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Old 31st July 2007, 02:58 PM   #1
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Default PSU for a Gram-amp phono? Regulated or not?

Hi all.

I'd like to replace the wall-wart ("get you started" kind of item, I guess) that came with my Gram Amp 2 with something a bit better/bigger.

It appears to be unregulated (measures about 15v no load on the 12v setting the GA uses), and I'm assuming it's a linear type (surely a phono stage wouldn't be supplied with a switching one?).

Would there be any advantages or problems using a 12v (linear) regulated supply?

thanks.
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Old 31st July 2007, 03:10 PM   #2
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Doesn't the Gram amp have an internal rectifier, smoothing and regulation section? Also depending on how the power is set up, you might have to feed it AC.
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Old 31st July 2007, 03:19 PM   #3
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Hi -

the GA is definitely internally regulated (I recall hearing it's something Graham Slee pays some attention to), although I've no idea what voltage the rails are, but it uses 12v DC in.

The wall-wart is a fairly cheap, selectable-voltage 300mA one, so basically I'd like to get something with more current headroom (using it with a Decca cartridge, so some fairly hefty voltage swings required for transients from the GA, I imagine).
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Old 31st July 2007, 03:31 PM   #4
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The cartridge does not suck any power out of the pre-amp, it generates a signal by it's electromagnetic properties.

If the Gram Amp is internally regulated I'd be surprised if changing the wall wart made a big difference. 300mA current is massively plenty to power a few op-amps and to drive any amplifier input impedance I can think of.

The only mod I would bother with is trying to crack open the wall wart and increasing the size of the capacitor. Or adding a capacitor across the Gram Amp power input. The second option is probably the most feasible.
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Old 31st July 2007, 03:48 PM   #5
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Adding some more reservoir capacitance is an idea, hadn't thought, thanks.

I guess I'm going with received wisdom that PSU's can make difference - people go to a lot of trouble over them, I've noticed. Like most makers/designers, Graham Slee himself recommends upgrading the one that comes with his cheaper phono-stages.

BTW, the wall-wart in question is actually a bloody 'Uniross', IOW as cheap/basic as you'll find - one way or another I am going to try something 'better'!
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