Can I use a polarity checker, kind they sell in Home Depot, to accomplish the same, unless you meant to do this test for a purpose, other, than to check polarity of each receptacle?
I cannot understand one thing, though- how come the hum is louder in one channel??? No, you will not be checking if the receptacle polarity is correct. You will be checking if the 120V AC polarity orientation of the primary of the power transformer of the power amps is correct. If you do not have a multimeter you might just try a simple listening test. Same set up with the ground cheater just listen for any difference..... The meter is the best sure way though. You can pick up a decent one at Rat Shack for around 50 bucks.... ====================== http://www.audioasylum.com/audio/general/messages/449743.htmlhttp://forum.audiogon.com/cgi-bin/fr.pl?htech&1014011751&openusid&zzSean |
Got you,
Here are the measurements.
Meter set at ACV 50
Left amp: Right amp:
Right cheater plug: 38 37
Reversed: 33 30
So, what's the verdict? |
The answer to the big question- no, hum is the same after AC plug is reversed |
Just realized my meter settings were at 50, instead of 250 V
new measurements:
L amp:
Correct cheater plug 62.5 V.
Reversed 51 V.
R amp:
Correct 62.5 V.
Reversed 51 V. |
new measurements:
L amp:
Correct cheater plug 62.5 V.
Reversed 51 V.
R amp:
Correct 62.5 V.
Reversed 51 V.
01-31-09: Maril555 Wow, I could see where the reading might be high in one direction, but not high in both directions. I just checked my little ARC VT 50 power amp. Correct plug orientation with the ground lifted was 3.6Vac When I reversed the cheater in the receptacle outlet the voltage jumped up to 93.5Vac...... ================================= Would you do me a favor and conduct another small test for me? Set you meter on the 250Vac scale. Use the receptacle you were using for your test. Insert one probe in the T slot, (neutral), of the recept and the other probe in the equipment ground making sure of a good mechanical contact. Any voltage reading? It should be zero. If no voltage, set the meter on the 50Vac scale and repeat the same test. Any voltage reading? Again it should be zero. Move the meter selector down to the next lower scale and repeat. The meter should still measure zero Vac. One final test. Set the meter on the 250Vac scale. Measure the voltage between the Hot contact, small slot, and the neutral, T slot. Make note of the reading. Next measure the voltage from the Hot contact to the equipment hole contact. Both voltage readings should be the same. . |
OK,
Neutral to chassis- 0 v. on all meter settings
Hot- Neutral 120V.
Hot to chassis:
Power cord unplugged 25 V.
Power cord plugged-in, amp. is OFF- 112 V.
Power cord plugged-in, amp. is ON- 90 V.
As usual, I have no clue, how to interpret all this. |
Maril555,
You misunderstood what I wanted you to do. All the test measurements are taken at the wall receptacle outlet only. No audio equipment is involved with the test.
In simple terms the test will tell if there is a good electrical continuity between the main incoming service neutral conductor, of your electrical service, and the equipment ground. At some point the electrical service entrance neutral conductor is connected to earth and is also bonded, connected, to the main equipment enclosure as well as equipment grounding bus bar/s. In most cases this is done at the main service electrical panel. Not sure in your case though. I noticed from your pictures the main breaker is not in the main panel so it is more than likely out side by the electric meter. Connection to earth and equipment bonding may have been done there.
So the test is a simple way to look at the thing just from one branch circuit and receptacle.
I tried to explain best I can in layman terms.
So at the wall receptacle outlet only.
Measure from the neutral to the equipment ground, (U shape hole).... Should show 0 volts
Measure from the hot to the neutral.... Should be around 120V to 123V
Measure from the hot to the equipment ground, (U shape hole)... Should be the same as the voltage measurement from Hot to neutral.
And one more measurement if you would. Plug in and turn on one of the power amps and using the other receptacle of the duplex receptacle measure the voltage from the hot to the neutral. This will give a somewhat load condition on the branch circuit for any voltage drop. The voltage should be within about one volt of the reading with the power amp not connected and turned on.
A true test would be to play some music at a moderate level and take the measurement. |
Got you,
Hot- Neutral 120 V.
Hot- Ground 120 V.
Neutral- Ground 0 V.
With the amp. ON- Hot - Neutral 120 V.
BTW, thanks a lot for your patience. |
The measurements are good......
The bad news is it does not help the hum problem.
From the pictures you supplied of the sub panel what I could see the electrician you hired did a good job. The only code violation I could see was the (4) 30 amp breakers he installed for branch circuit protection instead of 20 amp breakers..... Just guessing he did what you probably requested.
At any rate that would not be causing your hum problem.
You seem to have isolated your hum problem.... The problem exists between the power amps and the speakers.
Could your problem be RFI/EMI on the AC mains of your home's electrical system? Well if you live in an area that is warm at the present time you could shut off every breaker in the main panel except the 2 pole breaker that feeds the sub panel. Then check the amps for the hum.
LOL, take a flashlight with you....
If the hum is gone then start turning back on the breakers one at a time until you find the source of the problem.
Still hum? Then, jmho, I would think that would rule out RFI/EMI noise, interference, on the mains. That is, at least from a source within your home. That does not mean EMI/RFI noise is not coming in from outside your home on the utility power.
==========================
Maybe the problem is the power amps and the sensitivity of the speakers??
By chance do you have another pair of speakers you could try? Less efficient?
You might try a different pair of speaker cables. For a test just some cheapo Home Depot rip cord would do.
Sorry, I am out of ideas......
I did send an email to an EE who posts here on Agon. I asked him to read the thread and post a response if he has any ideas.
Jim |
Well,
I already tried turning off all circuit breakers, no help.
Tomorrow I'll bring the amp to the living room to try with another pair of speakers and another outlet.
I have two other pairs of less efficient speakers, so I'll give it a try as well.
BTW, what's your take on the high chassis voltage, higher with the correct polarity? |
Maril,
Wow, I just read through all of this, at Jea's suggestion. Let me make sure I understand what amp we are talking about. If I followed everything correctly, you are having the problem with your friend's pair of BAT VK-150SE's, not the VAC amps that are listed in your system profile. And you previously had (or still have) a BAT VK-75SE (similar to the 150SE but in stereo configuration), and it exhibited similar symptoms.
Do your VAC's have these symptoms as well?
I notice that the BAT amplifiers have a bandwidth spec of 200kHz, which is extremely wide, and approaches rf frequencies. I'm wondering if there may be rf interference coming from somewhere that is radiating directly into internal circuit point(s) within the amp, and somehow then intermodulating or being AM-detected somewhere in the amp circuitry, resulting in the sound you are hearing.
Can you tell if the sound is really 60Hz, together with its 120Hz and possibly 180Hz harmonics (corresponding to the power line frequency and its lower harmonics), or could it be some other frequency or frequencies, which would be suggestive of rfi pickup?
The computer that you mentioned is in the room would certainly be one such possible source. If you haven't already, try turning it off AND unplugging it -- as you probably realize some circuitry on the computer's motherboard, and parts of its switching power supply as well, are always powered up as long as the ac is connected. For that matter, unplug all other computers in the house, and if you have nearby neighbors, consider asking them to do the same.
Perhaps you could bring an AM portable radio into the room, or better yet if possible a portable that can receive the long-wave band (below 550kHz) and see if it picks up any interference. If it does, you could track down the source of the interference by walking around with the radio and seeing where it is loudest.
Also, just to be sure, did the XLR shorting plugs you put on the inputs have all three pins electrically connected together (such as by having pin 2 wired to pin 1 and pin 3 wired to pin 1)?
Regards,
-- Al |
Almarg,
Yes, you're right, I'm talking about my friend's 150s.
I no longer have 75-SE, but am considering buying it again, that's the whole reason for this post.
VAC didn't have this symptoms, just some ground loop, that I corrected.
The hum is mostly coming from the tweeters, but can also be heard from mid and bass drivers.
Just a little bit of history: what started me on this wild goose chase, is a significant hum coming through the speakers with a phono input selected- I could see woofers moving.
In another lenghty troubleshooting session with Kevin of KAB, we narrowed it down to phonostage amplifying some AC interference. I could also hear phonostage picking-up a radio signal (actual radio broadcast).
All this information combined with BAT's bandwidth, gives your theory an extra credit.
I will experiment with computer and radio tonight.
Shorting plugs- I don't know how exactly they are wired, I'll look into it.
Thanks for your help. I hope you, Jea48 and others will hang with me for a while longer, until this gets resolved, or I commit suicide. |
BTW, what's your take on the high chassis voltage, higher with the correct polarity?
02-01-09: Maril555 Well the lower chassis to equipment ground voltage is the correct orientation polarity for the amps. Seems odd to me both amps would have the primary of their power transformers wire incorrectly. By chance are you using aftermarket or home brew power cords on the amps? If so it could be the cords are wired wrong. The wiring on the 3 wire NEMA plug could be right but the hot and neutral on the IEC are reversed. Easy to check with your multimeter. Just pull each cord from the amps and check the continuity from end to end on the pcs. |
Maril,
Yes, based on the facts indicated in your last post, I feel pretty confident that is what is happening -- the BAT's, with their 200kHz bandwidth, are picking up interference through the air.
The source of the interference is probably something closer to the left channel amplifier than the right, since the symptom is worse on that side.
Besides computers, other common sources of rfi in the home are:
-- Dimmer switches for lighting (either incandescent or fluorescent). If there is a dimmer switch nearby, make that your number one suspect after the computer!
-- Fluorescent lighting.
-- UPS's (uninterruptible power supplies).
-- Computer network cables.
-- VCR's, DVD players, etc. Like computers, they can generate significant noise when plugged in, even if they are turned off.
-- Possibly wireless devices like cordless phones, wifi, etc. Although they operate at far higher frequencies, they may have switching power supplies or other circuits which emit spectral components below 200kHz.
I have a portable AM radio that can receive the long-wave band (as well as short-wave and the medium wave regular AM broadcast band). You'll be interested to know that it's dial starts at 150kHz (!), well within the frequency range of what your amplifier can amplify!
Good luck!
-- Al |
Jea48,
I will check the power cords tonight.
Al,
Now, that you said it, I do have wireless router next to my desktop computer in the basement, transmitting to my wife's laptop, she's using in the kitchen upstairs. Transmitter is closer to the L channel amp. Also, Comcast cable goes along the same left wall to the desktop in the back of my listening room.
Can't wait to get home tonight and disconnect all that crap, to see what happens.
Will keep you guys posted. |
Jea48,
I have been working alot in this weather. hevac ya know.
Houstonreef can put any load on the other side that he wants. I would put another rooms outlets on it myself or light. Make sure there are no dimmers or florecent lights. Do not use kitchen outlets & motor loads are bad. I do not think the projector would be good he will connect the ground and common through the cables. It does not matter the amps if the breaker only has a 120Vac going throu it may not trip correctly.
Houstonreef: Where are your amps to your other equipment?
Do you have tube equipment, phono stage, have you tried to change out some cables. move equipment around a little can stop hum in some instances. Your equipment mite not like each other. Are your power cords 90 deg to your interconnects or 6 inches away as this can cause RF interferance. All a/c create RF. You could just have a bad shield or bad cable. |
Maril555,
The second paragraph in my reply to Jea48 is for you. I looked at the pictures of your system try moving things around a little and your speaker cable to your center speaker seems very close to your right amp. Speaker cables are not shielded and RF can be an issue. |
Maril555. Do interconnect cables connect to both your surround sound processor and your 2 channel. The 2 preamps can have a differant potetial to ground and cause hum. Try disconnecting cables to the SSPre. I have this issue and have not figured out how to stop it other than keeping both systems seperate totally. I got it down to a hum I only here right at the speaker but to me it is too much. |
Hevac1, The two pole 60 amp breaker will trip just fine if there is an overload or short circuit on just the one pole of the breaker. It is designed to do so. I assume the reason Maril555 paid to have the sub panel installed was to keep his audio branch circuits somewhat isolated from the loads in the main panel. If you look at the pictures, Maril555 supplied, you will see he had plenty of room in the main panel for the 5 branch circuits. Your post got me to look at the picture of the main panel again and that reminded me I was going to ask Maril555 why he didn't have the electrician move the two GFI breakers, across from the 2 pole 60 breaker, to another location in the panel. |
Don't know where to begin, well:
I was hoping to find interference from my PC or cable, but no luck. I disconnected and unplugged PC, cable modem, wireless router, switched off all breakers, except the power amps- hum is still there.
Tried different speaker- still there
Tried different power cord- still there
Plugged the amp into a different outlet upstairs, separate from the dedicated panel, through the long extension cord- still there.
Hum, or buzz, is very constant in nature and nothing seems to change it. it does sound like a ground loop buzz to me, more, than anything else.
Again, L channel amp hums more, than the R channel with everything disconnected from it.
Hevac1, thanks for your ideas, but in lieu of the above statement, I don't think compatibility of the different components is the culprit.
Jea48,
I don't know why I didn't ask him to move GFI breakers (they are the ones with yellow markings on them?).
Where do you think they should be in the panel?
Did I mention how frustrating that is ? |
One last thing- I switched the amps left to right, and the hum moved too. I don't know, maybe it's inherent to that amp? At any rate, hum is there. |
This question probably has been asked, but I missed the answer but if not, are you running balanced? or single ended?
If single ended have you put in the shorting pins? |
|
Maril -- Do try what I suggested with a battery-powered portable AM radio, checking to see how much interference or buzz it picks up in the room, and if it is significant, walking around with the radio to try to track down its source.
How close are your nearest neighbors -- maybe it's coming from them.
Aside from interference being picked up through the air, the one other possibility that occurs to me, given that the amps worked fine before being moved to your house, is that perhaps the mechanical jostling that occurred during the move affected something within the amps. Such as, perhaps, a screw loosening slightly, causing the contact between a metal transformer housing and the chassis to lose its integrity.
-- Al |
|
I would take the noisier of the two amps back to your friends house and have him connect it to one of his speakers...... Take along the power cord and the speaker cable. Take along your multimeter too.
If it does not hum/buzz there, &^#@$%#@, Check the voltage at the wall outlet he plugged the amp into. See if the voltage is lower than yours.
Are these amps self biasing? |
Actually, I just wanted to post about something I did last night-
I moved amps L to R, and the hum moved as well, but I have also noticed, that a level is lower on the side of a humming amp (center image moved to the opposite side),
I double- checked moving it back, there is disbalance.
So now I'm strongly suspecting there is something buzzing inside the amp. I'm going to ask my friend, if he wants to take it to BAT for check- up.
Question- what internally can cause this kind of buzzing?
Cap, resistor, bad tube?
Amps are self biasing |
That's very interesting. So the amp with the more severe hum/buzz also has lower gain. It could be due to a lot of things, but I suppose the most likely culprit would be a tube. Perhaps before taking it back to him it would be worthwhile switching tubes between the two amps.
Regards,
-- Al |
Al,
Yes, that's what I'll try tonight. |
A bad tube can definitely cause a buzz and a bad electrolytic in the power supply can cause a hum. I would also think a leaky cap in the signal path could cause a hum.
You might want to send an email to BAT customer support and ask them.
You never answered my question. Do the amps have auto biasing? If you do not know for sure I would not just switch the tubes around. |
Jim -- He appears to have answered that, at the end of his first post dated today.
-- Al |
Amps are self biasing.
02-04-09: Maril555 Al, Thanks I missed it on the first read. |
Well,
It's not tubes, at least not the power tubes. I switched them around, hum stays with the same amp.
I guess, BAT will have to take a look. |
