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DAM1021 NOS with a 3 Pole passive filter
DAM1021 NOS with a 3 Pole passive filter
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Old 8th February 2019, 04:34 AM   #21
hop.sing is offline hop.sing  Europe
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Quote:
Originally Posted by janho12345 View Post
I do have a few questions here.
Here is an except from the dam manual:

“The dam1121 upsamples everything to the final 2.8/3.1 Mhz DAC sample rate in two steps, there are three different filters in the dam1121”

I know that NOS filters were made, also by the so called “filter Meister Paul”. The latest was the NewNOS. As I understood from reading the dam1021 filter thread this inserts some zeros but it is still up sampling. If I’m wrong I happy take “no you’re wrong” for an answer.
Till then I’m not sure if the Dam can be considered as a true NOS DAC.

Second question. If you want to filter the high frequency’s with an extra filter after the DAM board, did you remove the onboard C? If not you're filtering twice, on purpose. I do have no problems with that but one seems useless then no?

Sorry if I’m repeating myself of get on someone’s nerves with this RC or “output” C Filter thing.
Filter from the Board was replaced with styroflex a while ago. Now it is replaced by my “brutal” filter approach.
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Old 8th February 2019, 07:52 AM   #22
analog_sa is offline analog_sa  Europe
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DAM1021 NOS with a 3 Pole passive filter
Quote:
Originally Posted by hop.sing View Post
Well it measures very NOS. beautiful steps on the scope, hf loss like predicted.
Too much ripple on top of those steps?

As for comparisons to other NOS dacs, perhaps i am wrong. It is hard to make a meaningful comparison as there are too many external variables, per example the presence of an i/v stage.
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Old 8th February 2019, 09:08 AM   #23
hop.sing is offline hop.sing  Europe
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I could not detect any ripple on the scope, and shouldn’t a voltage output be perfect? It allows a simple, pretty much lossless implementation of the filter.
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Old 11th March 2019, 09:01 PM   #24
hop.sing is offline hop.sing  Europe
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Default Filter slightly modified

Hi
Just a short update:
I changed the inductors to those: Fastron 09P-822J-50 8,2mH
They seem to have a different resonance behaviour despite the same inductance as the old ones.
And I changed the second capacity from 13600pF to 11500pF (6800pF and 4700pF in parallel)

The filter cutoff is now at a higher frequency and the resonant peak is flatter, it measures better than the original filter in the frequency domain, but the suppression of mirrors is worse.
I listen to it right now and I really like it, not sure it sounds better than the old one, but not worse for sure.
In the meantime I disconnected the filter to recalibrate my ears with the c128 filter from Paul, but coming back to NOS with analogue filtering sounds more natural to me, so I guess it will stay.
Unfortunately no one else tried this until now, I would love to hear some opinions....

First thumbnail is the new filter vs nos 44.1k
Second is the old filter vs the new one
Third is new filter vs nos at 96k. You look at the real filter response (With resonant peak) up to around 40k. The energy of the mirrors in the critical 40k area is massively reduced, they should not bother amps or speakers very much any more, I guess....
Attached Images
File Type: jpg NOS 44.1k response.jpg (107.3 KB, 80 views)
File Type: jpg NOS 44.1k old vs new filter.jpg (105.7 KB, 73 views)
File Type: jpg NOS 96k response.jpg (84.0 KB, 74 views)
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Old 11th March 2019, 10:31 PM   #25
hop.sing is offline hop.sing  Europe
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By the way, if anybody worries about the phase response of such a filter
red is NOS w/analogue filter
green is the default linear filter of the dam1021
Attached Images
File Type: jpg phase response.jpg (123.9 KB, 64 views)
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Old 12th March 2019, 12:14 AM   #26
canvas is offline canvas  Taiwan
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Quote:
Originally Posted by hop.sing View Post
I listen to it right now and I really like it, not sure it sounds better than the old one, but not worse for sure.
Try some of the violin pieces. You should hear the difference between different cutoffs, even after 20Khz. Personally, I think the cutoff at 18Khz is a bit early. I prefer a steep filter just right after 20Khz.

Poting
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Old Yesterday, 07:31 AM   #27
AD1865 is offline AD1865  China
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The high frequency attenuation of the NOS output is not true high frequency attenuation, but because the clock of the DAC is inconsistent with the clock of the instrument's ADC. After the ADC output is internally filtered and processed, the high frequency tested is attenuated. If the ADC and DAC use the same LRCK, there will be no attenuation problems.
On the other hand, even if the NOS does not add any filtering, the human ear hears that the NOS still feels that the high frequency attenuation is due to the interference of the image frequency, and the sound burr but the high frequency is not clear.
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Old Yesterday, 05:22 PM   #28
hop.sing is offline hop.sing  Europe
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I think NOS frequenccy response is due to the sample and hold nature of a dac. It is really inherent to that way of conversion. A digitally produced sine sweep is precisely measuring as expected at a NOS dam1021. So correcting that in the analogue domain is necessary, correct and easy as shown above.
Still using that mode and it sounds beautiful to my old ears.
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Old Yesterday, 06:53 PM   #29
Ken Newton is offline Ken Newton  United States
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Quote:
Originally Posted by AD1865 View Post
The high frequency attenuation of the NOS output is not true high frequency attenuation, but because the clock of the DAC is inconsistent with the clock of the instrument's ADC. After the ADC output is internally filtered and processed, the high frequency tested is attenuated. If the ADC and DAC use the same LRCK, there will be no attenuation problems.
On the other hand, even if the NOS does not add any filtering, the human ear hears that the NOS still feels that the high frequency attenuation is due to the interference of the image frequency, and the sound burr but the high frequency is not clear.
Setting aside the complexities of Sigma-Delta-Modulator conversion.

The famous NOS high-frequency roll-off curve also occurs via Oversampled operation. It is an function of the hold period of sample-and-hold ('Zero Order Hold') type D/A units. Which is to say, nearly all audio D/A units. The shorter is the D/A unit hold period, the higher in frequency will be the roll-off curve. Inversely, the longer is the hold period, the lower in frequency will be the roll-off curve. The D/A hold period itself is determined by the effective sample rate (meaning, the final sample rate, including any oversampling) sent to it. The higher the rate, the shorter the hold period. Therefore, NOS operation will exhibit the lowest frequency roll-off curve for a given native sample rate, simply because it exhibits the longest D/A unit hold period.

Analog EQ of the roll-off curve can be performed on the NOS DAC's analog output signal. As for Oversampling DACs, the digital interpolation/filter typically includes an built-in digital EQ function to correct for the reduced, but still present, roll-off effect.

Last edited by Ken Newton; Yesterday at 06:56 PM.
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Old Today, 03:14 AM   #30
AD1865 is offline AD1865  China
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It seems that the Nyquist sampling theorem cannot be established? For example, the PCM1704 has a bandwidth of at least 2MHz (setting time is 200ns), and there is almost no attenuation at 22.05kHz. But if you test the unfiltered NOS PCM1704, the 20kHz attenuation will be greater than 3dB。So what do you think is the oversampling of the digital filter to compensate for the high frequencies? The frequency response curve of the digital filter in the spec is problematic?
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