Tips from long-time Adcom 5800 owner
I've had my 5800 for many years now (third owner) and recently the wife mentioned that the M-L Quests were sounding a bit harsh on the high end. I decided to give my 5800 a check up and found that both the bias and DC balance were all out of whack and quite different in the two channels. I found that with the very cheap adjustment pots in each channel, it was virtually impossible to get the adjustments right. Shipping a 5800 would surely result in the pots changing position and compromising recent adjustments. So, I replaced the four cheap pots with 10-turn pots and was then able to adjust the bias and DC balance perfectly and easily. My wife noticed the difference immediately and pronounced the situation fixed. Note that she's not an audiophile and doesn't care a bit about the gear making the music, only the result. So, if you have a 5800, consider replacing the pots or having a qualified technician do it for you (he needn't be an audio expert, just able to follow instructions and read a schematic).