Rogers LS6 speaker crossover wiring help please.

[PJL]

As mentioned before, the LS6 crossovers on ebay look very similar the only difference being the additional LF AC coupling on yours which will have no impact at audio frequencies. All the caps are 6uF making the HF network identical to yours except yours is missing resistor R1=3.3 ohms 2W. I would give it a 90% confidence that this is the original value.

Yours is an early model and the LF AC coupling might be to provide roll-off at very low frequencies or to protect the speaker from DC from the amp and could have been removed as part of a cost reduction exercise. It also means the speakers would measure open circuit!

[mhennessy]

I've just spent a while going through my archive of Rogers photos, but I have nothing at all about the LS6.

I found the LS6 crossovers for sale on eBay. But they are radically different to yours, so I'm not sure these will be of any use. This raises an obvious questions - are your ones actually original?

Then I remembered that I had a Hi-Fi Choice review of the LS6 from 1986, so dug that out. It mentions that the bass is a 5th-order alignment with a series capacitor, so that confirms that you do have the original crossover PCBs. Hence, the eBay crossovers must be a different (probably later) version of the LS6. Thing is, there was the LS6, the LS6a, and the LS6a/2 - and those are the ones I can recall; there might be more! And within each of those models, there could have been modifications as time went by. The LS6a/2 had "buy-wiring" using one of those ubiquitous plastic terminal trays, so I'd guess they come from an LS6a (with the metal-dome tweeter).

That review also mentions that the tweeter is made by SEAS, and is a 19mm plastic dome. Not much to go on, but that might help us establish if the tweeters are original. From your photo, it's hard to be sure if it's fabric or plastic. As I said earlier, the LS6a (and LS6a/2) uses the SEAS 19mm metal-dome that was so popular in the early '90s.

It certainly looks like R1 was lost when the mod was done, but as has been said, we really need to see an original one to be sure. If you do follow the earlier suggestion to keep asking around on any forums you can find, please can you report back here?

Also, if R1 was just a wire link, they would have simply mounted the first capacitor at an angle to save the effort of plumbing in a link. So I'm sure it's missing.

The trouble with removing the resistor is that it would change the impedance "seen" by the capacitors, thus changing the frequency of the filter. So it's not just a level setting resistor that can be changed in isolation. Unfortunately, some folk who modify crossovers don't realise how much everything interacts with everything else.

For now, I'd put them back together, having sorted the wiring, and connect various resistors between the 2 red terminals (the extra black terminal can be ignored) until you're happy with the balance. Measurements, or (more likely) comparisons to a reference, would help enormously. I'm just sorry that I can't suggest a value to try, but it'll be a few ohms - possible low 10s. If you have access to a resistance decade box, or a low-value wirewound pot, then that'll speed things up. While testing at low listening levels, don't worry about the power rating - once decided, the final component should be rated at 2 to 5 watts....

Of course, the extra terminals can be removed and the holes filled in eventually.

Oh - you mentioned phase earlier. Usually (not always!) for a 3rd-order on the tweeter and 2nd-order on the bass, the tweeter is reverse-phase relative to the bass. Here, the polarity of both is clearly visible on the PCB, so that's easy

[PJL]

Mark, Have a close look as I don't see the ebay ones being radically different. The active part of the crossovers at audio frequency are identical and use exactly the same 6uF values and very similar looking inductors? The only difference are the 3 parallel capacitors which decouple the LF network which appear to be about 500uF giving a -3dB cutoff frequency of 40Hz.

[mhennessy]

You might well be right, but right now it's impossible to say. The trouble is, we're working with very limited data. Here's what we know:

1. When reviewed in 1986, the LS6 was 5th-order (capacitor in series with the woofer).
2. The LS6a and LS6a/2 uses the metal-dome tweeter.
3. The LS6a/2 (circa 1993) uses bi-wiring.
4. The crossovers on eBay lack the series capacitor on the LF circuit, so the bass loading will be 4th-order.
5. The crossovers on eBay are single-wiring, so they can't be applicable to the LS6a/2 model.

But since my last post, I've been searching around, and have found some addition information:

6. Some LS6as has two red terminals for "1.5-wiring": https://www.avforums.com/threads/bi-...akers.1417420/
7. There is an LS6a/2 which is single-wired: http://img.canuckaudiomart.com/uploa...gers-ls6a2.jpg

These latter two discoveries do muddy the waters somewhat!


So, based on the initial data, I originally believed - fairly confidently - that the eBay crossovers came from an LS6a with its different tweeter. But point #6 contradicts that - the eBay crossovers clearly have 2 terminals, not 3. But what we don't know is whether all LS6a models had 3 terminals.

Alternatively, perhaps they came from a single-wired LS6a/2? But they look older, somehow.

Maybe Rogers changed the bass loading of the original LS6 from 5th-order to 4th? But even with the additional discoveries, we have no hard data at this time to prove or disprove that. From what I know about the industry, I'd say that that's quite a big change to make in production without giving a revision to the model number, or some marketing "noise" at least - after all, so-called "special editions" appear with much less substantive changes than that!

So it felt most likely to me that the change from 4th to 5th order would have come about with the a-model, given that the whole design was re-examined at that point. If only I hadn't discovered point #6! If anyone can help, I'd love to know.

Ultimately then, it's possible that the eBay crossovers are driving the metal-dome tweeter. It might well have a different sensitivity to the plastic-dome model, amongst other things. Or not. We simply don't know.

Frustratingly, even if we knew that they were used with the metal-dome tweeter, the versions of those tweeters that we could have bought from Falcon or Wilmslow would be different to the OEM versions supplied to Rogers, meaning that datasheets won't help. Indeed, it's entirely possible that Rogers got them to produce a version of the 19TAF metal dome unit that was sufficiently identical to the original plastic-dome unit that no crossover changes were necessary! As I say, you might be right

I can't read all the capacitor values in the eBay pictures. I can see the input one is 6uF, but I'm really not sure about the next one. And I've got a nagging sensation about the tweeter inductor being a different physical size, though of course it could still be the same inductance/DCR.

In summary, perhaps the word "radically" was a bit strong (I nearly took it out), but having set it all out, we can see that there are many unknowns, and as such, I don't want to make assumptions about those eBay crossovers just yet. But as I suggested to the OP, the missing resistor is likely to be a few ohms, and 3.3 ohms seems a reasonable place to start. But if the speakers are conspicuously harsh, 3R3 might not be enough? We don't know Z, but if it's 8R resistive, that's only 2 or 3dB ("bright" rather than "harsh", perhaps?).

If nothing else, this is a useful data-gathering exercise for me - I do need to add something about the LS6 to my website. I invite anyone reading this to contact me with additional data - either via this forum if you're a member, or via my website if you came here via a search engine.

Sorry for the ramble.

Mark

[brainhertz]

I believe the tweeters to be replacements but of exactly the same type, as I got the originals with the speakers, one of the original tweeters as a blown coil, they were replaced by a HIFI retailer under warranty after a previous owners purchase, they were manufactured in Norway so are SEAS units originals labelled 3/4" DOME FF H225 8ohm 2/86 MADE IN NORWAY & the replacements labelled 3/4" DOME FF H225-8ohm Made in NORWAY 17/92, so although they have been replaced they are the correct type and manufacturer. Stated already we can probably confirm that R1 is the missing component, and Mark Hennessy has come up with a good way forward and reading through his web page earlier he is well informed with regard to rogers speakers, I do have access to a resistance decade box so I will probably once the wring is sorted try different values of resistance between the two red terminals so has to save stripping the speakers down numerous times to get at the crossovers. I have uploaded some more photos of the tweeters, the two originals and one of the replacements, meanwhile if anyone else can help it will be much appreciated. I must say how helpful you lot are and its a pleasure to be a member of this forum and I will keep you informed of the progress of the LS6s. Take a look at the photos, many thanks Mark !!!!

[brainhertz]

I really have to take my hat off to you Mark, your input is received with much appreciation and have enjoyed looking over your web page I have not gone through all it contains but have saved the link and will browse in more detail in the near future. Maybe it will help you to put more info onto your pages with regards to the LS6 variants for the future. I will keep everybody posted on these pages as to what develops meanwhile the more info the better, many thanks Mark !!!!

[brainhertz]

One other point I thought I would mention I don't do television and have only recently got a my own PC, all I do is listen to music mainly vinyl I have about 5000 albums, numerous turntables not to mention a few pairs of speakers, various valve and integrated amps, so most of my pleasure comes from listening to mainly analogue music although I do have some CDs and a couple of CD players, I really like my vinyl and used to own 6000 singles until the floods in 2007 as they were in a pub cellar at the time. So really music and Hifi mean a lot to me, so thanks to everybody who as contributed cheers Mark!!!

[brainhertz]

Just a bit of an update I have at this moment got 5 ohms in circuit for R1 and the one speaker sounds very well and I would not be amazed if the end value for R1 turns out at 4.7 ohms. I will let you all know the final result, and thanks to you all cheers Mark !!!!

[Radio Wrangler]

That's a good result. The end purpose of these speakers is to make you happy, so the umpire's decision is final.

You may want to redo the silly wire with something a bit more normal and maybe restore connection to the original terminals. I was a bit worried when I saw the photo with the damping material out.

David

[LNBAudio]

Hello
I suggest that you contact Falcon Acoustics who have a lot of experience with the LS3/5a (BBC monitor)
Malcolm Jones, the Tech Consultant there may be able to help
Regards
Mike

[Edward Huggins]

Falcon are super it comes to support when needed. These Rogers unit are very dependent on an accurately matched crossover to minimise insertion loss and phase shift.

[mhennessy]

I agree that Falcon are excellent, and their knowledge of the LS3/5A is up there with the best. Malcolm worked on the B110 and T27 when at KEF, and him and Jerry are manufacturing them today, as well as their own BBC-licensed version of the LS3/5A.

But this isn't an LS3/5A, and so they might not know much about this unit. Besides, we're pretty much there, are we not? Apart from some initial confusion about the exact model (I note the thread title is correct now - thanks!), the only unknown is the value of the missing resistor. A different crossover for another version of this model uses 3R3, and the OP seems happy with 5R at the moment. Job done!

As for "minimise insertion loss" point , someone in the past did exactly that when they misguidedly bypassed the resistor in series with the tweeter filter network. Astonishingly, with the "insertion loss minimised", the speaker sounded harsh. As is usually the case, the loss from that resistor is essential to bring the more efficient tweeter down to the same level as the bass/mid unit.

As that was the only change to the crossover, I think we can safely assume that the phase shifts, along with our chakras, are all in alignment. Just in case, there are markings on the PCB to establish the correct relative phase (tweeter inverted).

I'm part way through an update on my site, adding what we've learnt about the LS6 in this thread. As I said earlier, if anyone knows any more, it would be a great help

[andrewb]

I have a pair of Rogers LS6 speakers, purchased new by me in early 1986.

I am posting this information here in case it may be useful to someone in the future.

The speakers' serial numbers are ST993A, and ST993B. Crossover PCB is marked DCLX.

I have recently taken out the crossover to replace the capacitors, in case they had deteriorated due to age.

I took advantage of this to measure all the components with an LCR meter.

Measurements were taken after I had unsoldered one leg of each of the capacitors, to avoid parallel paths.

High pass (tweeter) leg.
consists of series resistor R1, series cap C3, series cap C5, with inductor (no designation) from common connection of the capacitors to ground.

Low pass (woofer) leg is series inductor (no designation) and parallel capacitor C2.

measurements
R1 (marked as 3.3 ohm 2W, measured as 3.5 ohm
C3 (marked as 6MFD), measured as 6.8uF, replaced with cap 6.243 uF
C5 (marked as 6MFD), measured as 6.6uF, replaced with cap 6.128 uF
L (HP) measured 260 uH with 0.53 ohm series resistance

L (LP) with 2.52 mH, with 0.68 ohm series resistance
C2 marked as 6MFD, measured as 6.6 uF, replaced with cap 6.272 uF

(Oddly capacitors are measured at higher value than case designation.)

Hope this is of interest/assistance.

Regards,
Andrew

[andrewb]

I have attached some more photos of the drivers. The speakers were bought new in 1986 in South Australia, and have not been modified up until now.

I hope that this provides some useful information to anyone wishing to determine how the speakers were configured in that era.