This is a series IV but as they note for you on bottom, this can be used for series III and series IV. The update for series IV was the IMPROVED EQ, and this is one of those. There are a few cosmetic issues but the overall appearance is pretty good. One side works, one doesn\'t. Either input and/or output is not working. I took a brief look inside; I don’t think it’s an RCA connector or solder point, but rather another component that I’m reluctant to task with.I do know that what I heard coming from the working side was sounding pretty sweet; this equalizer is simple, yet very effective at what it does. The slider pots both work noiselessly. So if yu\'re handy this is for you!
From my own experience series V and VI are really not particularly different than series IV - they are all acoustic matrix based and use the same drivers and the cabinet dimensions are essentially similar as well. I bet you could get those series to perform great with this too after you fix it.
The buttons for tape monitor and low filter are not here but pressing the little blue switches in accomplishes the task. Similar depress type knobs of a suitable nature are generically available if you choose to bother. The functions work as designed without them. If I find a couple of suitable ones hanging around I will include them for you.
Please note that articles about using \"just any eq\" are incorrect - you cannot use just any equalizer to get 901\'s to sound great - there\'s a ton about this on line but suffice it to say the curve is specific and for your 901\'s to sound their very best a Bose 901 EQ is what you must have. Accept no substitutes, it just won\'t sound right.
