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Kustom Amp power on noise [message #1617] Mon, 17 June 2002 11:20 Anonymous I'm preparing to sell my 1969 K400B-1 6-15 Bass rig. The amp makes a loud noise when first turned on, like Grandpa clearing his throat. Any thoughts how I can clean this up? Thanks, Mike Report message to a moderator

Re: Kustom Amp power on noise [message #1622 is a reply to message #1617] Tue, 18 June 2002 09:34 C4ster Messages: 686 Registered: June 2001 Location: Mukwonago, WI (Milwaukee... Senior Member Mike, it all depends on what the noise sounds like EXACTLY!!!. All Kustoms and most solid state amps thump when they are turned on unless there is a delay relay built into the speaker output line. If the thump or noise lasts longer than 1/2 to 1 second, more info will be needed to diagnose the problem. I would probibly replace the filter capacitors first as the caps will degrade after 30 years or so. The rated life of electrolytic caps is only about 10 years. After the amp has been on for a period of time and the noise has subsided, you will hear a white noise hiss that is normal. Turn the amp off and listen for the hiss to stop. if it stops immediately, the caps are bad. If the hiss hangs on for about 3 to 5 seconds before stopping, the caps are good but they still could be the problem. The replacements will be slightly different, smaller in diameter and longer, and you may have to mount them in a different position or location. Good luck. Conrad Report message to a moderator

Re: Kustom Amp power on noise [message #1625 is a reply to message #1622] Tue, 18 June 2002 14:31 Anonymous Thanks, Conrad, I do hear the thump when turning on the amp, but this is MUCH more than that, and quite loud- sounds almost as if I took the guitar cable jack out of the bass and tried unsuccessfully for several seconds to re-plug it. I do recognize the white noise hiss, too, and it also does hang on for 3 to 5 seconds after switching off. The amp IS 33 years old, but replacing filter capacitors and electrolytic caps is a little beyond my ability. Would this be something any repair person could take care of, and is it serious? thanks, Mike Report message to a moderator

Re: Kustom Amp power on noise [message #1626 is a reply to message #1625] Tue, 18 June 2002 15:28 C4ster Messages: 686 Registered: June 2001 Location: Mukwonago, WI (Milwaukee... Senior Member Mike, I would suspect the filter caps are bad. I think you are hearing hum from the filter caps. Once the caps are charged the problem goes away. The filter caps smooth out the 60 hertz ripple and create the steady DC voltage needed for the electronics to work. I suppose the bridge rectifier could be bad, but once a diode dies it does not fix itself. Any tech could change the caps. I don't know what model your amp is. The model number is on the back, in the lower left hand corner. It should start with a K100, K200 or something like that. That would give a little more info. Conrad Report message to a moderator

Re: Kustom Amp power on noise [message #1627 is a reply to message #1626] Tue, 18 June 2002 15:33 C4ster Messages: 686 Registered: June 2001 Location: Mukwonago, WI (Milwaukee... Senior Member Ignore the part about the model number. I just reread your first post. Do both sides of the amp make the same noise when turning on? There are 2 separate amps in that head, stereo if you will. The common thread between the 2 sides is a common power supply. If both sides do the same thing, I definitely would replace the caps and the bridge just to be sure. Conrad Report message to a moderator

Re: Kustom Amp power on noise [message #1628 is a reply to message #1626] Tue, 18 June 2002 15:34 Anonymous The model is K400B-1. This is really helpful info, much appreciated! Mike Report message to a moderator

Re: Kustom Amp power on noise [message #1744 is a reply to message #1617] Sat, 03 August 2002 08:49 atch1951 Messages: 1 Registered: August 2002 Location: Clearwater, FL Junior Member Mike, These guys all told you right. The growl you hear is most likely one side of the power supply reaching full voltage before the other does - you're hearing "d-c" on your speakers. Replacing the large caps in the power supply should fix it. And yes, any audio repair tech (music store tech) should be able to do it for you. DaLe Report message to a moderator

Re: Kustom Amp power on noise [message #1787 is a reply to message #1617] Mon, 19 August 2002 07:37   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member If you have not repalced the bridge rectifiers yet, do so, but get 4 fast recovery rectifiers or (FREDS for short) to make up the bridge.They cost more but difference in tone and clarity will more than make up for the cost! Report message to a moderator

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