The Best DAC is no DAC

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iperv

Member
Joined 2008
merlin el mago said:
Pot not varies the impedance seen by the source, pot varies the impedance seen by the load.
Click to expand...

This is not entirely true.
Ideal pot does it, but an actual pot shows a not constant input and output impedance.
A ladder one shows a good approximation of a constant input impedance, but a not constant output impedance - not a real problem.

Of course you can design your own ladder that shows a constant output impedance, but then the input impedance is not constant.

There are circumstances in wich you want a constant output impedance, but this is not that one.

Here we want a fixed input impedance and the only (cheap?) passive way is to use a stepped ladder pot.
 
nautibuoy

nautibuoy

Member
Joined 2010
PCB Group Buy Update

PCB Group Buy Update: Since ordering the PCBs I've had some PMs asking to buy boards and I have so far managed to squeeze people in, however, as of this moment the PCBs are 'Sold Out'.

I am keeping a small number of boards back just in case anyone's boards get lost in the post; I will only offer them once those who have paid for boards have received them.

Ray
 
nautibuoy

nautibuoy

Member
Joined 2010
quanghao said:
Hi.
I use lf =470 R, Cf = 0.015 uf.

Or 3.3k and 1000pf

I still see white noise.
Thanks
Click to expand...


470R/0.015uF will give you a -3dB point at around 22.5KHz whereas with 3K3/1000pF -3dB will be approx. 48KHz?

When you say you can "see white noise" do you mean see on an oscilloscope or do you mean you can hear the white noise?

I've been using a 1K0/3.9nF filter (approx. 40KHz -3dB point) and have heard no white noise on the outputs.
 
Koifarm

Koifarm

Banned
Joined 2005
RC filter is not steap enough. I use LCLC filter.

RC filter works only if the amp behind the dac has no high frequency respons. ( <25khz). When using amps with wider frequency respons like 100khz you need better filtration.
 

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iperv

Member
Joined 2008
Koifarm said:
RC filter is not steap enough. I use LCLC filter.

RC filter works only if the amp behind the dac has no high frequency respons. ( <25khz). When using amps with wider frequency respons like 100khz you need better filtration.
Click to expand...

Ok.

But if you hear white noise with an high frequency LPF, better you change DSD upscaling - 1X---->2X----->4X.

With 1X DSD - and maybe 2X - you can hear the noise because is very close to the audio frequency.
If you increase the upscaling, alias (noise) goes far away and then a simple RC filter is ok.

But a wide frequency amplifier always wants a steep filter, not against the noise, but because it can destroy your tweeters - if your tweeters are wide frequency too.
 
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nautibuoy

nautibuoy

Member
Joined 2010
quanghao said:
I can hear the white noise output.
Click to expand...

iperv has a good point about the DSD rate, what are you using?

I only use DSD256 and would go higher if I could.

Also, I've just seen a post from Gentlevoice over on Acko's Direct DSD thread that suggests JRiver and Foobar are noisier than HQPlayer - I think you said you use JRiver? Perhaps it would be worth trialling HQPlayer if your hardware is up to it.

Ray
 
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quanghao

quanghao

Member
Joined 2009
quanghao.com/
nautibuoy said:
iperv has a good point about the DSD rate, what are you using?

I only use DSD256 and would go higher if I could.

Also, I've just seen a post from Gentlevoice over on Acko's Direct DSD thread that suggests JRiver and Foobar are noisier than HQPlayer - I think you said you use JRiver? Perhaps it would be worth trialling HQPlayer if your hardware is up to it.

Ray
Click to expand...

Please try donlaod this file and test it:

this track: Ave Maria. Andante.flac

https://www.fshare.vn/file/3D8UAKOI9HE8
 
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