artto Posted October 16, 2015 Share Posted October 16, 2015 I have a Crown D-150A that, when turning it off, produces a high pitched "whistle" with a descending pitch as it fades in volume until silent. This takes maybe a second or two. Any idea whats causing this? Other than that it seems to work fine. At the time it was hooked up to Khorns or Belle Klipsch. Quote Link to comment Share on other sites More sharing options...
babadono Posted October 17, 2015 Share Posted October 17, 2015 I'll bet DJK will have a more definitive answer but it sounds like one or more stages in the amp is unstable (or becomes unstable) as the power rails are dropping and goes into oscillation. Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted October 17, 2015 Share Posted October 17, 2015 Considering the symptom and age of this model especially if still using original electrolytic capacitors I would suggest the following as a starting point. (1) If this happens in both channels I would check the main power supply electrolytic capacitors. (2) If only one channel check any electrolytic capacitors dedicated to that channel. I've not serviced any Crown amps so maybe someone with experience of this model can give you more suggestions. miketn Quote Link to comment Share on other sites More sharing options...
djk Posted October 17, 2015 Share Posted October 17, 2015 The main filter caps are drying out, tack a pair of 22µF electrolytics across the main filter caps and it should stop the noise (unless you want to throw money at it and replace all the electrolytics). Quote Link to comment Share on other sites More sharing options...
artto Posted October 17, 2015 Author Share Posted October 17, 2015 The main filter caps are drying out, tack a pair of 22µF electrolytics across the main filter caps and it should stop the noise (unless you want to throw money at it and replace all the electrolytics). Thanks! Actually, I want to sell it. I just want to make sure that there's nothing super wrong with it and I can inform whoever wants to buy it of it's condition and what's required. Personally, I don't want to mess with it. I haven't used it for years. Quote Link to comment Share on other sites More sharing options...
Wolfbane Posted October 17, 2015 Share Posted October 17, 2015 Did you bring this amp out of storage plug, hook it up and turn it on, or power it up slowly with a Variac? Quote Link to comment Share on other sites More sharing options...
artto Posted October 18, 2015 Author Share Posted October 18, 2015 Did you bring this amp out of storage plug, hook it up and turn it on, or power it up slowly with a Variac? No. I bought this amp used a long time ago (25+yrs?) for use on a Belle Klipsch center speaker, mainly for things like background music & parties instead of using (wasting) my Luxman MB3045 triodes for non-serious stuff. It has done this since I bought it. Never seemed to have affected the sound. Just whistles quietly on turn-off for a moment. I'm well aware of the cap re-forming process. But that seems to be much more important with tube amps than solid state. Quote Link to comment Share on other sites More sharing options...
djk Posted October 19, 2015 Share Posted October 19, 2015 Waste of time now, once it has been hit will full mains voltage. If you want to keep it, replace all the electrolytics, if you want to sell it, just add the 22µF. djk:http://www.diyaudio.com/forums/solid-state/127122-crown-d150a-problems.html djk:The link to the service data has been changed.http://adn.harmanpro.com/site_elements/resources/954_1425419036/D-150A-Service-Manual-Part-2-d150a_service_manual_part2_original.zipConsider replacing C4, C5 as well.The D150A now has the same circuitry as the DC300A, and no caps in the signal path. Quote Link to comment Share on other sites More sharing options...
babadono Posted October 19, 2015 Share Posted October 19, 2015 So its always been unstable at turnoff? How old was it when you got it? Now I'm really curious. I hope you do one or the other of DJK suggestions and report back. Quote Link to comment Share on other sites More sharing options...
djk Posted October 20, 2015 Share Posted October 20, 2015 Crown had problems with that, even when new. Some of the factory bulletins had you adding a 5µF to one rail. (Note: some D150 had 0.22µF on the positive rails, nothing on the negative, others had 0.22µF on the positive, and 0.1µF on the negative) Do a pair of 22µF for both rails. Quote Link to comment Share on other sites More sharing options...
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