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Hum Problem

9/12/1998 9:11 AM
Hum Problem
This is in reference to a solid state amp - a Crate model G-40C...i know they're meant to be disposable! Anyway, when first turned on the amp hums for 2-3 seconds then the hum goes away.The amp seems to be ok after that. Any ideas?  
9/12/1998 2:33 PM

I could be way off base here. But I think its completly normal. I seem to recall the same thing in some solid state amps I have had in the past and other solid state equipment. I wouldn't worry about it personally, but I'm sure I be corrected if I'm wrong.  
Good luck  
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9/14/1998 6:46 AM
Could be a number of things. A delay of several seconds to several minutes is often indicative of a thermal-related problem where something shorts or opens or gets flakey or better after it warms up.  
Unfortunately, there isn't any good way to define it down to something you can fix easily in a solid state amp the way it is in a tube amp (per the Tube Amp Debugging Page). If it's usable, use it, just bearing in mind that at some point it will fail more solidly. If it isn't usable or the waiting bothers you, take it to a competent solid state tech.  
If YOU are a competent tech, watch the power supply voltage for excess ripple, then start walking through the amp input to output, looking for which stage the hum starts in. Once you have the source isolated, you can find the cause or shotgun it.
9/14/1998 2:58 PM

Carlo: I worked on a peavey that had a bad triac, it would make a transformer sounding hum, I don't know if your amp uses one of these but its a thought.[Richie]
9/14/1998 6:57 PM

Am too lazy to pull the schematic for the G-40C right now but I do warranty work for Saint Louis Music. Most problems that I see with these smaller models relate to poor solder joints, especially where the potentiometers and other front panel controls meet the circuit board. I you know what your doing you could pull the circuit board and remelt all the front control solder joints and those connecting power supply components (filter capacitors especially) and the speaker connections. Don't remember perxactly but many of the smaller crates use plastic standoffs that require compression by using needle nose pliers before you can remove the circuit board. It isn't too awful hard if you've done some electronics repair before but it does require a steady hand and skill.  
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