Amp for Infinity QB

I never had QBs, only QAs, but I had them hooked up to my Heathkit AA-1800 (450 watts/channel into 4 ohms) and they played load and clean. You don't need anywhere near that much, though - a decent vintage 50 watt/channel amp would probably be OK in most instances.
 
I have RSM's, similar era (one series newer than yours) and style (3 way with EMIT).
I ran them with a Lafayette LR-9090 (90wpc) and a Lafayette LR-120DB (120 wpc) as well as an MCS 3125 (125 wpc).
All seemed to work well.
It might be wise to use an amp or receiver rated for 4 ohm usage though they aren't known amp killers like some of their bigger brother Infinities.
 
Nice speakers! They were my first pair of "real" quality speakers. They like some power, say 45-75 watts, to sound their best. They were rated 15-150 watts, and have a sensitivity of 89 dB. They sound better up off the floor, Infinity recommended one foot (30 cm) high , they made an optional stand for them too. Infinity also recommended that they were two feet away from the walls.
 
Thanks! I'' definitely looking to have them on stands. If anyone has a pair of original or otherwise stands they need to get rid of--hit me up! Thanks for amp recommendations--keep 'em coming!
 
I've owned Qb Infinity speakers since I bought them new in 1978. Used them for a few years with a 40wpc receiver and they sounded pretty decent. But when I moved up to a 110wpc amp, they really opened up.

Personally I would suggest an amp with 100wpc minimum capable of tolerating lower impedances.

I will say I have not grown bored with these. I still enjoy the sound they make.... they do a superb job.

One more note. Fairly early in their life the bass started sounding terrible. I traced it down to..... bad joints in the cabinets. They were leaking air. Acoustic suspension speakers must be airtight. Once those were sealed back up all was well, and has been ever since.
 
I'll second the idea of re-sealing them. I found a used pair with the baffel glued on one side only! I'd replace the silver 12.5 uF cap on the mid range circuit, it's toast by now. But leave the yellow film cap on the tweeter, they last forever and give part of the "Infinity sound".
 
Chef! Just saw an old post about your Qb set of four and your Mac 4100! Jealous! I bet that is a great match! I actual wonder if my Kyocera 861 would be a good match... I don't have the Qbs yet or i'd tell ya :)
 
I'm cheap, but I found a Pioneer SC-1222-K for under $200 locally and snapped it up. These have a Class D amp design that is rated for 4 ohm speakers. I had heard that good power really let's the Qb "Open Up", and I have to concur. They've never sounded so good, and I too have had this pair since 1978. I recently worked them over - sealed and braced the cabinets, and recapped the crossover per Chef Free's advice. The drivers were still in good shape, which was a relief. That work brought them back to what made me fall in love with them originally, and the new receiver really makes them come to life.

One other piece of advice - use 1 amp fast blow fuses in those. You really don't want to fry the Emit tweeter.
 
So initial options to the power the QBs, for me locally, at the moment a Pioneer a77x (100w) a Kyocera 851 (100w), Phase Linear 400 (200w) which seems like overkill or my current HK 770 (75w). Any thoughts on those?

I might save up for a McIntosh 2505 or something similar but for now that's what I'm looking at. Still open to thoughts and suggestions!
 
Hey guys my Infinity QB source fell through--so I am now looking for another pair. Let me know if anyone knows of an available pair?
 
on the Carver, make sure you have it tech'd, it's 25 years old now, but run, don't walk to buy it, or link me the amp and I'll buy it!
IMO, Carver and Infinity goes very, very well together.
 
ya it is from a reputable tech actually.... despite its 92' release date these are a bit newer than the "vintage" gear i've been reading about and becoming familiar with and wasn't sure these carvers have the same reputation but i love the design and simplicity of this unit--and if a good match for those power hungry QBs!!
 
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You may have done this already, but when considering all those amps, look at which ones are rated for a 4 ohm load and how close the 4 ohm output is to 2x the 8 ohm output. As I understand it, that's a fast way to evaluate whether you are looking at an amp capable of high current delivery.
 
You may have done this already, but when considering all those amps, look at which ones are rated for a 4 ohm load and how close the 4 ohm output is to 2x the 8 ohm output. As I understand it, that's a fast way to evaluate whether you are looking at an amp capable of high current delivery.

Good Point crusadr. So when folks say I need a 100w min to power the QBs are we talking 100w x 4ohm output? So I'm really looking for a 200w 8ohm amp that can handle 4 ohm loads right?
 
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