Ok, here's the follow up regarding my problem I've been meaning to post but I've been busy, I bought multiple units with the intent of reselling. Two of them were fine, to recap the problem with the other two, after playing for a few minutes one channel started to degrade quickly and became distorted then would only play at a much lower volume as well. This was through the preamp as well as the HA so the problem seemed to be in the DAC section. wsz (the seller) suggested I try swapping the OPA627 from the good units in to the bad ones and they worked fine, I test ran them for over 12 hours trying all inputs and outputs and had no further problem. So it turns out I had bad OPA627 Opamp modules
not really sure how that happens but whatever. Anyway I was sent replacements and all is good now.
So, if you've got a problem with one channel in particular being distorted or playing really quietly through both the pre- outs and the HA it's likely the DAC opamps are bad.
wsz on eBay has awesome communication and great customer service. He was prompt and as helpful as he could be in troubleshooting and solving the problem. He took care of the problem with no question as well, I would highly recommend him to anyone who has concerns about not getting a perfect unit.
LT1364 - I ordered samples from Linear Tech and popped them in. I'd listened to the stock HA section and it was Ok, with the LT1364s it got..different, in a better way I suppose. I didn't do any back and forth A/B but my first impression was that it opens up the sound as if you're in a bigger environment, if I didn't know better I'd say it was like a subtle Dolby effect or an EAX effect in games. It's not something I'd been used to in headphones so it sounded odd at first but I've gotten used to it and it's pretty nice. It doesn't actually change the source material, tightly mic'd or 'closed' recordings or don't have added reverb or anything like that but ones that are meant to have an open sound expand beyond what one would expect from headphones.
I also did the cap-cutting mod on the one I'm keeping, actually I unsoldered them because leaving leads sticking out of the board doesn't suit my anal-retentive style
I sort of did it before listening much
but the thought of filtering anything right at the output stage didn't sit well with me. Both my speaker system and headphones are sort of bright, or rather non-bass enhanced - NS-1000M speakers and Grados SR-80s. I can see how people with those phones might not like the mod but if so they might be better off with other phones instead. The LT1364s may help in smoothing things out a touch too but it's hard to tell. The next mod will be a better volume pot for sure, the stock one works OK but with low impedance phones like the Grados the volume difference between channels at very low levels is apparent. I'd actually like to try adding an impedance switch across the headphone out but that's for the mod thread.
Lengthy post, just figured I'd share in case anyone else is having a similar issue.
