RCA wires... disconnect one ground inside, if jacks are connnected?

Folsom · « **on:** 2 Jan 2009, 03:08 am »

I was thinking because of the situation that every time anywhere in your source and amplifier the grounds of the signal are connected you will create a group loop like it or not.

The only way I can come up with to eliminate it is to eliminate one path. Essentially disconnecting a wire on one of the RCA cords, if both source and amplifier have connected grounds. This is commonly the case.

Any thoughts?

NewBuyer · « **Reply #1 on:** 2 Jan 2009, 06:37 am »

Quote from: Destroyer of Smiles. on 2 Jan 2009, 03:08 am

I was thinking because of the situation that every time anywhere in your source and amplifier the grounds of the signal are connected you will create a group loop like it or not.

The only way I can come up with to eliminate it is to eliminate one path. Essentially disconnecting a wire on one of the RCA cords, if both source and amplifier have connected grounds. This is commonly the case.

Any thoughts?

Hi DOS,

Just wondering if you've considered an alternate approach of using some really good input transformers (Jensen, EBTech, etc)?

Folsom · « **Reply #2 on:** 2 Jan 2009, 06:56 am »

Not yet but I would be using them on the ground. I also think they sound unappealing based on what I imagine they could do to the sound.

I am starting to think a custom cable would be best for this application. Well maybe even more than one cable. I tried to test it by plugging in an RCA just a little ways with a connecting wire but I would have to un-solder the RCA as it was not long enough (some are).

JoshK · « **Reply #3 on:** 2 Jan 2009, 02:44 pm »

DOS,

I think you stumbled upon the standard grounding conundrum. However, all is not hopeless, but if I understand your proposed solution, it is a bit misguided, no offense.

All the information on how to really ground a system is in these forums. It comes up over and over again, and I don't really feel like typing it all again. Look for an article on Elliot Sound Projects on earthing. Look for Dan Banquer's posts (here on the lab) about grounding. Read them till you truely understand them.

The solution turns out to be incredibly simple in your case, if I understand correctly that your system is sources + amp, no preamp? Then add yin/yang ground buster to amp if your source is grounded (via 3rd prong), if not, let your amp be grounded. So you add a switch to tie audio grounds to earth ground in amp directly or through yin/yang.

Your earlier problem with FM is a different problem, that needs to be addressed effectively or all this is going to keep you running in circles.

Folsom · « **Reply #4 on:** 2 Jan 2009, 06:37 pm »

My amp is grounded properly. I have done a lot of reading on this.

I tried grounding the RCA's differently to avoid a loop that went through the amplifier boards but realized you still create a loop with the RCA's themselves, which become antennas, at least with my amplifier boards, no matter what you do, unless you reduce the ground from source to one wire, or you separate the grounds at the source.

When I tried it, it actually had a very bad affect making one of the cables a super antenna by the way.

NewBuyer · « **Reply #5 on:** 2 Jan 2009, 06:48 pm »

I too worried about the effect that line-level input transformers might have on the sound, but found that the good quality ones from Jensen and EbTech are excellent - very transparent and effective. Hope you'll get a chance to try them out! Good luck with your projects.

andyr · « **Reply #6 on:** 7 Jan 2009, 02:01 am »

Quote from: Destroyer of Smiles. on 2 Jan 2009, 06:37 pm

My amp is grounded properly. I have done a lot of reading on this.

I tried grounding the RCA's differently to avoid a loop that went through the amplifier boards but realized you still create a loop with the RCA's themselves, which become antennas, at least with my amplifier boards, no matter what you do, unless you reduce the ground from source to one wire, or you separate the grounds at the source.

When I tried it, it actually had a very bad affect making one of the cables a super antenna by the way.

Mmmm are you sure (it's grounded properly)?

Let me describe to you my system - it's about as complex as you can get in that:
* it's a 3-way active system
* the amps are up one end of the room (plugged into one dedicated spur), and
* sources/preamp are plugged into 2 other dedicated spurs at the other end of the room.

I get zero hum!

If I select, say CD on my preamp (without pressing play on the CDP) and turn the preamp volume control up to full ... I cannot hear a thing with my ear right up against each of the drivers.

But then, all the earthing in my system (all DIY except for the sources) is arranged according to what I believe is the "proper" way!

So you don't have to resort to strange things like disconnecting the 'ground' wire at one RCA plug (which I suspect would stop the signal being tranferred, anyway?) in order to banish hum.

Regards,

Andy

Folsom · « **Reply #7 on:** 7 Jan 2009, 04:13 am »

According to Peter Daniels everything is proper.

I might just need some capacitors between pin 7 and 8 to get rid of the RF seems to be what some have done and Peter recommends. However I am pretty sure the RF might be eliminated by reducing possible loops, and having two transformers (not enough room or ability to get one) and two rectifier boards would do the trick, and in different cases. Monoblocks... no loops to be had! However since mine share the chassis as a ground, and my source does not have separated grounds on the RCA's it greats a loop in the RCAs through star ground. (it would be like if each speaker's ground was connected)

What is your way of grounding?

andyr · « **Reply #8 on:** 7 Jan 2009, 04:30 am »

Quote from: Destroyer of Smiles. on 7 Jan 2009, 04:13 am

According to Peter Daniels everything is proper.

Sorry, DoS ... don't know who "Peter Daniels" is.

But I don't agree that any way is the "right way"! (IE. everything is "proper".)

Quote from: Destroyer of Smiles. on 7 Jan 2009, 04:13 am

What is your way of grounding?

My way of grounding (this can really only be done if you build all your equipment and your ICs yourself)

is as follows:
* all components have 3 core PCs.
* the earth tag of the IEC socket is attached to the chassis. This provides a "safety ground" but also earths the (metal) chassis to provide protection for the internals against RFI.
* no part of the circuit or PS within a component touches the chassis ... ie. yes, you have a "star earth" in a power amp which connects together the PS ground, the 0v land on the amp PCB and the speaker returns but this is isolated from the chassis. RCAs are isolated.
* transformers are oriented (re. active/neutral on the mains switch) so they produce the minimum chassis ground voltage.
* ICs are shielded - however, the shield does not form part of the signal circuit. The signal circuit is a pair of wires underneath the shield ("psuedo-balanced") and the shield is soldered to the RCA barrels at one end only (the source).

Regards,

Andy

Folsom · « **Reply #9 on:** 7 Jan 2009, 07:45 am »

The only difference I have is that my star ground is connected to chassis, and the shields soldered at source (I can change that easy)

Daryl · « **Reply #10 on:** 10 Jan 2009, 01:44 am »

Hi Smile Destroyer,

Unbalanced systems use the ground connection as the return path for the circuit.

So you may not ground lift them or else you will have no ground reference between componets and ground noise between componets will be fed directly into the circuit as you already have discovered.

Balanced systems have two signal wires and the difference between them is the signal.

No ground reference is necessary with balanced systems and lifting ground may reduce noise by eliminating noise current on the shield.

Unbalanced systems should not have any componet grounded except a turntable which is prone to static.

You haven't grounded any componets have you?

markC · « **Reply #11 on:** 10 Jan 2009, 04:39 am »

andyr has it in : "no part of the circuit or power suppply within a component touches the chassis"... you mix signal ground with earth ground and wala...hummmm...

Folsom · « **Reply #12 on:** 10 Jan 2009, 06:50 am »

The star ground is connected to chassis. That is as far as that goes.

It seems to be less humm and more RF. I am told that a 330pf capacitor between the inverting and non-inverting input pins on the chip might rid the RF (7 and

.

Daryl · « **Reply #13 on:** 10 Jan 2009, 02:34 pm »

Quote from: Destroyer of Smiles. on 10 Jan 2009, 06:50 am

The star ground is connected to chassis. That is as far as that goes.

It seems to be less humm and more RF. I am told that a 330pf capacitor between the inverting and non-inverting input pins on the chip might rid the RF (7 and .

If you have system ground connected to the chassis you don't have the chassis also connected to earth ground do you?

That is hopefully you are using a two prong power cord or if you are using three wires the ground wire should not be connected to anything.

I remember you were working on an JFET preamp but this doesn't sound like that project.

By "chip" are you referring to an LM3886 project or something like that?

Your grounding scheme needs to be carefully thought out when designing componets.

I would include a 'ground plane' under the circuit board.

This could be a sheet of copper or aluminum connected to system ground and can dramaticly lower noise levels depending upon the situation.

Folsom · « **Reply #14 on:** 11 Jan 2009, 01:23 am »

This is an Audiosector 3875 chip amp kit.

In other builds having chassis grounded to star ground, and also to earth ground (separate) have worked out (Peter Daniels own). I could disconnect either.

The boards, well it would be sort of hard to do some sort of shield.

Daryl · « **Reply #15 on:** 11 Jan 2009, 04:40 am »

Definately disconnect any ground from the AC receptacle.

Folsom · « **Reply #16 on:** 11 Jan 2009, 05:55 am »

Everyone else says to have earth ground to the chassis, and I am nuts not too. Should I just have system ground (star)?

I could also remove the connection from chassis to star ground.

Niteshade · « **Reply #17 on:** 11 Jan 2009, 10:41 am »

Noise travels through the ground circuit just as readily as anywhere else. You could have something feeding noise into the ground system. Try grounding one side of your RCA cord and then probe around with the RCA's ground wire inside the amp for a quiet spot. Some amps have a capacitor that goes from one side of the AC mains to ground. Does yours have that? Is your amp grounded via the third pin on the IEC socket? Try disconnecting that.

I forgot to mention: Are your RCA jacks insulated from the enclosure? Mine always are so I can choose a quiet ground location.

Daryl · « **Reply #18 on:** 11 Jan 2009, 03:39 pm »

Quote from: Niteshade on 11 Jan 2009, 10:41 am

Noise travels through the ground circuit just as readily as anywhere else. You could have something feeding noise into the ground system. Try grounding one side of your RCA cord and then probe around with the RCA's ground wire inside the amp for a quiet spot. Some amps have a capacitor that goes from one side of the AC mains to ground. Does yours have that? Is your amp grounded via the third pin on the IEC socket? Try disconnecting that.

I forgot to mention: Are your RCA jacks insulated from the enclosure? Mine always are so I can choose a quiet ground location.

NO,

You don't want any connection (not even capacitors) between the mains (or mains ground) and an unbalanced componet.

That is where the loop is created.

The power transformer isolates the mains from the circuit, the only connection is the primary/secondary capacitance of the transformer and you wan't that to be as low as possible.

Unbalanced systems can only use the output voltage from the previous componet and compare it to it's OWN ground potential.

If you have a noise signal between the grounds of two connected componets their grounds will not be the same potential at a particular moment in time.

Thus that noise signal will be incorporated into the music signal.

So to avoid ground differentials in unbalanced systems you need the ground of all componets not to be influenced by anything.

Then when you connect the componets together the ground shields of the your RCA interconnects short the grounds of all componets to the same potential.

If you have each componet grounded different ground levels can be induced in each componet which the shields of your RCA interconnects wont easily be able to short out since they have a finite resistance and inductance.

I will point out here that the shields of coaxial interconnects have lower resistance (due to the amound of metal) and inductance (due to the tubular shape) than interconnects using a strand of wire for ground.

So by minimizing any influence on a componets ground it is easier for the shields of your RCA interconnects to short all of the componets grounds to the same potential.

If 0db (maximum level) is 2 volts for a line level signal and you want the ground noise to be -100db then the differential ground signal between two componets would need to be 20 microvolts.

Niteshade · « **Reply #19 on:** 11 Jan 2009, 03:48 pm »

I should have been more clear- you're right. If that cap is in there (going to the AC mains) take it out.