Atkinson SOTA TL

[kaleb84]

Last year I picked up some DIY built, P. Atkinson designed 'State Of The Art' Transmission Line Loudspeakers, as featured in the HiFi News and Record Review April 1976.

I listen chiefly to digital files (FLAC), through a Pecan Pi DAC and Temple Audio Monoblocks. This system works beautifully on my smaller room speakers (Linn Index), and also powers the SOTAs very nicely, although I can't get away from the fact that they're very fatiguing to listen to. I'm very fond of them, visually, and for the low frequencies, and for the back story of having been designed and built by enthusiasts sharing designs in magazines.

So I'd like to make them work well for me.

The drivers are

KEF B139
KEF B110
Celestion HF 1300 (8 ohm pair)
KEF T27
Coles 4000

I suspect that by now the crossovers will need re-capping, and that this may be the main issue.

I'm also considering replacing the B110s with something newer. What's confusing me is that when I removed a B110 to explore the cabinet fitting (in view of replacement), then listened without it - the fatiguing aspect disappeared. There was certainly a 'hole' in the midrange, but I'm astonished by how much detail is coming through the HF1300s and the B139. More than I can usually hear, because I suppose the B110 is spilling over everything. When I switched the other monoblock on to listen to the same passages through the intact speaker on the other channel it seemed almost unlistenably bright in comparison.

So, could this be the B110s themselves, perished after 40+ years, or should I suspect the crossovers are dying and leaking frequencies all over the place? I feel like I've had a little insight into how could these could sound if I just get that midrange back where it should be.

Apologies if my terminology, or very basic tech knowledge is way off, I'm quite the novice, but I'd love to understand more about getting this system singing.

Thanks in advance

[spendorman]

In my view the B110 was not a good choice for a mid speaker, it did not work well in the KEF Concerto, however in an LS3/5a it does midrange OK.

Years ago I sat an LS3/5a on top of a Concerto (both use the B110 and T27) with the exception of the low bass, the LS3/5a was far superior, no doubt because of the sophisticated crossover.

Replacing your B110 with a good large dome midrange should help a lot, this would probably need alterations to the crossover.

The reversible electrolytic capacitors would probably have drifted as you say.

[Pharos]

I suggest you write to Wilmslow Audio.

[spendorman]

I might take Wilmslow's advice with a grain of salt, they gave a suggestion to me for a replacement bass unit for a Spendor BC1, I bought them, not a good match at all.

[Pharos]

I'm surprised, if they do lots of repairs one would expect them to get things right, at least eventually.

[spendorman]

I remember this design coming out in the Hi-Fi news.
I would think that with some alteration, it would be a great speaker.
Here is the crossover circuit

https://live.staticflickr.com/65535/50820060272_56696dcac2_z.jpg (https://flic.kr/p/2kqN6nJ)Clipboard01d (https://flic.kr/p/2kqN6nJ) by A60man (https://www.flickr.com/photos/41679262@N02/), on Flickr

I have another design from the Hi Fi News, about the same vintage, The Daline, using KEF B110, KEF T15 and Coles 4001G. It's quite a good speaker.

There were different versions a two way and a 3 way.

Crossover

https://live.staticflickr.com/65535/50820078517_622b8965c6_z.jpg (https://flic.kr/p/2kqNbNi)_daline xover mod (https://flic.kr/p/2kqNbNi) by A60man (https://www.flickr.com/photos/41679262@N02/), on Flickr

[walpurgis]

More.

http://www.t-linespeakers.org/projects/jakob/index.html

[spendorman]

More.

http://www.t-linespeakers.org/projects/jakob/index.html

He says "2 Coles 3000", no, 2 Celestion HF1300.

I have a scan of the original Hi Fii News article, but it's not a very good scan.

[walpurgis]

He says "2 Coles 3000", no, 2 Celestion HF1300.

A variant or a mistake? The Coles 3000 was pretty similar to the Celestion HF1300 if I recall.

[spendorman]

A variant or a mistake? The Coles 3000 was pretty similar to the Celestion HF1300 if I recall.

Sounded rather naff I thought!

[Puffin]

when I removed a B110 to explore the cabinet fitting (in view of replacement), then listened without it - the fatiguing aspect disappeared
.
You could try an L-Pad which would enable you to have the B110 at any level...or off

[walpurgis]

If the crossover capacitors are tired the filter slopes could be all over the place, best sort that first. Then play with phase and see what that does. And as mentioned, adjust levels if need be.

[kaleb84]

Thanks for all the input.

Wilmslow recommend a Monacor unit to upgrade a B110.

It was a bit of an anxious router job modifying the cabinet, but the one I've swapped so far sounds great. Once my local audio electrical engineers reopens after lockdown I'll ask them about the crossovers.


Thanks all

K