Hi everyone, i just joined this forum today .Problem is my quest for a perfect Music / home cinema system has landed me in a spot of bother.
My 5.1 system comprises of a krell kav 250a for my klipsch RF82 front speakers , My Klipsch surrounds Rs -42 are currently driven by a rotel rb1050 and so my yamaha dsp ax-761 only acts as a pre -out and drives the Klipsch centre channel . I have had this yamaha for eternity.
I use to have an active sub but I got rid of it and obtained a large 15" subwoofer. I have also managed to come across a vintage Rotel Rb 890 which I thought would be perfect for it.
PROBLEM
The problem is when I tested it I found out that the left channel was operational but had a distinct low freq hum. I downloaded the manual for this amplifier and started looking at it, Initially I thought it was either an earthing problem or a capacitor issue , so I started ruling each out.
1) for the power supply capacitors I simply swapped the 2 independent power supply +71V supplies and removed fuses on the good channel , the hum was still there😕 .
2)I checked all the earthing connections I could see , nothing appeared loose ,or out of the ordinary.
3) I then disconnected the soldered pre out cables on the channel and all hell broke loose . when I switched it on , it smoked my subwoofer with the hum and blew all the 2 fuses on that channel, from the corner of my eye I also saw a tiny 150pF capacitor glow(C615)
Now I , didn't major in Electronics bit I do know that with no input signal signal an amplifier should have no output.Does anyone Know whats happening ?
Can anyone Please enlighten me ??
I would appreciate it , very much
My 5.1 system comprises of a krell kav 250a for my klipsch RF82 front speakers , My Klipsch surrounds Rs -42 are currently driven by a rotel rb1050 and so my yamaha dsp ax-761 only acts as a pre -out and drives the Klipsch centre channel . I have had this yamaha for eternity.
I use to have an active sub but I got rid of it and obtained a large 15" subwoofer. I have also managed to come across a vintage Rotel Rb 890 which I thought would be perfect for it.
PROBLEM
The problem is when I tested it I found out that the left channel was operational but had a distinct low freq hum. I downloaded the manual for this amplifier and started looking at it, Initially I thought it was either an earthing problem or a capacitor issue , so I started ruling each out.
1) for the power supply capacitors I simply swapped the 2 independent power supply +71V supplies and removed fuses on the good channel , the hum was still there😕 .
2)I checked all the earthing connections I could see , nothing appeared loose ,or out of the ordinary.
3) I then disconnected the soldered pre out cables on the channel and all hell broke loose . when I switched it on , it smoked my subwoofer with the hum and blew all the 2 fuses on that channel, from the corner of my eye I also saw a tiny 150pF capacitor glow(C615)
Now I , didn't major in Electronics bit I do know that with no input signal signal an amplifier should have no output.Does anyone Know whats happening ?
Can anyone Please enlighten me ??
I would appreciate it , very much
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PROBLEM SOLVED
After numerous tests, I replaced all the output transistors type B817 and D1047 and biasing transistors, cost less than $30. she's as good as new and sings like a canary. Drives that subwoofer like its gonna tear it .
After numerous tests, I replaced all the output transistors type B817 and D1047 and biasing transistors, cost less than $30. she's as good as new and sings like a canary. Drives that subwoofer like its gonna tear it .
Hard to say what you have done exactly...
Unsoldering the output leads could have floated a ground somewhere and as a consequence the whole thing was unstable.
Are you sure the 150pf cap was glowing 🙂 What is its function ?
If the bias current was high (originally) then that can influence the amount of audible hum present. Have you checked the bias current now ?
Unsoldering the output leads could have floated a ground somewhere and as a consequence the whole thing was unstable.
Are you sure the 150pf cap was glowing 🙂 What is its function ?
If the bias current was high (originally) then that can influence the amount of audible hum present. Have you checked the bias current now ?
Rotel Rb890.
Maybe not I was so freaked out I could have been seeing stars , I replaced it anyway. Thanks.
Maybe not I was so freaked out I could have been seeing stars , I replaced it anyway. Thanks.
Maybe not I was so freaked out I could have been seeing stars , I replaced it anyway. Thanks.
PROBLEM WAS SOLVED !!
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