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Old 7th March 2013, 01:10 PM   #8561
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Quote:
Originally Posted by a.wayne View Post
+10 On Thorsten ...



Article : McIntosh transformers | PS Audio

This part of the linked article is obviously wrong:

"As the Ohm number goes down, the need for power goes up proportionally. So the power needed to make an 8 Ohm speaker produce sound in the room needs to double when the Ohms cut in half to 4 and double again for 2 and so on. Lower Ohms, higher power to achieve the same sound pressure."

The writer must be confused between amps and power. The amps will go up with a 4 Ohm speaker as compared to the same in an 8 Ohm version, but it will do so at half the Volts, so power remains the same. After stumbling across something like that I stop reading.
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Old 7th March 2013, 01:15 PM   #8562
a.wayne is offline a.wayne  United States
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Yes i saw that , i assumed paul meant amps and not power ....
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Old 7th March 2013, 01:20 PM   #8563
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Originally Posted by nigel pearson View Post
Auto transformer output has plenty to recommend it especially if one can access the direct output for 8 /4R . If the 1R tap is used any crossover distortion is reduced . My bet is nicer all round . In the the late 1970's I was invited by Sony to a show . There I saw a class D amp . The engineer said it had a nice sound not unlike valves . He reasoned the output choke was doing that . His words " now we understand it was the transformer we liked " . The amplifier was not produced , a range of conventional amps called Esprit instead .

BTW . 5.7 R was said to be an optimum power transfer resistance . Most 8 R speakers approximate to that . 16 R generally helps distortion in an AB amp . The 1 R tap used with an 8 R speaker should offer excellent performance . Class AB should be almost as class A if so .
Interesting points Nige and the sonic signature of the transformer was one of the main reason why i had moved away from using them....
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Old 7th March 2013, 07:21 PM   #8564
dvv is offline dvv  Serbia
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Originally Posted by a.wayne View Post
...

The funny part is Mac owners believe theres an advantage to autoformers on the outputs of SS amps and while i will admit to being a mac fan and have owned their stuff over the years , there is no doubt to their limitations , weak drive and dark sounding , working at their best where power is required at 8 ohm , the autoformer allows them to cheat a bit by being able to provide high wattage at 8 ohms and not worry about load tolerance ...

Thoughts ...
Well, you said it yourself - a neat cheat.

The last thing I would ever put at the output end of anything I make is something made of ferrous materials, even if sintered. Here I am, struggling to get rid of capacitors in my signal path, and then ruin it all with an autotransformer?

I would agree that an autotransformer would make life easier to much easier on my actual semiconductor output stage and my power supply, but my feeling is that the price for that is unbearable.

MacIntosh has built a very solid user base over the decades, and even if I haven't heard their older stuff, I suspect this has happened for a good reason. But this is, to me, a plain and simple cheat, as well as a wrong way to treat transistors as you would tubes.

I am nowhere near that level of power output, but if I was, and wanted a bit o' that ye olde sound, I'd stick in two handfuls of MJ21195/21196 Motorola 250W trannies. While they may not be cheap, I wonder how they and associated heat sinking compare price-wise with the cost of an autotransformer?

@vacuphile

My dear colleague, I assure you that was a typo on Paul McGowan's part. I have had some communications with him and I can assure you he knows the difference between volts, amps and associated watts like not too many people around.

I may not agree with him on everything, but doubting his knowledge is not an option, believe me.
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Old 7th March 2013, 08:17 PM   #8565
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+10 On Paul McGowan ......
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Old 8th March 2013, 06:25 AM   #8566
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Well, if we heed the old Roman proverb that all roads lead to Rome, we also accept that there is more than one way to get from here to there. We may not like some of them thinking them to be too bumpy, but they do get you there.

I admit I don't like MacIntosh's choice of how to get there, but if it makes some people happy, who am I to complain?
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Old 8th March 2013, 08:53 AM   #8567
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I think the auto-transformer could give far more than it takes away . It is a superb way of having a volume control . Run the amplifier at it's best distortion point . For example a simple chip amp run at 30 of it's 100 watts might via the transformer seem to exceed typical class A performance . The volume could work by selecting the best tap then using a switched resistor chain to fine adjust . The taps could also be under manual control when a known difficult load is being used . The example shows clearly the plateau where the distrotion is optimum . Like a gearbox it keeps it in that region ( analogy 2000 to 4500 RPM ) . The advantage over class A is the power supply isn't saturated . Also less capacitance might in some cases actually improve the sound , especially at mid to HF . A lot of people never do the maths of tube amps verse transistors in the PSU department . If you take CV of the PSU it might be 1000 uF 500 V tops for a valve amp . That is a CV of 500 000 . 2 x 22 000 uF ( = 11 000 ) 100 V = CV of 1 100 000 for a typical 100 watt transistor amp . Some of the better sound of valve amplifiers is PSU being forced to use less capacitance and chokes to compensate ( or gyrators ) . Even more interesting is that the valve amp will be class A and the transistor class AB . I will speculate that the chip amp with a high ripple current 6 800 uF ( x 2 ) through an auto-transformer might be surprisingly good ? Sweet sounding , great portrayal of depth , punch in bass and mid . The auto-transformer might even help RFI issues ? A superior output choke if judged correctly ?

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Old 8th March 2013, 12:33 PM   #8568
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Remember you still have to run that signal thru miles of copper , on its way to more miles of VC copper before you can hear it ...

Good on the bench , not so good to the ears ... ? Hysteresis ? Poor damping? Limited bandwidth ?
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Old 8th March 2013, 01:18 PM   #8569
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Not really . If the one to one tap is used it virtually isn't there unlike the isolation types . I doubt if any of the factors are so bad as to make it not worth trying . Doubtless it will cost more than $200 per side if the quality is to be acceptable . The transformer might work OK inside the feedback loop . I would imagine a 1000 VA core in M6 metal to be a good idea . I would design as if 1000 VA . That should get rid of all doubts . The bandwidth might be better than you imagine . If class D and the amp will accept the transformer the switching might even help the hysteresis . One can use a bit of DC to help hysteresis .
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Old 8th March 2013, 02:24 PM   #8570
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Nige,

I thought you were the one supposed to the minimalist, and here you are, advocating what may possibly be the worst of parts to be included ?????

What the hell is going on here?
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