Craig Sawyers

For rating transformers I use a free simulation package from here http://www.duncanamps.com/psud2/ . For a capacitor input filter (the usual sort) the transformer VA rating is always significantly higher than the power delivered to the load. This is entirely a result of the pulse-like capacitor charging current. Just as a for instance, Tx with 100V, 1ohm secondary, bridge rectifier, 10,000u capacitor and 700mA load. Power to load = 0.7 x 135V = 94.5W. VA from Tx = 1.8 x 99 = 178W. This is typical - you need somewhere about 1.5 to 2 times the VA rating for the Tx than is delivered to the load. The other way to do this is to use the nomograms in a classic paper by Schade (Proc IRE, July 1943, 341-361, "Analysis of Rectifier Operation, O. H. Schade). There is an update with measurements in Linear Audio, V8, Sept 2014, 83-127 "The Otto Schade Method, A practical design method for Rectifier Circuits" by Rudolf Moers. All of this agrees with http://sound.westhost.com/power-supplies.htm which concludes with Transformer The voltage is determined by the power that you need from the amplifier. Calculate power from the formula ... P = Va² / R Where P is power in Watts, Va is RMS speaker voltage, and R is speaker nominal impedance The supply voltage (allowing only for basic losses) is calculated as follows VRMS = Va * 1.1 Where VRMS is the transformer secondary voltage (for each supply rail) VA Rating - Class-AB The minimum VA rating suggested is equal to the amplifier power. A 50W amp therefore needs a 50VA transformer, or 100VA for stereo 50W amps. Larger transformers (up to double the amp power rating) will provide a 'stiffer' power supply, and this may be beneficial. For continuous operation at full power (never needed for hi-fi but common for guitar amps), the transformer should have a VA rating of up to 4 times the amplifier power. It is suggested by some transformer manufacturers (and no doubt gleefully adhered to by many amplifier makers) that the VA rating needs only to be 0.7 of the maximum amplifier power. While this will work well enough in most cases, you will not have a 'stiff' power supply - a more appropriate term would be 'soggy'. The DC voltage will collapse as more current is drawn. VA Rating - Class-A The minimum VA rating suggested is at least 4 to 5 times the amplifier power. A 20W Class-A amp therefore needs a minimum of an 80-100VA transformer, or 160-200VA for stereo 20W Class-A amps. Transformer rating may need to be as much as 10 times output power, depending on amplifier topology and quiescent current [2]. The constructor needs to be able to work this out, or transformer failure is likely.

^This.

This surely is a fucked up world we're living in. 50 confirmed in Orlando. Jeez. Out of a clear blue sky. Europe is far from immune. The Charie Hebdo killings in Jan (12 dead) and the mass attacks in Nov (130 dead), both in Paris last year, show that. And we're not immune in the UK either - last attack was the London bombings (52 dead), and that was 12 years ago - time's ticking for us too. Let's not forget the Madrid train bombs in 2004 (191 dead), the Mumbia attacks in 2008 (157 dead), in the Phillipines 40 separate terrorist bombings in the last 16 years (720 deaths), and the worst of all 9/11 (2977 dead). All numbers not counting many, many thousands of injured, or terrorist deaths. Absolutely all Islamic extremists, alas - a tiny, tiny minority of right minded Muslims, but boy do these bastards get the lion's share of publicity, may they rot in hell. And pretty much all home grown.

2nd one is better than first. Or maybe I have partially acclimatised....

Where is the Darwin Award when you need it? http://www.darwinawards.com/darwin/darwin2014-09.html or even the legendary http://darwinawards.com/darwin/darwin1995-04.html

Isn't that the TV channel that shows old episodes?

That is whole new levels of insanity. Watched the whole thing, of course.

That is all we have in the UK, except it is 230V (well 240V in reality).

Well it can only be down to a hum loop somewhere, induction through stray magnetic fields from the transformer, or ripple on the DC output from the regulator. Also, are you hearing the 60Hz fundamental, or the second harmonic at 120Hz? What does the mains power look like - ie is it symmetric or asymmetric? Just firing ideas - cause of hum can be a bitch to find. But once you find the cause, it will seem to be blindingly obvious....

Is it mechanical hum from the transformer, or electrical hum that you hear in the headphones?

The Ali quote is a line from the movie. But it is based on an almost identical off the cuff, and unscripted speech to microphone to white students- so much more powerful to see the great man deliver it in his absolute prime. It is 1m52s in.

^This

He was the man who turned heavyweight boxing into a thing of beauty. RIP Ali. I have a life size photo of one of his fists (without gloves) in a sports book. If you put your fist next to it - well it almost looks like a child's fist next to an adult. Also RIP Dave Swarbrick, one of the best traditional folk violinists ever http://www.bbc.co.uk/news/entertainment-arts-36443117 . Saw him with Martin Carthy in a tiny venue in Nettlebed Oxfordshire last Autumn, and had a CD signed by him. He did not look well at all.

For a "first stab" I didn't think it was too awful. But it needs a lot of work to be as polished as the original. Let's see how it goes - the one we saw was filmed in January.

This off-key singing reminded me of the late and exceptionally great Douglas Adams, in Hitchiker's Guide with the company song a flattened fifth out of tune

Total harmonic distortion, intermodulation distortion for example - I thought the comment on Fourier Analysis kind of gave it away.

RIP Burt Kwouk. The Pink Panther movies were a must watch back in the day. At least he was a full thirty years older that Sellers (who died aged 55)

Quotes from http://physicsworld.com/cws/article/news/2013/jan/31/human-hearing-is-highly-nonlinear , originally published in Phys. Rev. Lett. 110, 044301 – Published 23 January 2013. "The information available from Fourier analysis is bound by an uncertainty relation called the Gabor limit. This says that you cannot know the timing of a sound and its frequency – or pitch – beyond a certain degree of accuracy. The more accurate the measurement of the timing of a sound, the less accurate the measurement of its pitch and vice versa." "Oppenheim and Magnasco discovered that the accuracy with which the volunteers determined pitch and timing simultaneously was usually much better, on average, than the Gabor limit. In one case, subjects beat the Gabor limit for the product of frequency and time uncertainty by a factor of 50, clearly implying their brains were using a nonlinear algorithm." In other words, conventional analysis of non-linear distortions in an audio system tell you absolutely nothing about how it sounds, because human hearing beats measurement by a healthy margin.

Isn't this the movie where you wake up in a bath of ice minus a body part?

And here was I thinking a biscuit was a jammy dodger or a chocolate bourbon! Have a great birthday Brent.

Happy birthday!

There are stress points allocated to certain activities. If you reach 10 you are in serious trouble. The top ones are buying and selling a house, death of a close relative, and divorce. Any two at about the same time and pow - your brain explodes.

This is how Guinness used to do it up to 60-odd years ago. The only machine task was trimming the length of the staves first. At the time, Guinness employed 200 coopers (who served an apprenticeship of 7 years) maintaining the stock of 250,000 barrels.

Is it any wonder that Norse mythology is all to do with fire and ice?

Audiophilia 6 - cinephobia 6