I finished my GC yesterday and it sounds incredible through my KEF speakers. My problem is that when both input cables are plugged into CD player, there is a slight but annoying 60 Hz hum. When only one or none are plugged in, the amps are silent. I'm using a single torroid PS and two seperate amp cases. CAses are plastic w/ foil lining. I have no attenuator and am going to place a 47K resister and 100pf cap across inpot to signal ground although, I believe this only avoids problems when no input is present.
Any help appreciated.
David
Any help appreciated.
David
possible ground-loop
David
It sounds to like you have a ground-loop. Since I don't know your wirering, I think the most easy way to solve it is to disconnect the ground in one of your signal-connectors. Just disconnect it at the power-amp end.
You could also try to put you inout cables as close as possibel together to make the loop as small as possible.
let me know how you get on.
Thomas
David
It sounds to like you have a ground-loop. Since I don't know your wirering, I think the most easy way to solve it is to disconnect the ground in one of your signal-connectors. Just disconnect it at the power-amp end.
You could also try to put you inout cables as close as possibel together to make the loop as small as possible.
let me know how you get on.
Thomas
thanks tlmadsen
Hi Thomas, thanks for the imput . I'll give it a shot. I read somewhere that a cap from input shield to ground may help...what do you think.
David
Hi Thomas, thanks for the imput . I'll give it a shot. I read somewhere that a cap from input shield to ground may help...what do you think.
David
Re: possible ground-loop
Thomas, I tried disconnecting the signal ground..horrible HUM!
If I connect the grounds from each amp together, the hum is reduced but still present, but seems to reduce the base response.
David
tlmadsen said:
Thomas, I tried disconnecting the signal ground..horrible HUM!
If I connect the grounds from each amp together, the hum is reduced but still present, but seems to reduce the base response.
David
Hello
I have same kind problem in my Crescendo amp...
I think those input shields should be connect to same point (starpoint) in amplifier. I must try that too when I have time to do that. I will tell you if this is cure for hum poblem.
I have same kind problem in my Crescendo amp...
I think those input shields should be connect to same point (starpoint) in amplifier. I must try that too when I have time to do that. I will tell you if this is cure for hum poblem.
Re: Re: possible ground-loop
Can you draw an actual diagram of your ground arrangement? Please include all parts from your amp that should be grounded.
Until now all cases here from people complaining on hum could be traced to an incorrect (loop) star grounding.
Carlos
sounder said:
Can you draw an actual diagram of your ground arrangement? Please include all parts from your amp that should be grounded.
Until now all cases here from people complaining on hum could be traced to an incorrect (loop) star grounding.
Carlos
sounder said:
😱
Hey David,
Sorry to give you the bad news, but that doesn't work.
If you have a single PSU for both channels you have to run a very short (and thick) wire from one channel's star ground to the other.
Impossible to do with two separate boxes.
In your implementation you have a huge ground loop.
Or put the two channels inside one case or buy another toroid and use an independent PSU for each chanel.
or just use 2 input transformer's ... but then again this aint cheap but will fix ALL the hum
still using 2 main transformers is a the easy way to go
still using 2 main transformers is a the easy way to go
Thanks for all the input guys, I have reconfigured the amp wiring twice since I posted this. I'm beginning top see the light now and there IS a huge ground loop from one star ground through the two outputs at the CD back to the other star ground. That's why it is dead silent with only one input plugged into the CD. So I'll live with the hum...which actually distorts the lows and mid-low..a kind of rumbling break up. Too bad none of the schematics point this out. What does 47 Labs do with the Gaincard and the standard single humpty configuration?
David😕
David😕
sounder said:
First of all Thorsten's IGC schematics do point out how to handle your star grounds.
Second, I don't see why you have to live with the hum if you have identified the source of it. Why not correct it?
The Humpty supply, as far as I know, is not a complete mono one. But I'm sure they do provide a way to handle likely ground loops.
Carlos
David,
If you don't want to spend more money on another toroid, then put the two channels close to to each other on the same box.
Does it fit?
Or buy/make another box.
Man, after the work you had I don't understand how you can leave it that way.
You don't know what you're loosing.😉
Oh, BTW, the ground loop you have is on the PSU too.🙄
If you don't want to spend more money on another toroid, then put the two channels close to to each other on the same box.
Does it fit?
Or buy/make another box.
Man, after the work you had I don't understand how you can leave it that way.
You don't know what you're loosing.😉
Oh, BTW, the ground loop you have is on the PSU too.🙄
I run one PSU supplying:
- 2 chip amps per channel, and
- 1 active crssover per channel
So, same PSU for 2 channels at 2 amps and 1 active XO each, and I get no hum in spite of the ca. 6 ft. long PSU cables.
So, it can be done. BUT, the star ground must really honor its name. So my paths go like this: amp1left joins grounds with amp2left and XOleft at one single point (spades clamped on top of each other). This single point then runs to the PSU box and connects to ground at the center of the PSU main caps. Analogous for the right side.
In star grounding I found out that millimeters do matter. I did get bad hum or interferences whenever I didn't follow the star ground logic religiously. And of course, I don't quite like this arrangement, separate transformers make life much much easier.
- 2 chip amps per channel, and
- 1 active crssover per channel
So, same PSU for 2 channels at 2 amps and 1 active XO each, and I get no hum in spite of the ca. 6 ft. long PSU cables.
So, it can be done. BUT, the star ground must really honor its name. So my paths go like this: amp1left joins grounds with amp2left and XOleft at one single point (spades clamped on top of each other). This single point then runs to the PSU box and connects to ground at the center of the PSU main caps. Analogous for the right side.
In star grounding I found out that millimeters do matter. I did get bad hum or interferences whenever I didn't follow the star ground logic religiously. And of course, I don't quite like this arrangement, separate transformers make life much much easier.
carlmart said:
OK Carlos, point well taken. I should have mentioned too that I was thinking of building MKII, ie. another GC which has a little more "air" as my present one is a little mashed in.
But, before I give up on the present one, I have a Piltron toroid 115v/30v/30v ie. single primary and dual secondries 300VA.
I also know the peak voltage exceeds the chip max and that is is why it runs a bit warm. Could the higher voltage be causing a problem? Or, could the problem stem from switched secondary wires; that is the start point of the secondary windings? The torroid diagram denotes the start of each secondary winding with a dot. If the winding "phases" are inconsistent between the two amps, can that be causing the 60hz hum? And if so, would it only manifest itself when both input grounds are bridged by the CD player?
I guess I need to tear it all down and check it again.
Thanks David
moamps said:
MOAMPS, Thanks for the time and the input. I layed out your diagram in Illustrator (it's one of the things I do in my other life)and will post it if you don't mind as soon as I figure out how to. Still puzzled at how to attach it so it displays in the post?
Anyway, iIf one uses a seperate power supply case, must the star ground be in that case, and if so, would I run two ground wires from ea. amp to the star ground in addition to the +V amd -V. Is that a correct interpretation of your diagram?
Regards David
Just realized the bridge rectifer is drawn incorrectly.
🙁
Any suggestions or corrections welcome
David
🙁
Any suggestions or corrections welcome
David
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