There is a pop. Nothing that hurts my ears so I imagine it is not something that hurts the IEMs. I do tend to turn on the amp first before plugging in my IEMs just to be on the side of caution.
On rare occasion, yes, I have had to turn the amp on and off before it will start. But not repeatedly, just one on-off cycle.
In terms of sound, I'm really enjoying the iPod > Portaphile > Heir Audio 4 Ai sound. I don't miss the big headphone rigs I used to own. Aside from the small quirks, price + battery life are holding back many others from taking the plunge. All legitimate reasons. However, sound quality performance has never been an issue with the 627. It performs like a full size headphone amp.
hey I just checked that you own the Portaphile627, how noisy is the pop sound when you connect or turn on or off the amp when using your iem's with it, and I heard that you have turn it on and off repeatedly to turn the amp on because of the capacitors needs to get some kind of charge, is that true, and once again how hard is the POP on your iems?