Do I Rebulid Infinity Qb's?

[mohare134]

Hello All,
Need some advice; I found a pair of Infinity Qb's at the curb-side store...initial look is they're in pretty good shape, then I tested them with mixed results. I took them apart and discovered they've been WAY overdriven to the point that the plastic controls plate melted inside from the 8ohm 10W resister and the mid-range potentiometer on the x-over getting way too hot (their insides are melted). The EMIT's are both shot too...one just needs a new diaphragm, but the other has broken magnets. Both woofers and midrange speakers are Ok (sound good and tested with ohm meter)

In total, I'm looking at like almost $150-200 to restore them (including finishes).

So my question is, are these worth restoring? I have some spare tweeters from SL-30's, but would I just be wasting my time since they wouldn't have the same sound as the EMIT's?
tks

 

[toxcrusadr]

That's getting up to the point that you won't get out of them what you put in. Not to mention the labor. Of course that's not the goal always.

Sounds like you need a parts pair to get those melted panels. Or, part em out to get others running that need woofers and mids.

 

[goodolpg]

They really should have EMIT's.
Qb's are well regarded.
If you are going to keep them it might be worth the effort to make them right.
No idea how easy or difficult finding replacement l-pads would be. I suppose you could bypass them with fixed value resistors.
If you want to discuss their $ value you need to do that in Dollars and Sense.
Buying and selling is only allowed in BarterTown, a paid subscription ($25) area.

 

[mohare134]

Thanks for your input! I'd really like to see how these sound on my NAD 2200...so maybe they'll be a slow restore

 

[BilboBaggins]

That would be a good amp for them. They are power hungry speakers that do their best with high current amplifiers. All the infinity I've tried are like that. NAD seem to do them quite well, although I've never tried that particular model with them, or even heard that model. But I've had a good range of the 70XX, 71XX, 72XX, C372, and C320BEE. They give the Qbs what they need. If you can, try buying a Qb crossover pair. You might be able to get a combo deal from someone parting a pair out. That would eliminate needed to find a replacement, and they do show up from time to time.

 

[mohare134]

Thanks for your insight.
I'm a big fan of the older model NAD's like the 2200 and 2700THX...these were powerhouses. I find them and repair/upgrade them. I have a hard time finding speakers that can even challenge these amps.
Here is a dyno test of the 2200 on YT

 

[tubed]

Hello All,
Need some advice; I found a pair of Infinity Qb's at the curb-side store...initial look is they're in pretty good shape, then I tested them with mixed results. I took them apart and discovered they've been WAY overdriven to the point that the plastic controls plate melted inside from the 8ohm 10W resister and the mid-range potentiometer on the x-over getting way too hot (their insides are melted). The EMIT's are both shot too...one just needs a new diaphragm, but the other has broken magnets. Both woofers and midrange speakers are Ok (sound good and tested with ohm meter)

In total, I'm looking at like almost $150-200 to restore them (including finishes).

So my question is, are these worth restoring? I have some spare tweeters from SL-30's, but would I just be wasting my time since they wouldn't have the same sound as the EMIT's?
tks

You might be able to epoxy the broken Emit magnets in place.
Remove the diaphragm from the non-working one and scotch tape a tiny slice of foil in order to "bridge" any breaks in the racetrack traces.
And as mentioned above, bypass the bad potentiometer.
If that works out perhaps replace the midrange capacitor.
You might get lucky.

 

[goodolpg]

I bought a couple sets of crossovers off ebay, mostly for spare L-pads after a search for OEM spec'd ones wasn't all that successful. So that is a possibility.
Aftermarket EMIT pot wasn't that hard to find but the only midrange pot properly spec'd I found was HUGE. And pricey if I remember right.

 

[elnaldo]

I own a pair of Qbs, completely restored, including new cabinets with real wood veneer, new stands. $$$$$$$$$$ invested, but those speakers are not available down here where I live. Just last month somebody offered me $ 1K to buy mine, and of course my answer was No.

If you have access to buy another pair of Qb, I think it will be easier and cheaper to buy a working pair.

I'd do some math before starting the project.

 

[mohare134]

So it's been a year and I wanted to provide an update. I wound up restoring the speakers. I only have the veneers to finish and make new grills and I can call them done. I rebuilt the x-overs with new products to match, however I did go with a larger (voltage capacity) L-Pad from Parts Express. I also took reference from some of the other posts regarding the QB's and reinforced the interior and resealed them. I repainted the faces too. I did kinda cheat with the tweeters and went with EMIT-K's instead of the original EMIT's...so I guess they're not considered QB's any more... Here are some pics. Oh, I also had the stands custom built by my brother-in-law (owns a machine shop) per the spec of the original stands...painted them matte black.

 

[AudioGMan]

I had a pair of Infinity Qb. They were in pretty good condition. Nothing wrong with any of the drivers or pots. Listed them for $200 on CL and they took a long time to sell. Almost a year. I would lower the price by $10 at a time until finally someone bought them for $120.

 

[mohare134]

I found mine on the curb...honestly I wouldn't have bought them operational. It was more about taking something dead and bringing it back to life. Qb's were never on my radar because I didn't know about them. Only learned about them in forums. Now that I have them, I can't believe what I was missing using book shelf speakers for my mains...now the bksf speakers are my center channel.