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About mtarr

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  1. Dolores, I just fixed my amp, same symptoms. I changed C4 and C5. -Morty
  2. Hi Lou, I changed C5 and it worked for about a week (C5 was open, both times). I then changed C4 and C5 and it seems good. Occasionally, I hear what might be a low level oscillation in one channel. Each time I was ready to debug, it was not there. To answer your questions, the buzz was there all the time, even when the inputs were disconnected. It did not get appreciably louder with the input pots turned up. The input stage is not blown, but it is not ruled out as the source of the possible oscillation. Thank you for your help, Morty
  3. I have a Crown DC300A that I bought new in 1975. This amp has lived a comfortable life in my home for the past 30 years. It has performed well for a long time. Over the past year, it has developed buzz and hum in both channels. The output is also distorted. Since sound does get through, I'm thinking that the output stages are still good. Also, when I turn the unit off, it takes about a minute for the amplifier to stop driving the speakers, so I think the 13,000 uF main filter caps are also still good. I would like to repair the amp; I have some experience repairing audio equipment. I know that it is easier to cause more damage than to get it right. I am concerned about damaging devices that are still good and are difficult to find today. I have not started to debug the problem. I have two questions: 1. What is the most likely cause of buzz and distortion on both channels? The buzz seems a little louder on one channel. 2. Is there a way to current limit the power stages to minimize the chance of causing damage to them while I'm working on the amp? With some amplifiers I have been able to add current limiting resistors in series with the V+/V- supplies to the power PCB. If that is possible, what values/wattage do you recommend? Thank you, Morty