LM1972

[Freddie]

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

 

[paulb]

You did do a search, right Freddie? There has been some discussion around here on the LM1972.

 

[sonnya]

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

 

[Freddie]

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?

 

[sonnya]

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

 

[Freddie]

Sonny,

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

/Freddie

 

[sonnya]

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

 

[sonnya]

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