Hum (pun intended). One more thing - or two. Firstly, how about shunting the diode-resistor connection between signals grounds and earth? In some cases a direct connection (but only at ONE point) may be better. Also, in your PSU, where did you connect the signal/power grounds, in the middle between caps or at some distance? The best sequence for PSU ground connection would be, rectifier>interference caps (if any)>filter caps>small decoupling caps>some distance, maybe 1-5 cm>star ground.
Just some thoughts... grounding layout is always tricky. I often have a little hum at first, that goes away with a little thinking and 1 or 2 rewirings or moving things 1 or 2 cm.
Then again, how loud is that hum anyway - maybe we are chasing the normal residual PSU hum... What is your capacitance for filtering?
Just some thoughts... grounding layout is always tricky. I often have a little hum at first, that goes away with a little thinking and 1 or 2 rewirings or moving things 1 or 2 cm.
Then again, how loud is that hum anyway - maybe we are chasing the normal residual PSU hum... What is your capacitance for filtering?
Boris,
I am really sorry. I thought this problem would have been fixed by now. I wonder if the ground loop is not in your amplifier but your preamp. If you are using a CD player as a source why not try connecting it directly to your amplifier without your preamp. If the hum goes away you have a problem in your preamp. It is worth a try as it seems you have tried everything else. It looks as if I am out of suggestions.
I am really sorry. I thought this problem would have been fixed by now. I wonder if the ground loop is not in your amplifier but your preamp. If you are using a CD player as a source why not try connecting it directly to your amplifier without your preamp. If the hum goes away you have a problem in your preamp. It is worth a try as it seems you have tried everything else. It looks as if I am out of suggestions.
Problem solved!!!!!!!!!!!!!!!!!!!! 
No hum or buzz anymore. Don't laugh now.
Here goes the story. After me and Sparkle tried all of the possible combinations of connecting ground, he thought it would be a good idea to try connect different input wires from RCA jack to PCB. He changed my expensive shielded silver wire with a piece of **** Tasker cable/wire. Guess what happened. No hum or buzz whatsoever. Complete silence, until we connected it to a preamp and CD player, then the music starts. No hum or buzz, just a wonderfull Diana Krall's voice.
It looks like my home made shield for the silver wire wasn't a very good shield after all.
Sorry for making such a big deal of it. But I'll make it up to you. I'll write down all of the possible grounding connections anyone ever used or suggested on the net (because I have a ton of material on my computer) and I'll put it on the forum, so you won't have to answer this kind of questions anymore because somebody (like me) is just stupid.
Thank you very much.
I'm buying drinks for all of you
No hum or buzz anymore. Don't laugh now.
Here goes the story. After me and Sparkle tried all of the possible combinations of connecting ground, he thought it would be a good idea to try connect different input wires from RCA jack to PCB. He changed my expensive shielded silver wire with a piece of **** Tasker cable/wire. Guess what happened. No hum or buzz whatsoever. Complete silence, until we connected it to a preamp and CD player, then the music starts. No hum or buzz, just a wonderfull Diana Krall's voice.
It looks like my home made shield for the silver wire wasn't a very good shield after all.
Sorry for making such a big deal of it. But I'll make it up to you. I'll write down all of the possible grounding connections anyone ever used or suggested on the net (because I have a ton of material on my computer) and I'll put it on the forum, so you won't have to answer this kind of questions anymore because somebody (like me) is just stupid.
Thank you very much.
I'm buying drinks for all of you
Funny, I have noticed before that my own Aleph can pick up hum and noise with shielded cables at the inputs if they are not plugged in at the other end. Wonder if your problem is related.
I asked a question elsewhere on this forum on using shielded cables inside an enclosure and where to ground the shield, but the consensus was it's unlikely to make a big difference. So much for theory
I asked a question elsewhere on this forum on using shielded cables inside an enclosure and where to ground the shield, but the consensus was it's unlikely to make a big difference. So much for theory
I'll try to check out what is wrong with that shielded silver wire as soon as I find some equipment for that.
Interesting thing is that I'm using the same wire without shielding for the speaker terminals to PCB and ground and it looks that's not important.
Thanks guys one more time, I see I can count on you!!!
Interesting thing is that I'm using the same wire without shielding for the speaker terminals to PCB and ground and it looks that's not important.
Thanks guys one more time, I see I can count on you!!!
MBK said:
What are the cases where a direct connection between signal ground and earth are better? I'm currently having a hum problem in my BOSOZ preamp, but only when a source is connected with power on and selected by the input switch. Hum is completely eliminated when I mute (which basically disconnects the source and shorts the input to the preamp circuit), or is reduced when I connect my signal star ground point directly to earth rather than through a thermistor as is done in the BOSOZ document.
-Greg
Not shure what I had in mind when I wrote that. I had a specific case I thought of. I think it was if, for instance, you have a source that is not earthed (2 prong plug) and an unbalanced connection. In that case your shield is also the signal ground. A direct connection from signal ground to earth would earth the entire shield, while a diode connection would leave a lot of low level noise coming from the shield "in the circuit", with a direct connection only to ... signal ground, where you don't want it.
In your BOSOZ I assume XLR balanced input. If so, you should connect pin 1 (shield) to chassis at entry and exit, and NOT to signal ground, according to the wise men of the internet (actually some pro audio documents I read). Again it prevents having the shield currents injected into signal ground, and in a bal connection , the shield is not part of the signal.
MBK,
Thanks for the responses. Your first response seems to match my case, as my BOSOZ is used only with unbalanced inputs. My sources all use two prong plugs: DVD player, digital cable box, Playstation 2. I suppose if it's not bad to have the signal ground connected to earth, I should do it to reduce the hum.
-Greg
Thanks for the responses. Your first response seems to match my case, as my BOSOZ is used only with unbalanced inputs. My sources all use two prong plugs: DVD player, digital cable box, Playstation 2. I suppose if it's not bad to have the signal ground connected to earth, I should do it to reduce the hum.
-Greg
Yeah, the problem with unbalanced connections is that the grounding and earthing can not be done absolutely right, by definition: because the shield is also the signal return.
One workaround would be to use 2-wire shielded microphone cable, to use one wire for signal and one for signal ground return, and to connect the shield with a spade lug to a chassis screw on both ends. That way, you could leave your signal ground diode-decoupled from earth (the shield now being part of earthed chassis loop, the signal ground being independent). But, chances are, your sources have signal/shield connected to chassis directly anyway - hereby undoing any benefits you would gain. In other words, unless you are inclined to play around a lot, I'd leave it at that and connect signal to earth in your BOSOZ as well (star ground is earth)...
One workaround would be to use 2-wire shielded microphone cable, to use one wire for signal and one for signal ground return, and to connect the shield with a spade lug to a chassis screw on both ends. That way, you could leave your signal ground diode-decoupled from earth (the shield now being part of earthed chassis loop, the signal ground being independent). But, chances are, your sources have signal/shield connected to chassis directly anyway - hereby undoing any benefits you would gain. In other words, unless you are inclined to play around a lot, I'd leave it at that and connect signal to earth in your BOSOZ as well (star ground is earth)...
Rodd,
in unbalanced mode, you don't have a choice - the shield will have to conenct
For balanced, as far as I have read (Rane, Jensen also has some stuff on it, and others), the recommendation is to conenct the shield to chassis at entry point at both ends (send and receive). The point is to form a complete shield enclosure around your circuit. In a balanced system, the shield is not part of the system, ground / earth loops can and will flow between the chassis, but not caus hum.
And anecdotally, I have gotten hum in my Mini-Aleph when just a loose cable was attached to the inputs...
in unbalanced mode, you don't have a choice - the shield will have to conenct
For balanced, as far as I have read (Rane, Jensen also has some stuff on it, and others), the recommendation is to conenct the shield to chassis at entry point at both ends (send and receive). The point is to form a complete shield enclosure around your circuit. In a balanced system, the shield is not part of the system, ground / earth loops can and will flow between the chassis, but not caus hum.
And anecdotally, I have gotten hum in my Mini-Aleph when just a loose cable was attached to the inputs...
Grau, teurer Freund, ist alle Theorie
und grün des Lebens goldner Baum.
(Goethe, Faust)
(Grey, dear friend, is all theory
And green life's golden tree)
I just completed some chip amps for my woofers follwing my own "ideal" suggestions: chassis earthed, earth to signal ground via diodes. The system is set up for bridged, that is, balanced mode, but for now I have to use it unbalanced with my current active X-O. Guess what: strong hum. Guess what cured it: direct connection between chassis/earth and signal ground.
Had I run this balanced, the common mode rejection would probably have covered up that there even was a problem.
I s'ppose the different impedances of the various transformers in interconnected systems may have something to do with it. I don't think it was a ground *loop* in that it would have had to jump the diodes that connect earth to signal ground in most of my gear, including the preamp and active X-O...
und grün des Lebens goldner Baum.
(Goethe, Faust)
(Grey, dear friend, is all theory
And green life's golden tree)
I just completed some chip amps for my woofers follwing my own "ideal" suggestions: chassis earthed, earth to signal ground via diodes. The system is set up for bridged, that is, balanced mode, but for now I have to use it unbalanced with my current active X-O. Guess what: strong hum. Guess what cured it: direct connection between chassis/earth and signal ground.
Had I run this balanced, the common mode rejection would probably have covered up that there even was a problem.
I s'ppose the different impedances of the various transformers in interconnected systems may have something to do with it. I don't think it was a ground *loop* in that it would have had to jump the diodes that connect earth to signal ground in most of my gear, including the preamp and active X-O...
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.