Craig Sawyers

Well, here we are in not-quite-in-the-21st-century England. This is 6 miles from Oxford, so hardly hicksville. The excuse is that we are more than 4km from the BT exchange.

Woof woof! That sounds like a serious way of moving a large volume of air. One of my unfinished projects is a pair of dipole sub woofers to reinforce the output of my ESL57's. Used Shiva X2 drivers http://www.diycable.com/main/product_info.php?products_id=693 which have a maximum power handling of 1kW, although they do a very serious 18" or 21" driver - the Maelstrom, which can handle 1.5kW with a peak-peak excursion of 64mm (2.5"). 'Nuff to blow the windows out. Nelson Pass has done some really crazy things with bass drivers - such as the KleinHorn http://www.passdiy.com/pdf/KleinHorn.pdf and El-pipe-O http://www.passdiy.com/pdf/el-pipe-o.pdf

Have a great one!

I've had only limited sonic success with loudspeaker building over the years, and long ago went for commercial (and sometimes very quirky) options. Magneplanar, Martin-Logan, Podium 1 and now ESL57 among others. However, one thing is clear - cabinet colouration is a major issue. Various high-end manufacturers use constrained layer damping - Wilson and Rockport as examples. Rockport use either fibreglass or carbon fiber inside and outside skins, and fill the gap with an epoxy/ceramic powder filler. Seriously heavy - the Arrakis are 900lbs each (and cost a Jaguar's-worth of dosh from your pocket) - and totally inert. Of course the idea of contrained layer damping is not new. The Wharfedale SFB (sand filled baffle) was there in the mid 1950's, a good account being here http://www.inner-magazines.com/news/28/72/Whaferdale-SFB3/ along with comparisons to the Quad ESL57 and the Klipsch Horn. Oh - and back in the early 1970's I built an irregular pentagon footprint cabinet (to defeat standing waves), and lined the things with an inch of concrete. My parents though I had seriously lost the plot. They were a dangerously heavy two-person lift. They drew the line at an underfloor mounted bass horn firing upwards through an aperture in the floorboards though.

I think that I put the models (simple text) on the thread a while back - check and see what is there Nice thought - but I suspect not. The innards of the original T2 get incendiarly hot - nothing like as much heatsinking and air circulation as KG's clone and *that* gets quite hot enough! I think they just used a method similar to the one I worked out - again on this thread a way back.

Wow - well done sir! The only problem is tracking down spice models for the typical transistors we use in audio - particularly (but not uniquely) of Japanese origin. You can get quite a long way by writing a simple spice description file for the major transistor parameters from the spec sheet. Good enough for DC and low frequencies where the various capacitances can be ignored. There is enough on the web describing how to do this. But a complete Gummel-Poon model needs quite a bit of measurement/guesstimation to put a full description in place if the manufacturer has not made a full Spice model available. Plus the fact that there is a large spread in parameters typically, so to do the full nine yards you need to do a sensitivity analysis over the parameter spread. Not counting layout parasitics...... I did the simple description route to work out a foolproof method for how to set the battery voltage. The graphs (Excel spreadsheet) used to be on my webspace, but they probably got trashed in the ISP debacle. If anyone has a burning desire to get these, let me know and I'll upload them again.

Why not build the T2 (instead of endless spice analysis an what-if's) and then carry out mods using real components so that you can evaluate them by actual measurements and (shock, horror) what it actually sounds like? I've got precisely this problem on my major project at the moment, where the subcontract engineering company insists on only using analysis tools, and pooh-poohing measurement. This is a system for lauch to Mercury in 2014 - and they are studiously missing the point that you don't lauch analysis - you launch actual hardware that must not fall to pieces when subjected to launch loads. They are in the last chance saloon at the moment on this topic. So, jcx - lets see some building and measurements. And does it sound like audio nirvana or a bag of hammers?

OK - just restored it at http://www.tech-enterprise.com/tekstuff/T2deconstruct.pdf Anyone else need any files that I have supplied links for that are now dead, let me know and I restore them. I just don't have a record of what was stored, because my half-assed ex-ISP corrupted the damned folder when they had the fatal crash. Complete wasters that aren't worth the desk they sit at.

Have a virtual beer on me, Nate!

Doh

Thanks one and all! Actually that is a Siemens & Halske T52. Those who know me a bit might have spotted that I restored the world's only known complete Lorenz SZ42 for Bletchley Park a few years back. I can get *really* boring on this topic - please don't encourage me

Nice idea - but Top Gear is a BBC show, and the BBC have never broadcast advertisements. The Beeb is funded by the Television License Fee (£145 per year), which all TV owners have to pay by law http://www.tvlicensing.co.uk/about/legislation-and-policy-AB9/ . Part of which is what is used to pay Clarkson's wage. Massive advantage is of course no commercial breaks - just end to end uninterrupted TV. All other TV channels broadcast in the UK (the many hundreds of them) self fund through advertising or sponsorship.

The ones that Paul wound for me were 93mm OD x 55mm height for the HT ones and 98mm OD x 69mm height for the LT one. All windings had a double thickness insulation barrier between each mainly as a precaution, but essential on the LT transformer since the EL34 heaters sit at -500V. They were centre epoxy filled with a single bolt hole, and the top of the centre fill was below the top of the windings. I used 65mm long dome headed steel bolts with plain washer, lock washer and nut to fix them. If they were conventional fixings with rubber washers and a steel disc, you'd have to think carefully if they would fit or not into the case height.

Problem is that they are now paying Clarkson, Hammond and May so much that they have no money left over for big stunts like the Reliant Robin space shuttle launch. Clarkson earned £1m from his general BBC contract and another £819k from Top Gear last year. Add that to the half million plus each that Hammond and May get, for a total salary bill of near enough £3m. Nothing like Kelsey Grammer's $1.6m per episode of Frasier, but more than enough to cramp they style of a UK motoring show.

Well guys and gals - I'm back! With a new and shiney ISP called ICUK http://www.icukhosting.co.uk/ . The transformer question is interesting. Hot is OK, provided that it is within the design ratings of the insulation used. Mine were designed to a specification of 42C temperature rise at full load - so 62C with an ambient of 20C. I've confirmed that with a thermocouple. That temperature is conservative, considering that the design maximum temperature is 120C. Anyone for fried eggs? The most thermally stressed transformer is the HT one with all three secondaries connected. Based on power supply modelling, the RMS transformer currents are: 475V, 0.19A 285V, 0.08A 75V, 0.1A The problem arises because of the spike-like current that the rectifiers deliver to the storage caps. The RMS/Average ratio is higher than you might imagine, so 66mA (average) taken out of the 500V supply caps needs an rms feed of 190mA from the transformer (for a 30-ohm effective winding resistance; lower resistance is worse becasue the charging spikes get shorter). All of which calls for 120VA in total. A lower-power transformer will of course still be OK provided the core doesn't start to saturate and the regulation is OK - all that will happen is that it runs even hotter - which is generally OK provided the insulation standards are good enough. I'd suggest that a failure in the transformer is due to failure of insulation, or a pressure point from a pigtail solder joint. One thing that has to be borne in mind is that cycling a transformer puts the internals under repeated mechanical stress as it heats up and cools down. So any weakness is found out in due course. My 120VA transformers are at the limit of what will physically fit in the chassis. To use really underrated transformers which run significantly cooler would require mounting the transformers externally to the T2. Mine are not SUMR - they were custom designed by Paul Houlden in the UK, who used to do (and still does) transformers for high end manufacturers like Krell. I recall somewhere hearing that the original T2 transformers used to burn out, and were replaced with more conservatively rated ones by Stax.

Happy birthday Dan!

Duur - late... But hope you had a good one!

Beans on toast. Sad ass dinner for one while wife is playing tennis. But I LIKE beans on toast - so why am I bitching?

Double birthday - double congratulations

I'm going to sound like a real dork - but I read the thread topic as "Official Hockney Thread", as in David Hockney the artist. Honestly. Time for (another) Scotch, I think. Thought it was a bit of a wierd topic on Head Case

Apologies for anyone trying to access files on the T2 from my website. My crap ISP suffered a server crash , and it has taken them over three weeks to restore a modicum of my website - but currently still missing the critical folder in which all the interesting files on audio and other technologies are stored . Needless to say I have a request for quote out to half a dozen small-business focused ISP's so I can move away from hotchilli.com. They used to be great ten years ago - small and hungry. But they sold out to a private equity outfit , who have transferred all their support to India. Now I have no problem at all with Indian support - but when there is no option at all now to talk to someone in the UK, and they are bungling incompetents to boot, it is clearly time to jump ship. I'll let you know when the ensuing chaos of this decision settles down again

Hey - have a great one

Have a great one. I'm drinking your health right now.

I was just talking to my brother-in-law Steve about the Clarkson/Mexico international incident, and Clarkson's beautiful not-apology. We got onto insults of the same sort - like the "cheese-eating surrender monkeys" by Groundskeeper Willie about the French that was in the Simpsons back in '95. Anyway, Steve pointed out that you get an interesting result is you type "Famous French Victories" into Google and then hit "I'm feeling lucky". Enjoy

Buzzing transformers are caused by incorrect manufacture in the first place. The only way to shut one up is to decouple it from the chassis big time. Assuming for the moment that it is a toroid, first take it out. Then make a vey thick layer of RTV - maybe 3/8" or so - and gently seat the transformer onto it. Make sure it does not squeeze out. When that has set somewhat, make a similar layer on the top and set the clamping washer on it. Put the bolt through to keep it lined up. When everything has set, nip the bolt up. The transformer is now vibration isolated from the chassis via two thick resilient layers. A similar thing can also be done with EI core transformers of course, but it would need some extra thought about how to deal with the bolt fixings. Using rubber grommets instead might work fine and is quick to try out. Precautions - try to chose an RTV that will cope with a transformer temperature of 60C.