My good friend has recently came across a B&K 7520 Series 11 amplifier...worked great for a few weeks and then ran into a problem the other night. Seemingly, he was watching a show and then encountered a loud pop...center channel ran away on a siren type noise and then he shut the system down. He left for a couple of days and returned to turn the unit on and then encountered a white noise sound emitting from the center channel then the B&K lost power...the dreadful smell of electrical malfunction was present.
The funny thing about this is that he is not pushing the amp to anything close to it's limits...rather each channel is turned WAY down on the amp and the individual channels from the pre-amp are allowing a great deal of headroom.
He was able to remove the fuse from the back and we inspected it. No telling the condition of the fuse as it is coated from the factory in a matte finish and does not allow a clear view to the inside condition of the fuse. the plan is to obtain a new fuse this morning.
In closing, I am curious to know if anyone in the forum has had a problem with an amplifier like this? Is the channel that he using for his center toasted?
Any help/ideas would be great. Thanks in advance and have a great weekend Polk folk.
Can you give more details on why he's running the gain controls on the amp way down? The B&K amps from that generation are designed to be run normally with all gain controls at maximum, and was only equipped with individual channel gain controls to allow custom installers flexibility in balancing speaker volume in different applications. Under normal use these days, the volume levels are controlled only from the preamp. My guess is, he was clipping the output signal from the preamp by running it too high. Hopefully, a new fuse is all that's needed.
The individual settings on the back of the amp were set low for two reasons...
1). He is using entry level speakers that really do not even need to be ran with this kind of power.
2). The system is in a bedroom that is 12x10...small space and figured that he did not need to run the system at a high level.
Each channel on the back of the B&K is set just above half. The settings for each channel on the Marantz pre-amp are very low with the exception of the center which is 3db's hotter than the rest of the channels.
that doesn't sound like any easy fix.. i'd take it in for service to a qualified service center... sounds like some serious power issue with the amp. good luck.
Sure doesn't seem easy at all...this model is known to be damn near bulletproof. From the looks of things, there is a main fuse on the back and two for each channel on the inside. While a fuse may be an easy fix, who is to say that this will not happen again.
I have had great help from this forum and thought that someone might have had such a similar issue. Thanks.
Emlyn hit the nail.
The owners manual clearly states to run full gain on that amp.
"When using the level controls, first start with them turned all the way up (clockwise).
Then adjust them according to your system requirements to match the sound level
coming from each speaker. This is a rough adjustment for matching different driver
impedances. Any fine tuning should be done by the preamplifier"
Most problems happen when people don't know how to setup seperates correclty
Agreed, the fact that there was the smell of burned components would indicate something more serious than just a blown fuse.
Originally Posted by danger boy
Apparently your spelling is not quite as good as your home audio opinions...like I would trust a guy who does not know how to spell the words *separates and *correctly.
Originally Posted by mantis
On a better note, I thank you all (sans the retard who cannot spell) for your help. I set up a meeting with a B&K retailer here in La Jolla, CA. Take care and have a great weekend.
good luck with your B&K it's really nice gear.. hope it's nothing to costly with your gear
FYI: Tell your friend that he will probably get the best service by sending the amp directly to B&K in Buffalo, NY. They know these inside and out and their repair rates are very reasonable. I sent a 2ch amp and pre there for repairs and the total repair was only $250 included the return shipping (for 2 components).
EDIT: I forgot to mention, B&K will often upgrade certain components while at their shop and overall improve the unit. My amp came back with a newer case that had better venting, no charge. They also removed some relays that were "problematic".
Originally Posted by Meechsterlee
Many Polk members are likely to spell poorly on the weekends.
Has something to do with alcohol....
B&K does have a very good repair service. I would also check the center speaker.
B&K amps don't just stop working for no reason.
I would hate to see the amp repaired, then have a repeat problem.