[nuforce]

We were investigating noise problem with certain preamps and found out that some preamps violated the "star ground scheme" and normally it will not affect linear amp (not entire true) but cause trouble for high performance switching amp such as NuForce. To proof our point, after we corrected the grounding error of a cheap (unfortunately discontinued) Cambridge preamp, its THD went down from 0.5% to 0.003%!!! And it sounded very good. All we did was to remove to incorrect ground wires.

For the details, see
http://www.nuforce.com/support/recommendations.htm

If you find any preamps with grounding errors and fix it, please let everyone know how you did it and the improvement. Post the pictures here please. If you spotted the error but not sure how to fix it or measure THD, contact NuForce support and we can help (priority given to NuForce customers but we can assist non NuForce customers for a small fee).

Jason & Casey

[nuforce]

Correction: THD+N improvement is from 0.05% to 0.003%

Jason

edit: measurement was THD+N using HP 8903B

[Rocket]

Hi Jason,

Considering the amount of posts you make at audiocircle why don't you see if you can have an owners circle?  I know you went thru the process of trying (i still can't figure out how you didn't get one) to get a manufacturers circle but you are posting an awful lot and it would be better for your customers.

Regards

Rod

[Occam]

Would you elaborate on the specifics of how you are measuring that THD %?  What is typically reported is (THD + N)% i.e. a component of that measurement includes the contribution of noise in addition to actual total harmoninic distortion. This is a result of the methodology usually used in which a fundamental is fed to the DUT (device under test) and removed via a notch filter at the output. The resulting residual is reported as (THD+N)%.
Would you describe your testing protocol? What specific instumentation is used? I certainly agree that proper grounding can do much to eliminate noise and hum, but am uncertain as to whether these mods you reccomend actually reduce THD or are simply minimizing noise, which in and of itself is a very good thing.
TIA

[gonefishin]

Hi Jason,

Considering the amount of posts you make at audiocircle why don't you see if you can have an owners circle?  I know you went thru the process of trying (i still can't figure out how you didn't get one) to get a manufacturers circle but you are posting an awful lot and it would be better for your customers.

Regards

Rod

   here, here!

  I'm not in the market for any new amp at all.  But I find that nuforce (Jason & Casey) have more than "proven" themselves.  Also, the advice has been much more than the ever constant self promotion of the other individual who raised all this caution to begin with.

    These are two completly different people.  I think nuforce has earned a circle.

  dan

[Doc Jr 8156]

I hope Nuforce will get its own Circle.  It's about time.  Godspeed.

[audioengr]

Star-grounding isn't all it's cracked up to be IMO.  Paying more attention to current paths, particularly current-return paths is more important.  External ground-loops are also a concern of course.  In general, the current paths for power delivery should not share with the paths for signal returns.

[nuforce]

Occam is correct to point out that we need to post more quatitative analysis of the THD improvement.  We have AP equipment at a different lab but so far, the measurement for the Cambridge preamp THD is just using an HP audio analyzer that generate sine wave to the preamp and then take the THD+N measurement from the preamp out.  The HP analyzer has 30K and 80Khz filter, and can only take single point measurement.  But the improvement is clear enough that it is worth posting. We'll like to find out if others can make similar observation with their preamp or phono. It is quite easy to spot this type of grounding violations. There is also a very clear listening improvement on the preamp after the fix.

[Dan Banquer]

"Star-grounding isn't all it's cracked up to be IMO."
I'll disagree with that, but what usually happens is that the star ground is usually "violated" somewhere in the unit and therefore nullifies it.
After 15 years part time in audio I not aware of any grounding standard per say, and am still convinced that gounding problems are the major reason why most consumer audio gear does not perform anywhere near as well as it should.
Let's face it: grounding issues cause units to be more susceptible to interference, and grounding issues cause more hum and noise therefore nullifying many units with good SNR. I strongly suspect that this could well be one of the major contributors to what audiophiles call synergy, or the lack thereof as the case maybe.
I even strongly suspect that the major reason why many people use AC line isolation transformers has a lot to do with grounding.
But hey; what do I know.
               d.b.

[nuforce]

What we'll like to find out is how widespread this is happening (the Cambridge preamp that we fixed is not a high end preamp and not surprising that it has grounding error). And how much improvement we can get out of it.
My friend Casey always open up every CD/DVD players he bought to adjust the ground connections.

Jason

[guest1632]

Occam is correct to point out that we need to post more quatitative analysis of the THD improvement.  We have AP equipment at a different lab but so far, the measurement for the Cambridge preamp THD is just using an HP audio analyzer that generate sine wave to the preamp and then take the THD+N measurement from the preamp out.  The HP analyzer has 30K and 80Khz filter, and can only take single point measurement.  But the improvement is clear enough that it is worth posting.

Could you give more details as to how to spot bad grounding or mixed grounding issues? Thanks.

Ray

[nuforce]

Occam is correct to point out that we need to post more quatitative analysis of the THD improvement.  We have AP equipment at a different lab but so far, the measurement for the Cambridge preamp THD is just using an HP audio analyzer that generate sine wave to the preamp and then take the THD+N measurement from the preamp out.  The HP analyzer has 30K and 80Khz filter, and can only take single point measurement.  But the improvement is clear enough that it is worth posting.

Could ...

Multiple groundings would be the first indication of bad grounding, as multiple grounding paths lead to ground loop.   For example, with the preamp we worked on, these were the groundings:

1)  Output RCA grounded to the chassis
2)  Input RCAs grounded to the chassis
3)  Digital volume control circuit board grounded to the chassis
4)  AC ground wire grounded to the chassis

** plus the aboves are not 'star-grounded', they are all over the chassis.

The first grounding we severed was (1), as the output is on the isolated (secondary side) of the transformer, it should never be grounded directly to the AC ground.  Next we removed (2) as it caused a ground loop between output RCA and input RCA shells.  

The modified preamp now having (a) signal ground through the center tap of the secondary transformer widing;  (b)  one single ground from the digital board to prevent digital noise corrupting the audio signal and (c) the original AC ground still connected to the chassis.

[Dan Banquer]

I am going to take the liberty of putting up a post I did quite sometime ago on this forum because it directly applies to what is being talked about in this thread.
                        GROUNDING PRACTICES IN CONSUMER AUDIO

As many of us have observed over the years grounding practices in consumer audio have for many of us been a frustrating experience. Compatibility/Synergy are consistently major issues, as well as safety, reducing ground loops, noise and interference. Designers are equally frustrated by this problem. Some of us wish it would go away and others attempt to deal with as best as we know how. There does not appear to be much of any standardization that I, and many others are aware of. Many of us who work in the electronics industry outside of audio who have observed the posts from audiophiles, designers and dealers scratch our heads in near disbelief.
The following is not only an outline for reducing these problems, but a wake up call to this end of the industry. The following is for the application to consumer unbalanced audio, and could well be a possible outline for positive discussion and direction. It is also a way to use Earth Ground to our advantage instead of a problem.
Chassis Grounding:
The following is a technique used in instrumentation for low frequency applications.
The chassis will be earth grounded via the earth ground at the three-prong outlet. The audio signal ground contained in the chassis is not connected to the chassis ground. This will require the design to be electrically isolated from the chassis ground which is easily solved by using nylon stand offs to mount pc boards and isolated bulkhead RCA jacks. (I am going to break this rule later on but bear with me for the moment). The above forces the design to be star grounded at the return of the power supply, which is always good practice to reduce noise and ground loops. However, this does leave the present configuration susceptible to interference from the inputs. This interference can be reduced by the using a simple common mode ac line filter at the AC input and using either a well shielded coax or microphone cable at the line level input. This configuration also poses an additional problem due the fact that we now have two different grounds with two different potentials. In the past I have observed this problem when using a certain brand of rotary switch for a volume control. The rotary switch was not well isolated internally and had enough of a leakage current so that noise was developed when it was used. Moving to a different vendor with higher isolation devices corrected the problem. I have not observed any problem with standard switches for on off applications or anything similar.
I have applied this technique to basic audio chain of equipment consisting of an outboard DAC, line level pre amp, and power amps using the chassis and grounding design I outlined above. The transport that I presently use is a modified consumer device and is equipped with a two-prong plug. The system also has an FM tuner and an old pre amp that is used as a phono pre amp. Both of these devices are standard consumer issue with a two-prong plug. I have observed no compatibility issues with the older style units.
As I outlined earlier I am going to break this rule at one point. The line level pre amp now has a connection from the return of the line stage pre amp power supply to the chassis of the unit. I have now connected earth ground to the analog “center point of the system.” This did not cause a ground loop at all, and to be more precise, for CD playback the inherent ground loops that are typical for unbalanced circuitry simply disappeared. The FM tuner and the old pre amp appear to be unaffected by the center point earth ground. A welcome addition was that the rotary switch that had a leakage problem because of the two different potential levels described earlier no longer had the problem due to center point earth ground.
The use of the system center point earth ground for low frequency applications has been in the textbooks for at least 30 some odd years and has been applied to other low frequency applications. Applied at this level to a simple chain of audio playback equipment, CD playback now has reduced hum and hiss to levels more akin to balanced design than unbalanced design. Playback of FM tuner and Phono pre amp remains unaffected.
One thing that has surprised me relates to the issue of low frequency applications. I was expecting to find problems with the digital portion of this playback chain. I have not found one to date but I think this needs to be investigated further when time allows.
A note to all of the tweakers who read this: I am not recommending any changes to existing designs; in fact I would discourage it.
To DIY folks: You may wish to rethink some of your present chassis/grounding schemes.
To the rest of the industry; this is a subject that not only deserves discussion but an active participation to reach acceptable standards.
The grounding system described above will not address the problem of toroidal transformers mechanically vibrating due to either DC on the AC lines or as I have observed on occasion, low frequency oscillations.
Dan Banquer

[DVV]

I am going to take the liberty of putting up a post I did quite sometime ago on this forum because it directly applies to what is being talked about in this thread.
                        GROUNDING PRACTICES IN CONSUMER AUDIO

As many of us have observed over the years grounding practices in consumer audio have for many of us been a frustrating experience. Compatibility/Synergy are consistently major issues, as well as safety, reducing ground loops, noise and interference. Designers are equally frustr ...

While I completely agree with the above, I must point out a practical problem. Grounding via the three prong plug, be it in North America, Europe, Australia, Japan or elsewhere, can be a risky business simply because the nominal electrical standards for the ground are hardly ever observed in real life.

Nominally, the ground should have a potential of 0.8V or less and an impedance of 100 ohms or less. However, in real life, with modern slap 'em together construction practices which extend to electrical wiring, I have yet to see this in real life on buildings made after say 1960.

A friend from Paris, France reported his ground potential to be - believe it or not - all of 70V! True, he lives in a 19th century building, where electrical wiring was definitely an afterthought, but my own experience shows the ground potential to be hardly ever better than 12-15V best case.

With a potential like that, grounding itself becomes a dicey proposition. So, if you are able to, I would advise you first make sure your home grounding is what it should be. Ultimately, use a 3 by 3 foot copper plate sunk some 6 feet into the ground with a THICK wire connection; that should give you something awfully close to an ideal grounding point. That alone will make a @#$%^&* of a difference, believe me.

Then follow Dan's rules for even better performance. The rest of us, living in condos, can only envy you.

Cheers,
DVV

[JoshK]

I have heard it said that using the third prong earth ground in addition to a stake in the ground ground is a big no-no.  I'd be a bit nervous to do this.   Are you suggesting that one disregard using the third prong ground and in lieu of use a copper stake in the ground?  

To me grounding schemes are really a dark cloud.  I like Dan's suggestion because it makes sense to me and makes me wonder why it isn't more widely used, since it seems so straight forward.

[DVV]

I have heard it said that using the third prong earth ground in addition to a stake in the ground ground is a big no-no.  I'd be a bit nervous to do this.   Are you suggesting that one disregard using the third prong ground and in lieu of use a copper stake in the ground?  

Exactly, Josh. That way, you know for sure you have proper ground. There's no better way, as far as I know.

Not easy for us urban dwellers, eh?

Cheers,
DVV

[JoshK]

Well now that I own a house I do have such an option.  I will have to ponder this some....   I do need to drive a grounding stake in the BY for my antenna.

BTW, stupid question but how do you test the potential of ground?  Between the third prong and what?

[nuforce]

Here's another example of bad preamp grounding. May be NuForce can be used as the reference amp to find out if there is any grounding problem in your system.  

http://www.nuforce.com/support/preamp2-grounding-errors.htm

Again, our customer reported noise problem with NuForce and we ended up improving his preamp's performance by an order of magniture. All the measurement and fixing were done on his preamp and did not involve any changes in NuForce amp.

[Dan Banquer]

Josh K: You really should call an electrician. Where I live the earthground of the house is tied directly to the incoming water pipe, which is about as good as it gets. Recently I have been concerned of the use of plastic/PVC pipe in construction but from what I understand that is only allowed on the waste side of the pipes and not the incoming side. If you are tied into the main water system I would definetly consult with your electrician and proceed as he suggests.
If there are qualified electricians monitoring this thread please feel free to respond.
               d.b.

[guest1632]

Here's another example of bad preamp grounding. May be NuForce can be used as the reference amp to find out if there is any grounding problem in your system.  :wink:

http://www.nuforce.com/support/preamp2-grounding-errors.htm

Again, our customer reported noise problem with NuForce and we ended up improving his preamp's performance by an order of magniture. All the measurement and fixing were done on his preamp and did not involve any changes in NuForce amp.

I wrote Curt, and here's part of his reply.

"The heavy trace we solder the ground wire to is connected directly to and only to the pad the screw is in (to the chassis), his mod didn't change our ground circuit at all,  impossible for this to be a ground loop.

Actually the only thing grounded (AC earth ground) in the Purist is the chassis, all the audio is floating. We depend on a good audio source ground and just use the earth grounded chassis as a shield around our circuits. There is no chance of an audio ground loop in the Purist.

The only thing I can think of right now is that if the amp puts a lot of noise on the AC lines it could come in on the Purist's power cord and if our screw was not making a good connection (perhaps a little paint in the standoff) this power line noise might get into our power supply (because the IEC filter might not work at peak performance) which could cause noise. But this is a long shot. It's possible but no amp should be putting out that much noise. Actually I can't see how that solderless connector could make any difference."

 He then memtioned that people had reported to him about the noise problems with the Purist--Nuforce combo.

I suspect something rather small is going on on the Nuforce side, enough to elude you. Anyhow, that is it for now.

Ray.