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Is it possible for dc voltage to be present in the AC line in my house? Can you measure this with volt meter?
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SCR light dimmers. Motor starting capacitors that are starting to leak like in your refrigerator or freezer compressor. If you've got any of these in your home, then get rid of them. You could hear this over your stereo if you have such problems. They don't so-exist well with a fine stereo. Also the electronics industry is anti-transformer; a device that DC doesn't like and is a wonderful filter of DC. But the electronics industry in an effort to save weight and cost is bypassing and avoiding them. Hence the move to switching power supplies. If I had spent a lot of money on an entertainment system, I would sure protect it with an isolation transformer. Power from the power company is getting dirtier and dirtier. And when the power fails it often comes back on with a dangerous spike. Ray
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Skunk-bear, carcajou, bloodthirsty
Non-survivor.
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I have new frig no freezer. I have hum thru system that is present at all times. When music is playing it is barely audible. I have FI 2A3 mono blocs with KCS BLH 98db eff speakers Wright Sound LS and phono. Never noticed this problem when I had PP amps and less eff speakers. I have turned off every breaker in house except main and the dedicated 20 amp breaker system is on, hum still there Just trying to track this down. I have tried cheater plugs on everything. Amps are new 2 months old. I had some 300B mono amps to try and they did same thing.
Hi
I have about the same experience...
Going from dead quiet KT88 P-P stage, to a 300B SE stage, I ended up with about 6-8mV 100Hz hum from my +100dB/W speaker teminals (measured with DVM).
(100Hz = fullbridged recified 50Hz mains (Sweden))
I asked around.
And the problem seems to be in the DHT tube nature, sins the cathode is the heater (filament).
Very low ripple at the cathode/filament is amplifyed to audiable levels, and absolutelly zero hum is very hard to reach.
IŽll changed the 7805 filament regulators, which had to hi dropout levels to better Linear devices.
This lowered the hum to 3-4mV 100Hz ripple, which was just about audiable when listening very close to the speakers (changing records).
Regards
Pix
The most common source of DC is galvanic action on the grounding system, such that the bond at the utility xfmr is at a different DC potential than the bond at your service entrance. Battery action takes place between the two probes, with the earth's resistivity in between.There are a number of possible sources for this potential, some measurable and proven, others more esoteric. Who cares for this discussion.
Regardless, this is different from what I believe you are trying to measure. I would say the chances of having DC between hot and neutral are slim to none, if all wiring is correct. There is a slim and rare chance that half wave rectification imposes a little DC, but that is miniscule and of no concern in today's full wave world.
DC between neutral and ground is probably also unlikely, as your neutral should be solidly bonded back at your service entrance. The ground currents identified above could impose some DC current back to the utility service, but that would not affect your downstream utilization equipment.
I agree your meter is probably rectifying the AC to measure as DC, and would say there is no way you have true 11VDC. Stray currents, geomagnetic fields might impose a few mV of DC, but again, affect is small.
What is your concern? Regarding audio equipment, 99% of it is transformer derived power supply, and is unaffected by DC.
I have hum thru system that is present at all times. When music is playing it is barely audible. I have FI 2A3 mono blocs with KCS BLH 98db eff speakers Wright Sound LS and phono. Never noticed this problem when I had PP amps and less eff speakers. I have turned off every breaker in house except main and the dedicated 20 amp breaker system is on. Just trying to track this down, hum still there. I have tried cheater plugs on everything. Amps are new 2 months old. I had some 300B mono amps to try and they did same thing.
Have someone place their hand (gently) on the top of the chassis to dampen while you listen at the speakers. Perhaps the trannie/covers are mechanically transmitting vibes that are being picked up by the tubes....
Hum is not a problem with DC. Hum is usually either 60Hz or 120Hz. You can't hear DC.I am a power engineer, so I can help with the breaker panel better than I can with the amplifier guts. However, I would say 60Hz hum is entering your signal path either through the heaters or through electromagnetic induction (signal leads too close to transformers, lack of shielding, poor grounding, etc). 120Hz buzz is typically through the power supply (electrolytic caps poor, inadequate filtering).
PP usually has good PSRR, especially with feedback. Now that you've gone SE, I would suspect you need additional filtering. Or else heater leakage through the 2A3.
I really believe this is a power line issue. I live in a house with 40+ year old romex wiring and panel box that is in a damp basement. I live in the country with three large corporate farms as neighbors and I am about an 1/8th mile from large metal tower high voltage power lines.
When I was using a MM cartridge and the oil furnace base board hot water would kick on and off I would get a crack thru the system that would sound like a really bad scratch in the record. I went to a MC cartridge with a MC step up and that furnace noise ceased.
Could you provide a schematic of your components, or at least a block diagram of how things are connected together?Really sounds like a grounding problem to me.
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What is the cause fo this? Bad power from electric company? I measured 11.5 volts DC with volt meter. What's the best way to eliminate this.
They can be had on ebay for a few bucks or a hundred or two new.
nt
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> I measured 11.5 volts DC with volt meter.Most DC voltmeters can't make an accurate measurement in the presence of AC. The reading you took is probably in error. Before you assume its the line voltage that's at fault, try reversing the voltmeter leads to see if the polarity changes.
I get the same readings after changing VM leads.
That strongly suggests that your DC voltmeter is being fooled by the AC. If the meter was in fact accurately measuring DC, the polarity would have changed. A conclusive test will require a scope. DC will show up as an offset of the sinewave. An asymmetrically distorted waveform, while not technically DC, can produce similar results when the waveform is averaged.
nt
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