We had a perfect stay at Edu y Charlie. A large and comfortable room and bathroom, excellent location and all facilities we needed for a city visit.
Although several more people are staying in the building we were never disturbed by any noise.
One thing to note: they are strict about the house rules (and rightly so) leading to a small misunderstanding upon arrival when no one was home to let us in. Best to have a clear understanding about your arrival time to avoid having to wait. If you would end up in the same situation as we did, there is a nice cocktail bar (Jose Alfredo) around the corner to kill the time :)
All in all a lovely stay, we'd book here again without hesitation if returning to Madrid. Thanks guys!