EMI everwhere !

[PeterSt]

Quite applicable Joachim. Largely my story, but now with some drawings coming along with it. Good.

Peter

[Nick]

http://www.monoandstereo.com/2011/06/why.html

Interesting to read!

Cristoffe hi,

The article is bang on point for my problem ! I think all four of the fr interference types could apply here. The article also points out that VHF level signals only propagate short distance down power lines is useful. This is the final encoragement meded for me needed to invest in some decent quality shielded mains leads (RF is so good for justifying upgrades  ).

I am trying to read as much as possible before I start to making changes to the system, so this is a really useful article, thanks.

Nick.

[Nick]

Hi,

I said I would post a better trace of the VHF noise.

This trace is recorded with more scope memory depth and shows a lot of transmission detail not apparent in the trace I placed in the first post.

The trace is taken from the speaker cables of the system with the pc dac and amp turned off. The 100mhz fm transmission is actually highly modulated, with approx 30db pulses at 60khz and lower level pulses at ~480khz. This looks much more difficult to deal with as a result. The noise extends from 10s of kHz to 100mhz.

Word clock frequency in the my NOS is 706khz and bit clock at 22.6mhz you can see why this interference in the wrong locations in the system can hurt sound quality.

Nick

Edit - updates to the frequencies quoted to properly reflect the trace details.

[PeterSt]

Nick,

By now it could be interesting to see whether you can capture a testsignal (a sine) by this means with the DAC section shut off. So, that you have some sort of carrier for it is new information, but how it can do it still beats me. The 100Mhz seems sufficient though to let it act as some sort of "interference D/A converter". But for example, you then must be able to see that the 100MHz is indeed doing this (the smallest spikes) hence the larger remain sticking out of the signal.
I can't predict what you will see (if anything) and I have the idea that you will see it a kind of other way around : that signal being the carrier on which the high frequency modulates; possible the lower frequency. But, when this happens it will be the peaks riding on the signal which make the signal audible (because the amplitude gets higher). So, you could focus on the peaks of it all to "wobble" along with that test signal, which signal itself you won't see (now the peaks all show on the same maximum level).

Is this important ? I guess not. But a small explanation how without D/A converter digital (music) data is converted to audible sound (though distorted) would be welcome.
haha

Peter

[Nick]

Peter hi,

Thanks for suggesting the test, I see what you are saying about the peaks possible carrying the decoded signal, it would be facinating to understand what could decode the signal with the DAC off, i'll try to capture some traces.

Best Nick.

[Nick]

One problem that's proved to be nothing to do with noise, it's a  bit embarrassing but quite funny   

I have blamed everything in sight for the past 3 years for weird and frankly cr*p Bass. 'Noise', DAC, amp, OS, mains, they have all come under suspicion as possible causes of the problem. Paul and my friend Pete were most polite when they listened to the bass at my place, I'm still waiting to receive their claims for damaged hearing  .

Armed with the new oscilloscope and a 40hz tone track I decided to trace through the system from DAC to active subs to see if there was anything amiss.

The real culprit ? Each of the active subwoofers on my Avantguard Duo's has a gain knob and a cross over frequency knob to adjust these settings on the sub's internal amplifier. Now the right hand sub has always been the one that would just not work, always too loud or too quiet or just cr*p balance ever since the sub amp modules were upgraded about 4 years ago. With the amp module out of the left sub and poking about in the amp module, I noticed that the knob for the cross over setting was slipping on the potentiometer shaft, but is was just tight enough to not be obvious !! This means that the calibration mark on the knob could in effect be anywhere up to 360 degrees out from the actual setting on the potentiometer in the sub that sets the cross over point. Loads of swearing, followed by big smiles when I sat down to listen with subs properly matched and setup. I cannot say what a difference correct settings have made.

What a hobby, never take anything for granted I guess.

Nick.

Ps after looking at the amp module i'v got a nice list of upgrades worked out so maybe even better bass is to come 

[AlainGr]

One problem that's proved to be nothing to do with noise, it's a  bit embarrassing but quite funny   

I have blamed everything in sight for the past 3 years for weird and frankly cr*p Bass. 'Noise', DAC, amp, OS, mains, they have all come under suspicion as possible causes of the problem. Paul and my friend Pete were most polite when they listened to the bass at my place, I'm still waiting to receive their claims for damaged hearing  .

Armed with the new oscilloscope and a 40hz tone track I decided to trace through the system from DAC to active subs to see if there was anything amiss.

The real culprit ? Each of the active subwoofers on my Avantguard Duo's has a gain knob and a cross over frequency knob to adjust these settings on the sub's internal amplifier. Now the right hand sub has always been the one that would just not work, always too loud or too quiet or just cr*p balance ever since the sub amp modules were upgraded about 4 years ago. With the amp module out of the left sub and poking about in the amp module, I noticed that the knob for the cross over setting was slipping on the potentiometer shaft, but is was just tight enough to not be obvious !! This means that the calibration mark on the knob could in effect be anywhere up to 360 degrees out from the actual setting on the potentiometer in the sub that sets the cross over point. Loads of swearing, followed by big smiles when I sat down to listen with subs properly matched and setup. I cannot say what a difference correct settings have made.

What a hobby, never take anything for granted I guess.

Nick.

Ps after looking at the amp module i'v got a nice list of upgrades worked out so maybe even better bass is to come 

Hi Nick,

Do you mean that this EMI thing is solved ?

Alain

[Nick]

Alain hi,

This subwoofer settings are not the cause of the "noise" problems. I just found it funny that something a simple as setting knob slipping on its shaft had caused such a fustrating problem.

The noise problems are still here, but for some reason at the moment the symptoms in my DAC are almost gone, this means that I can use my NOS1 at 8 and even 16x up sampling rates. There is still noise in the system particularly the amp but sound is much better.

I will post a small update on the noise soon.

Cheers,

Nick.

[AlainGr]

Hi Nick,

Ah... I wasn't sure. Well at least there is one problem solved

I will read on as it evolves

Regards,

Alain

[music33]

I have also had troubles with EMI/EMF and have tried numerous things over the years.  I recently tried the Stein Speaker Match and am just flabbergasted at the positive effect it had.  In fact I didn't realize the true affect EMI/EMF was having on my system.  At a minimum you should talk to Holger Stein as he knows about the subject of EMI and if you can try them out.  Below is a link to a review which I think is spot.  He has a plus version which is even better.
http://www.positive-feedback.com/Issue61/stein_speaker.htm

Good luck.

[Nick]

I have been waiting to post an update, all will become clear.

The post above outlines a nasty EMI problem that I thought may be the cause of noise related poor sound quality problems I have been having with my system for a looong time. It was driving me nuts trying to work out how so much EMI was in my domestic environment. Eventually i started to suspect the test equipment and I tried the oscilloscope in a number of places around the UK including Paul's house on a visit to listen to his music system. The noise level was exactly the same at every location. Humm what is the common factor ?... the oscilloscope. The realisation began to dawn, next google for Owon SDS7102 noise and this came up !

http://www.eevblog.com/forum/testgear/review-of-owon-sds7102/1065/

Tens of pages describing what people refer to as "SDS7102 ground noise".

So it turns out the £400 Owon SDS7102 Oscilloscope is plagued with internally generated SMPS noise. Frankly it seems like Owon set some graduate on the design of the internal power supply boards and the result is a scope that is not even a toy in terms of reliable measurement. Any measured trace below about 1v is swamped in the internally generated noise.

Owon as a company have their heads in the sand. There must be hundreds or thousands of customers with SDS7102 scopes that are as useful as a building brick. According to Owon this level of internally generated noise is normal and acceptable in a piece of test equipment. They will not respond to direct warrenty claimes of users (thier products are supposed to have 3 year warrenty...haha) and are basically hanging out all of their users to dry with an expensive and useless product.

DO NOT BUY AN OWON SDS7102 OSCILLOSCOPE UNDER ANY CIRCUMSTANCES.

Rant over.

(Peter if I have broken forum rules above please let me know and I will change the post)

So onto the good / more interesting developments, in the end I still have a problem to solve in my music system so I bought a Rigol DS2072 oscilloscope, after a 5 week wait it was delivered a couple of days ago. It is an incredible instrument, I'm very very pleased with it.

I will start a new thread on tracking down noise issue in my music system with the new scope.

www.phasure.com/index.php?topic=2640.msg27277#msg27277

Regards,

Nick.

Edit  -  typos and add link to new post on system emi noise