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Linn Sara DMS to PMS Procedure - Printable Version

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RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2014-06-04 14:39

(2014-06-04 10:46)moomintroll Wrote:  
(2014-06-03 21:05)flatpopely Wrote:  We have some cunning ideas about the loading of the various chambers as differences in air pressure are not insignificant..........

I assume that the pressure in the rear chamber has to be lower than in the isobarik chamber?

'troll

Ideally the pressure in both the cabinet and pressure chamber would be the same. The cabinet needs to be ALMOST airtight. I achieved this with gaskets under the input socket plate. This allows the main cabinet to equalise with changing barometric conditions. The same reasoning made me employ gaskets under the B200's as well. To equalise with barometric conditions. Under dynamic conditions the pressure chamber is airtight though. There is a lot more to the Sara than you can see with the eye.
I spent months thinking about it, before I did the work.

When Peter announced they were the best Saras he'd ever heard, I knew I'd got it right.


RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2014-06-04 17:17

What one has to remember above all else is that if the main cabinet is totally airtight, then on days which differ barometrically with the day the cabinet was built then there will be either excess pressure within the cabinet or the reverse. Both situations will lead to an offset of the B200 drivers, which will impinge on performance. This is why some nights were more magical than others. After my new build the magic is there in full dose 24/7/365. Whatever the barometer is doing.

This is a very important point IMHO.


RE: Linn Sara DMS to PMS Procedure - YNWaN - 2014-06-05 13:58

(2014-06-04 14:25)Dr_Eddie Wrote:  Mark, if you are rebuilding Andrew's cabinets, I strongly suggest you read this whole thread. You are making a number of assumptions that are incorrect.

With respect, I am not making any incorrect assumptions - or any assumptions full stop. Everything I wrote in my earlier post is entirely fact based - either from direct observation or from 30 years of experience.

(2014-06-04 14:25)Dr_Eddie Wrote:  1.The tensioning rod does not need to be removed from the cabinet.It stays in situ when the baffle is removed.

Certainly with the Saras I have here the baffle absolutely cannot be removed without removing the tensioning rod - this rod can only be removed from the rear of the cabinet - this is obviously how it was fitted in the first place. Perhaps you are thinking of the inserted sub-baffle that holds the two mid/bass drivers - I am referring to the entire front of the speaker that carries the mid/bass driver, the tweeters and the crossovers.

(2014-06-04 14:25)Dr_Eddie Wrote:  2. It does not screw into a brass bush.

It absolutely 100% does - definitely on these Sara's - I looked at this very aspect 5 minutes ago.

(2014-06-04 14:25)Dr_Eddie Wrote:  There are 2 nuts and fibre washers on the other side of the baffle in the chamber.

Absolutely and definitely not on these speakers.

(2014-06-04 14:25)Dr_Eddie Wrote:  These are locked together when the tension is correct and then sealed with hot melt glue. If you have unscrewed it you have compromised the air tightness of the chamber already.

Don't be ridiculous! Removing any component form the cabinets will allow air into the cabinet - obviously. In a following post you refer to the need for a controlled air leak to allow for changes in atmospheric air pressure. This is correct, but you are incorrect when you claim that Saras allow this, they do not (unless modified to allow such).

(2014-06-04 14:25)Dr_Eddie Wrote:  3.There is considerable tension applied to this rod from within the chamber, as you have noted, it was enough to distort the washer.

No doubt you are attempting to be helpful, but there is little point in contradicting the evidence of tasks I have already done! The tension bolts are absolutely, definitely not done up with a great deal of tension - this is blindingly obvious when one actually undoes them in the correct manner! The washer is dished because it is thin, of a small diameter and the nut that tightens against it is of an even smaller diameter!

(2014-06-04 14:25)Dr_Eddie Wrote:  It is a major design feature of both the Sara and the Isobarik. The fact there is no tension now is because age has destroyed the foam rubber backing of the rear driver wooden bracing wedge.

There is no evidence whatsoever that any foam ever existed on the small ledge you refer to - no residue and no rotten foam in the cabinet - no residue or marks on the back of the drive unit.

(2014-06-04 14:25)Dr_Eddie Wrote:  4. The rear driver loses its torque on the baffle over time. The torque on the driver fixings is critical as well. They will be loose now, and the fact you have disturbed the baffle will not have helped. You cannot do this from outside, only from inside the chamber.

With respect – utter rubbish!

(2014-06-04 14:25)Dr_Eddie Wrote:  Although what you done is quite clever.

How generous! What you have done is to essentially bastardize a perfectly good pair of speakers.

(2014-06-04 14:25)Dr_Eddie Wrote:  There are no shortcuts to paradise, only hard work will get you there. Why bother to do anything otherwise ?
You must know that from building the Rubikon.

For Andrew's sake do the job properly, in the way the speaker was built, you have got through the hardest part already, the rest is just a bit of plodding toil, but it will make all the difference.

You clearly don't know me or you wouldn't make such ridiculous, patronising and outright condescending comments! I realise you have rebuilt a pair of Saras and consider yourself an ‘expert’ - but that doesn’t make it true.

(2014-06-04 14:25)Dr_Eddie Wrote:  On a note about the crossover components. They may not look anything special, but I'll bet a pound to a penny Linn listened to every single component under the sun mate.

I'm certainly not your mate and it is you who is making assumptions now!

(2014-06-04 14:25)Dr_Eddie Wrote:  change the x-over and you may as well start all over again. It was all built as one unit by listening, listening, listening and then some more listening. I would leave well alone if nothing has shown signs of burning or damage.

Nothing you have written or done persuades me that the above is true (or, frankly, that you have a clue what you are talking about). You happily replace all the drive units with ones having quite different specifications but you don't even look at the crossovers - it simply beggars belief. You’ll forgive me if I choose to ignore your ‘expert’ advice.


RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2014-06-05 14:21

As I said Mark, you will do what you want to do. I have built two pairs of Saras that have been converted from DMS to PMS. That was the intention of my thread. I showed people what I was doing and why. One pair of speakers was completely original in that it used white belly Linn SP1014's . The other pair was modified with SP1039's. On balance I prefer the speaker as Linn made it with a new tweeter unit that was not around in the day.
I didn't need to look at the crossover, because the intention was to go Active.
You haven't bothered to read the thread. That's up to you entirely of course, but the intention is to help people, not to criticise.
People who have heard both sets of speakers showered them with accolades. At the end of the day , who's right and who's wrong doesn't matter a jot. The speaker says it all.
Sorry if I upset you, it was meant to be helpful.


RE: Linn Sara DMS to PMS Procedure - moomintroll - 2014-06-05 14:32

(2014-06-01 21:34)flatpopely Wrote:  It just needed thinking about.

http://audioflat.co.uk/phpBB3/viewtopic.php?f=7&t=178&start=30

Nice thread and photos. The bitumen on the inside of the cabinets reminded me that I'd watched Kan Mk 1s being assembled when I first visited Drakemire Drive in 1984. They were treated in the same way, with bitumen (I think it was actually auto body proofing paint) on the inside of the cabinet walls and on the speaker baskets.

A messy job.

'troll


RE: Linn Sara DMS to PMS Procedure - flatpopely - 2014-06-05 18:20

Looking at what's being done I just can't wait, they are going to look better than new and hopefully sound better as well!


RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2014-06-07 00:23

(2014-06-05 18:20)flatpopely Wrote:  Looking at what's being done I just can't wait, they are going to look better than new and hopefully sound better as well!

Andrew, I sincerely hope they live up to all the expectations. Your partner obviously seems to believe totally in his abilities. I certainly wouldn't have been so cocksure that I could build a better crossover than the Linn design team who built the Sara. The world is full of speakers that have very highly specified components in their crossovers but how many sound as good as a pair of Saras on song ? Not that many. Why fix something that isn't broke ?
Still I wish you well to enjoy them......................Big Grin


RE: Linn Sara DMS to PMS Procedure - flatpopely - 2014-06-07 18:28

(2014-06-07 00:23)Dr_Eddie Wrote:  
(2014-06-05 18:20)flatpopely Wrote:  Looking at what's being done I just can't wait, they are going to look better than new and hopefully sound better as well!

Andrew, I sincerely hope they live up to all the expectations. Your partner obviously seems to believe totally in his abilities. I certainly wouldn't have been so cocksure that I could build a better crossover than the Linn design team who built the Sara. The world is full of speakers that have very highly specified components in their crossovers but how many sound as good as a pair of Saras on song ? Not that many. Why fix something that isn't broke ?
Still I wish you well to enjoy them......................Big Grin

Mark is somewhat robust in his posts but it comes from confidence. Having seen what he did to his NS1000s I can say he knows EXACTLY what he is doing.
As for the crossovers do you really think Linn listened to ALL the components available and then chose those that merely met the correct values? My crossovers will have exactly the same values but with modern better sounding versions. These girls are 25+ years old, things improve.

It is very interesting to see exactly how they were made though when one takes out the entire baffle. They are stunning!


RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2014-06-07 21:20

I think Linn chose the components they did because they were the most musical tried, and yet robust enough to withstand the juice that would be needed to drive them. Integrating those particular drive units is very tricky indeed.
If you succeed where many others have failed, I will be the first to take my hat off to you both.
It is a job that is not for the faint hearted.
May the force be with you both.


RE: Linn Sara DMS to PMS Procedure - Dr_Eddie - 2014-06-08 01:11

Just for reference, this pamphlet contains information about the crossover
http://postimage.org/image/10h7gkhj8/