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December 2012 Issue
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DODGY DAVE?

I notice in the latest issue of Hi-Fi World that a letter has been answered by Dave Cawley of Sound Hi-Fi – and not for the first time. As a long time reader I would like to know if you really think this is an appropriate action for your magazine to take? Surely by sending a letter to you the sender is looking for an opinion based on the experience of the magazine staff who have knowledge of a wide range of products? Looking at Sound Hi-Fi’s website it appears that Mr. Cawley has recommended items that he stocks and whilst I certainly do not blame him for doing this, surely you are affecting your own supposedly neutral position by allowing someone to give an answer that will naturally be limited by his own interests? 

Sincerely, 

J. Lewis

 

 

Yes and No is my answer. Yes, his answer was partial and he did recommend his own products, but as they are very good that did not worry me unduly. It was made clear that he was Sound Hi-Fi and this gave readers the chance to make up their own minds. 

Why did I use him? The answer is simple: Dave Cawley knows more about turntables and, in particular Direct Drive - including their electronic servo-feedback circuitry - than just about anyone else in the UK. So I use him for his knowledge and the fact that he gives Hi-Fi World readers an informed answer that is valuable and not misleading. 

I admire expert contributors and Dave happens to be one of them. Needless to say, he loves his subject and works hard at it. You have to understand that most reviewers are not engineers and have little or no understanding of background technical issues in many products, and what makes them tick. Specialist listeners like Rafael Todes, and specialist engineers, like Dave Cawley are a mine of information and have prodigious ability – and that is what you get in Hi-Fi World. 

On balance I think it is better to provide informed comment, even if it is partial. We have run replies from manufacturers in the past and this attracted no complaint. So I hope your complaint is truly impartial too and not prompted by rival manufacturer. NK

 

 

NOT SO DODGY DAVE 

Many thanks for pubishing my letter in the September issue. Please pass on my thanks to Dave Cawley for his reply. 

I have to agree about the mains. Mine looks a little rough but is quite variable. Probably though for a town the size of the Medway towns in North Kent there can be little difference to most power sources across the UK. We have only recently become aware of the subtle way it can affect things and realistically we have never really analysed it except from a voltage point of view in which case it always looks within parameters. With the use of remote power switching by the grids, mains for network traffic, the noise of the solar power systems delivering their 10 pence worth of electricity onto the grid and all those horrible energy saving bulbs etc it will only get more noisy out there!

On another point entirely, the review of the Burmester 032 suggests an interesting issue. For an amp to be balanced throughout then the way to look at this is actually to view the output stage exactly the same as if it were bridged. The technology is the same. A balanced input with one signal lead 180 degrees out of phase with the other transfered to the output amp requires two output amps to work on those signals maintaining that phase relationship the commoning point being the loudspeaker. 

Now unless you have some sort of custom power amp stage that does balanced up to the output transistors (so thats the long tailed pair, current mirrors/sources, class A driver etc) then the only way to balance it right through is with what has been called bridged for as long as I can remember. 35 years ago I built a keyboard PA system using the Maplin MOSFET 100 watt module and their bridging module and have to say that a three way mono active system of that configuration is still something quite impressive to hear. I wonder what happened to that system! 

Bridged and therefore balanced output has always had a subtle but impressive advantage to my ears.

Many thanks once again.

Regards

Dave Tutt 

www.tutt-technology.co.uk

 

For an amp like the Burmester 032 to be balanced throughout  the output

stage must be bridged, says Dave Tutt. 

 

 

Hi Dave. Yes, bridged does give a balanced output with respect to ground and as you say sound quality does usually seem better. I have thoughtlessly assumed this is likely due to the extra power available, but perhaps not. Perhaps it is due to rejection of common mode interference. 

A similar debate exists with balanced outputs and balanced lines. These normally demand the use of ‘transmitter’ and ‘receiver’ chips (line drivers) at either end of the line, meaning extra circuitry. But in spite of this, sound quality is usually better. The benefit is a signal line free of earth currents and interference (balanced cables are usually shielded) and it is this that seems to most affect sound quality. So balanced working would seem to hold promise, especially with pickup cartridges – where it is almost never used. Oh well! NK



 

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