Audio Amp ground.. which one?

[1-3-2-4]

This is from a Logitech Z680 amp

The pins are labeled

SHIELD
VREGSS
SGND
VREGDD
MUTE AMP
STANDBY AMP
SGND
SUB AMP
SGND
CENTER AMP

 

[crutschow]

My guess is:
SGND is the signal ground. All are connected together.
SHIELD is for the shields on shielded wire.

 

[1-3-2-4]

I think you could be right, I just checked with the meter and they are pretty much all connected together

 

[dr pepper]

They probably are all connected.
A common pcb practice is to connect all the grounds to one point on the board, to combat ground hum and other issues.
High currents going out to the speaker returning on the common line (assuming its not a brdged amp) would cause the ground to fluctuate a little due to pcb trace resistance, so if you grounded the speaker right at the audio in connector you'd get feedback issues, same applies for power connections etc.

 

[1-3-2-4]

They probably are all connected.
A common pcb practice is to connect all the grounds to one point on the board, to combat ground hum and other issues.
High currents going out to the speaker returning on the common line (assuming its not a brdged amp) would cause the ground to fluctuate a little due to pcb trace resistance, so if you grounded the speaker right at the audio in connector you'd get feedback issues, same applies for power connections etc.

This amp is bridged from what I last heard, it uses two tda7293 chips.

 

[KeepItSimpleStupid]

Shields should be connected to Earth at one side only. The side is usually the souring side of the signal.

Home audio violates that rule.

 

[dr pepper]

Tha above is a good idea, however the sending device needs a ground!, which can be a seperate cable.

 

[1-3-2-4]

Tha above is a good idea, however the sending device needs a ground!, which can be a seperate cable.

Shields should be connected to Earth at one side only. The side is usually the souring side of the signal.

Home audio violates that rule.

A little confused here.. I know RCA jacks you can buy they have a separate cable in my case my cable is not separate because I hacked a jack out of something else no longer any use for me, anyways On the amp the connections Shield and SGND both ground as checked with the meter.. So as I have it now the shield cable is connected to SGND and the pin is connected to Sub Amp.

 

[dr pepper]

That sounds fine, I think you were getting confused by us techs babbling.
You can connect an rca jack to jack with ground thats fine, nearly every stereo does.
In some circumstances it might be better to use different grounding methods, if your system works as its connected up then use it that way.
It seems that your amp blew up because there was a cable fault, ie broken.
My opinion on home audio violating the grounding at one end rule is that not everyone connecting up a stereo is not an electronics technician, if I were to connect up mine with seperate grounds and loads of jazz then I'm sure something would end up in smoke.

 

[1-3-2-4]

lol the last amp I worked on was on a Hammond B3 organ from what the post office tracking says my chips will be here tomorrow but we have this storm coming so I don't know..

I have back up power so I can always heat the iron up that way

the chip which is the TDA7293 I think it might be better just cutting the legs off?

 

[dr pepper]

I hope you dont suffer any damage or harm from the storm, a relation of mine has been buffeted a few times, they are from florida.

Yes cut all the legs off with a dirty old pair of snips first, unless you have lab desoldering gear its the best way to get them out without pulling out the plated through holes (if it has them).
Another way I use if I want the device intact is to use a gas solder iron with a hot air tip, very effective and doesnt wreck anything with a skillful hand.

 

[KeepItSimpleStupid]

Yep, I do apologize for the confusion.

The point I wanted to make is consumer audio is an unbalanced connection and it's prone to problems such as ground loops and hum, but that is just the way it is to keep costs down.

Professional audio uses XLR connectors which use a differential signal. That system is way more expensive.

 

[dr pepper]

Balanced line low impedance has higher noise immunity than high impedance unbalanced yes, though the cost isnt in the circuitry, theres only a few resistors extra, ok quality neutrik connectors are pricey however I think less production figures and higher mark up are the culprits on that one.

 

[1-3-2-4]

Sorry for the long delay, everything is fine, I was on the generator for about 8 hours but I was out trying to clean stuff up..

Well I have my parts but still don't have power back on at my house yet so still staying at a family member's place. Can't wait to try this out.

 

[dr pepper]

You survived the storm then, excellent.

Keep us posted.

 

[1-3-2-4]

yep sure thing!

 

[1-3-2-4]

So I got back power yesterday night so I'm ready to start working, but clipping the leads what's the best way to clip them? I have snips but they I can tell will be too thick to fit.

 

[1-3-2-4]

OK no more blown stuff but another crazy issue I can just hear just a tiny bit coming from the sub but I have the subwoofer turned up on the receiver so I don't know if it's something on my end, I figure regardless the input wired to the sub amp or any of the other speakers won't have much effect on how it sounds.

Finally pretty much done just need to re-calibrate with sub now

thanks everyone for your input very much appreciate it!

https://www.youtube.com/watch?v=iv9kemlv9gg&feature=youtu.be

 

[1-3-2-4]

Ok must be a ground loop, but a little confused if I remove the subwoofer cable the hum stops, which I expected that but say if I touch a metal part of the heatsink or the RCA jack it's self I can get hum again.

would that mean a bad ground? I wonder if I put the ground wire in between the wrong spot/

 

[dr pepper]

Try disconnecting the ground to the sub, and connect a 100 ohm resistor in line with the ground, that will lift the ground at whatever end needs to be lifted.

Another way would be to connect a beefy cable from the ground on the sub to the ground on whatever feeds the sub signal wise.

Theres quite a lot of distortion on the vid, maybe the cam couldnt cope with the lf, either that or sounded like possibly excursion distortion.