Active Sara Project

[jimmymcfarrell]

This is what I recall them looking like internally.

That’s exactly what I was looking for; i thought it was something like that. Just gotta work out how to replicate it. Shouldn’t be too difficult, hopefully, but does highlight just how labour intensive Sara’s must’ve been to manufacture.

Been looking up the specs for the SP1014 B200 driver & I’ve found conflicting figures for power handling of 25-50 watt. Either way that’s far from a huge amount - and where I’m going to go active, each driver having it’s own amp, they will potentially each be hit with the full rated power of the amplifier being used (in my case iirc 90watt as a bridged monoblock). And this really will be the case as there will be no power sapping passive crossover or tweeter / dummy resistor in the circuit.

 

[jimmymcfarrell]

I’m pretty sure neither Linn no Nytech did active crossovers for them.

In the literature I had for my A&R Cambridge A60 SA60x it mentioned the ALSO (active loudspeaker standards (?)organisation(?)) and how electronic filter boards would be available for the SA60 for (amongst others) Linn Kan & Sara and certain models by Tangent. Generally if the boards were available for the Arcam they were also available for the Nytech CXA / EXO.
It was this original kit and retaining my ARC 101s that got me into this whole business of using active speakers in the first place.
My ARC101s with new Scanspeak D2008 tweeters fed from a brace of Crown amps and an Audiolab 8000 ap pre-amp is in use all day every day and makes a wonderful noise.

 

[jimmymcfarrell]

Suggestions for what sockets to use would be greatly appreciated. I notice in the thread linked above you made up a snazzy looking panel to mount everything on - I won’t be doing anything like this but don’t know whether to buy 4mm binding posts with long threads & mount them straight to the (through the) cabinet; or if it’d be easier to fit them to a piece of Perspex first & mount this to the cabinet with holes drilled to suit.

Also need to decide if it’s cheaper to have the original Scanspeak tweeters (blown up by previous owner) rebuilt; if it’s even possible or just buy new. I could pinch the pair out if my ARCs but would rather not.
Is there any benefit in going to D2010s or D2905 as they’re not massively more expensive?

And changing the subject a bit; can anyone suggest how I go about setting the gain controls on the amps so they’re all putting out the same level. I’ve got 3 Crown D75s (well at the minute 2 D75s & a D60 in the rack and a 3rd D75 waiting in the wings - hopefully soon to be 4 D75s, for the 4 B200s in the Sara’s & a D60 for treble; but I digress) and they’ve all got gain controls on them. Now I’m not expecting every amp to be working either to spec, or the same as each other SO for a given input, I want all of them to be amplifying that input by the same amount. But if there’s any variation between them how do I set them all to the same level. I’ve tried feeding a 50hz signal into the pre-amp & setting it to 0db & measured the output at the first (bridged mono) amp with a volt meter. Setting gain at about 3 o’clock (approx 75%) I got 13v. Then tried setting (mono’d) amp no 2 to get 13 volts and the gain wasn’t at 3 o’clock. Similarly on the stereo amp doing treble - bypassed active crossover & fed it 50hz straight from the pre-amp; set channel 1 gain to 3 o’clock ish (again about 75%), noted voltage and set channel 2 to achieve same voltage & knobs were nowhere near each other - one at 3 o’clock the other at about 12 (so 50%). Any ideas what’s going on and if there’s a better way to go about setting this up. Also noticed as I increased gain from 0 I’d get a reading in milivolts for first 25-50% of the movement of the pot then suddenly it would jump up to 9 or 10 volts and be around this sort of figure (say 9v-15v approx) for the last 50-100% of the gain pot’s range. Wound it not be expected to be a smooth, consistent increase? Someone suggested using a microphone to set this up but I cannot see how this would help.

 

[Colin L]

Interesting. I’m pretty sure I never saw a pair though. A long time ago though if you used a Nac42? I’m pretty sure neither Linn no Nytech did active crossovers for them.

I also had a pair..again with the 42 xo. Linn had the active crossover module which you could configure for several speakers

 

[YNWOAN]

Regarding connectors on the back panel, I actually wanted to use SpeakON connectors for Andrew’s Sara project but, for some reason I can’t now recall, he didn’t like the idea. Oh yes, I remember, he wanted a lower profile solution and so we went for Naim spacing so he could use the ninety degree banana plugs Naim do.

Regarding setting levels, what I have done in the past is to play a test tone at a mid range frequency and measure the output (you can do this at the speakers) with a multimeter - then adjust till they match (many pro amps allow this).

Edit: sorry, I see you already know all this. All I can really add is that the gain on my amp is done in the digital domain (rather than an analogue pot) and is extremely predictable and linear in adjustment versus measured output. I can only conclude that the problems you are experiencing are down to dirty, or poor quality, adjustment pots.

 

[hp1]

The 4mm sockets that naim use for there amps and speakers are a good choice, farnell sell them ,i think they may be schurter.

I have played around with 2008, 2010, hiquaphons, old linn modded 2008s and the ones linn chose ie the ones with the doped domes intergrate alot better with the b200 than the undoped ones.

The damping was made from a loose woven cotton tube which had lambs wool inside and was hot glued in place, I have had a few burnt fingers replacing these.

I think the cotton tube may be something that car body shops used to use prior to tackrags or still do.

I hope that helps, good old girls saras when they are right.

 

[jimmymcfarrell]

Well very little progress so far (been waiting for payday!!) but I have just ordered what I hope are all the bits I need to get on with this.

New Scanspeak D2008s from Falcon,
Red & Black 4mm sockets.
Wool & cotton to hopefully replicate the internal damping in the isobaric chamber.
Lots of glue for the glue gun.
XLR splitter boxes to feed multiple amps from same output on active crossover.
XLR cables.
New rack to hold all the amps (however I overlooked “collection only” from Derby so this maybe a problem).

Can anyone tell me what size bolts I need to get for securing the drive units (some are missing)

Thinking of mounting the 4mm sockets on some thin plastic “hygienic cladding” I’ve got lying around. Any thoughts on this. Guessing I’m going to need to drill holes in the cabinets for the sockets however I go about doing this but I’m concerned about getting it sealed.

I’ve got silicone to seal everything up but I see mention of leaving a hole to allow the pressure to equalise. Does this not defeat the point of the whole idea of the isobaric cabinet?

Hopefully make a start on this at the weekend.

 

[jimmymcfarrell]

How does one go about working out what size bolts are? Can’t see any obvious correlation between measuring them & the sizes they come in?

Also any suggestions where to purchase the rubber caps that fill the screw holes in the ring that covers the front bass driver or even what they are called for purposes of searching for replacements.

Many thanks in advance for any suggestions

 

[hp1]

Hi , They used m4 capscrews for the bass units and m3 for the tweeters ,the length does not include the depth of the head.

The covers are the same item as linn used on the lp12 arm board .

 

[hp1]

Just found eurocar parts stockinette, thats exactly the stuff for making the damping tube thingy from.

 

[jimmymcfarrell]

Well I had very limited time at the weekend so didn’t get nearly as much done as I would’ve like.
Sanded the cabinets and given them a couple coats of oil so far. Looking better for sure ( I wish Flickr would let me insert pics from my iPhone on here - this would be so much more interesting with pictures) however there are a few patchy looking bits where I’m wondering if they haven’t been sanded enough (or perhaps sanded too much in certain places) if they don’t improve after a few coats of oil I might need to sand them again - although I’m paranoid about going too far through the veneer because at the moment I think I managed to just lightly go over the whole of the cabinet so maybe it’s sun damage I’m seeing. As I’m having to work on them in my Dads garage I’m hoping he’s going to give them another coat each day this week so they should be good to go by next weekend.
Tweeters turned up today, as did lambswool for redoing the “pillows” in the Isobarik chamber.........

Just found eurocar parts stockinette, thats exactly the stuff for making the damping tube thingy from.

Thanks for that. I’ve found some cheese cloth & if that doesn’t work I’ll have a look at eurocar part.

Hi , They used m4 capscrews for the bass units and m3 for the tweeters ,the length does not include the depth of the head.

The covers are the same item as linn used on the lp12 arm board .

That’s ok then, they should be easy to source. Thank you.

 

[hp1]

Hi Jimmy ,
The cap screws are actually m5 , sorry if you have already ordered or what not.try ebay , kay fasteners.

The stockingette from euro is £3 something.

 

[jimmymcfarrell]

Hi Jimmy ,
The cap screws are actually m5.

I’m talking about the bolts that hold the bass drivers. Not the trim ring around them.
Although I do need to check exactly what’s missing before I order them.
Got lots to do before I’m going to need to permanently fix the drivers in place.......


Need to find the caps to cover the screws on the....err..... ring-piece although I haven’t tried searching with LP12 in the search

The covers are the same item as linn used on the lp12 arm board .

 

[jimmymcfarrell]

Also been wondering why did they use 2 separate passive crossovers & not just put 2 woofers in parallel & a tweeter and resistor in parallel off the 1 crossover? Am I missing something?

 

[hp1]

I think the bolts are the same for the ring and the driver.

Afaik Naim did the crossovers and its easier to get right if the units have similar impedance,so the they did the pair of driver s you can see as one circuit and the rear bass unit and a dummy load resistor for the other then wired them in parallel.

Its basically the same circuit as mk1 kans but being paralleled the impedance drops as low as 2.6 ohms, I often wondered what they would sound like passive with the crossovers seperated and an amp for each one.

Dont remove the crossovers by removing the bass drivers it cant be done, instead remove the baffle .

 

[david ellwood]

Also been wondering why did they use 2 separate passive crossovers & not just put 2 woofers in parallel & a tweeter and resistor in parallel off the 1 crossover? Am I missing something?

Well the Sara9 was exactly that. The original Sara was designed in the 1970’s and they didn’t have access to the required computer power to design a 4ohm crossover.

 

[hp1]

I have a pair of sara 9 crossovers if any use to anyone.

 

[david ellwood]

I'd be interested in a decent photo to compare with my Sara 9's

 

[PL135]

Hi hp

I have a pair of Sara's with Sara 9 drive units that I am in the process of refurbishing. I would love the Sara 9 crossovers. Please see PM.

Regards
Peter

 

[jimmymcfarrell]

Speakers roughly assembled. All wired up with each driver connected to its own banana socket, new tweeters fitted and thrown together with half the number of screws and no sealant just to check they work. Will need to take them apart again to seal up & assemble for final time but gave them a dry run this afternoon with 5 amps fed from the active crossover and it sounds very promising indeed. Each B200 getting a potential 110 watts and even without any lambs wool damping or sealant they still sound good. Wish I could post photos.