Resurrecting an older thread, but wanted to weigh in...
I've had a Sugden ANV-50 for about 1.5 yrs. It is fed by respectable upstream digital and analog sources and cabling, and delivers output to relatively inefficient (83dbW, 10 ohms) downstream speakers. It is spec'd at 50W/ch into 8 ohms.
In a few words, I am continuously blown away by the soundstage, clarity, speed, and holographic presentation that the ANV-50 serves up on many, many albums and hi-res FLACs. Even with the severely inefficient speakers, I get usable, high quality volume all the way up to 12 o'clock on the dial.
However, there are a few things that I'm not 100% enthusiastic about. First, and most importantly, the sound does compress a bit and lose some dynamics as that volume knob gets closer to 12 o'clock. Perhaps that's when it's switching to more A/B bias or something, but you can hear it kind of run out of gas in the upper power range. In fairness, I play my music loud in a very large room with bookshelf speakers. I'm asking a lot from the Sugden. If you really need to lean on it for power delivery with very inefficient speakers, you may want to look elsewhere.
Second, there's a feel to the volume knob that feels cheap. It works fine, no issues mechanically, but it feels "plasticy" to the touch, and seems like it won't age well as an heirloom piece.
Third, and not that big of a deal at all, the current volume indicator on the dial is incredibly difficult to see from 10-12 ft away. I had to put a piece of black tape on it so I could see the volume knob rotate when using the remote. Speaking of the remote, it's super cheap, plastic, and lightweight, and the volume up/down labels are already wearing completely off after 1.5 years. But, it works.
I just upgraded my phono stage to an Allnic H-5500, and holy cow... The Sugden ANV-50 throws an incredible, holographic soundstage! All the detail, inner detail, speed, and clarity that you could ever want - unless you have to really crank it, when it will start to compress.
The Pass INT-60, Luxman L-509X, and Allnic T-2000 30th Anniv. are all on my short list for potential upgrades, but I am extremely happy with my ANV-50 right now. It's allowing me the time to upgrade all of my sources and cabling, get my power supply cleaned up, and really appreciate and enjoy each and every upgrade that I've introduced so far. I've never felt that the ANV-50 was holding me back, but there will come a day when I need to replace it with something that won't compress at very high volume.
Hope that helps some. I auditioned the Sugden A21SE but not the IA-4 prior to purchasing the ANV-50. The ANV-50 was much better than the A21SE in my system, but couldn't begin to tell you how it compares to the IA-4 or Pass gear.
