Sony DVP-S9000S loud humming :(

[OneManDIY]

Hi all,
Here is my latest issue.... I got a rather unkempt Sony DVP-S9000ES DVD/SACD player and it works rather nice for having rusted a bit in the back BUT.... I noticed that it is humming rather loudly :/

Now one day I turned on my system and I noticed a humming sound and as I increased the volume at reference level and it progressively it got worse with the increase in volume. It is very distracting and you can clearly hear it :/

Ok here is the short story:
- when the Sony is not PLUGGED in the power cord, the reciever input makes a very small humm that is not really detectable at 0db but it is there. I'll attribute that to the receiver and all other crap that is plugged in.

- as soon as the Sony gets Plugged in (not powered, just plugged in) the hum gets louder at that input ( i think also several other inputs increased in humm as well)

- than i plug in the interconnects and.... supper annoying hum and buzzing at 0db and at +20b it is just crazy.

- I was testing for the humming with my headphones so i wont damage my speakers.

Mind you that the thing isn't even powered up so it immediately is pointing towards an Earth loop. The earth wire on the Sony connects to the chassis and guess what... when you buzz out the RCA output shield or any ground circuit ground connection, it connect to the chassis earth.

I had the idea that the RCA interconnects are touching the chassis/backpanel and are creating a loop trough there and shorting the earth ground trough the RCA interconnects feeding the hum. I tried isolating the back panel from the RCA interconnects but that didn't help :/

Than I disconnected the earth wire from the IEC socket to the chassis and naturally the whole system became DEAD QUIET! better than my SACD input even :/

I am really temped to leave it disconnected BUT that isn't particularly safe now is it?

I am thinking to isolate ALL circuit boards from the chassis but that will be a major pain and it might not fix the issue since it all leads to earth ground at one point.

Any suggestion guys?

 

[OneManDIY]

excellent reference material found

I did soe research adn found the following excellent reference material.

My solutions seem to be:

1) Istolate the RCA interconnects with a 1:1 transformer. As shown here (Ground Loop Isolators)

- I dont want to do that, I think it might affect the audio quality (not that the hum isn't) and it's bulky. I just don't like having anything in-line with my nice Neotech Interconnects.

2) Buy an AC isolating device like the HUM X (Amazon.com: Ebtech Hum X Voltage Hum Filter: Musical Instruments)
[IMGDEAD]http://www.ebtechaudio.com/humxsplashbanner.jpg[/IMGDEAD]

- There is about $60 price tag.... costing almost as much as the DVD player itself... rather do a DIY job.

3) There might be a short somewhere on the system that makes an impropper loop, Earth to GND connection, instead of a star gnd config. BUT the connectors are not isolated from the chassis (or the chassis paint has rusted and unisolated the connectors) and that some of the screws seem to link PCBs GND to chassis. I isolated the backapanel from the RCA outputs but it didn't help the hum. It seems that the PCB's connect to the chassis trough the screws... or I really need to isolate each one and test.

Should I check for shorts and isolate the PCBs? Would that help?
If the original design didn't care for that type of isolation than it will be major task to do that.

4) DIY Approach based on the article by following article Elliott Sound Products article Earthing Your Hi-Fi – Tricks and Techniques which was linked from the Tomi Engdahl’s ePanorama blog

The article references isolating all the connectors from the chassis (naturally), and creating a small circuit connected to the Earth wire.

the circuit has the following components in parallel:
-diode bridge (both inputs are shorted together and both outputs are shorted together)
- 10Ohm 5W Resistor
- 100nF Capasitor


Earth------\----->---Diode bridge---->----/----> GND
__________\----->---10 Ohnm ------>---/
Chassis-----\---->--- 100nF Cap ---->--/

Has anyone tried this before?




Here are some excellent references I found on grounding and ground/earth loops.

UNDERSTANDING, FINDING,& ELIMINATING GROUND LOOPS IN AUDIO & VIDEO SYSTEMS (.pdf)​

- 43 pages of excellent explanations of how ground loops works, 2 vs 3 prong outlets, cable shielding and cable importance and other relevant stuff.

Jaycar Electronics Reference Data Sheet: HUMLOOP.PDF (1)​

EARTH LOOPS AND HUM
- another excellent read. Shorter and to the point. Excellent diagrams

 

[OneManDIY]

Here is the test solution

Ok, so I've made a quick and dirty Loop Breaker Circuit, and it worked! It reduced the noise significantly and it is barely noticable at 0db, but apparent at +23db.

-Circuit was based on Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

The circuit is the same but with minor changes since I used what I had at the time.

components:
R=8.2Ohm (at least a 1-3W)
C= 47nF 400V Film Cap
Bridge Rectifier: 600V at 6A, P/N: G5SBA60

The Bridge Rectifier will have to be replaced with a much beefier model, and a higher watt rated resistor.

Important - the 9000 also uses a 3-wire system which plugs into a 2-wire system receiver! It basically generates loop current from Earth ground straight trough the shield of the interconnects from the 9000 to the receiver (Sony STR-DA5400ES) an back to Earth.

The difference in my circuit is that the Sony DVP-S9000ES' circuit boards are grounded to the chassis, tough the screws that mount them. Therefore the Chassis is not really isolated from circuitry and tying the Earth to chassis, like Elliott suggests, wont work since nothing else is isolated from the chassis and the circuits will connect straight to Earth bypassing the Loop Breaker. Therefore I had to tie the chassis to the other side of the loop breaker like in my diagram.

It is not optimal but the loop breaker basically filters out some high frequency noise via the Capacitor. Than the Resistor sinks some of that ground current and reduces the dirty voltage from the mains, therefore breaking the "loop"! The diode bridge will provide a path to Earth if there is a failure and electricity wont try to flow trough the interconnects.

I tested the resistance from the loop breaker to Earth of the outlet and it's about 8.2 Ohm (as much as the resistor).

Problem: By using the loop breaker I am not entirely confident that current will flow trough it in case of a failure and that all of that current will shoot trough the interconnect shielding and into the receiver :/. Elliot mentions that the capacitor will also let the circuit see a direct path to ground but I am not entirely understanding that. The loop still exists tho at 0db since there is very unnoticeable hum, so he might be right.


Also, grounding to Earth, BEFORE, the transformers causes this loud hum, but if I ground to Earth AFTER the transformer, the hum is gone.... is that safe, same thing as just lifting the Earth from the chassis, and the transformers isolate the electronics and large currents and voltages can go throughout the chassis, and that of course is dangerous.

Feedback anyone?

 

[OneManDIY]

Turns out.... you would never believe it.... my power strip was what was causing the hum.

Aparently the power strip or one of the contacts on the cables is the cause of this. I twisted the power cables a bit at the power strip and made sure to insert them all the way nice and tight and the hum died down and went away!

At +23db you can hear a slight hum/buzzing but nowhere near what it was before.

BUT the ground loop breaker DID work!

 

[marce]

Interesting, also nice that you found the problem, instead of just treating the symptoms, adding an earth breaker, as like you I have concerns over these, and failure modes, always use a capacitor that will fail as a short if you have to do this.
You mentioned rust, and different grounding before and after the transformer, I wonder if there is a highish resistance contact caused by the rust somewhere in the protective earth path.
Of course another way of solving loops is thick low impedance earth cables between everything, a technique often used with electronic equipment during development, extra holes added for adding ground wires when you get some noise, till the problem is found.

 

[GeorgeBoles]

Hi zxgravediggerxz.

Thanks for writing about such a mundane thing. I have suddenly got this problem in my setup with a cheap Panasonic and Sony DVD player. It is giving me the the willies. I have never read of anybody else making Rod Elliott's bridge, so just some advice please.

1. Could you explain what the WHITE alligator clip is connected to?
2. It looks like the red clip is connected to the chassis. Is that correct?
3. To do the modification, I presume that I need to install a new three lead AC cord and wire it according to your diagram?
4. (I thought of running a flying earth lead to the chassis of an earthed piece of equipment, but that would still need to run through a grommet in the DVD player's chassis, which would be harder to do - and possibly less safe with mechanical abrasion of the lead on the chassis - than with standard mains parts for running a new AC cord, I think.)
5. Should I expect the Chassis and the Electronics Earth/0V to be NOT connected to one another in a double insulated DVD player?
6. And would I expect a Sony or PanasonicDVD to be running +/0 or +/0/- voltages to the electronics?

But, I shall check and change out the power boards first, looking at your experience!

Regards,
George

 

[OneManDIY]

George/All,

Actually the exact cause of my aliments was not the power strip but one of my DIY cables connected to it! It was my star quad cable that I probably messed up the wiring on. Funny thing is that this cable was connected to ANOTHER sacd player which gave me very slight hum but for some reason once I plugged the dvp-s9000 or another player extra it caused more ground loops or something making things worse for everything.


Anyhow.
1. The white aligator clip is connected to EARTH wire in the plug not chassis. Look at my diagram and not the picture for what is happening in terms of wiring.
2. Yes but I would stick to the diagram because I moved the clip around and ended up clipping the ground loop breaker closer to the psu as possible. They say you should insert it near the transformer ground but I couldn't clip to any so PSU ground for me.
3. Hmm this was made for the 3 prong outlet hence the "ground" part in ground loop breaker. I reckon it would work for two prong as well but you need to be careful and maybe read up on it first. You will be isolating your player from the return and it will be somewhat floating.
4. Flying earth wire might be better. What you will have to do is attach it to the chassis but you might introduce more noise and if that happens disconnect it! Be careful!


My advice would be to look at your wiring first. Those players shouldn't hum! Check your power cords, outlets and power strips. It could be another piece of gear causing you this.

 

[GeorgeBoles]

Thanks for the advice, zdigger. I shall search out other problems before I start fiddling too much with the innards of a commercially produced piece of equipment.

What a horrible thought: something I have made might be FAULTY!!?? Egads. Shock. Horror. Impossible! ...

Regards,
GB