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Old 26th December 2008, 05:29 AM   #161
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Old 26th December 2008, 07:46 AM   #162
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by zikinho
Any experience with the PSU voltage regarding the sound? With what kind of rail voltage did you get the best sound?
you must follow the recommendations for maximum rail voltage as spelled out by National.
This depends very much on the load impedance and the heatsink dissipation ability.
You can use a lower voltage but I do not recommend you adopt a higher voltage.
Generally, supply <=+-40Vdc for 8ohms, <=+-30Vdc for 4ohms.
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Old 26th December 2008, 07:25 PM   #163
zikinho is offline zikinho  Croatia
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Thanks, been thinking about 200VA, 2x18 ct tranny.
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Old 26th December 2008, 10:04 PM   #164
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Quote:
Originally posted by zikinho
Thanks, been thinking about 200VA, 2x18 ct tranny.
How many LM1875s are you going to drive with 200 VA?
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Old 26th December 2008, 11:09 PM   #165
zikinho is offline zikinho  Croatia
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Only two of them. Tought it wolud be enough.
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Old 27th December 2008, 04:13 AM   #166
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18 + 18 = 36

There are 5.56a of 36v in 200va.

You have 5.56 ampers there.
This is like: "That's kind of big, and you're planning to put it WHERE?"

The transformer is slightly oversize on amperage, possibly resulting in additional bass or a bit less mids at end result.

I would predict possible results at any point between fantastic or overdone.
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Old 27th December 2008, 07:14 AM   #167
zikinho is offline zikinho  Croatia
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I'll try it. I've had that one lying around for quite some time, and there is no extra cost.
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Old 27th December 2008, 07:17 AM   #168
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Theoretically, at that voltage, it is suited to 8 ohm speakers.
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Old 27th December 2008, 07:39 AM   #169
zikinho is offline zikinho  Croatia
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Ok. What rail voltage would i need to drive 4 Ohm speakers?
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Old 27th December 2008, 07:57 AM   #170
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Quote:
Originally posted by zikinho
Ok. What rail voltage would i need to drive 4 Ohm speakers?
To answer that particular question, I'd have to say 21vdc rails (or less).

Optionally, you can use the transformer you already own along with a parallel LM1875 amplifier (two chips per each channel). That will work on either 4 ohm or 8 ohm speakers.
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