Michael,
In the
HiFi-M8 blog's "27 Sep" entry, the following statement can be found:
HiFi-M8 will feature a very powerful headphone amp. Our customers expect that, since our other products offer that level of performance. In order to feed that monster and a bunch of digital circuitry to do USB and iPhone connectivity, you need a really beefy battery. So we had a to take a compromise between “very small” and “very good.” HiFi-M8′s dimensions are roughly 125x80x30.
That's awesome! I've been using both the Meier Corda Stepdance and the iBasso PB2 Pelican amps with a 5-cell LiPo Energizer XP8000 external battery pack, in combination with inline voltage regulator cables (the XPAL WI15 and WI16) so that I can maximize the audio performance of these amps (at their respective maximum supply voltages) while trying to remain "portable."
The original Meier Stepdance was chastised for the short play time offered by its internal 9V battery, so Jan Meier answered the complaint by replacing the OPA1611 op-amps of the Stepdance with more battery-conserving OPA209 in its successor, the 2Stepdance. (Datasheets reveal, however, that the OPA1611 offers lower THD+N and a faster slew rate than the OPA209). People complained about battery life, so he gave them what they wanted, in addition to making the case flatter for stacking, as well as smaller, and offering an external gain-control switch - again responding to the market's wishes. I've never compared the Stepdance to the 2Stepdance, but people say it sounds every bit as good as its OPA1611 predecessor. As always, YMMV depending on your choice of source and headphones, so I remain curious as to the impact of going to OPA209 in the 2Stepdance. The punch line here is that, I would personally prefer
a really beefy battery with better SQ to a really long-lasting battery with compromised SQ.
In hard-to-find comparisons of iBasso PB2 Pelican performance vs. Ray Samuel's SR-71B, it goes unnoticed and unmentioned that the SR-71B has a four-cell internal LiPo battery, delivering 16.8V on a full charge vs. the iBasso PB2's three-cell internal LiPo battery, which delivers only 12.6V on a full charge. Just looking at the their internal batteries alone, it seems that a PB2 cannot compete with an SR-71B when self-powered (on the internal battery).
The Triad Audio L3 uses two 9V batteries internally, but owners wanting to unleash its potential end up buying the Triad Audio LLP external battery pack, with switchable output of 24V or 30V - all to improve performance while remaining portable. The L3 will actually accept external voltages as high as 32V, but piddles along at 18V or less when using the internal 9V batteries - with reduced dynamics and everything else that's lost with a reduction in Watts RMS out.
In recent e-mail exchanges with David McKrell (at CEntrance), he has confirmed that my recently purchased DACmini CX can accept any external voltage ranging from 9V to 19V, without concern for the supply voltage impacting sound quality. Indeed, I am unable to hear any difference in dynamics or bass extension, for example, when powering the DACmini with 9V, 15V, 16V, or 19V external 3-amp power supplies. For "portable" use, or at least, when using the DACmini CX without access to an AC outlet, I've settled on using it with the 5-cell Energizer XP8000 LiPo pack and a 15V inline voltage regulator cable. I selected the XPAL WI15 cable because the 5-cell XP8000 pack will discharge to its minimum 3.0V per cell (from 4.2V when fully charged) at an output voltage that perfectly matches the 15V input requirement of the WI15 voltage regulator. In other words, by choosing the XPAL WI15 regulator cable, I am deep-cycling the XP8000 battery pack instead of shallow-cycling it (as would be the case if I used the 19V regulator cable, instead) - obtaining the maximum possible play time from the XP8000 between charge cycles. This would not be possible, but for the very sophisticated power supply design of the DACmini CX, that maintains a constant swing voltage at the rails, independent of supply voltage.
All that said, believe it or not, I have some very relevant questions regarding the HiFi-M8.
1) Will the HiFi-M8 incorporate technology similar to that of the DACmini CX to ensure a constant swing voltage at the rails, independent of internal battery state of charge or external PSU voltage?
2) What is the fully charged voltage and mAh rating of the HiFi-M8's internal battery pack?
Here's hoping that much of the HiFi-M8 case is filled with at least a five-cell LiPo battery or, better still, that the voltage at the rails does not decrease with battery state of charge - which would be a first in portable amps, to my knowledge.
The DACport, DACport LX, DACmini CX, and DACmini PX have already established CEntrance as the KING of sophisticated internal power management, so I'm expecting to hear great things about the HiFi-M8's capabilities in this regard.
Bring on the really beefy batteries and smart power management! I want the HiFi-M8 to deliver its maximum performance all the time, with all power sources, internal or external battery, or plugged into an AC outlet - just like my DACmini CX!
Thanks!
Mike