Fender Bassman 200 Crossover

[EricssonB]

Again, Bassman's horn is blown out. Woo.

First time, with great recollection was when we took it to the field at my then High School, plugged in on the grass and serenaded the football team - full volume, horn turned up. Perhaps not the wisest idea, but a great time. The copper leads on the diaphragm broke. Easy replacement.

Second time was an accident - using it as a vocal amp immediately after playin bass, I switched on the microphone without silencing the horn. I'll just say that my ears were ringing into the next day due to the feedback.

This time, the diaphragm is fine. I'm testing the resistance through the crossover (oh yeah, schematics: Fender Bassman 200. See page 7 for crossover.) and it passes fine through to the woofer, but is open through the horn.

I've isolated it to the capacitors. (C1/C2, 3.3K). Has open resistance and the other has ~23.8Ω. I'm not entirely sure, but would the one presenting resistance be faulty, given the nature of capacitors to discharge upon reaching a certain current?

...I might just go ahead and replace both to be sure.

[negativeions24]

Bump. I was a part of that jam at the high school...gonna stay tuned and see how this turns out.

[EricssonB]

Meh. No replies! Think I'll just go ahead and swap out both've them capacitatinators. Care to tag along to Radshack?

[BassmanPaul]

Did you check the fuse lamp??

[will33]

Originally Posted by BassmanPaul

Did you check the fuse lamp??

+1

You can't check caps using resistance, they don't work that way. If you've eliminated all other possibilities just replace them with ones of the same value, they're pretty cheap.

[EricssonB]

Someone I work with suggested that I could by comparing on the other other. One of them showed the resistance posted above while the other was open. Rather than mess with it though, I decided that I'd replace them both. I can do the soldering, but I haven't been able to find any to match the specs.

I'm not entirely sure what to order according to the schematics. Ideas?

[will33]

The old caps should have the values printed on the side if you can still read them/not burned or worn off. The dayton caps at Parts-Express.com sells Speakers, Replacement Speakers, Speaker Building Parts plus HDMI Cables, Home Audio and Video, Pro Audio and Commercial Sound. We offer services for Speaker Reconing, Speaker Refoaming, Speaker Repair. Great selection of Elect are good for crossovers. I guess you could tell something was different if they read differently but that wouldn't tell you if they're good or not. They block low frequencies and allow highs to pass through but they're not supposed to pass dc which is what your meter uses to check resistance.

[will33]

Originally Posted by EricssonB

Someone I work with suggested that I could by comparing on the other other. One of them showed the resistance posted above while the other was open. Rather than mess with it though, I decided that I'd replace them both. I can do the soldering, but I haven't been able to find any to match the specs.

I'm not entirely sure what to order according to the schematics. Ideas?

Something with a value within 5% will work fine, most tolerances differ that much anyway, or you can put a couple smaller ones together to get the dead on value.

[EricssonB]

That's a great link -- appreciate it! I should order these when I get paid and post a followup!

[EricssonB]

This looks like the one! Thanks again!

Dayton Audio DMPC-3.3 3.3uF 250V Polypropylene Capacitor

[will33]

If you want to protect your tweet a little better you could add an inductor shunt to make it 2nd order, that'll cut the lows out of it at a steeper rate. For an 8ohm tweet at 4k that'd be a 3.5uf cap and a .45mh coil. That offers better protection than a single cap does set higher.


If all you're doing is highpassing the little tweet in a bass cab a simple crossover calculator like this one. 2-Way Crossover Designer / Calculator will get part values for you. Just look at the highpass side only, let the woofer get the full signal. Anything more complicated than that is a lot more involved than just plugging in numbers but it works fine for little bass cab tweets, the woofers have hogh impedance and no response up there anyway. Set a 1st order at 5k, second order or steeper at 4k.

If all that's too complicated just replace your cap with one of the same value and don't blast it with highs. Put a bulb fuse between the filter and the tweeter if there isn't one in there now.

[EricssonB]

You know, I hadn't considered changing that, but I might. There's plenty of room on the circuit card to throw in a part or two. I think for now though, I'll just replace them both one-for-one and just be more careful with my stuff. Should it happen again, I'll definitely consider changing it.

I blew out the diaphragm once a few years back, as told by the above story. That was mostly foolishness. So, once I get it fixed, I'll just make sure to not do that again.

And I'll be adding a cutoff switch, too, that will bypass the entire crossover unit and horn when I'm not using it.

[will33]

The switch is cool. The bulb should light up when there's too much power on the back side of the filter and hopefully you'll notice the light through the portholes and back off.