As requested by @andreasmaaan here I made some measurements of an old DAC: the Arcam Black Box 3 MK1 which I bought new in 1991 (without MK1, see below). It retailed for around € 780 then (converted). Here are the front and the back:
It supports 44.1 and 48 kHz samplerate with 16 bits - that was the standard back then ...
Somewhere later around 1997 I fell victim to op-amp rolling and replaced the original op-amps (LM627CN) by OPA134PA. Two can be seen on this photo of the internals on the right PCB (audio mother board).The LF411 is used as DC servo. Two others are hidden on the backside of the left PCB (digital audio board). The result is my version MK1:
The measurements are done with REW, using an RME ADI-2 PRO fs, an old Edirol UA-25 and a brand new SIGLENT SDS 1202X-E (2 channel 200 MHz digital scope).
Lets have a look to the output level (measured with the digital scope):
The left channel (yellow) delivers 2.50 Vrms, the right channel 2.35 Vrms, a difference of 0.5 dB.
For the THD, IMD and Jitter measurements I used the RME only, feeding the Toslink input of the BB3 with 44/16 sinus signals.
32 times averaging reveals remains of the power supply:
This is not 16 bit performance.
The actual IMD is not that bad, but there is a lot of spurious stuff. With 32 times averaging we can see that it is not noise:
EDIT: while repeating the measurements with the fixed power supply and back in original state I realized that I did not enable dither during the IMD measurements. With dither enabled the result is much better: the spikes are still there but reduced in amplitude by about 10 dB.
Jitter suppression looks really awful (using J-Test signal):
And this stuff covers the full spectrum:
At last I measured the frequency response. Here I used the Edirol to feed the BB3 with 44/16 signals and used the RME with 384/24 to cover a wide band spectrum. REW did not allow me to display the full spectrum (the RME meausres until 180 kHz) so I can show only up to 100 kHz. First white noise with heavy averaging:
Oh oh - this does not like like a good reconstruction filter. I would expect a lot of aliasing here, so let's check with a 19.1 kHz sinus (same as JA uses in his tests for stereophile), 64 averages:
The aliased image of the 19.1kHz tone at 0 dBFS is suppressed by 72 dB. This is much more than the white noise result suggests (beats my why) but it should be at less than -90 dB.
Conclusion
We should be glad that we live in modern times where 100 € buy you a DAC which measures much better than this vintage gear. I would not say that the BB3 was high-end (that would have been Proceed or Wadia which were at least twice as expensive), but it was not cheap either.
Please remember that this unit is not in the state as it left production (it's MK1!). Without reinserting the original op-amps and a retest we cannot be sure that the THD and IMD measurements reflect the original performance. The jitter and aliasing problems however should not be affected - but we never know ...
EDIT: corrected the type of the original op-amps (from LM327 to LM627CN).
Somewhere later around 1997 I fell victim to op-amp rolling and replaced the original op-amps (LM627CN) by OPA134PA. Two can be seen on this photo of the internals on the right PCB (audio mother board).The LF411 is used as DC servo. Two others are hidden on the backside of the left PCB (digital audio board). The result is my version MK1:
The measurements are done with REW, using an RME ADI-2 PRO fs, an old Edirol UA-25 and a brand new SIGLENT SDS 1202X-E (2 channel 200 MHz digital scope).
Lets have a look to the output level (measured with the digital scope):
The left channel (yellow) delivers 2.50 Vrms, the right channel 2.35 Vrms, a difference of 0.5 dB.
For the THD, IMD and Jitter measurements I used the RME only, feeding the Toslink input of the BB3 with 44/16 sinus signals.
32 times averaging reveals remains of the power supply:
This is not 16 bit performance.
The actual IMD is not that bad, but there is a lot of spurious stuff. With 32 times averaging we can see that it is not noise:
EDIT: while repeating the measurements with the fixed power supply and back in original state I realized that I did not enable dither during the IMD measurements. With dither enabled the result is much better: the spikes are still there but reduced in amplitude by about 10 dB.
Jitter suppression looks really awful (using J-Test signal):
And this stuff covers the full spectrum:
At last I measured the frequency response. Here I used the Edirol to feed the BB3 with 44/16 signals and used the RME with 384/24 to cover a wide band spectrum. REW did not allow me to display the full spectrum (the RME meausres until 180 kHz) so I can show only up to 100 kHz. First white noise with heavy averaging:
Oh oh - this does not like like a good reconstruction filter. I would expect a lot of aliasing here, so let's check with a 19.1 kHz sinus (same as JA uses in his tests for stereophile), 64 averages:
The aliased image of the 19.1kHz tone at 0 dBFS is suppressed by 72 dB. This is much more than the white noise result suggests (beats my why) but it should be at less than -90 dB.
Conclusion
We should be glad that we live in modern times where 100 € buy you a DAC which measures much better than this vintage gear. I would not say that the BB3 was high-end (that would have been Proceed or Wadia which were at least twice as expensive), but it was not cheap either.
Please remember that this unit is not in the state as it left production (it's MK1!). Without reinserting the original op-amps and a retest we cannot be sure that the THD and IMD measurements reflect the original performance. The jitter and aliasing problems however should not be affected - but we never know ...
EDIT: corrected the type of the original op-amps (from LM327 to LM627CN).
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