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Old 10th March 2006, 11:06 AM   #11
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Also note that you can easily switch the input to balanced mode also:
http://www.klaus-boening.de/html/sch...tml#MKIIInew_B
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Old 10th March 2006, 04:38 PM   #12
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by Onvinyl
Also note that you can easily switch the input to balanced mode also:
And that is far more important. If there's one place where you're likely to pick up hum it's on a moving coil input.
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Old 10th March 2006, 05:08 PM   #13
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I agree with all posters here. Keep it balanced to the preamp. An MC cart is inherently balanced. IF you are going to use transformers for balancing, better spend the money on good or better step-up transformers. At least that's how I see it.

The cables following your phono preamp are the most crucial cables in your system. Keep them short, under one meter.
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Old 10th March 2006, 07:22 PM   #14
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Quote:
Originally posted by phn

The cables following your phono preamp are the most crucial cables in your system. Keep them short, under one meter.
Are you sure you don't mean 'the cables preceeding your phono amp'?
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Old 16th March 2006, 10:58 AM   #15
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Just for fun then:

I favor an unbalanced phono stage.

First, noise generated by or induced on the MC cartridge or phono cables does not dominate the noise seen on the line output of the phono stage. The noise on the output is rather generated by the phono amplifier circuitry itself. Or it is if you are doing things right, at any rate.

So its more important to have a low noise amplifier than an amplifier with rejects common mode noise at its inputs.

With a balanced circuit, you have two input stages, each one seeing half the input signal voltage that the input of an unbalanced stage would see. The gain of each input stage is the same of course. So, all things being equal you end up with twice the noise at the output. Which being random sums to 1.4 times the noise, but thats still a 3 dB hit on your noise floor.

I dont have an issue with balanced outputs though. Since a good way to set up your system is to have the amplifier next to the speakers and your turntable as far away from them as possible, a long interconnect is often needed. Given the added complexity this adds to the circuit - the joy of phase splitters - its not something I'd implement lightly.

/rjm
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Old 16th March 2006, 11:24 AM   #16
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Quote:
Originally posted by rjm
With a balanced circuit, you have two input stages, each one seeing half the input signal voltage that the input of an unbalanced stage would see. The gain of each input stage is the same of course. So, all things being equal you end up with twice the noise at the output. Which being random sums to 1.4 times the noise, but thats still a 3 dB hit on your noise floor.
Absolutely true, unless you use a transformer before a non-differential input, in which case:

(1). A step-up transformer allows you to increase the voltage applied to your (noise generating) input stage, thus improving S/N ratio. This statement might not necessarily be true for a bipolar transistor input where current noise usually predominates.

(2). You enjoy the unparalleled common-mode rejection offered by a properly designed input transformer.

A transformer-coupled MC input really does make sense...
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Old 16th March 2006, 06:30 PM   #17
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Going to a balanced riaa made a huge difference. Hum was lowered a lot. Had to rewire my arm for it, but it was worth it.
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Old 16th March 2006, 06:52 PM   #18
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Quote:
Originally posted by Onvinyl

Are you sure you don't mean 'the cables preceeding your phono amp'?
Rüdiger
If you use step-up transformers, yes. Hagerman writes this:

"Keep in mind here, that at 10:1 gain, every foot of output cable is equivalent to 100 feet of input cable."

But the cables from the turntable aren't that important, though more important than many others.
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Old 16th March 2006, 07:46 PM   #19
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Quote:
Originally posted by phn
"Keep in mind here, that at 10:1 gain, every foot of output cable is equivalent to 100 feet of input cable."
I'm not sure what he's thinking of there, although it's clearly to do with impedances. However, it is important that the output leads of the transformer are kept as short as possible. Put the transformers in the pre-amplifier, not in a pretty box outside with extra leads that add capacitive loading to the secondary.
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Old 17th March 2006, 04:42 PM   #20
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Hi EC8010,

I think he meant that a 1:10 voltage ratio means a 1:100 impedance ratio. I.e. if you load the tranny with 10Kohm, you will load the cartridge with 100 ohms. So the load at the secondary should be at high impedance where you need to avoid too much capacitance.

This is a bit of disadvantage of a step-up with some MC’s when they are more pleased with a high load impedance (> 1K).

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