Hi all,
Here's a short review of the LT1028ACN8 as a buffer in the iBasso PB2:
I've done a lot of A/B testing with the iBasso PB2 this morning, to compare the LT1028ACN8 as buffers vs. dummy buffers and the popular HA5002.
The LT1028ACN8 is absolutely the the "cleanest sounding" buffer op-amp I've ever used in the iBasso PB2 - noticeably better than the HA5002 for resolution and transparency, but offering less advantage in terms of current gain.
For transparency and resolution, however, the LT1028ACN8 is not the equal of using dummy buffers in the iBasso PB2.
Here's the chain I use to test resolution and transparency of op-amps in the PB2:
FiiO X5 Line Out > iBasso PB2 on 16V battery power (not the switchmode PSU) balanced out > Toxic Cables Silver Poision cables > HD800
My most detailed and transparent op-amp for use in I/V is the OPA1612. The LME49990 is "prettier" sounding, but not as analytically detailed and neutral as the OPA1612.
With the OPA1612 in I/V for the above chain, I can easily detect the degradation of resolution caused by the HA5002 relative to using dummy buffers. It's night and day with that chain. Not so if I use my lower-resolving LCD-2 rev. 1, which really appreciates the extra current provided by the HA5002.
But the HD800 thrive on voltage - they don't need a boost in current (as had with the HA5002 vs. dummy buffers), and they're so revealing they can detect any loss of transparency.
Despite my conviction that the LT1028ACN8 is not as transparent as dummy buffers, the difference is subtle - which is saying a lot. In fact, with dummy buffers in place, switching from the OPA1612 to LME49990 in I/V imposed about the same, small reduction in resolution as was imposed by going from dummy buffers to LT1028ACN8 when the OPA1612 were in I/V.
When I then switched to using LME49990 in I/V, to compare the LT1028ACN8 to dummy buffers, the reduction in resolution imposed by the LT1028ACN8 was less noticeable than when using OPA1612 in I/V. I had to go through several of my favorite resolution-testing tracks before I started finding some sections where the difference was great enough to convince that I wasn't imagining things.
So that says a lot for the LT1028ACN8's abilities, but I have to ask what benefit is providing?
I've scoured the LT1028ACN8 datasheet, found here:
http://cds.linear.com/docs/en/datasheet/1028fc.pdf
Sadly, I am unable to find
any reference to max. output current in that datasheet. There are several references to the word "current" and "mA," but I cannot find any specs or charts that I, at least, can clearly interpret to discern how much current the LT1028ACN8 can deliver. They provide max. output voltage, max. input offset current, max. supply current, but not the all-important max. output current. (Perhaps I need another cup of coffee, but I just can't find it.)
That said, I have no use for the LT1028ACN8, especially given that adding them to the PB2 (vs. dummy buffers)
did not allow me to turn down the volume, due to any increase in SPL. In terms of added power, they almost seem to be inert when used with the HD800, where the HA5002 make a much bigger difference in providing additional power to the current-hungry LCD-2 rev.1, which again, can't really appreciate the resolution advantage of the LT1028ACN8.
I'd rather run HA5002 buffers with the LCD-2 (with LME49990) and stick to using LME49990 and dummy buffers for the HD800.
But... For headphones that don't thrive on power as much as the LCD-2, nor thrive on transparency and resolution as much as the HD800, the LT1028ACN8 is definitely "cleaner" than the HA5008, and no doubt provides more power (how much?) than dummy buffers.
And you can't beat the price of the LT1028ACN8.
Lastly, I'll add that some HD800 owners might want to deliberately "soften" the HD800's analytical nature just a wee bit, to reduce fatigue, and for that, I would say the LME49990 with LT1028ACN8 is a great combination - because it's subtle - not as drastic a "softening" as that caused by HA5002.
Mike
UPDATE: I've just realized, having previously concluded that using the LT1078ANC8 as buffers would work well with headphones that don't need the resolution demanded by the HD800 or the current gain demanded by the LCD-2, they would probably sound great with the relatively efficient and not exceptionally detailed OPPO PM-1 / PM-2 / or PM-3. But I've already put everything away, with the PB2 holding LME49990 and dummy buffers. LOL
