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Old 27th January 2002, 04:03 PM   #1
Freddie is offline Freddie  Sweden
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Default LM1972

I've just browsed through the forums and the "National LM1972" digital volume controll looks promising.

So, is there anyone who has tried the LM1972 yet?

If it's no good I will use relays and resistors instead, but this is much cheaper.

/Freddie
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Old 27th January 2002, 05:37 PM   #2
paulb is offline paulb  Canada
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You did do a search, right Freddie? There has been some discussion around here on the LM1972.
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Old 27th January 2002, 06:43 PM   #3
sonnya is offline sonnya  Denmark
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I do not now if it is good or bad but Thule and Arcam use it in their amps. And i think their amps work just fine.

The price is 1/2 of the PGA2311 from TI.

Sonny
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Old 27th January 2002, 06:52 PM   #4
Freddie is offline Freddie  Sweden
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paulb,

Yes, I did do a search and I've read through all post concerning the LM1972. But it seems like noone here has tried it. The thing I was interested in was if it sounds good and works well.

sonnya,

Yes, I know that Thule and Arcam uses the LM1972 so it shouldn't be too bad. I haven't checked out the PGA2311 yet, but I will!


One more thing,
Almost all DACs have a function to attenuate the output signal. But I have heard that it's a really bad solution, can anyone tell me why?
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Old 27th January 2002, 07:41 PM   #5
sonnya is offline sonnya  Denmark
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The reason is :

They do it in the digital domane, so you reduce the resolution. If you reduce you volume by 6 dB you will divide the resolution by 2. It is okay to do this with a 24bit signal when you can live with this :
-6dB=23bit,-12dB=22bit,-18dB=21bit, -24dB=20bit,-30dB=19bit,-36dB=18bit.

Sonny
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Old 27th January 2002, 07:51 PM   #6
Freddie is offline Freddie  Sweden
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Sonny,

Thanks for the reply. I want a -70dB attenuation, and with a 16bit signal....... well that's out of the question.

/Freddie
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Old 27th January 2002, 08:24 PM   #7
sonnya is offline sonnya  Denmark
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Well .. if you use a 24Bit dac and feed it with the 16 bit signal as 24bit where you don't use bit 0 - 7. Then the digital filter will "convert" this signal into a 24 bit signal.
Why? The dac's filter do 24bit calculations.
A bit hard to understand... But you will only have big sound change under -48dB.

Sonny
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Old 27th January 2002, 08:55 PM   #8
sonnya is offline sonnya  Denmark
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I have just checked again ... AD do this before the filter wich makes more sense. It will not destroy the performance of the digital filter.

Sonny
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