Hi Richard and others,
Today I finished my single-enclosure stereo VSPS, I'm pretty happy with the limited sound samples I heard from it, but its late already and serious listening will have to wait
Now for the issues...
I have a rather loud humming when nothing is playing. I assumed it was a grounding issue but I played around a bit and didnt find a satisfying solution yet.
So my initial try was as follows :
- Signal ground / com was disconnected from the enclosure.
- Turntable ground is connected to VSPS ground only.
- Mains earth is connected to the case as is the transformer shield (triad medical ones) and it's mounting screw.
- No continuity between the signal and mains grounds
Second try, I connected the turntable ground to the case, which in turn grounded everything together. I did this because the hum seemed lower at first, but Im not sure I had any real gain.
It is quite crammed up in there, but I know some people are getting them silent, so Ill take any advice you have on the grounding scheme for a single enclosure unit.
Thanks!
Today I finished my single-enclosure stereo VSPS, I'm pretty happy with the limited sound samples I heard from it, but its late already and serious listening will have to wait
Now for the issues...
I have a rather loud humming when nothing is playing. I assumed it was a grounding issue but I played around a bit and didnt find a satisfying solution yet.
So my initial try was as follows :
- Signal ground / com was disconnected from the enclosure.
- Turntable ground is connected to VSPS ground only.
- Mains earth is connected to the case as is the transformer shield (triad medical ones) and it's mounting screw.
- No continuity between the signal and mains grounds
Second try, I connected the turntable ground to the case, which in turn grounded everything together. I did this because the hum seemed lower at first, but Im not sure I had any real gain.
It is quite crammed up in there, but I know some people are getting them silent, so Ill take any advice you have on the grounding scheme for a single enclosure unit.
Thanks!
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@cok666n
I expect this is solvable. Your build is neat and tidy so I don't anticipate an error on the VSPS itself or the wiring connections but rather a grounding/layout issue.
Upfront I know from experience those cases are problematical because the black paint insulates the different sections of the case so a fully grounded case may not be realized even if one section is earthed. You need to scratch off the paint at the joins.
Second I notice the green ground lug is the isolated kind, it is not making contact with the case so a separate connection from the VSPS GND to the case is needed.
What is currently connected to the case at the bolt to the left of the VSPS board? It should be the AC earth safety and the board GND and the transofrmer sheild. You can defeat the safety earth to see if that makes a difference to the hum. The case must connect to GND pad of the VSPS board, as well as the green TT earth connection.
I'll leave it there for now. If you can check it's 60 Hz hum not 120 Hz ripple, you can confirm its not a problem with the power supply or voltage regulatyors. The other concern is the proximity of the audio signal lines to the raw AC voltage.
I expect this is solvable. Your build is neat and tidy so I don't anticipate an error on the VSPS itself or the wiring connections but rather a grounding/layout issue.
Upfront I know from experience those cases are problematical because the black paint insulates the different sections of the case so a fully grounded case may not be realized even if one section is earthed. You need to scratch off the paint at the joins.
Second I notice the green ground lug is the isolated kind, it is not making contact with the case so a separate connection from the VSPS GND to the case is needed.
What is currently connected to the case at the bolt to the left of the VSPS board? It should be the AC earth safety and the board GND and the transofrmer sheild. You can defeat the safety earth to see if that makes a difference to the hum. The case must connect to GND pad of the VSPS board, as well as the green TT earth connection.
I'll leave it there for now. If you can check it's 60 Hz hum not 120 Hz ripple, you can confirm its not a problem with the power supply or voltage regulatyors. The other concern is the proximity of the audio signal lines to the raw AC voltage.
Nice! Conceptually, it looks a lot like my VSPS before I upgraded it with buffered outputs, see first picture in post #3416!Hi Richard and others,
Today I finished my single-enclosure stereo VSPS, I'm pretty happy with the limited sound samples I heard from it, but its late already and serious listening will have to wait
Now for the issues...
I have a rather loud humming when nothing is playing. I assumed it was a grounding issue but I played around a bit and didnt find a satisfying solution yet.
So my initial try was as follows :
- Signal ground / com was disconnected from the enclosure.
- Turntable ground is connected to VSPS ground only.
- Mains earth is connected to the case as is the transformer shield (triad medical ones) and it's mounting screw.
- No continuity between the signal and mains grounds
Second try, I connected the turntable ground to the case, which in turn grounded everything together. I did this because the hum seemed lower at first, but Im not sure I had any real gain.
It is quite crammed up in there, but I know some people are getting them silent, so Ill take any advice you have on the grounding scheme for a single enclosure unit.
Thanks!
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Hi Richard, thanks for answering, my comments are below.
So what I did is I ran another small ground wire from the green lug to the chassis screw where the safety and shield are (See attached picture), but I still get some hum.
So now the GND from the VSPS runs from the board to the green lug, then to the chassis screw. Would it be better if I ran 1 wire straight from the board to the chassis screw and 1 wire straight from the green lug to the chassis screw?
@CHiroshi
Are you suggesting my cart might be picking up the hum? It is possible but when plugged directly on my integrated amp phono stage it doesn't pick up any. I did notice the gain seems quite a bit higher on the VSPS though. Test cart is a Shure M97xE.
Thanks all for the comments!
So what I did is I ran another small ground wire from the green lug to the chassis screw where the safety and shield are (See attached picture), but I still get some hum.
So now the GND from the VSPS runs from the board to the green lug, then to the chassis screw. Would it be better if I ran 1 wire straight from the board to the chassis screw and 1 wire straight from the green lug to the chassis screw?
@CHiroshi
Are you suggesting my cart might be picking up the hum? It is possible but when plugged directly on my integrated amp phono stage it doesn't pick up any. I did notice the gain seems quite a bit higher on the VSPS though. Test cart is a Shure M97xE.
Thanks all for the comments!
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If tying the ground lug to chassis didn't fix the hum, I suspect induced hum from the proximity of the transformer and AC wires to the signal board. Ideal is to separate the transformer and at least bridge/diodes into a different chassis. Remember, there's a pretty big signal step-up in any phono stage, so even a small induced hum can result in a pretty loud hum at the output. If you have a way to install a shield around the signal board, that might help, but it looks like that would be a difficult task.
Edit: If using a single chassis, I'd highly recommend a much bigger one with more separation.
Edit: If using a single chassis, I'd highly recommend a much bigger one with more separation.
Hi Carlp,
You might be right, I was warned from the start to use 2 enclosures but still wanted to risk it. Thats why I went with the shielded torroid but it seems it still picks up quite a bit. Live and learn I guess?
I have to crank up the volume way over listening level to hear the hum, so worst case I might just use it like that. I will still take any advice for reducing the hum.
Thanks,
You might be right, I was warned from the start to use 2 enclosures but still wanted to risk it. Thats why I went with the shielded torroid but it seems it still picks up quite a bit. Live and learn I guess?
I have to crank up the volume way over listening level to hear the hum, so worst case I might just use it like that. I will still take any advice for reducing the hum.
Thanks,
No, I wasn't suggesting anything in that sense. I just happened to see that funny comment from rjm while looking for my own posts about my VSPS!
I did have some hum at the beginning of my build, but then i followed rjm's (and other's) advice by connecting all grounds and PE to one common point on the chassis, which made the whole thing almost completely silent. Of course, if I turn the volume all the way up, I do hear som faint hum, I never need to go over 1/3 or 1/2 the volume range on my amp to listen to music at comfortable levels.
However, what I have noticed lately is that my VSPS picks up line noise very easily. I started to use some powerline adapters in the house for the tv-box, and I have to disconnect them to listen to records.
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I would say, and I'm speaking from a lot of experience in building Richard's amps, that the VERY close proximity of the input signal wires to the mains input socket and the mains run to the transformer most will DEFINATELY cause audible mains frequency hum.Hi Richard and others,
Today I finished my single-enclosure stereo VSPS, I'm pretty happy with the limited sound samples I heard from it, but its late already and serious listening will have to wait
Now for the issues...
I have a rather loud humming when nothing is playing. I assumed it was a grounding issue but I played around a bit and didnt find a satisfying solution yet.
So my initial try was as follows :
- Signal ground / com was disconnected from the enclosure.
- Turntable ground is connected to VSPS ground only.
- Mains earth is connected to the case as is the transformer shield (triad medical ones) and it's mounting screw.
- No continuity between the signal and mains grounds
Second try, I connected the turntable ground to the case, which in turn grounded everything together. I did this because the hum seemed lower at first, but Im not sure I had any real gain.
It is quite crammed up in there, but I know some people are getting them silent, so Ill take any advice you have on the grounding scheme for a single enclosure unit.
Thanks!
So if you want to use such a small enclosure the solution would be to use a second one to house the transformer and bridge rectifiers - as advocated by Richard.
Oh, and uninsulated solder lugs on the mains input socket are potentially lethal!
Good luck!
Before starting rebuilding enclosure, you can try some more ground tricks:
First, remove short green wire between board and green lug.
I don't know, have you connection between board and enclosure elsewhere. You can measure continuity between PCB ground and chassis screw(after removing short green wire). If there is no continuity, put wire between white wire on bridges and chassis screw.
After thees mods, you can experimenting with connecting or not connecting ground wire to green lug, even disconnecting ground from input socket to PCB in one or both canals.
For the mechanical layout, some easy things to do:
release transformer bolt and try rotate transformer in one and other direction, try to find position with less hum. Sometime it helps a little.
maybe you can rotate mains input socket by180 degree, so mains wires are not too close to PCB
First, remove short green wire between board and green lug.
I don't know, have you connection between board and enclosure elsewhere. You can measure continuity between PCB ground and chassis screw(after removing short green wire). If there is no continuity, put wire between white wire on bridges and chassis screw.
After thees mods, you can experimenting with connecting or not connecting ground wire to green lug, even disconnecting ground from input socket to PCB in one or both canals.
For the mechanical layout, some easy things to do:
release transformer bolt and try rotate transformer in one and other direction, try to find position with less hum. Sometime it helps a little.
maybe you can rotate mains input socket by180 degree, so mains wires are not too close to PCB
Thanks everyone, it is quite helpful.
Here's what I'm planning for tonight :
- Make sure the grounds meet with the case at a single point (kinda star ground).
- Playing (as much as is possible) with the wires placement and transformer orientation.
- Insulating the mains solder lugs (hehe)
- Rotate the power socket (I would prefer not to since the fuse will be hard to put on there when upside down, but if it helps, it helps.)
If it all fails I'll either follow the consensus and order another box, or just use it like that for a while until I get the hitch to fix it.
Here's what I'm planning for tonight :
- Make sure the grounds meet with the case at a single point (kinda star ground).
- Playing (as much as is possible) with the wires placement and transformer orientation.
- Insulating the mains solder lugs (hehe)
- Rotate the power socket (I would prefer not to since the fuse will be hard to put on there when upside down, but if it helps, it helps.)
If it all fails I'll either follow the consensus and order another box, or just use it like that for a while until I get the hitch to fix it.
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Cok,
I think the rotation recommendation was to rotate the transformer (e.g. turn it on it's side) as that can sometimes affect the coupling of the EM field to nearby items (though I've done that with EI transformers with success, but haven't tried it with toroids). That's a decent idea and might be able to be done with a simple change. Worth a try. Rotating the socket wouldn't likely do anything. And prior to ordering a new chassis, try just moving the AC power supply component outside of the box (breadboard it for now) and then close up the signal box. If that helps, as I suspect it will, then order a new chassis.
I think the rotation recommendation was to rotate the transformer (e.g. turn it on it's side) as that can sometimes affect the coupling of the EM field to nearby items (though I've done that with EI transformers with success, but haven't tried it with toroids). That's a decent idea and might be able to be done with a simple change. Worth a try. Rotating the socket wouldn't likely do anything. And prior to ordering a new chassis, try just moving the AC power supply component outside of the box (breadboard it for now) and then close up the signal box. If that helps, as I suspect it will, then order a new chassis.
I think Carlp is on the right track when he said that since connecting the case to the circuit common didn't fix the hum the problem is most likely inductive pickup from the AC part of the power supply. The fact that the hum level is relatively low backs up that conjecture. As Carl points out, the basic issue is your case is too small.
The best way to test that hypothesis is to temporarily remove the power supply bits from the case, and feed the rectifier output back through the hole where the IEC socket used to be.
However, before you go do that I recommend disconnecting the safety earth at the IEC socket (or with a power cord with only two prongs) and see if that makes a difference.
The best way to test that hypothesis is to temporarily remove the power supply bits from the case, and feed the rectifier output back through the hole where the IEC socket used to be.
However, before you go do that I recommend disconnecting the safety earth at the IEC socket (or with a power cord with only two prongs) and see if that makes a difference.
Here's my recommended layout for a small single chassis build. It looks a little bit like a power brick, designed to be placed behind the turntable or otherwise out of sight as there is no "faceplate" as such.
Note that any noise from the charging currents will be 120 Hz (double the line freq.) So if you only hear 60 Hz you can say the diodes and secondary windings are not the cause and it is most likely straight up noise pickup off the AC wires or primary transformer winding. Note also that by far the most sensitive area of the VSPS is the input signal from the RCA jacks to the op amp input pins.
You want to keep AC as far away from that point as possible.
Note that any noise from the charging currents will be 120 Hz (double the line freq.) So if you only hear 60 Hz you can say the diodes and secondary windings are not the cause and it is most likely straight up noise pickup off the AC wires or primary transformer winding. Note also that by far the most sensitive area of the VSPS is the input signal from the RCA jacks to the op amp input pins.
You want to keep AC as far away from that point as possible.
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Thanks again everyone.
So the star ground didnt change anything but gave me a chance to test without the board grounded to the enclosure (same as first picture) and it was indeed way louder hum.
Now I'm back to "normal" hum.
Per Richard's advice I tried a 2 prong cable and the hum got even lower, I nearly loose it in my test amplifier noise.
I did the 2 prong test before, but that was when the case wasnt properly grounded. So now.. what do I make of this? Running without safety would be quite bad wouldn't it?
Also something just hit me, that Technics amplifier and turntable I have on my bench dont have any safety earth... would that possibly worsen my situation? I didnt want to test on my main system just yet.
Thanks again for all the help.
Ps: yes the layout richard posted wouldve been a whole lot better but I wanted something nice looking.... I will probably order another case at some point.
So the star ground didnt change anything but gave me a chance to test without the board grounded to the enclosure (same as first picture) and it was indeed way louder hum.
Now I'm back to "normal" hum.
Per Richard's advice I tried a 2 prong cable and the hum got even lower, I nearly loose it in my test amplifier noise.
I did the 2 prong test before, but that was when the case wasnt properly grounded. So now.. what do I make of this? Running without safety would be quite bad wouldn't it?
Also something just hit me, that Technics amplifier and turntable I have on my bench dont have any safety earth... would that possibly worsen my situation? I didnt want to test on my main system just yet.
Thanks again for all the help.
Ps: yes the layout richard posted wouldve been a whole lot better but I wanted something nice looking.... I will probably order another case at some point.
For the induced hum, I would certainly change the input/output cables to something shielded.
I always prefer single copper core twisted wires for audio purposes, but when noise creeps in I have to use shielded ones.
For that situation I'd usually employ the use of an RG58 coaxial or for tighter spaces like yours something thinner, like RG178 or RG318.
I always prefer single copper core twisted wires for audio purposes, but when noise creeps in I have to use shielded ones.
For that situation I'd usually employ the use of an RG58 coaxial or for tighter spaces like yours something thinner, like RG178 or RG318.
It is, most likely, both. I'm trying to make the most out of a non-ideal situation to see just how viable it is.
Would shielded input cables really change anything on such short lengths assuming I leave them so close to the AC mains? If so, where should I connect the shield? RCA negative?
The PCB traces must be picking up even more noise than a few inches of wire anyway right?