First, when you said…
Even though the manual states 1.5 v gets maximum output, increasing the voltage input from there continues to increase the volume, all the way to 10 v rms…
…Is that with the volume control on the amp at max, or with it turned down significantly? I suspect you meant that the volume increases all the way to 10 vrms with the amp’s volume control positioned significantly lower than max. If the volume controls of the DAC and the amp were both at max and the amp was not severely clipping and distorting it would certainly point to the statement in the review about 10 volts being grossly incorrect.
In any event I think it might be a good idea to contact Burson and ask them if they can clarify or confirm the relevant statement in the review. (I did some further research, btw, which failed to turn up any information supporting the statement). For the benefit of others, that statement was:
If you want to use the HA160D as standalone DAC into a preamp/integrated, click 3 on the stepped attenuator equates to 1VRMS out, click 5 to 2V, fully open to 10V. This will vary just a bit with sources of course.
Also, as a point of information the attenuator is stated to have 24 steps. And in that regard I would add that the steps are almost certainly not linear (which they shouldn’t be), and become finer as the setting is increased. So your estimate of 4 volts might be off somewhat, with the actual number being somewhat lower. For example a change of 2 clicks, from position 3 to position 5, results in a change of 6 db (from 1 volt to 2 volts), that being an average of 3 db per click. While a change from position 5 to position 24 can be calculated to average about ¾ db per click, which I suspect means ½ db per click near the upper end of the range, and 1 db per click at some of the lower settings.
Also, I’m wondering if a miscommunication with the reviewer might have occurred, and the voltages that were stated should have been indicated as peak-to-peak, rather than as rms. For a sine wave (which is what such specs are based on), 10 volts peak-to-peak corresponds to about 3.5 volts rms, and the 4 volt number you referred to, if peak-to-peak, would correspond to about 1.4 volts rms.
And perhaps another contributing factor is some degree of inaccuracy in the sensitivity spec of the amp. Also, a minor contributing factor may be that some (although not most) recordings are engineered such that their peak levels are a few db below "full scale" (the maximum possible digital value), which would cause the DAC to output less voltage than it is capable of for a given setting of its attenuator.
Finally, I saw a reference somewhere to 10 db of gain the unit provides when it is used as a preamp, rather than as a standalone DAC. Perhaps that factored into a possible miscommunication with the reviewer. 10 volts rms less 10 db of gain would be about 3.2 volts rms.
That’s about all I can think of at this point. As I said, perhaps Burson can shed some further light.
Regards,
-- Al
