The 828 really had very few problems…. The Belclere transformers are a little delicate, particularly some of those used in Mk 1 mixers; they had a habit of sheering off pins if the mixer was dropped….. but then, one shouldn’t drop a mixer! No, noise was not a problem. The predominant noise was from the power supply but as long as the levels were kept high this was not a problem. On the earlier mixers channel 8 noise was worse than channel 1 because of the proximity of the mains transformer.
As with all highly sensitive audio gear, the biggest ‘problem’ is always the power supply and if it causes operational difficulties…. too much hum, then it’s a good idea to run it from an external supply. Most 828 versions have a pair of sockets on the back where you can plug in a 24V DC supply and this works well. But the supply has to be a decent one! The answer is to try it!
The early mixers (Mk1) had discrete transistor circuitry, all class A so the overall sound was smooth and warm. Although the later Mk 2 mixers changed to include some IC circuitry, I was careful to keep the gain demands in the ICs very low to avoid this hidden plague that we have (ever since the invention of operational amplifiers) of transient instability….. a high proportion of gear nowadays sounds ‘over clean’ because of transient distortion which is difficult to measure and seems to be unknown to designers! So all the 828s actually sound warm and smooth….. that’s why I have one in my office ‘studio’ to this day.