More Noise Musings

[Scroobius]

I have been listening to my system a lot since I reduced noise levels as described in http://www.phasure.com/index.php?topic=2697.msg27867#msg27867. Each album has been a surprise and sound quality is just so so good - smooth detailed and just so easy to listen to - better than ever achieved before. More detail better sound stage everything. But why? I just do not know why because using the "ear against the cone" test I would not say that background noise is any lower than it was at its best with my SE GC amp. OK there are better ways to measure noise (ha ha) but even so!!

But last night I played a recording which was my standard "bad recording". Good music but it just always sounded "bad". Clearly it was a bad recording with a nasty hard edge to it. And MUST have been recorded that way. It has always been "bad" even with my SE GC amp in low its lowest noise configuration. Even on my mate Dave's expensive (but not up  XX/NOS standards) system.

So imagine my surprise when I put that album on last night. It is the first time I have actually sat and listened to the whole album all the way through. Amazingly it sounded good - and surprisingly good - there was no hard edge to it anymore.

That has to be interesting. I do not believe that the recording is suddenly OK. Surely there really are nasties on the recording. So why do I not hear them anything like so much now. Maybe there actually is a noise profile on the recording and maybe it "clashed" with my previous system noise profile - that has just changed / reduced substantially in my system.

Then there is the question just how good are Gainclone amps? every time I make these "small" changes to my system the effects are profound - not subtle in any way. What does that say about Gainclone amps? Well for sure they are good but I have no idea how they would stack up against the very "best" amplifiers on the market. Or maybe that is missing the point because with a home made Gainclone you have total control over all grounding both inside and outside the amp - which means in principal you can get noise down to levels that are just not achievable with commercial amps. And maybe that is more important that anything.

I would be interested in Peter's view on the suddenly redeemed bad recording and why?

Cheers

Paul

[Nick]

Paul hi,
Im really interested in this the star earth seems very encouraging, since you posted on this I have been working through how to put a star earth back to my systems dedicated PE spikes as well. I’m just placing the order for wire and sockets etc today and I’m hoping for good things when they go in.

I’v been poking around with my ‘scope and logic analyser for a while now. There is MUCH more happening than I expected with respect PC to DAC to AMP noise. I am still looking for the flash of inspiration that will help to understand and make sense of what I am seeing but thoughts right now are.

In the audio frequency range noise on the USB connections and measured at the output of the DAC is low. However wide bandwidth measurements (up to 200mhz) at the same test points show SMPS and general noise (often with characteristic SMPS and other frequencies) at these test points in the 10mv+ range. Given that my amp inputs generate audible sound from input signal levels of around 100uv this is stuff to worry about. Interestingly these noise measurements improved when I changed my mobo recently and sound quality also improved significantly.

What I am seeing is showing that the electrical noise from the PC is carried both via the USB connection the DAC and also via the mains and the mains PE connections to the DAC and Amps. In addition the DACs own USB interface creates is own noise signature at the DAC outputs (eg the I2S transmission noise I posted on and other and characteristic frequencies from oscillators etc on the board).

Evidence of mains and PE borne noise can be found by measuring at the DAC outputs with only the PC only switched on (eg DAC turned off). It is easily possible to see SMPS and other elements of PC noise at the DAC outputs. Even with the USB lead disconnected there is still noise on the DAC outputs which can only be transmitted via the mains wiring (or radiated) into the DAC from the PC. In fact when only the ATX PC supply is switched on and without the PC booted SMPS noise can be seen on the DAC outputs and with the PC booted disk access noise etc can be seen !

Frankly it’s a little depressing seeing what we are up against and I am struggling to decide what noise is relevant and how to manage all this high bandwidth noise out of the system (I don’t have experience filtering SMPS noise and it seems to propagate everywhere). Perhaps the best approach would be to use the PC only to transfer processed Data to the DAC interface and have an FPGA time the data out of interface memory and into the DAC chips. This would allow for total disconnection of the USB and PC whilst music is played. I guess even wireless transfer to the DAC interface of some sort might allow the PC and DAC to be electrically disconnected from one another.

Going back to the star earth and why it works so well, I am thinking that is could be to do with better referencing of the signal grounds to a common potential within the systems components but also it may be that in some way the star earth is helping manage the USB and Mains wiring transmitted noise between components.

I am looking forward to trying the earth and will try to get some comparative measurements with and without the star earth in place.

Cheers,

Nick.

[manisandher]

Hey Nick, if you ever fancy doing a bit of 'consulting' with that analyzer of yours, let me know.

Great stuff!

Mani.

[AlainGr]

Thanks Nick and Paul !

This raises some questions for me, like "What is a star earth configuration ?" - quite a newbie question I know, but it would certainly be interesting to have a thread with an article about this ?

Anyway, much appreciated food for thought

Alain

[Scroobius]

Hi Alain,

Very simply a star earth configuration is as follows:

Consider that every item of equipment in a hi fi system has to be connected to "earth". Lets say that the earth point is an earth rod or spike in the garden (but it could be the earth in your mains distribution box). Whatever it is a single point.

OK lets say that you have 3 items in your system 1. Amp 2. NOS1 DAC 3. PC. If you connect the earth of each item directly to the earth point i.e. three wires each run separately to the earth point then that is what is called a "Star Earth". But note that this assumes there is nothing else in the system connected to earth (i.e. in the interconnects).

That is not the way the earthing in many hi fi systems is arranged. Typically you may find that the earth of one item is connected to the earth of another and another. In fact what you often find is that (thinking about the 3 item hi fi system again) that the earths of the 3 items are all connected together and then say item 1 is connected to the earth rod and then item 3 is also connected to the earth rod. In that case you would have a loop - and loops are a VERY BAD THING because tiny voltages in the loop can give rise to big currents running round the loop - and that is probably one of the biggest causes hum and noise.

A Star Earth is a GOOD THING because the little voltages on the earth of each item in your hi fi all go directly to the earth rod and are not transferred to other items of kit (well they could be but that is another story) and as there is no loop they cannot run amok running round in circles round the loop.

Oh also note that star earth also is the way that earthing should be arranged inside each piece of equipment so all "things" inside the equipment are separately earthed to a single point on the chassis.

But unfortunately the above is NOT how most hi fi systems are and that is partly because manufacturers are restricted often on the way they earth their kit.

Anyway it is really interesting to get a piece of paper and draw out what the earth layout of your own system is. Where do all the mains earths go? but also remember that the interconnects can have an earth wire in them. But that is where things start to get more complicated.

But that is simplistic it gets way more complicated than that!!!

Cheers

Paul

[AlainGr]

Ah... Finally I understand the principle ! Paul, thanks for this clear and useful example.

I will have to rethink how my system is actually plugged and linked (components to earth and between themselves, which link carries ground and which do not). And I am now aware that some components internals may not be correctly grounded...

It's a lot more motivating to hunt for the "grrrrs" and "zzzzs" that I am hearnig now that I understand what this is about

Regards,

Alain

[Scroobius]

Alain,

now aware that some components internals may not be correctly grounded

Not necessarily the case that a component is incorrectly grounded like Mani's Berning amp it may need to have the electronic ground connected to protective earth for good technical reasons but it does mean the overall system then could have an earth loop depending on how the other components are earthed. Earthing is potentially a whole nest of problems.

What fun!

P