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Measurements on amplifiers with speakers and cables connected

Opus111

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#41
You can see the 3rd increases from -150 to around -140dB on the plots.
I was assuming that the fundamental appeared at the top (-100) but then the noise 'floor' seems rather high so what's the real fundamental's amplitude (cropped off the top of the plot)?
 

DonH56

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#42
I presume thats an acoustic measurement? We are really looking at the electrical measurement at the speaker WRT amp and cable performance.
Well, heck, I meant to post this over in the Magnepan thread, not here, sorry. Long day... Yes, it's acoustic. I noticed REW has some guidelines on using it for impedance measurements, be interesting to try that. I am not sure where my parts bin is (out in storage in our shed), but I do have a variety of 0.1 % temp-stable Rs out there, or I may just use one of our fancy DMMs at work and measure one. I no longer have access to an audio-frequency VNA; in the past I used an audio analyzer or VNA through a power amp (calibrating out the power amp, naturally).
 

March Audio

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#43
I was assuming that the fundamental appeared at the top (-100) but then the noise 'floor' seems rather high so what's the real fundamental's amplitude (cropped off the top of the plot)?

Its mentioned in the first post but I may not have been clear.

There is no further signal conditioning on the ADC so I am currently stuck (will be changing soon) with a full scale input of 4.2 V rms. Which is quite convenient for testing balanced DAC outputs.

I have been testing with the 8ohm resistive and speaker load at 2.83V rms as this is a nominal 1 watt output. To keep the ADC in its most linear range ( <-20dB ) I decided to make an attenuator for the ADC input. I intended it to be 20dB but it ended up about 30 dB because I read one of the resistor code wrong - aging eyesight DOH! :).

I am not interested particularly in absolute values, rather the differences in distortion that show up.

If you look in my first post the noise floor of the Nc400 is measured without the attenuator. This again ref a FS of 4.2 V, so is not a true representation of the amps dynamic range as it can obviously swing a lot higher than 4.2 V RMS - more like 42 V RMS. It sits at about -93 dB(A) rms FS showing around -130dB on the 131000 line FFT. The NC400s are very quiet for power amps.

So with the attenuator in place the 1 kHz fundamental (2.83 V rms) is at about -42 dB. You can gauge this from the RMS readout at the bottom left of the plot.

One thing that also should be noted is that with a switching amp such as the NC400, its is possible that the switching frequency (480kHz) can cause issues for the ADC.

http://www.hypex.nl/docs/NC400_datasheet.pdf
upload_2016-4-11_16-26-4.png
 
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March Audio

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#44
Opus, 200Hz plots as requested. Long cable shows 3 & 5 harmonics at low level.

Noise floor is changing, unknown if ADC or amp at this stage.

With this amp it is difficult to see cabling as a significant contributor to distortion. Will try the other amps soon.

1m cable

ncore 200Hz spk 2-83volts 1m cable.png

10m cable

ncore 200Hz spk 2-83volts 10m cable.png
 
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John Kenny

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#45
Looks to me like there is the same low periodicity ringing after each tone signal - with the first oscillation period = 5 times the tone signal frequency
Is the cause of this some inductance issues in amp or ADC circuitry?
 
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AJ Soundfield

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#46
With this amp it is difficult to see cabling as a significant contributor to distortion. Will try the other amps soon.
Not sure why a sane person like yourself would waste their time kowtowing to this idiotic believer nonsense. Let the infantile Santa hearers produce a single bit of reliable listening evidence for audible "cable distortion", before chasing wild geese.
Something a bit more adult sensible would be the likes of GedLee distortion metrics for amplifiers. Linkwitz, being the latter, has been doing an interesting 2 tone test: http://www.linkwitzlab.com/Amplifiers-etc/Distortion.htm
I would still want to see reliable listening tests, but at least we have plausibility here.

cheers,

AJ
 

March Audio

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#47
Not sure why a sane person like yourself would waste their time kowtowing to this idiotic believer nonsense. Let the infantile Santa hearers produce a single bit of reliable listening evidence for audible "cable distortion", before chasing wild geese.
Something a bit more adult sensible would be the likes of GedLee distortion metrics for amplifiers. Linkwitz, being the latter, has been doing an interesting 2 tone test: http://www.linkwitzlab.com/Amplifiers-etc/Distortion.htm
I would still want to see reliable listening tests, but at least we have plausibility here.

cheers,

AJ
Well, it simply puts the debate to bed :)
 

RayDunzl

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#48
I am doing a series of tests with what I have available to me.
Try measuirng from one end of the cable to the other instead of across the terminals.

Assuming a single ended amplifier, measure against ground at the speaker end of the negative speaker cable.

.

Just to see, of course.
 

cjf

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#49
It seems a not very well known fact that when a speaker is connected to an amplifier the distortion increases. This being due to the speaker presenting a non-linear load to the amp. Here's an article which includes several FFTs demonstrating the kind of distortion increase that occurs with differing cables : http://www.eetimes.com/document.asp?doc_id=1274851

So yes its really true - different cables do measure differently when they're in circuit.
Thanks for posting the link to that article, very interesting stuff.

I myself have actually battled with, what I believe to be, some of the issues that are discussed in that article in terms of noise,interference..etc between my amp and speaker combo of choice. I had a thread running over on WBF http://www.whatsbestforum.com/showt...n-aluminum-speaker-cabinet-attract-more-noise a while ago describing my issue which was ultimately resolved by significantly increasing the length of the speaker wire between my Class D Hypex amp and the speaker in use (Magico S3). I still don't have a full grasp on what exactly the root cause was for that problem but the article linked by Opus111 does shed some light on possibilities of why the issue is happening in the first place. For what its worth, the issue occurs with EVERY Hypex Class D amp I have tried when teamed with my particular speaker in my listening room. This includes NC400,NC1200 & the Mola Mola Kaluga amps I use today.

After reading thru the "eetimes" article a few questions came to me. It seems possible that there may be downsides to having a very, very, very low Output Impedance on the amplifier side. If I was reading the article correctly, it looks like a very low Output Impedance does not do a good job of resisting the EMF Backwave heading towards the amplifier which is generated by the transducers in the speaker cabinet. In my case I wonder if by increasing the distance of the cable this EMF Backwave is then dissipated enough to not result in hearing the noise I describe in the WBF thread.

I'm not sure if anyone is familiar with this tweak or not but I've considered trying it just for the heck of it. There have been a few long threads posted about it on different forums over the years. The "Tweak" I am referring to is know as the "Exemplar Audio Loop" which is basically an extra strip of 2ft long wire that is attached to the Negative Terminal of the speaker cabinet which supposedly "catches/attracts" EMF Backwave noise on its way back to the amplifier. Snake Oil? Probably, but some day when I'm bored I may give it a try in my setup to see if it magically allows me to then use shorter speaker cable in my setup.

I do wonder though if these additional lengths of wire attached to the negative terminal of the speaker cabinet would interfere with the Damping Factor of the amplifier?

In any case, good thread and interesting information :)
 

RayDunzl

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#50
I do wonder though if these additional lengths of wire attached to the negative terminal of the speaker cabinet would interfere with the Damping Factor of the amplifier?
I don't see how, since the negative terminal tends to be at ground and not an active point of amplification.

I'm always willing to see the error of my ways, so try it out for me.

This?



The Exemplar Audio loop (on left of terminal) is 12 inches long and is one wire of their speaker cable, which is long linear crystal.
 

cjf

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#51
I don't see how, since the negative terminal tends to be at ground and not an active point of amplification.

I'm always willing to see the error of my ways, so try it out for me.

This?
Yes, yes indeed that is it.

I guess my thought on if/how it could result in a reduction of DF at the amp was based on there needing to be a completed circuit created by the positive/negative wires back to the amp and if somehow by adding additional wire to the negative terminal it would maybe delay or weaken the completion of that circuit (by adding to the length which the electricity needs to travel on one leg of the wire only).

But then again, maybe I'm hitting the crack pipe too hard o_O
 

fas42

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#52
This is an example of when weird and wonderful ways of fiddling with audio systems keeps altering the sound - been there so many times it scares me :p ! It's all about altering the spectrum of still audible distortion artifacts, and when a system gets to a certain point just about everything one does can have an impact on these nasty little critters !! The only way of getting off this silly treadmill is to get those distortion anomalies below subjective audibility, which is a major exercise in itself, but is worth the effort because then the sound quality is sufficiently high that slight variations no longer matter, they become trivial in the context of the playback.
 

cjf

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#53
I don't see how, since the negative terminal tends to be at ground and not an active point of amplification.

I'm always willing to see the error of my ways, so try it out for me.

This?



The Exemplar Audio loop (on left of terminal) is 12 inches long and is one wire of their speaker cable, which is long linear crystal.
Gave this tweak a try today in an attempt to see if it would offer any benefits/fixes for me while using a shorter speaker cable in my system.

More Snake Oil...err...I mean DDS (Didn't Do Shit) :rolleyes::mad::(:)
 
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#54
It seems a not very well known fact that when a speaker is connected to an amplifier the distortion increases. This being due to the speaker presenting a non-linear load to the amp. Here's an article which includes several FFTs demonstrating the kind of distortion increase that occurs with differing cables : http://www.eetimes.com/document.asp?doc_id=1274851

So yes its really true - different cables do measure differently when they're in circuit.
but cable needs for sound no?
 

ceedee

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#56
The only way of getting off this silly treadmill is to get those distortion anomalies below subjective audibility
But audiophiles don't want to get off the "silly treadmill," do they? Isn't that the point of all of the so-called tweaks?
 

fas42

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#57
But audiophiles don't want to get off the "silly treadmill," do they? Isn't that the point of all of the so-called tweaks?
Seems to be different points of view ... some people just love foolin' around with their systems as a hobby, like car lovers having a fetish about THAT car, that means so much to them; but others just want the best possible performance. Apparently Ferrari, the man, had no particular interest in or passion for the cars he made, they were merely a means to an end, which was winning races - he was an endless tweaker, doing whatever it took to get his vehicles into the best possible shape to do that job.

I'm one of those with a very precise end goal, I know exactly what "winning the race" means - so my tweaks are solely directed to that purpose. Many people in the audio game have no idea where the finish line is, or that it "exists", or even the path of the "race course" - tweaking for them is just foolin' around, so, yes, they will be on the treadmill forever ...
 

March Audio

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#58
Thanks for posting the link to that article, very interesting stuff.

I myself have actually battled with, what I believe to be, some of the issues that are discussed in that article in terms of noise,interference..etc between my amp and speaker combo of choice. I had a thread running over on WBF http://www.whatsbestforum.com/showt...n-aluminum-speaker-cabinet-attract-more-noise a while ago describing my issue which was ultimately resolved by significantly increasing the length of the speaker wire between my Class D Hypex amp and the speaker in use (Magico S3). I still don't have a full grasp on what exactly the root cause was for that problem but the article linked by Opus111 does shed some light on possibilities of why the issue is happening in the first place. For what its worth, the issue occurs with EVERY Hypex Class D amp I have tried when teamed with my particular speaker in my listening room. This includes NC400,NC1200 & the Mola Mola Kaluga amps I use today.

After reading thru the "eetimes" article a few questions came to me. It seems possible that there may be downsides to having a very, very, very low Output Impedance on the amplifier side. If I was reading the article correctly, it looks like a very low Output Impedance does not do a good job of resisting the EMF Backwave heading towards the amplifier which is generated by the transducers in the speaker cabinet. In my case I wonder if by increasing the distance of the cable this EMF Backwave is then dissipated enough to not result in hearing the noise I describe in the WBF thread.

I'm not sure if anyone is familiar with this tweak or not but I've considered trying it just for the heck of it. There have been a few long threads posted about it on different forums over the years. The "Tweak" I am referring to is know as the "Exemplar Audio Loop" which is basically an extra strip of 2ft long wire that is attached to the Negative Terminal of the speaker cabinet which supposedly "catches/attracts" EMF Backwave noise on its way back to the amplifier. Snake Oil? Probably, but some day when I'm bored I may give it a try in my setup to see if it magically allows me to then use shorter speaker cable in my setup.

I do wonder though if these additional lengths of wire attached to the negative terminal of the speaker cabinet would interfere with the Damping Factor of the amplifier?

In any case, good thread and interesting information :)
Precisely what is the problem you experienced?

Initial reaction, definitely snake oil, emf "back wave noise" ?!?!?!?!?

Won't change the DF.
 

cjf

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#59
Precisely what is the problem you experienced?
As described in the long thread on WBF my issue was in summary as follows:

ANY speaker cable I tried (many) connected between my Amp and Speaker that is shorter than 12ft (depending on gauge) results in a noise like this coming out of my speaker:
https://www.flickr.com/photos/[email protected]/25030695085/

As the cable length is increased the noise goes away. Wire gauge does seem to play into this as well assuming due to the varying levels of LCRZ..etc that different wires have. I currently have a 4m length of Cardas Clear on hand which still results in noise presumably due to either A:\ its very low Resistance (6.5ga), B:\ its very high Capacitance, C:\ its very low Inductance or D:\ its Impedance

Based on my research the issue smells a little like what NAIM users deal with when using the wrong wire in there setup except mine doesn't cause the amp to shut down or anything as nasty as that. Just noise but I cant say if/how this noise could be detrimental to the hardware if it remained present after continued usage.

I do wonder if its more Inductance related than anything else because bog standard ZIP Cord (parallel wire run geometry) seems to offer the most success in avoiding the issue compared to the much more complex geometry used in the Cardas cables I have tried. A 10ga run of ZIP Cord works with no issues at a length of 12ft. A 14ga run of ZIP Cord works with no issue at a length of 10.5ft. A 12ga run of ZIP Cord works with no issue at a length of 11.5ft. :eek::eek::eek:o_O

Lastly, if the speaker is changed out for something else using the same Amps and short wire the issue goes away. If the Amps are changed out to a Class A/B model of a any kind using the same speaker and short wire the noise goes away. Funny thing is, according to Magico they have a Hypex NC1200 amp on hand that they use for testing and claim they don't have the issue I describe. BUT....when I queried them about trying a test with a short wire I received a rather dismissive response that "We don't have any wire shorter than 12ft on hand to test with". :mad::rolleyes:

When I queried Hypex about the problem they were clueless on what the issue could be but did state that the crossover network Magico uses could be a contributing factor.
 

RayDunzl

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#60
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