Audio Component Grounding and Interconnection

jcx

Member
2003-02-17 7:38 pm
..
Safety Codes and consumer product Standards are not necessarily logically consistent

if Reinforced/Double insulated mains xfmr, internal wiring is followed there should be complete freedom in what to do with metallic cases and outlet protective earth

further in Intrinsically Safe circuit design which keeps chemical plants from exploding diodes used within their continuous ratings are only assumed to fail shorted - with 2 redundant paths 2 cross connected bridge rectifiers would be accepted in this much stricter safety standard as an "infallible" connection for safety analysis
 
Last edited:
First of all: Thank you for a very good article!

I am planning a preamplifier based on the Figure 4.2-3 grounding layout. When unbalanced in- and outputs are used all their shields must be returned directly to the main star ground.

If all in- and outputs are placed close (8 RCA connectors isolated from chassis), could their grounds be interconnected with wire maling the main star? Or must each RCA ground be seperately wired to a common star point?
 
Hi Skorpio,

Think of two things: First is current loops and second is common impedance coupling.

For the inputs, you will have a loop between each input unit's chassis through the interconnect cable to the preamp chassis and back to the input unit chassis through the power cable. However, there will be signal current flowing in a loop when that input is selected. Therefore, since only one is selected at a time, you can share a connection between the input jack field and the main star ground.

There will be current flowing in the output grounds whenever there is music playing. You don't want to mix this output ground current with the input ground current by common impedance coupling, so the ground connection between the output jack and the main star ground should be separate from the ground connection between the input jacks and the main ground connection.

Dave
 
Hi again,

Since most of the chassis current origins from capacitive or magnetic coupling from the mains transformers, could it be an advantage to put all the mains transformers (except for power amp) in a common chassis, and by this holding the low level chassis free of these error/mains return currents?
 
Okay some of you guys have aqll the knowlege to criticise but I wish I had this article way back in 1964 when I seriously started to meddle with electronics. Remember them verydangerous AC/DC tube type equipment? I had some nasty shocks from them as our mains is 245 volts and this bites till I got an isolating transformer. battled with this same problems and had to battle for months on end as I was the only one to ask myself and the basics was to me unknown. I only solved problems by pure luck and was unable to work out for myself what went wong! Thanks for a super article.
 
Second, use a shielded twisted pair for the interconnect cable, with one of the wires in the pair (as well as the shield) being the signal reference
Actually the correct solution IMO is the twisted pair inside a shielded cable, with the shield connected just to the source end star ground.
Any stray fields picked by the shield will be returned to ground, it doe snot create ground loops, all while signal ground does not pick any stray fields.
 
Very nice article, simultaneously clear and comprehensive, which is some feat.

In 4.7 you cover grounding transformers e.g. AC mains transformer frame to safety ground, and tube output transformer isolated from the chassis and the frame attached to the power common, and secondary -ve to power common. It could be useful to also cover other common ironwork on tube amps, such as HT chokes (frame to power common?), anode choke load (frame to power common?), interstage transformers (frame to power common?) etc.
 
I never knew that I knew so little of all there is to know about Grounding equipment.
After hooking up an Active crossover incorrectly and blowing an amplifier after power up while adjusting cross over frequencies I began to take a serious look at the issue of Grounding.
Before -in my audio world, everything just worked out but I was typically only hooking up consumer grade home audio units.
As I have gotten into vintage tube gear and pro audio equipment the need for knowledge has increased far beyond my ability to consolidate all the theories into one place and create a meaningful and (somewhat) concise overview. This article has done that. I found it after scouring the Web - Rane, Peavy and other sites for bits and pieces. This ties much of the needed info together in a meaningful way without too much painful maths.

RANE has some great articles on grounding. Specifically concerning Cables and what should be done at the termination RCA to 1/4" or XLR depending on the type of equipment involved.

Thanks for taking the time to put this together
 

SandroN

Member
2006-12-14 12:08 am
Help with hum

My SE amp (L' Amp - http://www.diyaudio.com/forums/diyaudio-com-articles/200460-l-amp-simple-sit-amp-part-1-a.html) was done with star-grounding. Transformer has 2 secondaries, so I've built 2 PSU (1 for left and 1 for right). Their ground go to star. RCA shield from each channel input and its bias ground go to local references (source of FET).
- With inputs shorted, the amp is super silent (mute).
- With open inputs, almost mute.
- With RCA cable + open ends, almost mute.
- With RCA cable + 2k resistor in each end, mute.
- If the resistors at RCA end (left and right) share the same "ground", audible hum is generated. This occurs with any source connected to the amp (CD player, DAC, etc) because their RCA shields are connected to ground.

Where is my error?

Obs.: I tried loop breaker to star point, earth to star, no earth, all without success.
 

Attachments

  • D01_6430.jpg
    D01_6430.jpg
    481.3 KB · Views: 419

cspirou

Member
2014-08-19 11:55 am
Excellent post.

If I am building an amp around one of those class D modules from Sure or Yuan Jing with an external power brick, how do I deal with the chassis ground? Does everything just float in the chassis? Do I just connect the signal ground to the chassis?