dcolak
New Head-Fier
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The problem exists on both SPDIF and USB?
How can we get -3dB if we are using a CD player as a source?
Will the future versions of Valab address the issue and stop clipping if the source is not attenuated?
All the fuss began because I wanted to buy a Valab DAC and was afraid it would clip just as the two Gigalab Moon DAC's I had.
If you have one that does not clip, I will buy it at once!
| Originally Posted by TeraDak /img/forum/go_quote.gif For those concering the clipping issue. We current use a 390R resistor for the i/v conversion and it will output 2.19V at the full range audio data. It is impossible to listen the 0-db audio signal from the DAC , to pre/power amplifier and to speaker without any attenuation. It the source doesn't exceed -3db, there will be no clipping issue. However, if you would like to attenuate the signal in the preamplifier and keep the range as full as possible and without clipping. The i/v resistor in the TDA1543 output should be lowered to 340R ~ 350R to avoid clipping. The clipping issue is just a tradeoff for signal attenuation and it depends on the user listening condition. We will show the picture for analog output with i/v resistor 340R ~ 350R. For signal analysis, it should be 340R~ 350R, but it may not be the best for users in most real listening conditions. (1) For user using the original 390R resistor, if you care about the clipping issue, you can reduce the resistor to 340R ~ 350R without loss the audio quality. If you don't have 340R ~ 350R resistor at hand ( 340R ~ 350R resistor is difficult to buy), you can parallel a 3.3k or 3.6k on the original 390R resistor. However, a 330R resistor is good aslo. The main difference is the maximum output voltage when a 0db signal is input. (2) After that, connect the USB line to our DAC and repeat playing a 1kHz 0DB sine wave in PC. The wave could also be downloaded form our share space ( Public - Windows Live ) Use a meter and set it to measure AC voltage segment. Measure the RCA output or our DAC. The AC output is approximate 2.0V initially. Trim the VR nearby TDA1543 to find the maximum AC output. We usually trim the VR with the help of scope. But a meter is also good enough for tuning. If you have a scope, you can trim the VR such that the sine-wave is the most symmetric. The most symmetric output implies the maximum AC output in a meter. The second step can be skipped it there is no meter or scope at hand. There is only few difference after step (2) adjustment. /********************** Notice **********************/ The most important should be noticed is the VR trimming should be after the DAC power-on 30 mins. After that, the DAC will be in a stable state for adjustment. In the first 30 min, the TDA1543 was not in a stable stage. Trimming in the unstable state is no use. /**********************************************/ |
The problem exists on both SPDIF and USB?
How can we get -3dB if we are using a CD player as a source?
Will the future versions of Valab address the issue and stop clipping if the source is not attenuated?
All the fuss began because I wanted to buy a Valab DAC and was afraid it would clip just as the two Gigalab Moon DAC's I had.
If you have one that does not clip, I will buy it at once!
