2. amps-preamps
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Recurring Channel Loss on Power Amps

I have a recurring problem where my power amps keep losing a channel. I am wondering if it is just sheer bad luck or if it is possible that something else might cause this. Here is the story:

I am powering Celestion SL6si's (84 db sensitivity) using a Rotel RB991 bought new in 1998. I lost a channel on it 3 years ago and had it repaired. I then lost a channel this Spring and had it repaired again. After getting it back it blew a channel again within 3 months.

My backup amp was a Carver TFC50 bought in the mid 90's but seldom used. That also blew a channel this Fall while the Rotel was in the shop. Down to no power amps I bought an ancient Bryston 4B off Craig's List a month ago. It has now also lost a channel. The Bryston has a bad transformer hum so I know it is not in stellar shape.

Am I just overdue for some newer equipment or is there something in my setup that might be causing this? Other pieces of the system are:

Acurus RL11 pre-amp
Arcam Alpha 8 CD player

Any thoughts are appreciated.
sruffle
8 responses Add your response
ths364
181 posts
 
Hi, Are you losing the same channel every time? How loud were the amps playing at failure, and what was the nature of the failure e.g. Smoke? Bang? suddenly went quiet? Could be a number of things: Intermittent short in speaker cable or inside the speaker itself (check to be sure binding posts are tight, and no loose or stray wires at connecting points on both amp and speaker end), pre-amp may be putting some dc voltage into the power-amp (could be from the pre-amp or the cd player -you should be able to check this with a digital voltmeter -even a cheap meter). Could also be an arced voice-coil or crossover component. More info would help narrow it down.
sruffle OP
57 posts
 
I am not playing it loud or getting any smoke or noises, the channel just disappears. I can't be 100% sure but it seems to be the right channel. I have checked all the wire connections and tested both speakers to make sure it is in fact the amplifier.

Do you suggest that I buy a digital voltmeter to check to see if the CD player and preamp are doing something funny? Thanks for your input.
sruffle OP
57 posts
 
Edit to my previous post: the right channel is out this time but I am not sure if it is always the right channel that has gone out.
ths364
181 posts
 
Yes- I would check the preamp outputs for d.c. Procedure would be set voltmeter to DC volts, pre-amp on, volume at zero, set input selector of pre to an unused input (preferably cd or aux. input), (assuming rca style inputs) put the black test lead from the meter to the outer surface of right channel output, red test lead to the center of the input jack (you can use the input cable if you can't make contact with the center contact of the plug). You should have a reading near zero. Check the other (left) channel also. More than a few millivolts, or a large difference between the two channels would indicate a problem. Millivolts will read as follows example: .005 would be 5 millivolts, .010 would be 10 millivolts, .100 would be 100 millivolts.
sruffle OP
57 posts
 
Excellent. Thanks for the detailed advice. I will give that a shot.
glenner
28 posts
 
My brother just had this problem with his Rotel Integrated amp where his left channel blew.Opened it up to see that the fuse was blown.He replaced that,turned it back on and was fine for a few moments and it blew again.He eventually realized after much frustration that the only new thing he introduced was his IPod to his setup.He checked his RCA cables between IPod and amp to find a short in the cable.He changed the cable and has had no further problems.So long story..SHORT(pun intended),as mentioned,check all your cables and maybe test with other speakers.
sruffle OP
57 posts
 
Glenner, Thanks for that suggestion. I will give it a try.
sruffle OP
57 posts
 
I don't post much but I did want to resurrect this thread to thank all of the folks who responded. After several more blown fuses and another blown channel on an amp, I figured out the problem. The amp was on the same circuit as the TV and my other components. I moved the amp to another circuit and have not had any problems for the last 12 months.

That was a good lesson learned.
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