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Upgrading ATC SM75-150S MID WAVEGUIDE

cooky1257

cooky1257

pfm Member
As a few of you will no doubt already be aware I'm a long time fan of large studio monitor style presentation, having way too many pairs of large Tannoy DC's and/or JBL's in the house at one time or another.
A few months ago I satisfied a long standing itch to get some ATC SCM100ASL monitors, I was very familiar with their sound having regularly come across them in post production/dubbing suites/recording studios via the day job a few moons ago now.
A nice pair of domestic 'classic' versions in piano black(car black?) that had been fairly recently serviced(2016) with new SL bass drivers, mid super domes and new SEAS tweeters came up and I couldn't resist.
The only thing that bugged me was the mids-they hadn't updated the waveguides when they were re-domed to Super dome spec.
I've no intention of going to the expense and (now) big shipping palava of a tweeter upgrade as I'm more than happy with how they currently sound but I enquired at ATC if the curved mid waveguide were available as spares and if a swap was doable diy.
Peter Guppy was very helpful, he pointed out the dangers and pitfalls, in particular the consequences of a cock up would mean completely new drivers(£1250 each!!) as ATC no longer re-dome motor units made before 2006 owing to plating corrosion in some of the older drivers.
With some trepidation I ordered the parts and they arrived within a few days rather than the 10 weeks I was initially warned about.
These suckers weigh 65kg each and are firmly attached to their stands, laying them flat was a 2 person move.

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Peter explained that I would need to remove the bass drivers as the mids are removed through the bass driver hole. I removed one of the tweeters to try and get a better view of the inside.

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The new waveguide can be seen in the first pic.

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Unfortunately the netting to hold the wool damping in place is stapled on the inside of the brace ie before the baffle was bolted in place and I did attempt to remove the baffle but it just refused to budge so finding there was enough slack I just cut through the staples.
Carefully undoing the 4 bolts and holding the rear of the mid ready to take the strain as it drops into the enclosure was awkward, the driver is very heavy and difficult to manoeuvre with one hand all the time being mindful of dropping/fumbling it and damaging the dome.

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Next comes the careful removal of the old waveguide-after removing the 3 Allen bolts there's a thin film of glue under it that requires a gentle sideways tap with a mallet to dislodge it-all the while protecting the dome/surround.

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The next 'boobytrap' is the tinsel leads.
They pass through 2 slots in the waveguide and are held in place with some RTV 100 black silicone gasket goo.
I used a dentists scraping tool to gently push the leads out of the slots-again VERY mindful of not pulling on the leads.

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Careful 'first fix' of the new waveguide throws up a minor issue with the tinsel lead dressing not matching the originals-something that need paying attention to..

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A small blob of new gasket goo is applied into and under the slots. This was nerve shredding as it would be a disaster to get goo onto the surround roll or dome-I was seriously sweating at this point... By installing the waveguide rather like a clam shell lid with the tinsels as the hinge the leads kinda dress themselves into the desired positions.

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Reinstall the tweeter, the arrow is a polarity reminder(from this end white on the right) as the tweeters aren't marked(!)

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Job done, bloody marvellous.
We are all convinced chez moi that there's a significant improvement in what were already excellent speakers but I'm content just to like what I'm hearing and leave it at that.
I've got tons of experience reconing. refurbing, servicing direct radiator and compression drivers but this was seriously squeaky bottom stuff and so not something I'd recommend tbh.

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Tw99 said:
Rather you than me!

How do you find these compare to your usual big Tannoys ?
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Good question. Greater resolution of detail, cleaner, more articulate bass, mids to die for. Everything ATCs are noted for is there but I still love what Tannoys do, their coherence, point source holographic imaging and compression driver/ horn projection and the phat breathy bass. The ATCs are my end game loudspeaker though. Only the other day I remarked jokingly to my better half that they're so good they've killed my hobby!
 
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cooky1257 said:
Good question. Greater resolution of detail, cleaner more articulate bass, mids to die for everything ATCs are noted for is there but I still love what Tannoys do, their coherence, point source holographic imaging and compression driver/ horn projection and the phat breathy bass. The ATCs are my end game loudspeaker though. Only the other day I remarked jokingly to my better half that they're so good they've killed my hobby!
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I was just going to ask do you think think they are a better all rounder than the JBL Arrays, but i think you've answered that above. I wouldn't mind a pair a pair of PMC IB2, or a pair of 100As, although i think a pair of 50A/40As would be fine too.
Well done for changing the wave guides, perhaps a job in bomb disposal next!
 
Space is the Place said:
I was just going to ask do you think think they are a better all rounder than the JBL Arrays, but i think you've answered that above. I wouldn't mind a pair a pair of PMC IB2, or a pair of 100As, although i think a pair of 50A/40As would be fine too.
Well done for changing the wave guides, perhaps a job in bomb disposal next!
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Cheers. The Arrays - or at least my beryllium hf cloned take on them also have a Tannoy beating midrange- I still have them and can't really see myself parting with them - the vertical SAM1 horn is really special. I'd fully recommend giving the ATC's a go, 50's or the 100s, if you can, get recently serviced SL/ Super dome versions.
 
Congratulations. They are stunning, and I admire your courage doing the mod. It requires a high level of skill, and is an expensive experience if it goes wrong Have always always admired ATC, at least from the mid eighties, their engineering is impressive. For me ATC 100's were a dream, I first heard them at Aston Down in 1983/4 , demoing AVI monoblocks into ATC 10's. At the end of the session ''just listen to these, you won't be able to afford them.......you are an engineer, smile'' and of course I couldn't, however.....
I managed to buy the ATC drivers and crossovers around 96 and built the cabinets in the avator, the active amps came a few months later, only slightly used!
They are good enough, and sound superb despite perhaps a lack of finese on my part, like you I found is scary to be working on expensive kit, and without your level of skill. After 20 odd years they continue to give pleasure, I can't articulate as you but there is a great joy in the all round performance, even though my hearing has much deteriorated in latter years.
Oh, In the loft I have set up a pair of Tannoy 12 inch monitor golds in infinite baffle cabinets, love the transients, and the coherence, but the ATC's get more use!
I hope you keep them and give you as much pleasure as my 'make shifts', they look superb, and can only imagine how good they sound, certainly ATC have continued to develop over the years. The only problem is they are now so dammed expensive, beyond the pockets of most!
 
^I think it speaks for itself that you are still using/ enjoying your ATCs after 25 years. Good to see a love of Tannoy DCs too :)
 
Great job! Would not dare to try it myself. Luckily I have current spec model of the 50ASL's.

We'll see if they release some kind of upgrades to current models for their 50th anniversary soon to come. I hope not :D
 
Patu said:
Great job! Would not dare to try it myself. Luckily I have current spec model of the 50ASL's.

We'll see if they release some kind of upgrades to current models for their 50th anniversary soon to come. I hope not :D
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I'd be willing to adopt any non factory install upgrades for sure, ATC tend not to mess about with pointless 'improvements' designed to get money out of folk- their Pro pedigree keeps them honest, thankfully.
 
Patu said:
Great job! Would not dare to try it myself. Luckily I have current spec model of the 50ASL's.

We'll see if they release some kind of upgrades to current models for their 50th anniversary soon to come. I hope not :D
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A great job indeed and a really good read. Bravo! to @cooky1257.

I think the last ATC "Anniversary" editions were more about special cabinets than upgraded technology. I suspect that may happen again in 2024. Loudspeakers of any reasonable size are furniture IMHO and I like mine to look good. To some, appearance has a high priority, but to me it's the quality of the technology that matters first. There is a new high-excursion 12" driver in the recently-announced professional subwoofer (here) but I have no idea if anything from that development or other developments in progress might make it into other products.

I found some time ago from listening to loudspeakers with studio monitor style presentation that I could clearly identify things that many domestic style presentation loudspeakers got wrong. I can see why domestic style is the right way for many people to enjoy the hobby but once I had become clear about my priority list I started to look at ATC, JBL, PMC (professional), Tannoy etc. to replace floor-standing 'speakers from Proac. Other loudspeakers would have worked for me but I too bought modern SCM50A classics.

Perfection? I am sure not, but the real point for me is that they just don't ever do anything wrong that's on my priority list. I haven't experienced any temptation to change them, although In a bigger room I would have SCM100As, as per this thread, in a heartbeat.
 
John Phillips said:
A great job indeed and a really good read. Bravo! to @cooky1257
Perfection? I am sure not, but the real point for me is that they just don't ever do anything wrong that's on my priority list. I haven't experienced any temptation to change them, although In a bigger room I would have SCM100As, as per this thread, in a heartbeat.
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These are certainly an endgame speakers. Going bigger in the classic line brings more reach in the low end suitable for biggeer rooms. I'm perfectly happy with 50ASL's in my 4,75 x 7,1 x 2,6m living room + open concept kitchen space. Measured from the sweet spot, they go to ~24hz -0dB (speakers aren't positioned symmetrically in the room). I've only owned these little over one year but as you said, there's no temptation to change them. Little by little I've been able to extract more and more out of them with small tweaks, measurements, acoustic treatment and positioning.

As price of electricity climbs up to new record heights, I wish ATC would've implemented a standby function to their active speakers. But that's another discussion.
 
John Phillips said:
A great job indeed and a really good read. Bravo! to @cooky1257.

I think the last ATC "Anniversary" editions were more about special cabinets than upgraded technology. I suspect that may happen again in 2024. Loudspeakers of any reasonable size are furniture IMHO and I like mine to look good. To some, appearance has a high priority, but to me it's the quality of the technology that matters first. There is a new high-excursion 12" driver in the recently-announced professional subwoofer (here) but I have no idea if anything from that development or other developments in progress might make it into other products.

I found some time ago from listening to loudspeakers with studio monitor style presentation that I could clearly identify things that many domestic style presentation loudspeakers got wrong. I can see why domestic style is the right way for many people to enjoy the hobby but once I had become clear about my priority list I started to look at ATC, JBL, PMC (professional), Tannoy etc. to replace floor-standing 'speakers from Proac. Other loudspeakers would have worked for me but I too bought modern SCM50A classics.

Perfection? I am sure not, but the real point for me is that they just don't ever do anything wrong that's on my priority list. I haven't experienced any temptation to change them, although In a bigger room I would have SCM100As, as per this thread, in a heartbeat.
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Cheers John, I agree totally, I've been rather fortunate to have a partner who has indulged my domestically challenging passion and not made any demands on the aesthetics though she has just twisted my arm to reaquire some 70's-tastic white Tannoy Devons I'd refurbed/sold last year as she loved the look.
 
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