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Linn Sara DMS to PMS Procedure - Printable Version

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Linn Sara DMS to PMS Procedure - Dr_Eddie - 2011-07-08 16:31

Conversion of Passive Sara DMS Isobarik Loudspeaker to Active PMS

In this thread you can follow how it is possible to do what many people have, in the past, claimed is impossible. To be fair it is not an easy task, or for the faint hearted, but it is entirely doable, if you feel so inclined. The caveat is, it is safer to do this job on a donor pair you have acquired from somewhere else. I certainly wouldn’t have been brave enough to attempt this on my much loved DMS pair I bought new in 1984 from Grahams Electrical in Pentonville Road, London N1. The thought of ruining them would be unthinkable. A spare pair came my way courtesy of Peter at Cymbiosis. The value of a good relationship with your dealer is thus beyond price.
Many thanks, mate, you’re definitely a “geezer” in Londonspeak.

I believe this is, for many people with limited space, the best speaker Linn have ever manufactured and with the advancement of the source available now in the form of the LP12 SE the quality of the music making of these transducers is amazing. If you want to suspend belief, just play the Sheffield Drum record to hear what they are capable of. The only way to improve on this is to have the actual drum kit and artist in your room, playing it for real …………….or to have an Active pair being driven by 4 Naim 135 Monoblock Power amps.

One thing that emerged as I progressed through this project is the amount of love and care that the factory lavished on this small and unassuming speaker. The build quality is literally breathtaking. From the quality of the 50 Amp cabling and soldering, to the attention of firm fixing with hot melt glue, also used for sealing any possible place for air to leak into or out of the pressure chamber.

The components and layout of the two identical crossover boards, one for the tweeter and the other for the two bass midrange units is first class They could have got away with one board, but not with this speaker. The ethos inside this speaker just yells no compromise. The customer would never get to see this, in fact they didn’t need to, all they had to do was listen to them making music. Which is something that, because of all the above they are rather good at. They, quite rightly, have a cult following, because modern speakers fail to offer the same satisfying coherent musical performance. You only have to hear them playing woodblocks to appreciate this, believe me.

The passive version is a difficult load for a power amp. The impedance can fall well below 4 ohms and the phase angles can become difficult too. Since they were designed during the Linn Naim cooperative years it is hardly surprising that Naim power amps give the best results, since they were used for the purposes of tuning and testing the prototypes.

The Active version however is a much easier proposition for the amp to drive. Firstly the tweeters have their own amps to supply them direct, as do the bass units. The amp does not have to worry about supplying great gobs of current to reproduce a bass guitar and kick drum transient at the same time. Consequently each amp is in its comfort zone and exerts more control over the drive unit, having no inductive or resistive loads to soak up power. The result is more music. So the project begins.
Before I start lets have a look at the Linn pamphlet that described the product and its application.

Edit appears to be removed because of copyright infringement, sorry chaps.
Latest Edit. Appears to be back now, thanks HQ.

So there you have the meat and potatoes of this superb speaker’s potential and the word “revealing” is the one that strikes at the heart of what they can do. I’ll show with pictures and text, how I managed to strip the cabinets down without damaging either the woodwork, the drive units, crossovers, or the special high density plastic moulded baffle. The silicon sealant does not produce joints that can’t be separated, far from it in fact. It’s a doddle to take apart if you reverse the building technique that Linn employed. It’s not a five minute job though. Be prepared to spend a whole day on each cabinet. That’s enough for this initial post, it should have whetted your appetite for what’s to follow. Climb on board.

RE: Linn Sara DMS to PMS Procedure - CJ1045 - 2011-07-08 16:50

Looking forward to this, thanks for taking the time to write this up. If you are ever Dorset way then you are very welcome to pop by and listen to some activ Briks. Am intrigued to hear what you have used as an Aktiv crossover, presumably a tweaked NAXO.


RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2011-07-08 17:03

Thanks for the offer, at the moment I'm still working on the rebuild and initially I'll test them passively with the crossovers installed into 2 Aluminium cases I'm constructing.

Peter reckons we can get Naim to reconfigure a Snaxo for us with the Sara 3KHz crossover point. This is still a WIP, and there is no guarantee they'll equal my passive pair in the test scenario above. I'm optimistic though, it should be fun as well.

Keep watching for the first stripdown instalment.
Best Regards Eddie.

RE: Linn Sara DMS to PMS Procedure - CJ1045 - 2011-07-08 17:20

I have an olive SNAXO 2-4 set for SBLs that you are welcome to short term borrow. Think for SBLs the crossover is at 2.7kHz but I am not certain. I am on holiday until 19th though. I have a passive pair of Saras in storage too!


RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2011-07-08 17:25

I wonder if anyone noticed that the pamphlet referred to the S.A.R.A which tends to suggest that the name refers to words. The story goes something like this : Apologies to HQ if I've got this wrong but please feel free in the interests of the truth to correct me. It was a fair time ago and the person in question will be a fully grown lady now with possibly kids of her own.

Whilst this speaker was in development the company were trying to come up with a name for marketing purposes. At the same time Ivor became a proud father of a baby girl. The baby was named Sara. Ivor duly noticed that the new addition to the family and his new speaker had a lot in common, ie. they were both small and made lots of the speaker became Small Acoustic Reproduction Apparatus. Thereby hangs a tale.

The great thing about Linn, is they have always been a "people " company, and they are still a delight to deal with today. This is how the Sara became so called, as I understand it.

RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2011-07-08 17:39

(2011-07-08 17:20)CJ1045 Wrote:  I have an olive SNAXO 2-4 set for SBLs that you are welcome to short term borrow. Think for SBLs the crossover is at 2.7kHz but I am not certain. I am on holiday until 19th though. I have a passive pair of Saras in storage too!


Thanks for the offer CJ, I'll bear that in mind since the SBL's and Sara are very similar in their presentation and olive goes with the rest of my gear too. It will take time to get the speakers built so no sweat at the moment. You might want to play with those Saras too.
Much appreciated.
Best Regards Eddie.

RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2011-07-08 18:08

The first thing to do before you start work is to protect the drive units and woodwork from dirt ingress and damage. You can use duck tape to seal the baffle because the first stage usually results in a lot of muck all over the place.
The front baffle has rebates into which male Velcro tape is glued. This glue decomposes and becomes brittle. All the remnants of the glue have to be removed in order to find the fixing screws that are hidden beneath.
See the following pics.
You’ll notice the wood work is unprotected, if you are very careful you’ll not mark the cabinets, and it makes for clearer pictures.

Spirit Wipe can be obtained through any Automotive Paint factors as it is used to prepare surfaces for painting, but is excellent too at removing old contact adhesive.
The Velcro tape can be cleaned and reused later on by adding another Auto application , double sided trim fixing tape.
The clean speaker can now be taken indoors for the next stage which is , drive unit harvesting.

RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2011-07-08 18:54

The next stage involves removing the B200 Bass unit from the front baffle. The easiest way to do this is to use a small electrical screwdriver to lever up the chassis edge as showed in the following picture, once all the 4 fixing screws ( Allen headed on later models ) are removed.
Like so,

Gently lever upwards to break the silicone seal (you’ll hear it give) and then using a flatter blade driver lever up the unit gingerly.

Now get your fingers around the frame and carefully lift away.

Turn the speaker up the right way and reverse the drive unit so it faces in to the cabinet and retain with one bolt. This is to ensure that when unsoldering the cables the drive unit doesn’t fall onto the hot soldering iron and cause you or it a lot of grief.
It is very heavy and liable to cause injury otherwise.

Note the use of a warranty card to prevent molten solder running onto the innards of the spider where it will destroy anything it touches. You’ll need a 50 Watt iron to unsolder these beefy connections too.

Safely harvested, carefully pack this away, and now we’re into the guts of the cabinet where we must delve deep to remove the second bass unit visible.

More on this next time, must dash now.

RE: Linn Sara DMS to PMS Procedure - Tony Tune-age - 2011-07-08 18:58

Very detailed information Dr. Eddie, look forward to reading about the remaining steps of your projectCool.

The first set of Linn speakers I had the pleasure of hearing was the Sara 9, which was bi-amped with two Linn LK280 power amplifiers. We conducted a listening session with two different Sondek LP12 turntables, one had the Ittok tonearm, and the other had the new Ekos tonearm. Needless to say, both turntables sounded great to everybody in the room.


RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2011-07-09 01:09

The next job to tackle is to remove the baffle extension ring which will be necessary to gain access to the rear driver. This is secured with 8 Posidrive headed screws hidden under the domed plastic caps on the front ring. These can be simply removed by levering up with a small terminal screwdriver. Sometimes a blob of silicone sealant obscures the screw, just dig it out.

Once all screws are removed just grip the ring with your hand as in the picture and gently tug at it, whereupon the seal will break and it will lift away.

Now you can begin to see the care that Linn have taken with the acoustic lining of the pressure chamber. Wadding contained in pockets of Muslin around the periphery of the chamber. This is glued in and can be carefully unpeeled and the pockets of grey wadding removed and safely stored. You will notice that there are 8 bracing bars contained in the Linn baffle.

You can at this stage also remove all the front baffle fixing screws. Don’t worry the baffle will remain firmly fixed by a single hidden bracing bolt.

Now carefully peel back the muslin around the perimeter of the chamber.

Now the wadding balls are all safely stored, the muslin can be peeled away at the bottom circumference of the chamber to reveal the second bass unit we’re interested in removing.

To remove the second driver a special tool is needed. A cranked screwdriver handle which looks thus.

And it is placed as thus,

But only after removing all 4 fixing bolts first, this allows you to lever up the chassis against the wall of the chamber. The whole of the outer chassis is used to seal this driver with lots of sealant so the force needed to break the seal is higher than that needed on the front baffle, but it will yield to this tool.

Once you have gained a little clearance under the lip of the chassis you can pull upwards on the handle to remove the unit enough to get a hand under the chassis like this,

Now the unit is free to lift out with plenty of cable to help make it easy.

Utilise the front ring and one fixing screw in the corner as before to help you safely unsolder the second unit.

This time it helps to keep the cabinet laying down to do this.

Now remove all the wadding inside the second chamber beneath, there is a lot of it and it goes up right around the tweeter housing and crossover baffles on both sides. You should end up with a sizeable mound of the stuff.

Once this is all clear you will see how the front baffle is retained by a nut on a threaded bracing bar that comes through the second bass unit fixing plate from the back of the cabinet. This is smothered in hot melt fixing glue which is also puddled around the two holes in the fixing plate where the red and black wires come through from the second chamber to feed the front B200 unit. This ensures an airtight seal in the pressure chamber and will have to be reinstated when we rebuild the speaker later on. But now it will have to be removed by chipping it away with our small terminal driver. It is a long tedious job.

That’s it for now, more stripping down in the next instalment.