Need some advice on my Qb's power source

I was getting ready to do an A/B test on the Advent Laureates I just re-foamed. While warming up the AVR on the Qb's, I noticed something didn't sound right. I had played a couple hours of really loud stuff on the system a few days ago (Wife was out of town for the afternoon...). Now the Qb's just didn't have any highs. I pulled the fuses, and they looked intact. Pulled off the grills and the EMIT tweeters looked good, but were not producing sound. I had just checked the EMITs a week ago and they checked out to be right on spec. I feared the worst at this point.

Long story short - the 1 amp fuses were both blown. I'll pull one apart to see what happened later today. They sound fine with the new 1 amp fuses in place, and don't appear to have suffered any damage. I know the Qb had 1.25 amp fuses, but I went to 1 amp fuses to better protect them. Is my thinking correct there?

Here's where I need help. Did my receiver (in signature script) try to kill my Qb's? It did get quite hot after a couple hours, enough that I could smell it when I walked into the room. I had checked the EMITs a week or so ago, and they were right on spec. I'm reading a lot of comments about AVR's not being able to reliably push good speakers, and these Qb's are 4 ohm units.

I've been eying things like the Pioneer Elite SC-25 AVR. They have a better amp section than the old VSX series by far, but is that enough to run my Qb's for music? Do I really have to get a separate system to be able to enjoy these Infinitys?

1-replace fuse with 1.25's

2- AVR's are not really the best choice for 2 channel audio, lots of compromises to fit all that stuff in the case....

The AVR was too loud for the fuses. The fuses did their job and protected your tweeters. The 1.25 fuses were stock, use them but turn it down.

Perhaps your Pioneer doesn't play well with 4 ohm speakers and was overdriven blowing the speaker fuses.

Does anyone have a source for the 1.25A fuses?
I haven't found one.
I use 1A with my Infinitys as I'd rather they blow "early" rather than "late".

goodolpg said:

Perhaps your Pioneer doesn't play well with 4 ohm speakers and was overdriven blowing the speaker fuses.

Does anyone have a source for the 1.25A fuses?
I haven't found one.
I use 1A with my Infinitys as I'd rather they blow "early" rather than "late".

Click to expand...

Shoot - Amazon sells everything... http://www.amazon.com/Qty-1-25A-Fast-Blow-Fuse-AGC1-25A/dp/B004QIN3KQ

I think I'll stick with the 1 amp units too... Better safe than sorry.

I think my receiver sux... Now looking for a better power source. Really want only one system, but it needs to be Home Theater capable as well. Will look at newer (but still used, because I'm cheap) Pioneer Elite units. Maybe the Elite SC-25 or similar since it has a dedicated phono input. Need to look into whether any AVR can reliably drive the Qb's.

Spitfirejoe said:

Shoot - Amazon sells everything... http://www.amazon.com/Qty-1-25A-Fast-Blow-Fuse-AGC1-25A/dp/B004QIN3KQ

I think I'll stick with the 1 amp units too... Better safe than sorry.

I think my receiver sux... Now looking for a better power source. Really want only one system, but it needs to be Home Theater capable as well. Will look at newer (but still used, because I'm cheap) Pioneer Elite units. Maybe the Elite SC-25 or similar since it has a dedicated phono input. Need to look into whether any AVR can reliably drive the Qb's.

Click to expand...

Thanks for the link...I've searched previously and was not able to find 1.25A fast blow 1-1/4" fuses.
I thought they were unobtanium.
One more reason AK rocks!

I'm only guessing about your receiver. It's specs are for 8ohms, the Qb's are listed at 4 ohms. It may be fine, any mention in the manual or on the back panel about use with 4 ohm speakers?

check out B&K multiple channel amps...

goodolpg said:

I'm only guessing about your receiver. It's specs are for 8ohms, the Qb's are listed at 4 ohms. It may be fine, any mention in the manual or on the back panel about use with 4 ohm speakers?

Click to expand...

No manual - C List purchase. I've been unable to locate one online. I'm thinking we can say it is not stable at 4 ohm output. I'll play with it at lower volume some more, but looks like I'm going to have to upgrade.

My 2-channel Onkyo A-9070 feeds my Infinity RS-IIIa's w/o a sweat to insanely high decibel levels (I like my hard rock / progressive metal loud ). The amp pushes ~75 wpc at 8 Ohms, and ~140 wpc at 4 Ohms, at 0.05% distortion level:
http://www.onkyousa.com/Products/model.php?m=A-9070&class=Reference&source=prodClass

In short I have been very happy with this amp.

Now, Onkyo has some really nice looking multi channel AVR units that use some of the same tech (particularly WRAT, and H.C.P.S.) as A-9070 under the hood. Check out e.g. TX-NR838 which seems to be rated for 4 Ohms (see the 'Product Sheet'):
http://www.onkyousa.com/Products/prod_class.php?class=Receiver&source=globalnav

Although they do not list wpc's for both 8 Ohm and 4 Ohm loads which would indicate better how well it handles low impedance loads.

Let me finish by posting my favorite PDF on this topic, "JBL - Danger Low Power"
http://www.jblpro.com/pub/technote/lowpower.pdf

I wouldn't use 1.25A fuses if you want to protect the Emits.

Your Emits are OK because the 1A fuse.

Read all the threads about burned Emits, all of them had "1.25A" fuses and were blown, including mine. It´s a fact: the Emit tweeter can be burned before a 1.25A fuse. I don't know about the "fast blow" fuses, but I wouldn't risk my tweeters.

I use 0.75A fuses today.

clean power listening at reasonable levels, you shouldn't have to worry about this at all...jammin' at 3:00 with suspect power....pooof, sizzle...

Onkyo TX8522

Based on what you guys told me, I started looking for a "good" 2 channel amplifier or receiver to power my Infinity Qb speakers. On Craigslist this weekend was a Onkyo TX8522 with a pair of KLH "indoor/outdoor" speakers - all for $45. Sold! It's not a planet shaker, but should more than serve my needs. It is rated as stable at 4 ohms, and (if I read the specs correctly) the WRAT amplifier section should give me over 100 watts per channel.

I've decided to set up two systems.
1) The Onkyo and Qb's with a decent turntable and CDP for a dedicated music listening system.
2) An audio/video set up with my Pioneer stuff. The Pioneer AVR just won't handle the 4 ohm Qb speakers. I'll get a decent set of matched surround sound speakers sometime and pair those with the Pioneer. I may just upgrade the Pioneer receiver anyway. It was cheap enough that I can afford to get something nicer - maybe something with HDMI connections.

The KLH speakers will be perfect for our control room at work. My little Kenwood separates (KA1400G and KT1300G) are in there running 24 hours a day / 7 days a week. They are being fed by a Sirius satellite radio and pushing some crappy little "boom box" speakers.

So - good upgrades all around for a total outlay of $45.

100 watts is just right for those Qb's! I'm only feeding mine 75 and they sound really good. I think they were rated to 150 watts. Once I hooked them up to a "200" watt amp (that bench tested to 265!), got a little crazy and Jimi literally blew the metal traces right off of the tweeter! (Maybe those 1 amp fuses ARE a good idea! )