Typically, they exhibit high noise, although many will fail completely. It has been shown that some of these components have lead contamination problems and are prone to failure. Early production runs of the 802 and 901 Series IV equalizers used National LF 353 op-amps. "Failure tracking has shown that a higher than average incidence of failures in equalizers has been due to a parts problem. If this is old or commonly known information with older 901 EQ problems, I apologize.Īccording to Bose service bulletin #EQ-83-02, dated January 3, 1983: Just came across this old thread and thought I'd throw in my 2 cents. There are too many other more fun projects to deal with like exploring electrostatic and old studio monitor designs. As far as changing the the frequency shaping, I'd prefer to not dink around with that without measuring equipment, both electronic and acoustic.Īs for the chance that I'd ever spend the time dinking around with Bose 901s in any DIY project: Very, very low. I've only seen one schematic of one version so you'd have to de-engineer the circuits to figure out what to do. Given the age of many of them, I suspect that the first order of business would be to update the power supply caps and swap out any interstage coupling caps in them. The cabinets themselves on all after the Series IIs were integrated in with the drivers so, again, not much to be done as I think about it.Ībout the only place I see where they could be changed in any way would be the equalizers. Since the drivers are full range, there's not much that can be done there. Beats me what kind of mods might be done to these speakers.
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