Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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RE: MC Trannie vs Head Amp

Posted by Steve Eddy on August 24, 2007 at 21:37:07

In Reply to: RE: MC Trannie vs Head Amp posted by sailor321 on August 24, 2007 at 10:33:00:

Please explain to this electronics novice. I figured, it would be better to increase the feeble cartridge signal as soon as possible to cut down the noise

Yeah, that would be the case if you could keep the output impedance low.

Transformers are passive devices and therefore they can't increase power. Power out can be no greater than power in. The consequence of this is that in order to get your voltage gain, you need to trade it for something else. In the case of step-up transformers, you trade your voltage gain for higher output impedance.

Transformers don't have an impedance of their own per se. What they do is reflect impedances by the square of the turns ratio. So if for example you had a 1:10 step-up transformer, while the voltage gain goes up by a factor of 10, the output impedance of whatever is driving it gets multiplied by a factor of 100.

If you run a phono cable all the way from the cartridge to the phono pre, then the source impedance driving that cable is that of the cartridge. But if you put your step-up as close to the cartridge as possible and then drive a cable to the phono pre, the source impedance is that of your cartridge times 100.

So to that end, unless you're going to buffer the output of the step-up transformer, you'd be better off locating the transformer inside the chassis so that its output is as close as possible to the phono pre's input.

This help?

se

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