Long-time lurker, just got a pair of EV S15-3's that I'm fixing up and this is what it has for a tweeter protection circuit. I'm guessing this is older than the pair of back-to-back zeners that they used later on.
Sure enough, it seems to be working just fine as the ST350s appear to be OK while the protection circuit is kaput. This seems cheap enough to debug - or just replace everything and not worry about it - but I haven't seen this schematic in any of the EV EDSs or service manuals, so I'm wondering if there's a good reason they moved on, and if maybe I shouldn't bother.
Anyone seen this before or have any suggestions? Building an STR seems overkill but I'd like to keep these ST350s intact.
Well, remember these circuits were often used for pro setups, which not only had lots of power, but could also be connected in unexpected ways.
A back to back Zener would probably be better as it won't be as likely to overheat. If I read this correctly, the transistor acts as an active load? Meh.
In home situation, unless the driver was particularly delicate I'd leave it out.
Best,
E
A back to back Zener would probably be better as it won't be as likely to overheat. If I read this correctly, the transistor acts as an active load? Meh.
In home situation, unless the driver was particularly delicate I'd leave it out.
Best,
E
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The driver is unfortunately rather delicate; I think it's only rated for ~5W continuous. I'll probably be using them mostly for amplifying an electric upright bass, though considering the midrange and tweeter complement have been used in a few of EV's hi-fi cabs they'll probably see a little dual use.
A very good question! I haven't really inspected it thoroughly. It's cheap enough to replace all these parts, so I figured I'd ask and see if it's worth inspecting further and then rebuilding... or if I should just go with a lightbulb.
From what I've read, the zener circuit is better with these tweeters than a bulb, but I haven't seen any mention of this circuit anywhere. I assume there's a reason why EV abandoned it.
Simplicity? It looks more complex but functions like the power Zeners couple, symmetrically limiting voltage.
How did you find out, it is broken, potatofarmer? What is the problem?
How did you find out, it is broken, potatofarmer? What is the problem?
Welp, turns out the tweeter was blown in the first place. I thought I'd checked it already, but I clipped its leads and tested it again and it's reading open circuit. Rats. Maybe I checked the tweeter in the other cab?
There go my concerns over how good this protection circuit is! 🙄
For now, I'm removing the tweeter high-pass and the midrange low-pass from the crossover so I can at least run it as a musical instrument 2-way speaker.
So eventually I'll have to get a pair of replacement diaphragms but it's not going to be for a while since I can't even get the horns out of the cabinets!
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