Passive I/V vs. traditional I/V, FFT pics.

[A 8]

-90dB

[A 8]

-100dB which will be the last.

[ojg]

Great measurements, certainly gave me something to think about.
It is interesting how the harmonics of the PCM1704 is very similiar to the measurements I did on my own dac.

Some questions:
- You say you used a USB soundcard, which one?
- From what I understand you run the balanced out from the DAC direct to the input of the power-amp. What does the power-amp input circuitry look like?
- Would it be possible for you to post the results of 0dBFS measurements? If it is too loud for your soundcard just use a resistor divider.

Thanks!

[Pedja]

Good posts, A8.

Why do all -60dB plots have similarly looking hash? Is it embedded in signal?

[Bernhard]

It shows that @ -60 dB a 20bit DAC is not better than the good old TDA1541.

Also harmonics are odd order which I find a bit critical...

[jean-paul]

It shows that @ -60 dB a 20bit DAC is not better than the good old TDA1541.

[Bernhard]

Or just bad implementation ?

My DENON DCD3300 is very noisy. Harmonics like a TDA1543

[ojg]

Originally posted by Bernhard
It shows that @ -60 dB a 20bit DAC is not better than the good old TDA1541.

I think the -60dB test signal is screwed up. Look at the picture in post #10 which is the reference signal, does not look good...

[A 8]

Hi guys,

For those of you who can't resist getting into a ****ing contest I suggest you save your TDA1541/nonos vs everything else for another thread.

I did not expect the passive I/V to measure as good and figured some of you would be interested considering this could open for a "lean & mean" signalpath without sacrificing traditional THD performance.

The two balanced dac chips have a resistor between each I-out, I-out on each chip is then directly coupled to the balanced input on a LC Audio The End Amp with all the resistors in series and to ground removed before the amps input transistors (se pic below).

The -60 dB signal looks bad but the noise is at a low level and as OJG points out it does so on the Denon analog out as well as the direct spdif dump from the Denon which is being used as source for all measurements.
For now I am assuming it is not my DAC, but rather the denons digital processing or the HiFi News&Record review Test CD II I used. I am going to try with a real cdp once I get a chance. It is strange though that it does not show on any other level measurements
All in all I think the denon is far from noisy and measures pretty good.

At 0dB the soundcard distorts heavily on both the denon and the passive I/V dac but as you say I've been thinking about using a divider once I get time for it.

The soundcard is (lord behold) a creative Audigy 2NX with a 24/96 ADC.
The first tests I did showed it was very noisy and the SNR readings I got was not better then around -93dB above 1kHz. It improved significantly to -120,-122dB when I put it on a 5volt NiMh pack and added oscons on the adc and digital processing supplies.
The line input on the soundcard is directly coupled to the adc input ie no additional op-amps other then whatever sits in the adc chip.

Note that the passive I/V measurements are taken at the poweramp speaker terminals with a pair of 3-4 ohms speakers connected so some of the harmonics might be related to the poweramp.
The denons are taken directly at line out which uses NJM2068 (bal) for I/V and AD825 for buffers.

[Bernhard]

Would be interesting to compare left and right channel of the Denon... @ - 60dB