Craig Sawyers

Also screws up heater voltage too - but that is common with most amps. Problem is that DC stabilised heater supplies are always inefficient. You need around twice the VA rating on the heater transformer to do DC.

I didn't realise that they were dipole woofers. I'm part way through a dipole subwoofer project to support the bottom end of the ESL57's. Using Shiva-X2 drivers http://www.diycable.com/main/default.php which I chose because there is no chuffing noise from the rear of the speaker ever at a scary 2" p-p excursion.

I can't claim that long bush idea was mine - Inu tracked those down as part of his T2 build. He used plastic screws as well, but the fact that the bush goes almost all the way through the alumina insulator means that steel fasteners work perfectly. Only thing to watch is that although the outer diameter of the bush *should* fit in a TO220 hole, tolerance stack up sometimes means that it is a very tight interference fit. Feel the force, kgsshv buider, feel the force. Believe it will go in and it will.

Now this I like Cheers Tyll

I've established that the UK supplier is http://www.highendworkshop.co.uk/ , run by a really interesting guy called Mark Dolbear. His price for a new pair of black Lambda pads is £25 including tax and shipping, which looks like a deal.

All this talk about rotten foam (my old low bias SR-lambda's have gone that way) has got me thinking about replacements. They sound quite a bit more forward as compared with the SR-007/2 so cloth/foam might act as a taming influence. Are all current replacement pads capable of being fitted to the 1986 vintage lambda? Superficially current production looks the same.....calling Spritzer, calling Spritzer...

Berkshire, eh? Happy birthday from a Geordie living in Oxfordshire

Here's an excellent article about Barrie Gilbert http://www.ieee.org/portal/cms_docs_societies/sscs/PrintEditions/200710.pdf

How about something based on a Gilbert Cell? This is a truly wonderful circuit that can be used for everything from four-quadrant multipliers, phase detectors, ultra-high bandwidth amplifiers etc. Developed by Barrie Gilbert while working for Tektronix, and the basis of may of Tek's custom high bandwidth hybrid and integrated circuit amplifiers. Still active and working now for Analog Devices in his 70's (AD set up a lab in Beaverton just so they could poach Gilbert from Tek). http://en.wikipedia.org/wiki/Gilbert_cell

Slight delay in evaluating the anti-650kHz mods - I've devloped a head cold (from my wife; thanks Carole!), so I've gone as deaf as a post because my sinuses are rebelling. Once I've got over this damned thing I'll get back on track and do some sonic evaluation and measurements.

I'm using an old Tek 475A with a P6106A 10x probe. All you need to do is put the probe anywhere near the output tubes (ie not physically connected to anything at all) and you can pick up several tenths of a volt to several volts at 650kHz. Then connecting between either + or - output and ground you measure around 10V p-p at 650kHz. The 475A is definitely overspecced for this, since it is a 250MHz bandwidth scope. The detail of this particular problem might have to do with the precise choice of resistors - I think Inu used PRP's throughout, and he doesn't seem to have the oscillation problem to anything like the same extent as I did. I used Xicor metal films.

I've tested the DALE ones that KG specified in the BOM on my RF bridge, and they are exceptionally good, measuring 80k even at 200MHz with an effective parallel capacitance (actually of course a series inductance) of 0.2pF. That is bewilderingly good performance for a 3W power resistor. The Mills ones are wire wound IIRC, but non-inductive?

I've just sprung for the last pair of Justin's KGSS boards and a 50k 4-gang DACT. It'll be a while before I get it finished though, although I've already got most of the bits - but not transformer or casework.

Last series Chris Evans, a British radio DJ was on as the star in a reasonably priced car. He's stupidly wealthy having bought a company from Richard Branson and then sold it for a massive sum of money. Although he looks like a real plonker, he's a very savvy businessman. He went to a car memorabilia auction a few years ago intending to buy a signed photograph of some famous racing driver - but could not resist the temptation of buying James Coburn's 250GTO for a hammer price of £12m. Now that is serious folding money.

Jeez yes. That was a Jaguar XJ220 engine. 3.5 litre V6, twin Garrett turbos, 540 bhp and 475 lbft torque. Must have come out of a wrecked XJ220. Only 280 ever made, a fair number must have ended up wrapped round a tree in the last 17 years.

Not sure if this is the right list for this - but head case seems to be dropping way down the list of hits on Google - certainly here in the UK. Currently 6-7th hit, used to be second.

Yup - as Richard Feynman once said when a student knit-picked during a lecture "Don't listen to what I said - listen to what I meant"

That is exactly the way to go - and for sure is the way to remove interconnect cable dependence from sound quality. Kevin, my man - while waiting with bated breath for your KG-Blowtorch, I'm embarking on a Borbely pre with K216/J79 outputs that drive 50-ohm matched impedance. For precisely that reason.

I can see the confusion - both channels were identical, both oscillating with around 10V p-p at 650kHz wrt ground on + and - sides, even with the 5p capacitors across the 100k feedback resistors. The signal is in-phase, so the signal wrt bias is much lower. So at 650kHz, the gain is greater than unity when the closed loop phase shift gets to 180 degrees. And although the problem has its genesis in the frontmost EL34, it couples equally to the rearmost EL34 as a result of the way the circuit is both symmetrical and cross coupled. I think that it is some subtlety of layout. Stax clearly had the same sort of problem, which is why there is a 2p capacitor lurking in there. The physical size of any layout of this monster leaves it prey to any number of parasitics. I went for simple dominant pole compensation, although there are more advanced ways of achieving the same ends.

Now that is interesting - post 650kHz mod above, it now runs cooler. Previously, the temperature rise at the hottest part of the heatsinks was 28 - 29C above ambient. Now it is 24C above ambient. The only reason I measured it is that it felt noticeably cooler to the touch. Measured using a Fluke 87V DVM with thermocouple sensor.

Well, the K389 has a Ciss of about 30pF. Logically that is about right, since it is a low noise small signal JFET. So to roll off at a 3dB point of 25kHz would need a series resistance of 200k.

In my continuing quest to get rid of the 650kHz oscillation of the T2, I found that 5pF across each 100k feedback resistor did not completely sort the problem out. Currently, I have repositioned one of the 100k resistors (to the rearmost EL34). It is now connected diagonally directly between the anode and the 100 ohm, and cut the track at the 100 ohm. Removed the 2pF cap. Put 10pF across the remaining 100k resistor. Capacitance across the repositioned resistor had very little effect. I tried repositioning the other 100k (ie the one that now has 10p across it), but it had no significant effect. With that final combination there is no sign of instability, and the output noise measures <2mV rms in 20kHz bandwidth (ie 110dB below full output). Hum is about the same amplitude as the noise. I don't what to sign off on that mod until I've listened to it for a while and also measured the transient response.

Eh? You'll have to speak up, I'm not wearing my sculptedeers

That is the Brit in me - we apologise for everything, in many ways. Mine was the smart ass way of saying sorry

Maybe its an age thing - when you get to my almost walking frame age actual lectures are a dim and distant memory