What I have done wrong?
I have CD -player at other end of RCA, both channels connected.
If I connect only one input RCA to amplifier... let say left channel, and speaker is connected to left channel output, it is totally silent.
But if I connect speaker to right channel, then noise appears. It is more radio noise than hum or buzz.
I tested this also with right channel... an it is silent too.
But if I connect both input RCA's to amplifier, quite loud buzz appears on both channels.
It sounds like amplifier or preamplifier were oscillating
Maybe some trace blown in the circuit board?
You can try to measure resistance from input RCAs ground to speaker ground, in standard designs it should give almost cero ohms
Oscillation may also be caused by other reasons like some capacitive load connected directly on amplifier output [often with exotic cables]
Is there any noise in any channel without RCAs connected?
Is there any noise when you touch only input RCA ground with CD-player output ground?
Is there any noise when you touch input RCA ground with your fingers?
Maybe some trace blown in the circuit board?
You can try to measure resistance from input RCAs ground to speaker ground, in standard designs it should give almost cero ohms
Oscillation may also be caused by other reasons like some capacitive load connected directly on amplifier output [often with exotic cables]
Is there any noise in any channel without RCAs connected?
Is there any noise when you touch only input RCA ground with CD-player output ground?
Is there any noise when you touch input RCA ground with your fingers?
check the rectifier also...might have "blown" one side...causing unrectified AC to flow in...happened to me once...
Oops..
Sorry my little misleading text. I have so horry to movie so I forgot to my proofreading.
So now I give my last shot to my Crescendo project.
I try wrote this:
If I connect only one input RCA to amplifier... let say left channel, and speaker is connected to left channel output, it is totally silent.
I tested this also with right channel (only right channel input and speaker on right channel)... an it is silent too.
But if I connect only left channel input RCA and also speaker to right channel, then buzz appears.
I tested it also like vice-versa (speaker in left channel and only right channel input RCA connected)... same buzz.
If both RCA'a are connected then buzz appears again.
So problem is still that hum and buzz appears when both RCA's are connected.
That noise (roar or rush) appears when no inputs are conneted. So I guess there is some other problems too.
This problem have been quite long time in my Crescendo project so if I cannot fix this up soon, I will give up.
There is some other disadvatages too:
Too small heatsinks and too small main capacitors and this because chassis is quite small and there is not room enough for those.
It will be pity because I have build quite good metal chassis with very nice cherry wood plate for amplifer. Maybe I can use this for some other amplifer.
Does anybody have some nice amplifier schematic which does not get too warm, becauase those heatsinks are rated about 1C/W or so. Crescendo needs 0.5C/W.
Sorry my little misleading text. I have so horry to movie so I forgot to my proofreading.
So now I give my last shot to my Crescendo project.
I try wrote this:
If I connect only one input RCA to amplifier... let say left channel, and speaker is connected to left channel output, it is totally silent.
I tested this also with right channel (only right channel input and speaker on right channel)... an it is silent too.
But if I connect only left channel input RCA and also speaker to right channel, then buzz appears.
I tested it also like vice-versa (speaker in left channel and only right channel input RCA connected)... same buzz.
If both RCA'a are connected then buzz appears again.
So problem is still that hum and buzz appears when both RCA's are connected.
That noise (roar or rush) appears when no inputs are conneted. So I guess there is some other problems too.
This problem have been quite long time in my Crescendo project so if I cannot fix this up soon, I will give up.
There is some other disadvatages too:
Too small heatsinks and too small main capacitors and this because chassis is quite small and there is not room enough for those.
It will be pity because I have build quite good metal chassis with very nice cherry wood plate for amplifer. Maybe I can use this for some other amplifer.
Does anybody have some nice amplifier schematic which does not get too warm, becauase those heatsinks are rated about 1C/W or so. Crescendo needs 0.5C/W.
Check and see if it's a ground loop...try not to ground your sockets...at least dun make them touch the chassis...or disconnect one ground (at the RCA) and try again...
Thanks li_gangyi, but what you mean about sockets?
Did you mean line input socket or main socket?
Input sockets are isolated from chassis.
Is there any disadvantages if only one input ground is connected?
Some differencies between channels or something?
Did you mean line input socket or main socket?
Input sockets are isolated from chassis.
Is there any disadvantages if only one input ground is connected?
Some differencies between channels or something?
if you seperate youramps...(make them mono) and test them one by one...do you still get the hum?? Try using the same Power supply...but disconnect one channel...
Unfourtunately I cannot reply with a solution, rather, I have the EXACT same problem with my own kit amplifier.
I have tested many different cables, many different sources, and I always get a buzz from both speakers as soon as I plug *both* RCA connectors into the power amp.
I've just gone over the entire chassis setup yesterday to make certain there are no ground loops. All grounds are to the single chassis point, except the audio signal grounds which are isolated from the case. the amplifier make absoloutely no hum or buzz from the corresponding speaker, when one input is driven.
It's also starting to drive me nuts so I hope to resolve this issue soon 🙁
I have tested many different cables, many different sources, and I always get a buzz from both speakers as soon as I plug *both* RCA connectors into the power amp.
I've just gone over the entire chassis setup yesterday to make certain there are no ground loops. All grounds are to the single chassis point, except the audio signal grounds which are isolated from the case. the amplifier make absoloutely no hum or buzz from the corresponding speaker, when one input is driven.
It's also starting to drive me nuts so I hope to resolve this issue soon 🙁
Simboo... Tell me if you found some cure for your humm problem.
1.) Have you tried to connect both input RCA's to amplifier but cut out other channel ground?
2.) Have you only one set of main filter capacitors or do you have own filter capacitors for both channels?
I know... this is VERY annoying problem
1.) Have you tried to connect both input RCA's to amplifier but cut out other channel ground?
2.) Have you only one set of main filter capacitors or do you have own filter capacitors for both channels?
I know... this is VERY annoying problem
Eccu,
I don't know the amplifier you are talking about, but I have experienced this same problem when I built a multichannel amplifier with my friend.
It had exactly same symptoms you describe. I have determined that if relatively large bypass capacitors are used at each amplifier channel, and part of the capacitor ripple current starts to flow along RCA ground (ground loop that is, central ground -> channel 1 amplifier ground -> RCA ground -> RCA ground -> amplifier channel 2 ground -> central ground), thus creating hum. You can actually measure "degree" of your problem by connecting AC current meter between grounds of your amplifier channels. I have not tried this, since I have thought this quite recently, and amplifier is not near me, it is at my friend's place.
I simulated this using PSPICE, and indeed, this happens. Only solution (well, not only, since building separate power supply units would probably eliminate this problem) to this problem seems to be to connect signal grounds to central ground point separately.
Only thing that makes me doubt about that solution is that series inductance in the feedback node might cause HF instability, of course depending on the bandwidth of the amplifier.
Regards,
Janne
I don't know the amplifier you are talking about, but I have experienced this same problem when I built a multichannel amplifier with my friend.
It had exactly same symptoms you describe. I have determined that if relatively large bypass capacitors are used at each amplifier channel, and part of the capacitor ripple current starts to flow along RCA ground (ground loop that is, central ground -> channel 1 amplifier ground -> RCA ground -> RCA ground -> amplifier channel 2 ground -> central ground), thus creating hum. You can actually measure "degree" of your problem by connecting AC current meter between grounds of your amplifier channels. I have not tried this, since I have thought this quite recently, and amplifier is not near me, it is at my friend's place.
I simulated this using PSPICE, and indeed, this happens. Only solution (well, not only, since building separate power supply units would probably eliminate this problem) to this problem seems to be to connect signal grounds to central ground point separately.
Only thing that makes me doubt about that solution is that series inductance in the feedback node might cause HF instability, of course depending on the bandwidth of the amplifier.
Regards,
Janne
forget about the gnd on one RCA...try cutting it..instead just use 1 gnd...for signal that is...
ECCU:
I am working on this problem at the moment, I am about to go off and check out some combinations at the moment.
1) I have not connected both channels with one ground cut, I will try this out now and see.
2) I have two completely seperate amp setups inside one case (ie: two toroids, two amp modules, two sets of mains supply caps) Perhaps it's because they are sharing the common ground? cutting one would in fact fix this as others have suggested? I'll find out in a while 🙂
My star type ground setup consists of the ground from each amps mains toroid (40 - 0 - 40) with the two centers wired to ground for each toroid. Then I have both of the mains supply caps ground going to the same ground point. The PCB ground is connected to the same pin off the supply caps that is going to ground.
The RCA input connectors ground on both modules are connected.
I am working on this problem at the moment, I am about to go off and check out some combinations at the moment.
1) I have not connected both channels with one ground cut, I will try this out now and see.
2) I have two completely seperate amp setups inside one case (ie: two toroids, two amp modules, two sets of mains supply caps) Perhaps it's because they are sharing the common ground? cutting one would in fact fix this as others have suggested? I'll find out in a while 🙂
My star type ground setup consists of the ground from each amps mains toroid (40 - 0 - 40) with the two centers wired to ground for each toroid. Then I have both of the mains supply caps ground going to the same ground point. The PCB ground is connected to the same pin off the supply caps that is going to ground.
The RCA input connectors ground on both modules are connected.
Just tested it with only one ground on the input. The buzz becomes slightly louder when it's disconnected from one of the channels. it also gives me bad buzzing when a lead is connected to the input (but no anything else) so I leave it on now.
Normally I have an RCA splitter to go from my sub-out on the amplifier into two RCA leads, which goes into this power amp, to power two subs. So basically the easiest way to test this is that I get an RCA lead and connect it between both inputs (this will give me the same result as if I had this how I normally set it up for both subs?) I get the exact same buzz when this happens, it's slightly louder when one ground is disconnected.
I just went around the house checking for fluro's and the likes. My loungeroom has a light dimmer switch, could this be the possible cause to this annoying buzz?
I gave a crude test by sharply turning the dimmer knob and small intervals, and the buzzing noise had variations on each twist of the dimmer switch.
My question is this. If I were to wire up a new line from the fuse box to my audio room, will this eliminate the buzzing?
Normally I have an RCA splitter to go from my sub-out on the amplifier into two RCA leads, which goes into this power amp, to power two subs. So basically the easiest way to test this is that I get an RCA lead and connect it between both inputs (this will give me the same result as if I had this how I normally set it up for both subs?) I get the exact same buzz when this happens, it's slightly louder when one ground is disconnected.
I just went around the house checking for fluro's and the likes. My loungeroom has a light dimmer switch, could this be the possible cause to this annoying buzz?
I gave a crude test by sharply turning the dimmer knob and small intervals, and the buzzing noise had variations on each twist of the dimmer switch.
My question is this. If I were to wire up a new line from the fuse box to my audio room, will this eliminate the buzzing?
Heheh, that was going to be my last resort, as it seems to be the most expensive! however, I think I may as well do it now by the sounds of it as I have the exact same module in a mono subwoofer setup in another room, and it exhibits no problems at all.
I guess I've gotten to the stage that the only thing left that it could be is the two amps sharing one case..
Eccu, can you post a drawing or a photo showing the layout (at least grounds and placement of transformers)?
It seems a typical ground loop problem... a first, blind suggestion: use the Aleph wiring scheme posted on Krijstian's site.
Cheers
Andrea
It seems a typical ground loop problem... a first, blind suggestion: use the Aleph wiring scheme posted on Krijstian's site.
Cheers
Andrea
dont mean to take over, but since I have the same symptoms, perhaps these pics I just took could help with our problem?
Please ignore the disconnected RCA lead I was testing something and broke the signal joint 🙂
Ground is where the pink and yellow wires (toroids) go to and blacks going to the same spot are from the caps as well as a third black wire from the mains power socket earth.
Please ignore the disconnected RCA lead I was testing something and broke the signal joint 🙂
Ground is where the pink and yellow wires (toroids) go to and blacks going to the same spot are from the caps as well as a third black wire from the mains power socket earth.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
As I suspected there is a ground loop built-in 😉
This loop contains the transformers and this is not good as well.
I'd try exchanging position between trafos and caps first (so they are outside the loop) , then I'd change the central gnd point, placing it near the caps and then eventually going to the chassis with a single wire or a small value resistor. The safety gnd can be connected directly to the chassis.
If this is not enough you can disconnect the shield in the RCA pins and put at its place a wire that goes straight to the common star point.
This was the "single supply proposal".
Since you said you have a dual-mono capability, just work dual-mono: leave the amps isolated from each other and eventually go with the gnd fro only one to the chassis.
Cheers
Andrea
This loop contains the transformers and this is not good as well.
I'd try exchanging position between trafos and caps first (so they are outside the loop) , then I'd change the central gnd point, placing it near the caps and then eventually going to the chassis with a single wire or a small value resistor. The safety gnd can be connected directly to the chassis.
If this is not enough you can disconnect the shield in the RCA pins and put at its place a wire that goes straight to the common star point.
This was the "single supply proposal".
Since you said you have a dual-mono capability, just work dual-mono: leave the amps isolated from each other and eventually go with the gnd fro only one to the chassis.
Cheers
Andrea
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