I just picked up an AKAI AM-2400 integrated amplifier (circa 1978). The seller said that it worked well. I took a look inside and examined the capacitors, they all look to be in good shape. I hooked it up and it sounds really good. I noticed a static discharge when I touched the faceplate. It seemed to happen after a few minutes since a previous touch. It seemed a bit annoying so I thought about grounding the amp. (The electrical chord is only a two pronged (unpolarized) type used back in the seventies.) There is a ground terminal on the back of the amp. The manual says to connect that terminal to a metal bar buried in the ground. Well, I don't have access to that, but I thought I do have the ground for the house's electrical system. So I bought an insulated wire, took a three prong electrical plug, removed the two prongs for AC, attached the chord to the ground prong, and plugged it in. When I turned the amp on, I got a terrible hum. So I turned it off, unplugged the chord from the wall and turned the amp back on. No hum. I also do not get the static discharge anymore.
Can anyone tell me why I get a hum when I plug in the ground like that? Also, is there any efficacy in having a six foot insulated wire connected to the ground terminal on the amp? It seems to have stopped the static discharge or is that just a coincidence?
Thanks for your thoughts.
Jazzzman
Can anyone tell me why I get a hum when I plug in the ground like that? Also, is there any efficacy in having a six foot insulated wire connected to the ground terminal on the amp? It seems to have stopped the static discharge or is that just a coincidence?
Thanks for your thoughts.
Jazzzman
You might want to get one of these..
Home depot or lowes have them... 6-8$
They will show reversed polarity , bad ground , some have
a ground fault test button on them... they are 10$.
Also try different outlets in your house (not the same room),
if the idiot wired the first outlet in the branch (circuit)wrong ,
all will be wrong.
OS
An externally hosted image should be here but it was not working when we last tested it.
Home depot or lowes have them... 6-8$
They will show reversed polarity , bad ground , some have
a ground fault test button on them... they are 10$.
Also try different outlets in your house (not the same room),
if the idiot wired the first outlet in the branch (circuit)wrong ,
all will be wrong.
OS
What a strange way to do it !
My guess is that the chassis is not insulated from the 0V point in the amp, and that's why earthing it generates hum.
You could look inside for capacitors from line/neutral to ground. Sometimes these are fitted, and IMO it is a dangerous practice. I've also read of designs where the neutral is bonded to the chassis! This can be tested with a simple resistance meter.
My guess is that the chassis is not insulated from the 0V point in the amp, and that's why earthing it generates hum.
You could look inside for capacitors from line/neutral to ground. Sometimes these are fitted, and IMO it is a dangerous practice. I've also read of designs where the neutral is bonded to the chassis! This can be tested with a simple resistance meter.
Ostripper and jaycee have good suggestions.
Sometimes I get a static zap when I get off the couch and touch the pre-amp (depends on how dry the weather is, we get some nasty dry winds off the desert around here). Problem’s not the pre-amp, but my moving on the couch. So far I’ve managed to blow two CD players with ESD from my finger tip to the front panel buttons. I’ve since put an ESD matt next to the pre-amp to touch first to prevent the zappage.
If that’s not your problem, some amplifiers (usually with tuners) have a resistor connected from one of the power leads (ideally the neutral) to the chassis to control ESD build-up. If your plug is un-polarized, then it’s a crap shoot whether you’re connected to the neutral or the hot (depending on which way you plugged it in). Might be a good idea to replace the plug (or whole cord if it’s that old) and make sure the chassis resistor path is in fact to the neutral.
Sometimes I get a static zap when I get off the couch and touch the pre-amp (depends on how dry the weather is, we get some nasty dry winds off the desert around here). Problem’s not the pre-amp, but my moving on the couch. So far I’ve managed to blow two CD players with ESD from my finger tip to the front panel buttons. I’ve since put an ESD matt next to the pre-amp to touch first to prevent the zappage.
If that’s not your problem, some amplifiers (usually with tuners) have a resistor connected from one of the power leads (ideally the neutral) to the chassis to control ESD build-up. If your plug is un-polarized, then it’s a crap shoot whether you’re connected to the neutral or the hot (depending on which way you plugged it in). Might be a good idea to replace the plug (or whole cord if it’s that old) and make sure the chassis resistor path is in fact to the neutral.
Place one probe on the chassis, and try the others on the prongs of the plug. If you get a low ohms reading then you need to eliminate whatever's connecting the chassis to line/neutral - especially if the plug isn't a polarised one!!
Also yes, as ostripper recommended, test your outlets. Over here in the UK polarity reversal isn't a major problem as it's impossible to reverse polarise our plugs anyway (we have the best plugs in the world!! imo
) and outlets are very very rarely wired incorrectly (usually by incompetent DIY'ers if at all)
Also yes, as ostripper recommended, test your outlets. Over here in the UK polarity reversal isn't a major problem as it's impossible to reverse polarise our plugs anyway (we have the best plugs in the world!! imo
) and outlets are very very rarely wired incorrectly (usually by incompetent DIY'ers if at all)
As strange as this may sound, it works... On older equipment with non-polarized plugs, sometimes flipping the plug over will get rid of the slight "electrical-fuzzy" sensation. I don't know how to explain it any better, but it has to do with the hot and return being reversed- not on the house wiring, just how the electrical item is connected. I know it sounds strange, but it works.
Mike
Mike
I had the AM-2800 for a few years. Great amp, 80wpc at 8 ohm, 0.08%thd 20-20kHz with power meters and a great phono section.
The Am-2400 is 40wpc.
Forget the ground terminal thats for earthing a turntable to. Flip the unpolarized cord over in the outlet. If that doesn't work, get the tester as suggested above and check the home's wiring.
If it's correct, check the psu rectifiers and caps.
The Am-2400 is 40wpc.
Forget the ground terminal thats for earthing a turntable to. Flip the unpolarized cord over in the outlet. If that doesn't work, get the tester as suggested above and check the home's wiring.
If it's correct, check the psu rectifiers and caps.
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