I have built a giovanni Stochino Mosfet Power Amp and have been testing the amps, they work fine apart from what seems to be ground loops *** soon as I connect them either or both input to my Audiolab surround sound processor output.
I am confused as to what is going with the ground loops.
I am running both amps off 1 +/-50 V supply for the ouput
stage and 1 +/-55V regualted supply for the other stages.
The contruction notes specifiy using 2 sperate supplies for the amp.
I have connected the power ground for each amp to a star point
which is run well away from the center tapping of the power capacitors.
The Ov for the +/- 55V regualted supply is also connected to the star
point.
1.) When powered without the inputs connected there is a definited low level hum from the speaker, I am not sure why this is, When I conect the mains earth to both input signal grounds on the phono connectors for each amp the hum disappers and there is virutally no buz or hum from either amp. Not sure what is going on here why the mains earth should erradicate this.
When I connect my Audiolab to the either or both amp inputs then
buz and hum can be clearly heard from the speaker. And I cant think why this is, If its eliminated when I connect the mains earth to the signal ground then why does hum and buz come back when the audiolab is connected. If I then disonnect the mains earth from my amps signal ground so that only the audiolab is still connected to the the mains earth then the hum and buzz is still there.
I am well confused as to what is going on.
Can anyone help
Thanks
Steevo
I am confused as to what is going with the ground loops.
I am running both amps off 1 +/-50 V supply for the ouput
stage and 1 +/-55V regualted supply for the other stages.
The contruction notes specifiy using 2 sperate supplies for the amp.
I have connected the power ground for each amp to a star point
which is run well away from the center tapping of the power capacitors.
The Ov for the +/- 55V regualted supply is also connected to the star
point.
1.) When powered without the inputs connected there is a definited low level hum from the speaker, I am not sure why this is, When I conect the mains earth to both input signal grounds on the phono connectors for each amp the hum disappers and there is virutally no buz or hum from either amp. Not sure what is going on here why the mains earth should erradicate this.
When I connect my Audiolab to the either or both amp inputs then
buz and hum can be clearly heard from the speaker. And I cant think why this is, If its eliminated when I connect the mains earth to the signal ground then why does hum and buz come back when the audiolab is connected. If I then disonnect the mains earth from my amps signal ground so that only the audiolab is still connected to the the mains earth then the hum and buzz is still there.
I am well confused as to what is going on.
Can anyone help
Thanks
Steevo
Have a read at this -- all of it 
http://www.diyaudio.com/forums/showthread.php?s=&threadid=101321&perpage=20&pagenumber=1
http://www.diyaudio.com/forums/showthread.php?s=&threadid=101321&perpage=20&pagenumber=1
Because you are using one xformer for supply, which means a common GND node for both channels at star point and another one in your surround processor unit, it is caused a nice ground loop. Make a sketch on the paper and you will find the loop.
Now the only solution it is the seperation of the ground of the input RCA sockets with 2 resistors of 10Ù from the shield of signal cables. Maybe this can resolve a little your problem.
Regs
Fotios
Now the only solution it is the seperation of the ground of the input RCA sockets with 2 resistors of 10Ù from the shield of signal cables. Maybe this can resolve a little your problem.
Regs
Fotios
Although some advocate ground loops as being the cause of hum, it is not necessarily the case as it needs an understanding of what creates the hum.
Assume for a moment that your +-50V supply is actually +50.1V and -49.9V, then the 0V is actually not 0V. Now assume that the other piece of equipment has the same problem and you find the 100 Hz ac component superimposed on the "ground".
The amplifier will do its job in amplifying this and you will hear it as hum on the speakers. Hence nothing connected no hum and something connected produces hum.
Regulators and filtering does not get rid of this problem.
Assume for a moment that your +-50V supply is actually +50.1V and -49.9V, then the 0V is actually not 0V. Now assume that the other piece of equipment has the same problem and you find the 100 Hz ac component superimposed on the "ground".
The amplifier will do its job in amplifying this and you will hear it as hum on the speakers. Hence nothing connected no hum and something connected produces hum.
Regulators and filtering does not get rid of this problem.
The mains ground is a safety ground. It should be connected to the chassis or enclosure but not to any part of the circuit.
The star ground(s) of the amp should really be star grounds. I don't know what you mean by saying that the start grounds are 'well away' from the cap ground. The star ground should be the midpoint of the supply, the return of the supply caps and the speaker return. If you have a single supply for two amps, the star ground should be common for both amps, both speaker returns going to this star point. Then you have the signal ground. The input RCA's should of course be isolated from the chassis, and the screen continued to the circuit board input entry. There should normally not be a connection between that input ground and any heavy current points. For reference, you can connect the screen of one input only to the star ground or the chassis through a small (1-10) ohms resistor.
If your samp hums without any input then there is a problem with the grounding of the amp ground and ref points. Try to solve that rather then trying to cover it up with other stuff. Including other pieces of equipment before solving this only takes you further away. Divide and conquer!
Jan Didden
The star ground(s) of the amp should really be star grounds. I don't know what you mean by saying that the start grounds are 'well away' from the cap ground. The star ground should be the midpoint of the supply, the return of the supply caps and the speaker return. If you have a single supply for two amps, the star ground should be common for both amps, both speaker returns going to this star point. Then you have the signal ground. The input RCA's should of course be isolated from the chassis, and the screen continued to the circuit board input entry. There should normally not be a connection between that input ground and any heavy current points. For reference, you can connect the screen of one input only to the star ground or the chassis through a small (1-10) ohms resistor.
If your samp hums without any input then there is a problem with the grounding of the amp ground and ref points. Try to solve that rather then trying to cover it up with other stuff. Including other pieces of equipment before solving this only takes you further away. Divide and conquer!
Jan Didden
Giovanni Amp Hum Problem
I think my problem is more complicated than just a ground loop, with both amps running from the same supply, and 1 channel only connected to my audiolab processor preamp I still get hum/buz, without any inputs connected the amps are as quiet as a mouse, so with 1 input connected only there is no ground loop between the amp beacuse they are only coonected together at 1 single star point, I think each amp pollutes the ov's return to the star point when an input is connected , and to eliminate it I need to re-route the feedback returns, and coupling returns from each amp to the single star point, in other words redesign the grounding on amp . I would need to hack and cut the large ground tracks on each borad to do this so I aint gonna bother. The grounding arrangement was not designed for a common supply I think, the original article does recomend seperate supplys to avoid ground loops, so I'm gona stick with seperate supplys. I tried to save money but in the end not worth it, Then I can be confident of getting the performance specificed by Giovanni. But i have learnt alot about grounding in the process.
steevo
I think my problem is more complicated than just a ground loop, with both amps running from the same supply, and 1 channel only connected to my audiolab processor preamp I still get hum/buz, without any inputs connected the amps are as quiet as a mouse, so with 1 input connected only there is no ground loop between the amp beacuse they are only coonected together at 1 single star point, I think each amp pollutes the ov's return to the star point when an input is connected , and to eliminate it I need to re-route the feedback returns, and coupling returns from each amp to the single star point, in other words redesign the grounding on amp . I would need to hack and cut the large ground tracks on each borad to do this so I aint gonna bother. The grounding arrangement was not designed for a common supply I think, the original article does recomend seperate supplys to avoid ground loops, so I'm gona stick with seperate supplys. I tried to save money but in the end not worth it, Then I can be confident of getting the performance specificed by Giovanni. But i have learnt alot about grounding in the process.
steevo
Bearing in mind all the usual safety warnings, is your preamp connected to mains earth. Is the power amp ? Try disconnecting in the plug one or both grounds temporarily.
Anything like that would certainly create aground loop. Is the OV line of the power amp connected to mains earth ?
Do bear in mind all the safety implications, what I have mentioned above is just to try as a test, not to leave like that
Anything like that would certainly create aground loop. Is the OV line of the power amp connected to mains earth ?
Do bear in mind all the safety implications, what I have mentioned above is just to try as a test, not to leave like that
yes, hum can be caused by other things besides ground loops.
fwiw, i just recently debugged a hum problem in a RIAA board i was installing into the preamp im building. while trying the numerous usual approaches to eliminating hum, i noticed that when i placed my hand near the RIAA board (but not touching it) the hum got worse in a big way. so, i decided to try a trick that i use for RF circuits all the time ... enclose the sensitive circuitry in its own little metal box and ground the box, thus producing shielding from external signal pickup.
well, i found a metal dual outlet box (for wall outlets) and just placed this physically over the RIAA board face down, enclosing it. then the hum got REALLY loud. but as soon as i clamped a test lead between star ground and the metal box, the thing instantly got quiet as a mouse.
so, i guess some component(s) on the RIAA pcb were picking up the hum? idk, just happy its gone
fwiw, i just recently debugged a hum problem in a RIAA board i was installing into the preamp im building. while trying the numerous usual approaches to eliminating hum, i noticed that when i placed my hand near the RIAA board (but not touching it) the hum got worse in a big way. so, i decided to try a trick that i use for RF circuits all the time ... enclose the sensitive circuitry in its own little metal box and ground the box, thus producing shielding from external signal pickup.
well, i found a metal dual outlet box (for wall outlets) and just placed this physically over the RIAA board face down, enclosing it. then the hum got REALLY loud. but as soon as i clamped a test lead between star ground and the metal box, the thing instantly got quiet as a mouse.
so, i guess some component(s) on the RIAA pcb were picking up the hum? idk, just happy its gone
Hi
I think this is proper thread for my problem so I am posting it here.
So, I am bulding an amplifer which works, but i have a small problem with ground loops (buzz and hum). Well the problem was with no proper grounding so i decided to redesign a new grounding with central point. But there is one thing, which puts me in dilemma. I don't know exactly how to ground an amplifier to a ground point. Shoud I connect my amplifier stage directly to a cental ground or sholud I connect it through the "smoothing (capacitor)" module? I think this is not a difficult question for you guys. So what do you think?
There is a picture bellow, which illustrates what i mean.
I think this is proper thread for my problem so I am posting it here.
So, I am bulding an amplifer which works, but i have a small problem with ground loops (buzz and hum). Well the problem was with no proper grounding so i decided to redesign a new grounding with central point. But there is one thing, which puts me in dilemma. I don't know exactly how to ground an amplifier to a ground point. Shoud I connect my amplifier stage directly to a cental ground or sholud I connect it through the "smoothing (capacitor)" module? I think this is not a difficult question for you guys. So what do you think?
There is a picture bellow, which illustrates what i mean.
Attachments
Maybe I could shed some light on the subject as the sound is described as a hum/buzz. This is not necessarily a ground loop but it could very well be introduced by a offset in power supply ground.
A very common occurrence is that there is a potential difference between two or more pieces of equipment grounds. Even a very small voltage would be amplified by your amplifier in the same way that a valid signal is amplified.
This is a very common problem between PC and equipment as a PC power supply can be several volts different from the "0V" reference of you amp.
There are several ways to solve this and many uses a resistance of low value in the input ground. Another way is to decouple the transformer center tap from the rest of the system also through a small vale resistor, and of course my favorite the virtual ground.
A very common occurrence is that there is a potential difference between two or more pieces of equipment grounds. Even a very small voltage would be amplified by your amplifier in the same way that a valid signal is amplified.
This is a very common problem between PC and equipment as a PC power supply can be several volts different from the "0V" reference of you amp.
There are several ways to solve this and many uses a resistance of low value in the input ground. Another way is to decouple the transformer center tap from the rest of the system also through a small vale resistor, and of course my favorite the virtual ground.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.