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My cat tore up my Virtual Dynamics Power 3... - Page 46  

post #676 of 772
4/10/08 at 7:27pm
Quote:
Originally Posted by bigshot View Post
That sounds like inverted phase to me.

See ya
Steve
nope..wrong.
post #677 of 772
4/10/08 at 8:52pm
The Radio Shack sound meters have very questionable accuracy at low frequencies.
StereoTimes -- Useful Modifications to the RadioShack Analog SPL Meter

I don't think it got any better with the new digital readout version.

That said, one would think the inaccuracy would at least be repeatable.
post #678 of 772
4/10/08 at 9:05pm
I think a better test would be to use an oscilloscope on the speaker output terminals with speakers still connected (this would ensure the amp is acting as it would under load). Then sweep frequencies, or feed it some white noise and take the FFT (frequency domain) capture of the output. If one power cord was affecting the frequency response, it should be visible in this case. 2dB would be quite noticeable too.
post #679 of 772
4/10/08 at 9:41pm
Quote:
Originally Posted by Jam_Master_J View Post
I think a better test would be to use an oscilloscope on the speaker output terminals with speakers still connected (this would ensure the amp is acting as it would under load). Then sweep frequencies, or feed it some white noise and take the FFT (frequency domain) capture of the output. If one power cord was affecting the frequency response, it should be visible in this case. 2dB would be quite noticeable too.
yes that would be a better test; not a lab test but should be more accurate than than the radioshack sound meter.
post #680 of 772
4/10/08 at 11:22pm
get a virtual dog
post #681 of 772
4/11/08 at 12:26am
Quote:
Originally Posted by bigshot View Post
That sounds like inverted phase to me.

See ya
Steve
Quote:
Originally Posted by furball View Post
All very good ideas guys!
This is a power cable he is talking about... don't think you can invert the phase on single phase AC...
post #682 of 772
4/11/08 at 12:26pm

Probably means reversed polarity.

Quote:
don't think you can invert the phase on single phase AC...
You are correct in that most of the power is single phase coming out of residential homes. Unless you have commercial or heavy duty equipment that can utilize dual phase.
Reversing the polarity of a power cord might have a sonic impact depending on the sensitivity of the component.

Michael
post #683 of 772
4/11/08 at 1:55pm
Quote:
Originally Posted by Pars View Post
This is a power cable he is talking about...
Yow!

See ya
Steve
post #684 of 772
4/11/08 at 2:47pm
Quote:
Originally Posted by Jam_Master_J View Post
I think a better test would be to use an oscilloscope on the speaker output terminals with speakers still connected (this would ensure the amp is acting as it would under load). Then sweep frequencies, or feed it some white noise and take the FFT (frequency domain) capture of the output. If one power cord was affecting the frequency response, it should be visible in this case. 2dB would be quite noticeable too.
It would be a much better test. All you need to do is to feed a 30Hz signal. 2dB is about 1.6 difference in amplitude. It would definitely be noticeable.
post #685 of 772
4/14/08 at 12:59pm
Quote:
Originally Posted by Jam_Master_J View Post
I think a better test would be to use an oscilloscope on the speaker output terminals with speakers still connected (this would ensure the amp is acting as it would under load). Then sweep frequencies, or feed it some white noise and take the FFT (frequency domain) capture of the output. If one power cord was affecting the frequency response, it should be visible in this case. 2dB would be quite noticeable too.
Why not just test the power cord on the PSU? A PSU will convert the AC power to DC. Why not just measure the effect of changing power cords with the PSU DC output. If you get pure DC output with both cables, it stands to reason that power cords make no difference.
post #686 of 772
4/16/08 at 1:31pm
Quote:
Originally Posted by UseName View Post
Why not just test the power cord on the PSU? A PSU will convert the AC power to DC. Why not just measure the effect of changing power cords with the PSU DC output. If you get pure DC output with both cables, it stands to reason that power cords make no difference.
If that route is going to be taken then, it begs the question of how and what to test on a PSU. IIRC, there's a whole pile of tests that can be done on PSUs, and I don't think they are any less complicated than testing audio stuff.
post #687 of 772
4/16/08 at 2:21pm
Quote:
Originally Posted by Maniac View Post
If that route is going to be taken then, it begs the question of how and what to test on a PSU. IIRC, there's a whole pile of tests that can be done on PSUs, and I don't think they are any less complicated than testing audio stuff.
There are also an infinite number of tests for audio equipment as you have an infinite range of frequencies. As well, you have more equipment in the system.

All I want to see is if the output from the PSU stays the same. It is DC power, so if there is any noise that gets eliminated or added with either cord, you have a base for saying power cords can make a difference.

If the PSU works ideally and is stable for both cables (as it theoretically should), there are a lot of people on this site that can save quite a bit of money.

This is way more reliable than testing audio equipment because there are fewer components that could add error. When performing tests, it's important to eliminate as many variables as possible to promote accurate results. It would also help us determine exactly what is happening.

For example, perhaps a PSU is letting a certain frequency through that is eliminated with the use of an expensive power cord. It would likely be cheaper to simply add a filter to correct this problem then spending thousands on wire.
post #688 of 772
4/16/08 at 2:35pm
Quote:
Originally Posted by UseName View Post
There are also an infinite number of tests for audio equipment as you have an infinite range of frequencies. As well, you have more equipment in the system.

All I want to see is if the output from the PSU stays the same. It is DC power, so if there is any noise that gets eliminated or added with either cord, you have a base for saying power cords can make a difference.

If the PSU works ideally and is stable for both cables (as it theoretically should), there are a lot of people on this site that can save quite a bit of money.

This is way more reliable than testing audio equipment because there are fewer components that could add error. When performing tests, it's important to eliminate as many variables as possible to promote accurate results. It would also help us determine exactly what is happening.

For example, perhaps a PSU is letting a certain frequency through that is eliminated with the use of an expensive power cord. It would likely be cheaper to simply add a filter to correct this problem then spending thousands on wire.

There's also an almost infinite amount of condition and load situation that you can put a PSU through. Are you going to measure it at idle? at 50% load? at 100% load? at 120% in short bursts? or are you going to load it with a load that changes all the time very rapidly?

IMHO it isn't really making it simpler, it is just as complicated and the result may not directly referencing to what would be happening when you hook it onto audio equipments. Not to mention that noise is not the only measure of performance for audio equipments.

But personally speaking, I'd say that noises in the recording is what really annoying me. I once heard that 120Hz buzzing in a commercially released CD that just totally p*ssed me off. Power cable may help, but not to a dramatic degree of a bad recording vs good recording. However, a rather polluting switching power can come close if it is plugged into the wrong spot. I have used a few very nice sounding switching PSU on my own DIY projects, they sound clean, fast and very transparent... but they will make other equipments sound muddy and artificial if they share an AC outlet or are wired too closely...
post #689 of 772
4/16/08 at 2:50pm
Quote:
Originally Posted by Maniac View Post
There's also an almost infinite amount of condition and load situation that you can put a PSU through. Are you going to measure it at idle? at 50% load? at 100% load? at 120% in short bursts? or are you going to load it with a load that changes all the time very rapidly?

IMHO it isn't really making it simpler, it is just as complicated and the result may not directly referencing to what would be happening when you hook it onto audio equipments. Not to mention that noise is not the only measure of performance for audio equipments.

But personally speaking, I'd say that noises in the recording is what really annoying me. I once heard that 120Hz buzzing in a commercially released CD that just totally p*ssed me off. Power cable may help, but not to a dramatic degree of a bad recording vs good recording. However, a rather polluting switching power can come close if it is plugged into the wrong spot. I have used a few very nice sounding switching PSU on my own DIY projects, they sound clean, fast and very transparent... but they will make other equipments sound muddy and artificial if they share an AC outlet or are wired too closely...
I thought it was clear that my noise example was only an example... obviously it is not the only issue....

The point that I am trying to make is that any improvement found by a 'magic' power cord could likely be done cheaper on the PSU. If your PSU is very very good, the cord should not matter at all as long as it is proper gauge.
post #690 of 772
4/16/08 at 2:58pm
Quote:
Originally Posted by UseName View Post
I thought it was clear that my noise example was only an example... obviously it is not the only issue....

The point that I am trying to make is that any improvement found by a 'magic' power cord could likely be done cheaper on the PSU. If your PSU is very very good, the cord should not matter at all as long as it is proper gauge.

Well, in theory true, and like I said before, what are you going to test? There are just as many things that can be tested on PSU as in audio. How do you determine what's going to affect the resulting sound? Number don't really mean much if it didn't reflect what's being heard.


For example would be my CD Player, a Sony CDP-X5000. It have some of the best power supply setup that I've ever seen stuffed into such a small case. Large snap-in caps (looks like custom Silmic from Elna) and all kind of regulator circuit. there are even some OP controlled regulators in there as well.


But guess what? It is also one of the more sensitive equipments in my setup to different power cords, even tho I'm only using its digital output only.


I have no idea why it's affected like that, and it goes against all the electrical/electronics knowledge I have learned so far. However, it is always fun to find out stuff like that tho.
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