I've been brewing 6 batches of Ale and I've had problems with sweetness and banana like aroma and taste (esters probably). I think the problem is the fermentation temperature. My fermentation bucket sits in a room with a temperature ranging from 20 to 27 celsius (68-81 fahrenheit). The only brew that tasted "right" was a stout but the roasted barley might have just masked the sweetness. The sweetness is present after few days of fermentation and then gets stronger. I have used US-05, WY 1056 and WY 1272 yeasts.
I was thinking of making a fermentation chamber from a larger bucket (than the fermentation bucket) with insulation of the outside. The temperature would be controlled with adding cold water to the bucket and removing warm water. Do you think this would do the job? If I have understood correctly the first days of the fermentation are the most important temperature wise.
Something like this: https://dl.dropboxusercontent.com/u/3248030/beer/fermentation.png