Audiomaster MLS4 Speakers which I bought in 1980 and I wondered how these would be considered in comparison to modern day speakers. They have seen little use in recent years and could seriously do with a refurb. I think the drive units are OK but the cabinets are water stained on top, the walnut veneer has faded on the top & sides and the grilles are in poor shape. I would guess that after 30 years the crossovers are also probably long overdue for a recap.
I opened one up today and I think both the drive units may have been made by Audax, the woofer was marked HD20B25H and the tweeters HD100B but only the tweeter had an Audax sticker on it. From memory the speakers cost me around £200 at the time, which was about 5 weeks wages for a hard up teenager.
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/Misc051.jpg
Whilst I am willing to try and restore the cabinets and grilles myself, I would need to take the crossovers to an audio repair shop to get them recapped which is likely be expensive and so I would be pleased to here from those in the know whether they feel these speakers are worth spending money on? I appreciate that this question may be somewhat subjective.
Jac Hawk
05-02-2011, 17:47
In my opinion i would referb them, 1st off if you bugger them up they haven't cost you anything but your time and some materials, and 2nd you may improve on the sound and make em look as good as new too, also if you liked them when you 1st got them there's no reason you can't get them to sound better by changing the caps and inductors as well as improving on the internal wiring. i referbed my speakers recently you can read about what i did here http://theartofsound.net/forum/showthread.php?t=7023&page=5
With regards to recapping, it's quite easy just take the crossover out of the cab make a note of the values for the caps and get some new ones ordered, i recently referbed my Castles and used Ansar polly's and was astounded at the difference they made, you can get em from here http://www.cricklewoodelectronics.com/Cricklewood/search.php?mode=search&page=1
also get yourself a good soldering iron as that will make the job a lot easier, desolder each cap at a time and replace with a new one, so you don't make any mistakes
Rare Bird
05-02-2011, 18:08
Rich pop out the crossover board & take a good photo please
Andre, the Xover boards are bolted in place. Is this photo good enough? If not I'll try and remove one tomorrow.
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/Misc053.jpg
Jac Hawk
05-02-2011, 19:05
Is it bolted directly to the external speaker terminals?
Also that looks like an easy job to replace the caps even for a novice, like i said before a good iron is the key.
Reid Malenfant
05-02-2011, 19:19
Is it bolted directly to the external speaker terminals?
Nope ;) 3 sets of wires to the xover, 2 drivers & one set of input connections :)
I agree, change the most important capacitors - those that feed the tweeter if you are hard up. Don't even attempt to change the inductors for anything fancy unless you have a really accurate ohm meter so you can measure the DC resistance as it's vital that this isn't different in the new inductors!
Jac Hawk
05-02-2011, 20:31
Nope ;) 3 sets of wires to the xover, 2 drivers & one set of input connections :)
yes i see the 3 sets of wire, but one set doesn't go anywhere, that's why i asked, it could be bolted to the plastic surround, but the terminals connected via cables.
hifi_dave
05-02-2011, 20:38
It pre-dates the fashion for bolting the crossover direct to the speaker terminals. The red/black wires in the middle, go under the crossover to the terminals.
Just replacing that bell wire with some decent wire will make a huge improvement.
RIGHT!!!!!
Robin Marshall (later of Epos fame) designed these and worked bloody damned hard on the crossover to get it right with the drivers, which were very good at the time. The ONLY glitch in them was a dip at the crossover point, but it was benign in terms of being able to hear it..
Those capacitors can definitely be improved on I reckon. The ones on the board (which was almost certainly assembled by a great chap named Roger, who probably wound the coils as well) were par for the course back then and a bank of reasonable polyprops there would certainly make an improvement I think. The internal wires should be fine, especially the ones to the drivers - remember, a foot or so of copper wire is nothing compared to the hundreds? of feet of wire in the coils, which determines the coil resistance.
For those of you that don't know, the MLS4 was a goodie, cost around half the price of the likes of Spendor BC1's/KEF 104ab's/Rogers Export, yet sounded very nearly as good and were recommended in HiFi Choice. These are very well worth updating and restoring and I remember them (and the baby MLS1) with great affection :) These days, they'd sell for well over a grand the pair.
Rare Bird
05-02-2011, 21:05
Andre, the Xover boards are bolted in place. Is this photo good enough? If not I'll try and remove one tomorrow.
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/Misc053.jpg
I forget now but i seem to remember those four bolts are the same fixing centres to the terminal pod sat on spacers, the two short wires are from the terminals to the board.
You'll get all those caps in Ansar 'Supersound'
Make a list of the cap values & body length & i'll give you a link to the cap replacement, honestly you can get a massive sound imp by swapping these.All you have to do is de-solder those 6 wires, take the 4 nutz/washes off it will come out, you can't get mixed up re soldering the wires as you have them pictured there. Mike did it with the Ansars in his Castles.
Right guys thanks for all the advice, it would appear these are worth spending some time on.
Andre I'd like to take you up on your kind offer of help in sourcing the parts. The first job I suppose is to remove the crossover board. I'm assuming that to desolder the 6 wires I use a soldering iron which I don't have, so if someone can recommend a soldering iron starter kit (nothin to fancy) that would be suitable for DIY audio work then that would be a great start.
Lots more dumb questions to follow.
Rare Bird
05-02-2011, 21:40
The Antex XS25..only 25W irons but they are very good i use one for small work, you can get a massive selection of pop on tips for em.
On order, thanks Andre:).
Hi Mothman, hi all. Sorry to resurrect this old thread, but everyone's opinion and advice will be much appreciated.
I bought a pair of Audiomaster MLS4's, like Mothman's pair, in 1979 or 1980, IIRC. They gave me sterling service for several years, and I gave them to my parents in the late 80's. They were scarcely used while with them. Now my parents have passed away and I got the speakers back (with the home). I'm not selling them, they are not worth much except sentimentally. They remind me of my youth and they were the first thing I bought with my own money, so I'm keen on resurrecting them, along with the lovely brown Sugden A48II that drove them, as an office or bedroom system. The veneer has held up admirably through the years, and I don't really mind the back that's finished in something that looks like industrial cork, as long as it's hidden from view.
The original driver setup was the HD20B25 H4C12 8" bextrene woofer and the HD100D25 1" cloth tweeter. The woofers had to be replaced in the mid-80s after an accident that had them tear apart. The replacements were supposedly drop-ins: they look exactly the same, except for a white circular strip stuck on the front of the frame rim, right between the rubber surrounds and the four triangular lugs that the fastening screws go through. I suspect it's the HD20B25 J series, but I'm not sure. Of course I'll find out as soon as I take them apart, but in the meantime if anyone knows what model the white paper strips stand for, please let me know.
The speakers had one flaw that was identified in measurements at the time, and I had found mildly audible: there was a response depression in the presence region, between 2 and 3 kHz, and a prominence around 10-15 kHz. The latter would probably be welcomed at my age, :rolleyes: whereas the former was a bit unpleasant and I had devised a couple of electrical workarounds back then (playing with capacitive loading for the cartridge, or with the Sugden's comprehensive tone controls).
What I definitely need do is replace the crossover, or the capacitors in it in the very least. This should be fairly straightforward to do, as the crossover is stuck on the speaker's back wall and can be approached after removing the woofer.
In decreasing order of importance, and increasing order of ambition, I could concoct a new crossover, ideally one that takes care of the presence region problem, or I could replace the tweeter altogether, or even replace both drivers. I am not going to mess with new screwholes, as the veneer looks good and I'd hate to ruin it, being a total ignoramus in the woodworking department.
I googled about replacement parts and found that several Audax tweeters are claimed to be "drop-in replacements" for the venerable HD100D25, namely the TW025Ax series (x being 0, 1, 2 etc). It is not clear to me whether there is much difference between these TW025Ax variants, or much difference between them and the HD100D25. I have seen some CSD plots of them on the Web, and by gosh do they look atrocious - by today's standards anyway! So I wonder if possible replacements are limited to Audax models, or there are other tweeters that can be substituted. There is a number of modern soft domes, from the likes of Tymphany etc, that are so much better, and I'd like to use them if I could.
The woofer matter is more difficult. The HD20's are heavy and insensitive. Furthermore, there are cutouts on the baffle for them to fit in, and I don't want to do any sawing or sanding of the woofer hole. If I am to replace the woofers with something more modern, it should be a driver with the exact same screws at the exact same diameter. If need be, I could add some sealant underneath, but that's just about it. Any suggestions are welcomed.
As for the crossover, what I plan to do is work out the schematic, study it, and see if I can play with the element values in order to cover that 2-3 kHz response trough. I have a rudimentary understanding of electrical filters, so I plan to educate myself on the subject a lot more. If I manage to replace one or more of the drivers with something newer, there could well be lots of crossover solutions available on the Web for them, so that might work well.
Sorry for the length of the post. Any thoughts, suggestions, ideas, hints, tips etc will be very, very much appreciated!
Reid Malenfant
12-10-2011, 17:03
The speakers had one flaw that was identified in measurements at the time, and I had found mildly audible: there was a response depression in the presence region, between 2 and 3 kHz, and a prominence around 10-15 kHz. The latter would probably be welcomed at my age, :rolleyes: whereas the former was a bit unpleasant and I had devised a couple of electrical workarounds back then (playing with capacitive loading for the cartridge, or with the Sugden's comprehensive tone controls).
Hi Kai, i think you'll find this is probably due to the crossover & drivers & it may be rather difficult to cure :(
It sounds as though it's around the crossover region which is why i suspect it's an interaction between the tweeter & woofer being out of phase with each other. You see while it's difficult but none the less not impossible to get the drivers in phase there is one rather massive problem to overcome. That problem is the distances that the voicecoils are from your ear...
What tends to happen near the crossover point if this isn't taken care of is that the way the two drivers interact beams the sound down towards the floor rather than straight out in front of the speaker. I reckon this is what is causing the dip in response, try it out & see if that dip disappears if you move nearer to the speaker & move your head up & down in front of it with a nice load of material that is in the region affected ;)
Thanks, Mark, I'm still in "idea-gathering" mode anyway, so there's no rush. In due time I think I'll be able to do some gated measurements using my omnipotent Metric Halo. It seems likely to me too that the response dip is a cancellation of sorts, because it looks too sharp to be anything else. Two way speakers with an 8''er are tricky anyway. I think I should try to fit a slightly larger tweeter and use a lower XO frequency, but will a larger tweeter fit the hole? Wish I knew at this stage. :)
I need to find out what the crossover topology is, above anything else. Second order filters are easier to fix phasewise, as you say,; fourth order are unlikely to have been used; third order ones start with phase at quadrature, which means that they are hardly fixable: usually they either work or they don't.
If I'm not mistaken, the picture Mothman took shows six capacitors, three resistors and three coils (two of which are aligned next to each other, rather than being at right angles!). Could be second or third order filters, or both, with or without baffle step compensation, who knows?
Reid Malenfant
12-10-2011, 18:09
The only passive way of fixing these things tends towards adding a second bass mid driver above the tweeter, the D'appolito arrangement (MTM).
Doesn't really help you though!
You'd need to dig the crossover out & draw the circuit out to see what it's doing, as i'm sure you aware the crossover could well be second order but with extra components to tailor some midrange peaking due to the intrinsic breakup modes of the bass/mid driver..
Like you say, you need to dig deeper ;)
Yeap!
I dug up this BTW:
http://img231.imageshack.us/img231/1306/audiomaster.gif
The text says that the trough is a destructive interference issue but I'm not quite so sure. It does worsen below axis, but doesnt' correct itself above axis as it should; if anything, it becomes broader and shallower. I remember compensating for this by using the Sugden 4 kHz, 6 dB/octave filter and a generous twist of the treble control that produced a shelf of about 6 dB above 2 kHz. This killed the 15-20 kHz range, but sorted out the presence region. Overall it was a pleasing compromise, though not very accurate. I then removed the additional capacitance I had initially stuck on the cartridge terminals. This gave a droop at 15 kHz and a peak at 20 kHz or so, and it was pretty flat by ear. Some residual spitting from the HD100D25 remained, which I guess was a breakup/distortion issue. That's why I'd rather replace the Audax with a Scanspeak for example, if possible.
Correction: the text says it is not a phase anomaly, so my hunch was right after all. The HD100D25 is supposedly flat through this region, so I guess it's good ole bextrene breakup. One more reason to try to experiment with an LR4, ideally with a larger tweeter.
Reid Malenfant
13-10-2011, 16:27
You might get away with tweaking the crossover ;) When these things go into breakup they usually start to get a peaky output response rather than a dip. I have a suspicion that they may well have overcooked the rolloff of the crossover by doing it too early (which normally gets rid of the peaky nature). Overdone would cause the dip.
Of course fitting a tweeter with a lower resonance & tweaking the crossover to a lower xover would also work, probably better if you can get it right :)
A shame Robin isn't readily available to doscuss it, but I PROMISE you that these speakers weren't in the slightest bit "cobbled together" and that much listening, at our KJ branch amongst other places, was carried out in conjunction with measurements.
I think that presence dip is as much to do with the age and development of the drivers used back then - these things really have improved in recent times I believe. What you need to do is a computer model of the crossover slopes in conjunction with the driver characteristics to see how the crossover works and whether anything can be done without replacing either driver (or both). The fact that the off-azis performance in the review above is so good means that Robin got the phasing right (he's a great mathematician) - he'd had years fighting the LS3/5A batches he'd made for Audiomaster and was quite used to selecting components etc to get each batch through testing (KEF had tremendous variability issues with those drivers back then and every other batch would fail on forst testing - a bloody nighmare, the 3/5A).
You may just find that a modern tweeter will have far greater bandwidth at the lower end of its range and Wilmslow Audio may possibly be able to help. This really is where the DIY aspect comes in, together with computer simulations of the final results - someone here should be able to point you in the right direction..
Hope you can make something great out of something that's still good :)
I have a suspicion that they may well have overcooked the rolloff of the crossover by doing it too earlyThat's what I suspect too.
What you need to do is a computer model of the crossover slopes in conjunction with the driver characteristics to see how the crossover works and whether anything can be done without replacing either driver (or both)That's what I had in mind to do in due time, after learning how such things are done in the first place.
Robin got the phasing right (he's a great mathematician)Indeed I have the utmost respect for him. I understand that his speaker design philosophy evolved over the years, which would make discussion all the more fascinating but alas, one cannot have everything. If you are in touch with him, please convey my thanks for a 30 year old product that has stood the test of time. :)
something great out of something that's still good :)That's why I don't want to make any irreversible changes. In case things go wrong, I'd like to be able to put everything back and just make do with replacing old XO components.
BTW does anyone have any clue as to the white stripe Audax woofer?
Gentlemen, many thanks for the discussion so far. At this point I'd like to model what I can do with the existing drivers. Is there XO design and simulation software that you can recommend? Freeware or reasonably priced (less than three digits) is preferable. Since the box is ready, the quality and comprehensiveness of the enclosure design and tuning part of the software does not matter I guess, it's just the electronics/XO part of it that does. Any suggestions?
After much perusing the internets :) I came to the tentative conclusion that the Volt BM220.8 woofer
http://www.voltloudspeakers.co.uk/Loudspeakers/Studio_Range/BM220_8/body_bm220_8.html
could be a suitable replacement for the Audax HD20. It is very robustly made and should have impeccable sound quality for an 8 incher. It is also usefully sensitive, about 3 dB on the Audax, which means it can play as though driven with twice the power compared to the Audax.
My biggest problem with finding a replacement was mounting diameter. The Audax has 4 screws on a 222 mm circle, and this is too big for modern 8 inchers. The Volt has its screwholes on an 218 mm diameter circle, so I may have to file each about 2 mm outwards, which shouldn't be too hard to do.
It's the same problem that has hindered my search for a replacement tweeter. The Audax HD100 is mounted with 4 screws on an 86 mm diameter circle. I'd really like to use a bigger tweeter, hopefully around 1.2-1.3 inches, and these usually have large faceplates with widely spaced screws. The idea is to cross at around 2 kHz, maybe even lower, for an even dispersion characteristic. So far I have not been very fortunate. The only tweeter I have found to have a perfect fit is the Fountek NeoCD1.0, which is a fragile ribbon that cannot possibly be crossed low. There are 3 tweeters from the Scanspeak Classic line, the 2905 series, that fit on 90 mm, so they will need a little filing too.
The only other option I've been considering is to have a custom waveguide made, modelled after one of the few shallow plastic waveguides on the market, and then mount whichever tweeter I want on it. This will also improve sensitivity, lower distortion, and facilitate an even lower cross frequency.
As usual, any ideas will be very much appreciated.
Rare Bird
14-11-2011, 01:58
So how did Rich go on with his Crossover Rebuilld?
He probably does not follow the forum any more. I've sent him a PM with some questions, but he never answered.
My apologies for not replying to this thread and Kai’s PM’s at the time, though I don’t think I could have added anything useful to the discussion, his technical knowledge obviously being far greater than mine.
Earlier in the year I decided to step back from the forum for a short while after experiencing a number of gear failures within a short space of time which left me feeling deeply frustrated:(. I guess having an interest in vintage gear but without the knowledge or ability to keep it working is probably not a good combination.
Unfortnately the re-capping of the Audiomaster crossovers was one of my disasters. This was my first attempt at DIY electronics and it did not go well. I purchased some new Electrolytic Caps from Falcon Acoustics but my ham fisted attempts at soldering meant I ended up damaging the metal circuit path on this first crossover board, at this stage I decided to call it quits and have left the second board untouched. I am hoping that the damaged board may be salvageable by using some form of connector between the caps but have decided to leave this until I can get someone who knows what they are doing to look at them.
Again my apologies for not replying at the time.
:)
Reid Malenfant
27-12-2011, 20:57
Yes, easily salvageable :) Have no fear on that score ;)
Good to see you about again by the way Rich :)
Thanks Mark good to hear they may be fixable. It's also good to be back:)
Reid Malenfant
27-12-2011, 21:16
Not maybe, they are 100% fixable :eyebrows: Take it from me that there are 101 ways of getting round a damaged PCB track ;)
So that's that worry out of the way :D
Stratmangler
28-12-2011, 00:04
Good to see you about again by the way Rich :)
+1
Nice to see you back Rich :cool:
Take it from me that there are 101 ways of getting round a damaged PCB track....
Yup, and the best way is not to use any in the first place and hard-wire all the crossover components together instead! ;)
Welcome back, Rich! :)
Marco.
StanleyB
28-12-2011, 15:00
Unfortnately the re-capping of the Audiomaster crossovers was one of my disasters. This was my first attempt at DIY electronics and it did not go well. I purchased some new Electrolytic Caps from Falcon Acoustics but my ham fisted attempts at soldering meant I ended up damaging the metal circuit path on this first crossover board, at this stage I decided to call it quits and have left the second board untouched. I am hoping that the damaged board may be salvageable by using some form of connector between the caps but have decided to leave this until I can get someone who knows what they are doing to look at them.
Email me some pics if you can. I need pics of both sides of the PCB. After I have studied the pics I'll let you know if and when you can send them to me for corrective action. Or pass by with them :).
Hi Stan, many thanks for the kind offer of help.
The problem I will have is that once the crossovers are repaired the speaker wiring will need re-soldering in place and I am not confident that I would be able to do this. A fellow forumer has recommended a repairer who may be able to assist and is within traveling distance. If he is willing to have the complete speakers to work on then this may be the easiest option as he will also then be able to re attach or replace the wiring. I will contact him early in January to see if he can assist, if not then I will gladly be in touch.
Below are the photos you requstested, one cap has still to be replaced. Those of a nervous disposition may wish to overt their eyes:lol:
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/Board02.jpg
Rear shot, damage is in the bottom right corner.
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/Board04.jpg
Reid Malenfant
28-12-2011, 18:29
Easy as pie :) 1 minute job even allowing for the soldering iron to heat up :D
Pity you weren't nearer, I'd do the lot for you including refitting the crossovers etc for a tinnie :cool:
:eyebrows:
My apologies for not replying to this thread and Kai’s PM’s at the timeNo problem, Mothman, I actually forgot what my question for you was. :) I'm sure you'll find someone to do the soldering for you.
Oh yes, I remembered! Mothman, have you sketched out the Xover schematic and have you recorded the element values? Not all cap and resistor markings are clearly visible in your original pic, and the caps in the new pic are too shiny.
Hi Kai
Below is a list of caps that I ordered to do both crossovers
http://www.falconacoustics.co.uk/alcap-claritycap-solen-audio-capacitors/alcap-electrolytic-capacitors-low-loss-50v.html
Alcap 4.00uF Low Loss 50VDC Electrolytic Capacitor
Capacitor Tolerance 5% Qty 4
Alcap 8.00uF Low Loss 50VDC Electrolytic Capacitor
Capacitor Tolerance 5% Qty 2
Alcap 12.00uF Low Loss 50VDC Electrolytic Capacitor
Capacitor Tolerance 2% Qty 2
Alcap 16.00uF Low Loss 50VDC Electrolytic Capacitor
Capacitor Tolerance 2% Qty 2
I have not yet acquired replacements for the small 0.33uf caps, hopefully the tech who makes good my handy work will be able to source these.
Hope this helps
Many thanks, this is much appreciated.
Mothman, how come you chose electrolytics instead of MKPs?
hornucopia
04-01-2012, 14:52
Hmm.....maybe I should look inside my Leak Sandwiches.......15 ohm versions.
I'm sure, like many oldies, a re-cap might add some sparkle.
Mothman, how come you chose electrolytics instead of MKPs?
I went for replacement electrolytics rather than polypropylenes beacause this was to be my first stab at DIY elecetronics and as space was restriced on the boards I wanted to keep things as simple as possible. However had I known that I would end up having to pay someone else to do the work then I would have got the bigger polyprop caps and let them figure out how to fit them on the board, but hey thats life:lol:
Making new boards is very easy and dirt cheap. Any electronics technician should be able to make such a simple board in a jiffy. I think I shall have a new one made, larger and with better layout. As far as I can see the coils are cored, right? I wonder if it would be worth it to replace them with air ones.
Reid Malenfant
07-01-2012, 15:11
As far as I can see the coils are cored, right? I wonder if it would be worth it to replace them with air ones.
Only if the air cored inductors have the same DC resistance as the originals, which means they'll likely be quite large & expensive :(
If the DC resistance is different then the filter characteristics will change.
I know. They are not that expensive, unless one considers $15 expensive. One could also buy enamelled wire in bulk and wind them themselves, provided there is access to measuring equipment. Once correct values are reached, they can be doused in resin and baked to a crispy golden brown. :) As a matter of fact, one need not even use a circuit board; there are various ways to hardwire a simple circuit and stuff it in a spare plastic box with some fiberglass to keep everything snug.
RIGHT!!!!!
Robin Marshall (later of Epos fame) designed these and worked bloody damned hard on the crossover to get it right with the drivers, which were very good at the time. ...
For those of you that don't know, the MLS4 was a goodie, cost around half the price of the likes of Spendor BC1's/KEF 104ab's/Rogers Export, yet sounded very nearly as good and were recommended in HiFi Choice. These are very well worth updating and restoring and I remember them (and the baby MLS1) with great affection :) These days, they'd sell for well over a grand the pair.
Out of interest, do you know much about the ML5s, two bass units and maybe a stepped baffle for the tweeter? Might have a friend with some doing nothing - can't remember..
I went for replacement electrolytics rather than polypropylenes beacause this was to be my first stab at DIY elecetronics and as space was restriced on the boards I wanted to keep things as simple as possible. However had I known that I would end up having to pay someone else to do the work then I would have got the bigger polyprop caps and let them figure out how to fit them on the board, but hey thats life:lol:
You just poke the correct legs into the holes with the caps at a distance that means you can fit them all in! That's it...
Arrange them how you want, marking the lengths of leg you need and before you solder them in place, just cut up the internal ink holding part of a used biro and slip the tubes you've made over the legs so they never touch the legs of others..
To be honest, I'd have thought electrolytics were harder or at least no easier to use.
You just poke the correct legs into the holes with the caps at a distance that means you can fit them all in! That's it...
Arrange them how you want, marking the lengths of leg you need and before you solder them in place, just cut up the internal ink holding part of a used biro and slip the tubes you've made over the legs so they never touch the legs of others..
To be honest, I'd have thought electrolytics were harder or at least no easier to use.
Unfortunately Nat I have absolutely no experience in DIY electronics, I am sure if I had your knowledge I would have done things differently.:)
What a shame.
There are some ways to deal with difficult hardwired large component soldering.
For two or more lead joins the leads can be twisted together tightly and then soldered. This helps when you find that you cant hold everything in place as you apply solder and heat.
One way to deal with large diameter multi strand wire such as the leads from the drive units to the crossover board is to use good quality Lucar connectors; the type with a ring with a hole in.
Screw the Lucar connector to the board through the ring and then gently open up the part that takes the wire so the drive to board wire along with the last component lead just slides in. Give it a squeeze with a pair of pliers and then by heating the whole assembly let solder run into the joint.
Large capacitors can be held in place using fine cable ties. Just need to drill small holes either side of the cap to thread the cable ties through. I prefer this to using glue.
A bit late now. :(
Unfortunately Nat I have absolutely no experience in DIY electronics, I am sure if I had your knowledge I would have done things differently.:)
Ah... I have next to no experience in DIY electronics. Most I've ever done is replace things like capacitors which is simply a case of sticking legs through holes and soldering.
It's the soldering that may require practice but the rest is just thinking about it with a calm mind, knowing there are no rules and knowing that you can always back track or hand it to someone else if something goes wrong.
It's quite practical and all common sense and those only come out to the full if you're not afraid or worried. As I say the only skill really is the soldering part and you have to do that whichever caps you use.
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/Misc053.jpgIt seems to me that the blue and the two black cables share a track (the big crescent that starts at the top and swoops down the left hand side, under the 8 mF/50V cap) therefore they must be the negative leads sharing the earth/negative, but I'm not sure.
Mothman, do you happen to remember where the three pairs of twisted cabling lead to? One should be coming from the external terminals and the other two should be going to the woofer and tweeter, but which is which is which?
Kai
Here is a photo of the rear of the board before I started work on it. Hopefully with the other photo you can work out the connections. If not then I can look at the other untouched crossover, but it may take me a while before I can do this.
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/Misc062.jpg
Reid Malenfant
23-01-2012, 20:10
Input to the crossover is the red & black wires in the centre. Bass output is the other red & black wires, output to the tweeter are the green & blue wires :cool:
Each part of the network is 18Db/octave...
You are correct Mark:). Sorry I was being a bit dense and thought Kai wanted to know which wire was soldered on to which bit of track and not what each pair of wires was for:doh: Must read posts more carefully in future:lol:
Input to the crossover is the red & black wires in the centre. Bass output is the other red & black wires, output to the tweeter are the green & blue wiresThat's exactly what I was asking about, thanks everyone.
Eventualy got around to getting the refurb of my Audiomasters finished. Crossovers have been re-capped, internal wiring upgraded, cabinets rubbed down followed by 3 coats of Danish oil and then polished with beeswax. Grilles have also been recovered, though I would probably make a better job of these if I had to do them again. I'm pretty happy with the overall result though I'm still adjusting to the new sound:).
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/MLS4002.jpg
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/MLS4005.jpg
Beautiful job that is, Rich. Do they sound as good as they look then?
Martin. the re-cap has transformed the sound, there is far more detail & definition than I ever remember them having before, though if I am super critical I am finding the occasional touch of harshness, however this may just be the speakers now revealing what is happening further up the chain. They are being driven by an A&R A60 which I had re-capped not long ago and I also have rececently changed source in that I'm now using a Squeezebox Touch, so lots of changes to get used to:).
Yes like me that is, change a load off stuff at once and then forget where you came in :)Probably it will all need time to settle down a little.
Please excuse me if i haven't read the thread properly, but what did you do about the tweeters? Did you buy new ones?
Reason for askin' is that i had the very same tweeters in my Dali 40 speakers, and these had a reputation for getting sticky with age and consequently blowing the voice coil easily.
Anyways, i bought a repair kit for mine, consisting of an assembly with both the dome and voicecoil, easily replaceable. The did sound a little harsh and grainy though, after repair... Seemed also to add quite few decibels of efficiency which meant i had to tune them down a bit with a series resistor of about 1,5Ohms.
In the end i converted my Dali's to 40SE spec. instead, using ScanSpeak 2905/970000 tweeters and adjusted x-overs. Result was a thouroughly more enjoyable loudspeaker!
Beautiful job by the way, the speakers sure look good!
BrMike
Tweeters can lose efficiency after a few decades of thrashing and I don't know if this is physical age of the moving parts, or any ferro-fluid drying out (more likely), Changing the tweeter module may have removed what's left of any sticky ferro-fluid in there??????
If the Scan tweeter is the 28mm dome I think it is, it's an utterly civilised unit with smooth and wide response out to over 30kHz.
Please excuse me if i haven't read the thread properly, but what did you do about the tweeters? Did you buy new ones?
No the tweeters are the original Audax units. The crossovers were re-capped with Alcap electroytics of the same values as the originals, my tech also beefed up the internal wiring using some silver plated copper stuff he had.
Wakefield Turntables
20-05-2012, 20:07
Eventualy got around to getting the refurb of my Audiomasters finished. Crossovers have been re-capped, internal wiring upgraded, cabinets rubbed down followed by 3 coats of Danish oil and then polished with beeswax. Grilles have also been recovered, though I would probably make a better job of these if I had to do them again. I'm pretty happy with the overall result though I'm still adjusting to the new sound:).
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/MLS4002.jpg
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/MLS4005.jpg
I think you've done a great job here, well done! :clapclapclap:
Canetoad
21-05-2012, 11:33
Rich, they look lovely! :)
Top job there fella! :mex:
Thanks for the kind comments guys:). Cosmetically the speakers have come out better than I could I have hoped for as I did not think it would be possible to remove marks such as the water stains and flower pot rings from the tops. Can highly recommend Danish Oil if you are not looking fo a high gloss finish on your veneered speakers as it's cheap, easy to apply and doesn't need rubbing down between coats. A
Sonicaly I need to get some miles on the new crossovers and maybe experiment with a couple of different amps and cables. My Sansui AU-505 will hopefully have some new life breathed into it soon and so I'm looking forward to seeing how that stacks up against the A&R A60.
Such an awesome job, Mothman, they look lovely.
I am finding the occasional touch of harshnessI think it's just the speakers' own sonic signature, a dip in the presence region coupled to a peak in the top octave, as seen in the frequency response charts:
http://img231.imageshack.us/img231/1306/audiomaster.gifI recall the exact same flaw in my own pair when I was actually using them. Back then I sorta solved the problem with some lateral thinking. I experimented with cartridge (an Ortofon MM) loading. With moving magnet cartridges, increasing capacitive loading causes a presence hump and a corresponding treble droop. I tried various values and ended up adding an extra 220 or 330 pF, IIRC. This brought the presence region up to par and flattened the whole response out, at the expense of some high treble loss. It was not a perfect solution, but it sounded much more pleasing to my ears compared to the status quo ante. I was an intrepid young man back then; right now I don't think I could have detected the high treble loss anyway. :)
I can report zero progress WRT my own MLS4s :) as I am a notorious procastrinator, but if I am to do anything with them, it seems that I'll have to settle on new drivers, most probably the Volts I referred to earlier on, and maybe a pair of Scanspeak tweeters.
spendorman
27-05-2012, 14:46
I seem to remember that these speakers used the Audax soft dome tweeter, yes could be a tiny bit harsh at the very top end, seemed better with a good valve amplifier though.
Rare Bird
27-05-2012, 17:41
They sure are Audax units Alex
Hi All,
Does anyone know anything about the Audiomaster P202 speaker? There's some on a local auction site I like the look of, but I can find zero info on them.
I also asked on PFM, where they thought MS woofers and Audax tweeter. Pictures here (https://www.ricardo.ch/kaufen/audio-tv-und-video/raritaeten-hifi/sonstige/audiomaster-p202-englisches-produkt/v/an703068310/).
Thanks, Richard
spikeanded
22-10-2013, 21:51
Hi, I know I'm resurrecting an old thread but I have a pair of these which I picked up over the summer. I was expecting great things, as I used to have a pair of MLS-1 which I liked a lot and have also owned (and still do, in some cases) various Monitor Audio and Epos models, some of which are also Robin Marshall designs. What troubles me with the MLS-4 isn't the midrange dip, but the rising treble which sounds pretty obvious to my ears. I would like to resolve this. Interestingly, I don't remember the MLS-1's suffering from this, and I think the tweeters were common to both models, so it gives me hope. Is there a quick and easy fix for this (other than swapping out the tweeters which I am reluctant to do, and which I think is unnecessary as it isn't the quality of treble, but the quantity I am not keen on). I am considering trying either 2.2R or 3.9R 10W wirewound resistors in series with the tweeters in the first instance, but other tips and advice would be appreciated. If possible I would like to leave the mid-range dip unworsened but I am not sure if this occurs at the crossover frequency or just below it.
Yup, very easy to fix an overly bright treble. Add a Zobel network to the tweeter shunted across the tweeter output. This works with the input resistor to the treble filter to roll off the top end slightly. 7.5R and 1uF should do it. Technically it corrects the rising inductive impedance of the tweeter to a flattish 6 ohms at the top. Usually creates about 3dB attenuation.
http://www.wilmslow-audio.co.uk/10-df-mkp-capacitor-1119-p.asp
http://www.wilmslow-audio.co.uk/ceramic-resistors-205-p.asp
It does need some input resistance to work with, but I'd assume it is there, though I'd need to see the schematic to be sure.
FWIW, I've deconstructed the Audiomaster MLS4 crossover schematic as best I can from the photos supplied earlier:
http://imageshack.us/a/img198/1614/fg0f.jpg
With the values I can read, and the guesses in red, it looks like this:
http://img689.imageshack.us/img689/5141/v50e.png (http://imageshack.us/photo/my-images/689/v50e.png/)
Uploaded with ImageShack.us (http://imageshack.us)
I have shown the Zobel which goes across the tweeter to tame the treble. This schematic is quite like the old KEF Calinda (http://www.hifiloudspeakers.info/Anatomy/Crossovers/Calinda/CalindaCrossoverIndex.html), if memory serves. (I always thought that Calinda schematic was not quite right, but that's another story...LOL)
I won't attempt to explain it beyond saying the bass unit gets an LCR trap to create a notch around 2kHz for some typical bextrene horror resonance, and the treble is a third order butterworth filter quite a la KEF acoustic butterworth.
The centre pair of wires is input, left pair is bass output, and right pair is tweeter output.
BTW, does anyone notice, as I do, the terrible alignment of coils at the bottom? :doh:
http://imageshack.us/a/img198/1614/fg0f.jpg
That bafflestep coil is crosstalking very badly with the tweeter coil. The tweeter coil should really point out towards the viewer here. Keep them at right angles is the rule.
http://www.troelsgravesen.dk/coils.htm
spikeanded
24-10-2013, 21:16
Thanks for that, I will try the Zobel network. In the meantime even a 2.2R series resistor offers some improvement to my ears.
More serious attenuation is provided by an L-pad at the (6 ohm DC) tweeter terminals:
http://www.diyaudioandvideo.com/Calculator/LPad/
2.2R (5W wirewound) series and 15R (10W wirewound) shunt will knock the tweeter level down quite a lot. Maybe 4dB. You can buy them at Maplin along with a good 35-50W soldering iron suitable for modern lead-free solder.
L-pads are good because they preserve frequency response. They also improve the sound of the tweeter towards smoothness and low distortion. Particularly with older non-ferrofluid designs.
I'd sort out that awful tweeter coil alignment while I was at it. :)
spikeanded
25-10-2013, 22:19
More serious attenuation is provided by an L-pad at the (6 ohm DC) tweeter terminals:
http://www.diyaudioandvideo.com/Calculator/LPad/
2.2R (5W wirewound) series and 15R (10W wirewound) shunt will knock the tweeter level down quite a lot. Maybe 4dB. You can buy them at Maplin along with a good 35-50W soldering iron suitable for modern lead-free solder.
L-pads are good because they preserve frequency response. They also improve the sound of the tweeter towards smoothness and low distortion. Particularly with older non-ferrofluid designs.
I'd sort out that awful tweeter coil alignment while I was at it. :)
Hi, thanks again for the advice. 2.2R in series seems about right in terms of attenuation. 3.9R was too much and they sounded dim. The reason I want to try the Zobel network is because, if I understand it correctly, they will counteract the rising treble progressively (a sort of pivot around the crossover frequency), whereas attenuation, whether by a series resistor or L- Pad will create a kind of "step down" at the crossover frequency and then a gentle rise from there as per the original frequency response - is this correct? To my ears, they only need the slight edge taken off at the higher frequencies. What vales of L-Pad would you recommend for this effect, and do you think this is preferable to the Zobel network approach?
Looks to me like the Zobel is going to do the right thing here to the top end, but 1R/22R ought to do similar overall 2dB attenuation. Your ear is quite sensitive to small level adjustments at the top, but it may be these speakers should not be toed in for good listening. A bright top end falls off quite rapidly off-axis due to diffraction.
Let's reiterate things:
http://img231.imageshack.us/img231/1306/audiomaster.gif
http://i32.photobucket.com/albums/d45/okmothman/Hi-Fi/MLS4002.jpg
Personally I'd measure the cutouts and rebates and see what other tweeters we might fit here since the art has come on. The 104mm Morel CAT 298 ought to be a slot in replacement:
http://www.wilmslow-audio.co.uk/morel-classic-cat298-500-p.asp
The SEAS 29TFF/W is more efficient, but quite well suited to a modified 2 kHz crossover (http://www.troelsgravesen.dk/SEAS-CURV.htm) which would cure the midrange suckout caused by the steep rolloff of the woofer:
http://www.falconacoustics.co.uk/seas-29tffw-h1318-tweeter-prestige-series.html
spikeanded
26-10-2013, 18:36
Hi, I think I may stop short of changing drive units as I'm not sure if these Audiomaster speakers are keepers. I bought them to see if I could improve on a pair of Monitor Audio MA4 Mk1's and I must say these are proving hard to beat as they have a lovely warm sound and very smooth top end (which I highly value). I may well try to find a new home for the Audiomasters, nice though they are. Strange though that the mid 70's MA designs seem largely overlooked these days, whereas the likes of Spendor BC1 and Rogers Studio Ones are venerated and worth approximately nearly 10 times what I paid for my MA4's. Would be interesting to do a direct comparison, but I suspect the MA4 would not be too far behind. Must be the kudos of the BBC affiliation of Spendor and Rogers. Apparently theMA4 Mk2's use the same Audax tweeter as these Audiomasters and sound worse for it. Not the best looking speaker in the world though, the old MA4's, it must be said!
Well, frankly, Tony, you're a bit of a dead loss as a DIY person then. :lol:
The whole bextrene driver/BBC crossover thing was a a child of it's time.
KEF B139 subwoofer, 8" KEF B200 bass/mid, 5" B110 bass mid and T27 tweeter spawned myriad variations.
My own Chartwell speakers were Dalesford drivers plus an Isophon KK10/8 mylar dome.
http://img594.imageshack.us/img594/7163/chartwellpm400.jpg
I'd be interested to see the MA4 schematic. It would be fairly simple, I'd guess. It used a low Qts KEF B200 driver in a reflex box IIRC. Have a dig.
FWIW, the SEAS Curv 29TFF/W treble conversion is very easy to do on the existing crossover board. I'd use 3.9R, 6uF + 0.2mH, 4.7R/10R l-pad for starters:
http://imageshack.us/a/img198/1614/fg0f.jpg
You'd just need to run the 10R shunt of the l-pad from the removed 0.33uF capacitor to ground. Everything else just slots in. Adjust the l-pad for level if necessary.
spikeanded
26-10-2013, 20:43
Hi, I think I will stop short of swapping out drive units. I would like to keep them pretty much as original designed and built as I am not sure if they are keepers. I bought them thinking they might be a step up from a pair of mid 70's MA4 Mk1's, but I'm not so sure they are a step up, especially in terms of treble smoothness. The MA4's sound lovely and warm with no hint of roughness or fatigue at all. So I may well move the Audiomasters on in due course. I find it strange that these old MA4's seem more or less forgotten when their contemporaries like the Spendor BC1 and Rogers Studio One are venerated and cost an absolute fortune these days. Must be the BBC association I guess. I would love to be able to do a comparison but I reckon the MA4 would not be far behind. They are very well built, although not too hot in the looks department! Again, thanks for all your help.
spikeanded
27-10-2013, 14:22
Hi, yes, not much of a DIY'er really!
I did fix a nasty treble spike in a pair of old Ruark Sabres by swapping out the Vifa domes for Scanspeak, but it was a drop in replacement with no crossover mods necessary.
I notice your Chartwells have the same Isophon tweeter as my Monitor Audios (although MA claimed to have modified them heavily). Compared with contemporary models like Kef and Celestion, I reckon that Isophon is the sweetest sounding of them all!
Rare Bird
27-10-2013, 14:38
I always thought those Chartwell 400's were loverly speakers..
spikeanded
19-09-2016, 14:22
I always thought those Chartwell 400's were loverly speakers..
Just to add a postscript, around three years ago I sold that pair of Audiomaster MLS-4's as they were simply too bright for me and a bit harsh with it.
Earlier this year out of curiousity and because of the low price, I picked up another pair.
To my ears, and with no modifications they sound better right away.
They are still a little on the bright side, but without that sting in the top end.
So I don't know whether the original pair had bad tweeters or crossover components that had drifted out of tolerance, or whether there were big variations in the original production run, but these are very nice!
Also these are not even really a matched pair. Certainly the veneers don't match, and one speaker has four grille fixings, whereas the other one has six.
dantheman91
19-02-2017, 13:25
Just got a pair of MK1 MA4's being delivered in the next hour or 2...:eek:
I'm in too deep - HELP....:lol:
dantheman91
19-02-2017, 21:18
AH problems - both KEF B200's are distorting and have coil rub - is their a way to fix this tried 180D but still the same - at a guess ate the drivers fried or can they be fixed - i'm not sure im up to this - they were £10 so worth investing in i think.:scratch:
Any help - will geoff's fix in the other thread solve the issue.
if not they will be for sale very shortly...:) at a bargain
Martyn Miles
03-05-2017, 09:18
I have just been given a pair of Audiomaster MLS4s, so this is interesting stuff. I intend to restore the cabinets, but leave the rest as it is.
As for value, has anyone ever seen a pair for sale ?
57charles
03-05-2017, 20:09
Those Audax tweeters could well have reduced output due to ferro fluid evaporation and subsequent residue gunge hinderung movement of voicecoil. Get somenew tweeters from Falcon and change the caps in the crossover. You'll have a very competent speaker even today although personally I could never get along with that Audax tweeter whatever speaker it appeared in.
57charles
03-05-2017, 20:13
They're worth anything from £50 to £200 depending on condition including cabinets and electronics.
walpurgis
03-05-2017, 20:15
Those Audax tweeters could well have reduced output due to ferro fluid evaporation
I don't think ferrofluid was used on that generation of Audax tweeters.
walpurgis
03-05-2017, 20:16
will geoff's fix in the other thread solve the issue.
Quite possibly. After all, you have nothing to lose by trying it out.
Dynamics
03-05-2017, 20:28
Id say whatever you are willing to pay on a refurb, go to a shop and listen to new speakers at the same price. If they are better than yours it's probably a no brainer what to do. I'd heavily bet that whats possible now at this price is much more than you'd get in the 80s with economies of scale in production now etc.
My incling would be you'd probably be throwing good money at bad by refurbing them. If you want to improve sound I'd buy new ones.
57charles
03-05-2017, 20:30
Walpurgis, I can assure you they were.
57charles
03-05-2017, 20:33
By the way, I used to sell the full range of Audiomaster speakers and have taken many of those tweeters apart.
walpurgis
03-05-2017, 20:36
Walpurgis, I can assure you they were.
Hmm. I'm assuming these are an HD100 D25 variant. If so, I see no mention of ferrofluid in the spec. This model dates back to the seventies and ferrofluid was not in general use then. (which is why I like old tweeters)
I'm talking about Martyn's MLS4's by the way.
57charles
03-05-2017, 21:44
Walpurgis - you are incorrect. Apart from my previous comments, I still remember the original blurb published in the press announcing the MLS4 which incidentally was launched after the MLS5 and which used the same tweeter.
57charles
03-05-2017, 21:47
By the way, there were 2 variants of this tweeter - one with and one without ferro fluid. Audiomaster, along with many other box stuffers of the time, used the ferro fluid cooled variant.
walpurgis
03-05-2017, 22:02
By the way, there were 2 variants of this tweeter - one with and one without ferro fluid. Audiomaster, along with many other box stuffers of the time, used the ferro fluid cooled variant.
Could be. I wasn't aware of that though.
I might take the front plate (+ dome) off my last pair of HD100 D25 units that I still have tucked away and see what they have in the coil gap.
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