Infinity Qb problem

Natrik

Natrik

Member
Hello, I have a set of Infinity Qb's with an intermittent problem. The high end cuts out now and then, but the weird thing is, the tweeter doesn't cut out completely. While the music is playing, every once in a while it sounds like someone threw a blanket over the speaker. When it happens, I put my ear up to the individual drivers, and the Emit is still working- it's just muted. I thought the problem was with the crossover caps, so I replaced them and cleaned the midrange L-pads. The problem is still there. I narrowed it to the speakers and not the amp or the input by using a different set of speakers, and the problem never happens unless the Infinity speakers are hooked up. Could the fuses be the culprit? I cleaned the fuse holders with DeOxit and they hold the fuses tight, and rotating or wiggling them when the problem is happening doesn't seem to help. I took the Emit tweeters apart and re-melted the solder connections as well, and that didn't seem to help. Any ideas would be greatly appreciated.
 
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My Qb's only have a midrange level control, no tweeter level control. The midrange control is dead quiet and works just as it should after cleaning.
 
The EMIT on one of my RSII's quit shortly after I bought them...checked a bunch of stuff (won't bore you with the details) but it ended up being a problem with the fuse holder.
It's possible it's the fuse too. They are cheap, why not buy some spares and pop one in and see if it fixes the problem.
If you can't find 1-1/4 amp it's ok to use 1 amp....auto parts stores may have them.

Interesting how Infinity made Qb's with AND without tweeter controls.
And yet the RSa has mid and treble controls while not actually having a separate midrange driver.
 
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Does the same thing happen with both speakers? Does it happen independent of the volume that you're listening at?
 
It has happened with both speakers, but it's usually just the one. And yes, it happens at any volume. I suspect the fuse holder/fuse. I think I have a couple fuse holders somewhere, I may mount one inside each cabinet in place of the originals and see what happens. It seems like the only variable left.
 
I bet it's the tweeters. I had a pair of Qa's way back in the day. I was used to cranking my previous, bigger speakers (BIC Venturi 6). I played the Qa's too loud and they developed the symptoms you describe, first on one side only. I returned to the local seller and the guy ran into the stock room and emerged with another tweeter for me. Maybe it was a common problem. It was not long before both the new one and the other original were cutting in and out. The Qa was more vulnerable than the Qb, being a two-way and having only a blocking cap, not a good idea with a leaf. Stereo Review used 1000 watt tone bursts for testing, but that does not tell you much about real power handling. I did not know that at the time. I eventually threw in a couple of phenolic ring (cone) tweeters and sold them cheap to a friend of a friend. I told him the complete story first.
 
A couple things to try.
Bypass the fuse.
Remove the tweeters and measure with a multimeter for ohms resistance.
Remove the tweeter and introduce an audio signal to produce continuous sound, or not.
 
May be an intermittent in the diaphragm wiring that is heat or use dependent. Probably a warning that you may have to start looking for a new diaphragm or tweeter.
 
Thanks for the replies! I bypassed the fuses to remove that variable completely, and one speaker is still doing it- although it's much more subtle and faster to return to normal... just enough to annoy the sh*t out of me. I have a feeling it's the tweeters. At least they're available on eBay pretty regularly.
 
goodolpg said:
The EMIT on one of my RSII's quit shortly after I bought them...checked a bunch of stuff (won't bore you with the details) but it ended up being a problem with the fuse holder.
It's possible it's the fuse too. They are cheap, why not buy some spares and pop one in and see if it fixes the problem.
If you can't find 1-1/4 amp it's ok to use 1 amp....auto parts stores may have them.
Click to expand...

Agreed. You would be surprised how hard it is becoming t find this type of fuse though.
 
goodolpg said:
The EMIT on one of my RSII's quit shortly after I bought them...checked a bunch of stuff (won't bore you with the details) but it ended up being a problem with the fuse holder.
It's possible it's the fuse too. They are cheap, why not buy some spares and pop one in and see if it fixes the problem.
If you can't find 1-1/4 amp it's ok to use 1 amp....auto parts stores may have them.
Click to expand...

nclh77 said:
Agreed. You would be surprised how hard it is becoming t find this type of fuse though.
Click to expand...

Is this fuse the typical for the day 3AG glass fuse, 110V or 32V? Normally a 1.25 amp fuse?
 
nclh77 said:
Agreed. You would be surprised how hard it is becoming t find this type of fuse though.
Click to expand...
For a long time I didn't think 1-1/4 Amp fuses were available. They are but may have to be purchased online.
1 Amp fuses are readily available and several Infinity owners use them based on availability and possibly quicker protection in event of catastrophy.

For mech986, the OEM fuses are 1-1/4 amp, 250 volts, 1-1/4" long round glass fuses

Note: for speaker protection use fast blow fuses unless specified otherwise by the speaker manufacturer.
 
Those EMITS can have bad solder joints where the wire connects to the terminal inside the tweeter. I had one like that, reflowed it, worked fine. Worst part is disassembly/reassembly. There is a thread on how to do it without smashing your fingers between the magnets or breaking them.
 
In case anyone was wondering, I pulled the diaphragms again and tested them. When I had pulled them out to re-melt the solder joints a couple months ago, the resistance was 3.6-3.7 ohms on both diaphragms. The first one I tested now was 1.7 ohms. After having my meter clipped to the connectors for a couple minutes while I furrowed my brow trying to explain the reading to myself, the resistance slowly climbed to 17.3 ohms. Now I'm baffled. I used a magnifying glass to inspect the traces, and while I was poking around the resistance dropped back down to 3.7. Since there isn't any visible damage that I can diagnose and repair, I gave up and ordered a replacement set of EMIT's off the bay. What a strange problem.
 
I used a later pair of EMIT's because they were half the price of the chrome ones. I'm impressed at the quality of these compared to the chrome ones. The diaphragms are perfectly flat, not wavy like my old ones or the ones from the Qa's I had years ago. The connections are better and the rear housing is a much better design. The magnets in the rear housing are twice the size of the old ones. They sound and look great. I'm very happy with the upgrade. IMG_6037.JPG
 
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