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Old 24th September 2006, 07:12 AM   #1
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Default Earthing and how it effects sound.

Hi all,
I was messing about with my latest amp over the past couple of days, mainly shifting earth wires. I noticed that quite small alterations had quite dramatic effects on the sound of the amp. It was possible to vary the sound from very thin to bloated to just neutral.
I had read in passing about the effects of earthing on the final voicing of an amp but just thought it was a Hifi legend.

Anyone care to comment on what is going on hear.

Shoog
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Old 24th September 2006, 11:37 AM   #2
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This is a very useful thread, and I'd be personally grateful if it could include how to do the earthing between a seperate power supply chassis and signal chassis - I think a few of us are using umbilicals of various kinds.
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Old 24th September 2006, 12:01 PM   #3
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Hi Shoog

Interesting findings you mention there. About earthing I only know that it should consist of star ground, or two in power amplifiers. And that the thicker the wire, the better. All this to prevent humm and other unwanted effects. But that it changes the sound? I read that an amplifier with very low noise can increase the microdetail (see heretical linestage from SY). Can you give more details (or correlations) on how the wiring influenced the sound...thicker wire did... thin wire that... with/without sleeve... Just tying to understand it better.

Erik
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Old 24th September 2006, 01:38 PM   #4
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I noticed the main differences when tidying up earths which I had carelessly referenced to points on the chassis. The more star grounded I got the better the performance was. I am not talking about hum really, because there was practically no audable hum to start with. Possably its an effect of subtle earth loops and loss of microdetail.
I think we tend to measure voltage performance a lot and we tend to ignore issues of current performance.

Unfortunately I can only hazard a guess as to whats going on here, I was hoping for some of the real gurus to tie this down. I simply remember reading in a few threads about how bodging the grounding could have a detrimental effect on the sound.

Shoog
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Old 24th September 2006, 01:53 PM   #5
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with all the switch-mode power supplies, telephones operating in the giga-Hertz region, carpets made of polypropylene and nylon, earthing should be a very important topic. as well, consideration for line filtration is quite important as well.

in older houses romex shielded power cable was used to connect the boxes. often the shield becomes rusted in which case you have a "potential difference" between the mains ground and what you think to be earth at the receptacle! add to this problem that houses built in the 1950's and 1960's used aluminum wiring but didn't have contacts on switches and receptacles which could deal with the bi-metallic electrolytic effects -- not just noise, but fires as well.

good grounding practice -- your mains box should have a #4 stranded cable which goes all the way back to the street-side of the water connection -- or use a 6 foot length of copper pipe to make the ground connection to ground. if you have "whole-house" water filtration make sure that the filter system is bridged with a #4 stranded wire.

in ham radio land we get treated to frequent articles by the staff writers of QST on the importance of grounding, both for good operation and safety's sake.
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Old 24th September 2006, 02:08 PM   #6
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I think it was John Broskie who exemplified the earthing: he said you should imagine that every ground wire in the amp would be substituted by a resistor, what would it look (or sound) like? The idea was that the more resistance, more noise and so would be pickud up...the lesson, use the tickest wire you can allow (I am using 1,5mm2 solid core myself).

About the umbilical...one SG in the amp and one SG in the power supply. Between both one thick ground wire. This way there is no chance for ground loops. (that's how I learned it)

Erik
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Old 24th September 2006, 07:23 PM   #7
kopite is offline kopite  New Zealand
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I feel that moving an earth after an amp is built should not produce any difference in noise. It may be that there is a parasitic oscillation going on.
Curing hum and noise can be a big learning curve and there can be several things causing it and you can tear your hair out trying to get it right.
For my amp builds I use the Sakuma earth system and it works well for me.
My pre has an outboard psu and an umbilical, besides where the mains power enters the supply and here it has the safety earth connection to the chassis, there is only one other connection to chassis and that is right at the input to the pre, here it is connected to the bus bar.
With my ear to the speakers I can hear only the faintest of noise.
Hum and noise can be so frustrating for the diy amp builder and can really spoil things but so satisfying when you get it right but it aint easy and takes time to learn how to do it.
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Old 24th September 2006, 08:11 PM   #8
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Quote:
Originally posted by ErikdeBest
I think it was John Broskie who exemplified the earthing: he said you should imagine that every ground wire in the amp would be substituted by a resistor, what would it look (or sound) like?
I would add: and an inductor and a capacitance to ground and then look at RF frequencies. The tube sockets, RCA connectors and all ground returns in my learning amp (poor thing has been rebuild a dozen times and is currently a 9002 - a 900 MHz radar triode - driving an EL84 se) are fixed directly to the copper side of a PCB. The only speaker on which any hiss can be heard has a 98 dB/watt efficient horn tweeter, and it's just audible above ambient room noise when the ear is against the driver. I'm a huge believer in managing ground returns. One caveat, as the returns get cleaner and lower impedance it can create the potential for VHF-UHF oscillations. Consider plate and grid stoppers.
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Old 25th September 2006, 03:56 AM   #9
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A basic tool in earthing system analysis is to look at each 0V connection and make sure that for each stage there is a single "reference" 0V point. The main thing you are looking for is that any piece of wire should not have any other currents than the one intended in it. Also think interms of preferred (lowest IMPEDANCE) paths.
An example of what I mean by this is say:
The 0v side of the grid 1 resistor and the 0V side of the cathode bias resistor should have their own separate connections back to the 0V point. They should NOT share a common connection back to that 0V point. That will prevent cathode currents from adding micro noise back into the grid circuit.

They way I build amps (and its only one of many possible schemes ) is as follows.

1) Keep all mains wiring in one corner of the chassis with a local chassis SAFETY ground connection. Power tranny shields, mains filter grounds etc connect here.

2) Have the input socket(s) on the opposite corner of the chassis and have a single 0V chassis earth connection near here (as far from the mains earth connection as is physically possible with your chassis)

3) from that single 0V point I run a BUSSED 0V of reasonably robust (18 or 16AWG min) Tinned copper wire. and connect to it on a STRICT connections follows schematic basis. That is, the first thing that connects (closest to the chassis connection) is the stage 1 Rg1 resistor, then the stage 1 cathode resistor and any cathode bypass cap, then any stage 1 rail bypass cap etc. - right down the other end of the bus is the power supply filter capacitor. This way the largest return currents are confined to the end of the buss away from the low level input stuff.

Note: if using feedback from the secondary of the output transformer connect 0V side of secondary at the point where the feedback (from the hot side of the secondary) is being applied.

This is just what works for me BUT its worked for the builds of the last 6 amp projects and I will be sticking to it from now on.

4) My reference 0V/Chassis connection point is the stage 1 Rg1 connection. From that point I run shielded cable or twisted solid core wires stripped out of CAT 5 cable back to INSULATED RCA input connectors. At the input connector itself I use a 10nF ceramic cap between the 0V side of the input connector and chassis right next to the input connector. This ensures that the signal ground is at RF ground locally and more importantly it effectively extends the shielding action of the metal chassis back along the shield of the input interconnect cable.

Summary:
I have 3 chassis earth connections.
1) The mains SAFETY ground in one corner
2) The single 0V / chassis earth connection as far a physically possible from 1). Its master 0V reference is the stage 1 Rg1 connection.
3) A connection right at the insulated from chassis input socket with a 10nF ceramic connecting this point to the insulated 0V side of the input socket.

Note that the insulated 0V side of the input socket also connects to chassis at the Rg1 0V, start of 0V earth buss point, via the shield of the input wiring BUT its RF ground is to chassis locally via the 10nF ceramics.


Useful??
Cheers,
Ian
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Old 25th September 2006, 07:31 AM   #10
kopite is offline kopite  New Zealand
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Great answer Ian, and my earthing system follows the same routine. Your answer should be pinned up next to any build for reference.
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