I borrowed the Musical Fidelity V-DAC over the weekend to make some measurements. It has been bought by its owner some 8+ years ago for about € 200. It's no longer available and has been replaced by the V-DAC II which is also no longer available.
It comes with a 12V/500mA plug power supply which is presumably not switched (too heavy). This is how it looks:
Inputs are on the right side:
You can switch between USB and SPDIF Coax/Toslink, but you can use only one SPDIF input at any time.
Outputs are on the left side:
Teardown
I got kind permission to open the V-DAC. This is easy as you just remove 3 screws per side and the PCB slids out:
Right side open:
Left side open:
PCB top view:
PCB bottom view:
What a relief to see proper manufacturing at work.
Measurements
These are the specifications (excerpt):
Dashboard
Let's start with my Dashboard (well, not such a nice one like @amirm's), measured with a Siglent SDS 1202X-E (DSO), an RME ADI-2 PRO fs and REW, using USB input (connected to a Linux-PC running current Kubuntu):
Left channel: THD: -98.8 dB, Noise: -97.2 dB, SINAD: 94.9 dB, Output: 1,70 Vrms
Right channel: THD: -87.8 dB, Noise: -96.1 dB, SINAD: 87.2 dB, Output: 1.67 Vrms
THD: The left channel is some 10 dB better than the right channel regarding THD, but even the worse channel is (just) in the specs. It stays on this level over the full audible frequency range and is the same for both SPDIF inputs as well (not shown here, see attachments below).
Noise: PS noise is well within the inaudible region.
Output: Voltage is 1.4 dB below the standard of 2V which may give the V-DAC a disadvantage in a test without level matching. It's also quite short of the specified 2.2V.
IMD
I measured IMD using SPDIF Toslink with the CCIF signal (19 + 20 kHz):
Left channel: IMD: -97.6 dB
Right channel: IMD: -87.9 dB
Again the left channel (blue) is about 10 dB better than the right channel (red).
Multitone
The multitone signal with 32 different sinus signals of equal amplitude emulates "music". SInce it requires 192 kHz samplerate I played it with the vlc-player via SPDIF coax:
Again the left channel (blue) is about 10 dB better than the right channel (red).
Jitter
This is definitely inaudible. Via USB jitter was much worse but I don't trust the VLC player not to mess up the J-Test signal, as JA's measurements at Stereophile were identical to SPDIF, so I'm not gonna show it.
Reconstruction filter
I measured the frequency response of the reconstruction filters with white noise at -10dB and heavy averaging. Since the RME cannot use different sample rates for input and output I used an EDIROL UA25 to feed the V-DAC via its Toslink input.
For both 44.1 and 48 kHz samplerate the cutoff at the Nyquist frequency is not sufficient. However a 20 kHz sinus at 0 dB is totally suppressed in both cases (images being at 24.1 and 28 kHz, respectively) so we are probably good here.
Low Level Resolution
I fed the V-DAC a dithered 1kHz sinus signal at -90 dBFS in both 16 and 24 bit sampledepth to find out how much better 24 bit is over 16 bit:
The noise floor for 24 bit drops some 13 dB which results in a resolution of 18 real bits. Here both channels are identical.
Intersample Overs
Intersample overs are something which should not occur in theory, but does occur in reality due to loudness war and/or bad mixing/mastering. What it means is that the sample values are not higher than 0 dBFS (which they can't) but the reconstructed signal can be up to 3 dB higher. Here are examples of a sinus signal with and without intersample overs:
The frequency of the sinus is 1/4th of the sample rate, so it is sampled with 4 points. Now let's assume that the signal is sampled at the crossings of the horizontal lines, which is at 45, 135, 225 and 315 degree. The pink sinus is at full amplitude (+/-1) although the samples are at +/- 0.71 (green and light blue).
Intersample overs occur when those samples are higher than +/-0.71. If they are at the maximum possible values of +/-1 (yellow and blue) than the corresponding sinus (orange) has an amplitude of +/-1.42 which is 3 dB above 0dBFS.
There are not many DACs which can reconstruct such an illegal signal. Neither can the V-DAC. Shown are intersample overs at +3 and +1 dB:
This is what it should look like:
Crosstalk
I'm not sure whether the result is correct. Left to right is definitely out of spec but not audible at all. Remember that even the best cartridges for vinyl replay have no more than around 35 dB crosstalk suppression.
Conclusion
Oldie but goodie. The results are inaudible for most use cases, and if you own the V-DAC and need no better USB input or other fancy features you are well advised to keep it.
Edits
It comes with a 12V/500mA plug power supply which is presumably not switched (too heavy). This is how it looks:
Inputs are on the right side:
You can switch between USB and SPDIF Coax/Toslink, but you can use only one SPDIF input at any time.
Outputs are on the left side:
Teardown
I got kind permission to open the V-DAC. This is easy as you just remove 3 screws per side and the PCB slids out:
Right side open:
Left side open:
PCB top view:
PCB bottom view:
What a relief to see proper manufacturing at work.
Measurements
These are the specifications (excerpt):
- Maximum output: 2.2V
- THD: 0.004% (20 Hz - 20 kHz) (calculates to -88 dB)
- Frequency response +0/-0.1 dB 20 Hz - 20 kHz
- Signal / noise ratio: 116 dB A-weighted
- Crosstalk: -104 dB (20 Hz - 20 kHz)
Dashboard
Let's start with my Dashboard (well, not such a nice one like @amirm's), measured with a Siglent SDS 1202X-E (DSO), an RME ADI-2 PRO fs and REW, using USB input (connected to a Linux-PC running current Kubuntu):
Left channel: THD: -98.8 dB, Noise: -97.2 dB, SINAD: 94.9 dB, Output: 1,70 Vrms
Right channel: THD: -87.8 dB, Noise: -96.1 dB, SINAD: 87.2 dB, Output: 1.67 Vrms
THD: The left channel is some 10 dB better than the right channel regarding THD, but even the worse channel is (just) in the specs. It stays on this level over the full audible frequency range and is the same for both SPDIF inputs as well (not shown here, see attachments below).
Noise: PS noise is well within the inaudible region.
Output: Voltage is 1.4 dB below the standard of 2V which may give the V-DAC a disadvantage in a test without level matching. It's also quite short of the specified 2.2V.
IMD
I measured IMD using SPDIF Toslink with the CCIF signal (19 + 20 kHz):
Left channel: IMD: -97.6 dB
Right channel: IMD: -87.9 dB
Again the left channel (blue) is about 10 dB better than the right channel (red).
Multitone
The multitone signal with 32 different sinus signals of equal amplitude emulates "music". SInce it requires 192 kHz samplerate I played it with the vlc-player via SPDIF coax:
Again the left channel (blue) is about 10 dB better than the right channel (red).
Jitter
This is definitely inaudible. Via USB jitter was much worse but I don't trust the VLC player not to mess up the J-Test signal, as JA's measurements at Stereophile were identical to SPDIF, so I'm not gonna show it.
Reconstruction filter
I measured the frequency response of the reconstruction filters with white noise at -10dB and heavy averaging. Since the RME cannot use different sample rates for input and output I used an EDIROL UA25 to feed the V-DAC via its Toslink input.
For both 44.1 and 48 kHz samplerate the cutoff at the Nyquist frequency is not sufficient. However a 20 kHz sinus at 0 dB is totally suppressed in both cases (images being at 24.1 and 28 kHz, respectively) so we are probably good here.
Low Level Resolution
I fed the V-DAC a dithered 1kHz sinus signal at -90 dBFS in both 16 and 24 bit sampledepth to find out how much better 24 bit is over 16 bit:
The noise floor for 24 bit drops some 13 dB which results in a resolution of 18 real bits. Here both channels are identical.
Intersample Overs
Intersample overs are something which should not occur in theory, but does occur in reality due to loudness war and/or bad mixing/mastering. What it means is that the sample values are not higher than 0 dBFS (which they can't) but the reconstructed signal can be up to 3 dB higher. Here are examples of a sinus signal with and without intersample overs:
The frequency of the sinus is 1/4th of the sample rate, so it is sampled with 4 points. Now let's assume that the signal is sampled at the crossings of the horizontal lines, which is at 45, 135, 225 and 315 degree. The pink sinus is at full amplitude (+/-1) although the samples are at +/- 0.71 (green and light blue).
Intersample overs occur when those samples are higher than +/-0.71. If they are at the maximum possible values of +/-1 (yellow and blue) than the corresponding sinus (orange) has an amplitude of +/-1.42 which is 3 dB above 0dBFS.
There are not many DACs which can reconstruct such an illegal signal. Neither can the V-DAC. Shown are intersample overs at +3 and +1 dB:
This is what it should look like:
Crosstalk
I'm not sure whether the result is correct. Left to right is definitely out of spec but not audible at all. Remember that even the best cartridges for vinyl replay have no more than around 35 dB crosstalk suppression.
Conclusion
Oldie but goodie. The results are inaudible for most use cases, and if you own the V-DAC and need no better USB input or other fancy features you are well advised to keep it.
Edits
- Added missing attachments: THD+N from 20Hz to 20 kHz
Attachments
Last edited: