I'm building my first PTP amp, a version of Fred Nachbaur's Miniblok SE. I'm doing my initial assembly on a piece of plywood. I'm curious as to the proper method of mains grounding and component grounding when doing this.
Forgive my ignorance, but I figure this is no time for making a blunder.
Thanks!
Forgive my ignorance, but I figure this is no time for making a blunder.
Thanks!
Hi,
I'm not sure what you call it in the US, but mains grounding is the same as safety earth here.
The safety earth does not make the audio side work any better nor does it allow the sound quality to improve.
If anything the sound quality and audio performance deteriorate when the safety earth is connected to the audio side.
BUT, and this is very important, one cannot quarantee that the amplifier will be safe if you omit the safety ground. The rule is that all exposed conductive parts must be connected to safety ground.
For the moment let's ignore the safety ground.
Design the audio side to get the best performance possible with the grounding system you choose.
After this is done find a way to interconnect the audio side to the safety earth with the minimum audio effect and retain the safety function of the mains side of the build.
Good luck.
I shall await other inputs and listen carefully for any improvements the Forum can give me.
I'm not sure what you call it in the US, but mains grounding is the same as safety earth here.
The safety earth does not make the audio side work any better nor does it allow the sound quality to improve.
If anything the sound quality and audio performance deteriorate when the safety earth is connected to the audio side.
BUT, and this is very important, one cannot quarantee that the amplifier will be safe if you omit the safety ground. The rule is that all exposed conductive parts must be connected to safety ground.
For the moment let's ignore the safety ground.
Design the audio side to get the best performance possible with the grounding system you choose.
After this is done find a way to interconnect the audio side to the safety earth with the minimum audio effect and retain the safety function of the mains side of the build.
Good luck.
I shall await other inputs and listen carefully for any improvements the Forum can give me.
AndrewT said:
Let's not. As you said, all exposed metalwork should be connected to safety ground. Further, all dangerous voltages should have two protective layers between them and the user. The layers can be two independent insulating layers (double insulated), or one layer of insulation and one grounded conductive layer (like an aluminium chassis).
Connect the circuit's 0V ground to the chassis near its input. Connect the safety earth to the chassis where the mains comes in. Make each connection good and solid (none of these loosely tightened M3 screws).
Thanks for the replies. I appreciate the links and the comments. I do understand the basics discussed, and had both of those links bookmarked previously.
What I'm unsure of is how to do this while using a wooden plank while setting up the circuit. I intend to use the ever popular aluminum top plate/bottom plate, wooden side panel arrangement on the finished product, but for now do not want to do something stupid due to my ignorance and inexperience.
What I'm unsure of is how to do this while using a wooden plank while setting up the circuit. I intend to use the ever popular aluminum top plate/bottom plate, wooden side panel arrangement on the finished product, but for now do not want to do something stupid due to my ignorance and inexperience.
I cannot think of any DIY projects that use double insulation as suggested by EC8010. However, I think that his comments should not be dismissed.
The most crucial aspect of DIY building is to ensure that the user cannot touch anything that is electrically "hot." This includes circumstances where soldered / crimped wiring may become loose and touch any exposed metal parts.
I typically use a bolt with star washers that "bite" into the chassis for good electrical contact. I use two nuts combined with a lock washer. I can then connect grounding wires from the IEC Earth and the PCB earth to this bolt.
If anyone (ECC8010) has any ideas for double insulation, it would be good to mention them.
As for testing a circuit mounted to a plank. You have a couple of options:
1. Don't worry about the Earth, BUT ensure that only you do any testing of the system and be extra careful. Maybe have someone capable of telephoning for an ambulance be around when you poke around your test system. Then UNPLUG and allow caps to discharge. With anything like this, I try to ensure that my wife is in the house to pull the plug when I am poking around my projects.
2. I suppose that you could earth the transformers with ground wires connected to the earth of your IEC socket. However, your components will also be exposed.
3. When doing any testing, I try to ensure that I only have one hand near the component at any one time. I suppose the idea is that if both hands allow electrical discharge, then the shock is more likely to pass through your heart.
4. When messing about with your project (even when it is in its proper chassis), remember that even if you switch off your project, the inside of the IEC socket will still be "hot" in other words, pull the plug from the mains if you don't need it plugged in.
I have built a couple of projects in wood sided chasses with metal (steel) tops. I always ensure that I have a good earth point using star and lock washers. I often use a mounting bolt from the transformer. My projects have separate back chassis plates with the IEC socket. Again these are solidly earthed using sturdy bolts and star / lock washers.
A final point of note, is that I do remember reading an email from a DIY'er who had access to electrical testing equipment. This is the kind of equipment that tests safety earths. I guess that the equipments blasts a high amperage jolt through the metal cabinets and somehow tests how effectively it is carried away to safety earth. Anyway, this DIY'er reckoned that a reputable brand of audio equipment failed on his test equipement, while his own DIY creations passed with flying colors!
Charlie
The most crucial aspect of DIY building is to ensure that the user cannot touch anything that is electrically "hot." This includes circumstances where soldered / crimped wiring may become loose and touch any exposed metal parts.
I typically use a bolt with star washers that "bite" into the chassis for good electrical contact. I use two nuts combined with a lock washer. I can then connect grounding wires from the IEC Earth and the PCB earth to this bolt.
If anyone (ECC8010) has any ideas for double insulation, it would be good to mention them.
As for testing a circuit mounted to a plank. You have a couple of options:
1. Don't worry about the Earth, BUT ensure that only you do any testing of the system and be extra careful. Maybe have someone capable of telephoning for an ambulance be around when you poke around your test system. Then UNPLUG and allow caps to discharge. With anything like this, I try to ensure that my wife is in the house to pull the plug when I am poking around my projects.
2. I suppose that you could earth the transformers with ground wires connected to the earth of your IEC socket. However, your components will also be exposed.
3. When doing any testing, I try to ensure that I only have one hand near the component at any one time. I suppose the idea is that if both hands allow electrical discharge, then the shock is more likely to pass through your heart.
4. When messing about with your project (even when it is in its proper chassis), remember that even if you switch off your project, the inside of the IEC socket will still be "hot" in other words, pull the plug from the mains if you don't need it plugged in.
I have built a couple of projects in wood sided chasses with metal (steel) tops. I always ensure that I have a good earth point using star and lock washers. I often use a mounting bolt from the transformer. My projects have separate back chassis plates with the IEC socket. Again these are solidly earthed using sturdy bolts and star / lock washers.
A final point of note, is that I do remember reading an email from a DIY'er who had access to electrical testing equipment. This is the kind of equipment that tests safety earths. I guess that the equipments blasts a high amperage jolt through the metal cabinets and somehow tests how effectively it is carried away to safety earth. Anyway, this DIY'er reckoned that a reputable brand of audio equipment failed on his test equipement, while his own DIY creations passed with flying colors!
Charlie
Grounding can seem confusing, just remember that current comes from the transformer and returns to it. Always use a transformer don't rectify the mains. Earth ground is just used for voltage reference, both for the chassis and the audio/power ground, (if you choose to not let it float) current shouldn't flow through earth ground. The power transformer is first wired to the resivoir cap and then to the audio ground. Do the same with the power side. This will minimize hum from charge currents. I usually tie the power ground(from the resivoir cap) to audio ground at the output stage. Devices can share paths on audio ground, but make sure they only have one path to get there. Meaning avoid loops, they cause massive hum. If you do reference your power/audio ground to earth ground it is best done at the input jack rather than at your power/audio grounds star point. That way if you use a signal source that's earthed, such as a PC, it's more resistant to hum. Though sometimes it isn't possible to ground at the input without causing a ground loop in the amp (such as two mono amps sharing a transformer, since they will also have to be tied togeather at the transformer as well). In that case you would have to ground at the main star point(where power meets audio ground) and just isolate the jacks from the chassis. And if using a grounded source you would have to hack the sheild off one end of the RCA cables.
In one of the links from above you may read the following:
"Even better is a two-point star, where the power supply grounds (PT center tap, first filter cap ground) and output stage grounds (output tube cathodes for fixed bias, or cathode resistors for cathode biased, and output transformer secondary ground) are connected together and to the chassis at a single point, right at the ground of the first filter capacitor. "
Sakuma San did grounding in that way. You can see it here:
http://www10.big.or.jp/~dh/inside/abo.html
Does somebody have experience with this kind of grounding ? Is it superior to star grounding all-in-one-point ?
"Even better is a two-point star, where the power supply grounds (PT center tap, first filter cap ground) and output stage grounds (output tube cathodes for fixed bias, or cathode resistors for cathode biased, and output transformer secondary ground) are connected together and to the chassis at a single point, right at the ground of the first filter capacitor. "
Sakuma San did grounding in that way. You can see it here:
http://www10.big.or.jp/~dh/inside/abo.html
Does somebody have experience with this kind of grounding ? Is it superior to star grounding all-in-one-point ?
cbutterworth said:
Nor I. It's because it's too hard to ensure compliance. It's fairly easy to inspect an earthed metal chassis and determine whether it's possible to touch a high voltage. Having done that, it's reasonably easy to check that the resistance from the earth pin of the plug to any metal point on the chassis is < 0.5 Ohm (preferably 0.1 Ohm). By contrast, testing the insulation of a double insulated product is harder, needs specialised equipment, plus rather more knowledge of standards and specific construction of items like mains transformers.
Realistically, building a high voltage amplifier on an open wooden plank is dangerous no matter what you do. Nevertheless, lash-ups sometimes have to be done; I just hope you can live with it.
Cbutterworth: Yes, a typical Portable Appliance Tester (PAT) drives 25A from the earth pin on the plug to wherever you connect to the chassis and measures the resistance. The advantage over using a simple DVM is that a frayed lead with only one (very short) strand connecting could still have a low resistance, but the PAT tester will blow such a problem apart and reveal it. Simultaneously, my PAT tester applies 1.25kV to the live pin and checks that leakage to chassis is below 0.75mA.
I agree with you, I would certainly just go ahead and build your project in its proper chassis. I just finished a Hagermann Cornet2 phono. This was the first project over which I took time. Rather than solder parts, etc., I invested a few weekend mornings (my workshop is outdoors, and I live near Phoenix - hence only a few hours at weekends) getting my wooden chassis completed. I then methodically moved onto the steel top and back plates. Only when I had these finished, did I begin slinging solder. Anyway, the whole project was stress-free. Mind-you, I had to be very methodical as I was using $50 worth of quilted maple for the chassis, and this made for some stressful dovetailing!
Another reason for building your project into a "final" chassis from the outset, is that once you get your "plank" project working, you'll have the agonizing wait while you get it properly housed. At least I would be desperate to play music rather than rehouse it, and I would be stressed about breaking thinkgs as I did the re-housing.
So, take your time, making sure that you get each step right as you go along.
Good Luck,
Charlie
Another reason for building your project into a "final" chassis from the outset, is that once you get your "plank" project working, you'll have the agonizing wait while you get it properly housed. At least I would be desperate to play music rather than rehouse it, and I would be stressed about breaking thinkgs as I did the re-housing.
So, take your time, making sure that you get each step right as you go along.
Good Luck,
Charlie
69CamaroSS396 said:
It is sometimes easier to experiment with values and make changes when you breadboard the amp first.
To give a simple answer to your first question-
Just put a bolt into the breadboard material and connect the safety ground (earth ground, mains ground) to it. That is the green wire in a typical three-prong plug. Then run one wire from your power ground to this point and one wire from your signal ground to this point.
For the past couple years I've used a little setup I made that has a mains switch and fuse mounted on a metal plate that is screwed to a piece of MDF. The safety ground from my three prong plug is connected to the metal plate. Behind the metal plate I have a screw type terminal strip to which I can connect whatever transformer I need.
When I build a circuit I run a single wire from the power ground and one from the signal ground as described above to the safety ground point on the plate.
Still, with exposed high voltage be VERY careful when testing a breadboard project.
Thanks! Patience is one thing I'm not lacking. I am approaching 53 years of age, and something I have learned is that cutting corners always shows up in the finished(or in some cases, unfinished) product, whether it be in quality of appearance, performance, functionality, or reliability. Or all of the above.
Hi,
I often (always) breadboard my projects. I usually use an encapsulated mains transformer with flexible leads. These are connected via an insulated terminal block and Thermistor back to a mains plug top and the secondaries are then reserved for the various interconnections required. eg. centre tapped, or dual rectifier etc.
I have every circuit in the house (except the lounge) on RCCB circuit breakers for extra protection. But, I should never need that.
If you go for a temporary style of test installation then do ensure you can work undisturbed and that children and animals cannot gain access. And don't work when tired!!!
I always use a bulb tester (ballast) for first switch on, sometimes in conjunction with a Variac. And again when ever I modify anything, no matter how minor it seems.
BTW,
if you can bear with me.
I had a garage with external floodlight. The RCCB fed a remote fuse board that in turn fed the floodlight and workshop.
I pulled the fuse for the floodlight so that I could re-wire it. Then while up on the ladder I was slackening the screws on a terminal strip supplying the flood. I heard a click. What was that?
Carried on and completed the re-wire. Inserted the fuse and "no light".
Oh! the RCCB has fired.
Ahh. The click was when the insulated screw driver had touched the neutral screw terminal. The RCB has detected the current from my body passing to the neutral in the RCCB and it measured the unbalanced return current (there was no Live current because the fuse was pulled) and said "fault" and switched off. I was impressed. Since then I have always specified RCCBs on each of my power rings around the house.
I often (always) breadboard my projects. I usually use an encapsulated mains transformer with flexible leads. These are connected via an insulated terminal block and Thermistor back to a mains plug top and the secondaries are then reserved for the various interconnections required. eg. centre tapped, or dual rectifier etc.
I have every circuit in the house (except the lounge) on RCCB circuit breakers for extra protection. But, I should never need that.
If you go for a temporary style of test installation then do ensure you can work undisturbed and that children and animals cannot gain access. And don't work when tired!!!
I always use a bulb tester (ballast) for first switch on, sometimes in conjunction with a Variac. And again when ever I modify anything, no matter how minor it seems.
BTW,
if you can bear with me.
I had a garage with external floodlight. The RCCB fed a remote fuse board that in turn fed the floodlight and workshop.
I pulled the fuse for the floodlight so that I could re-wire it. Then while up on the ladder I was slackening the screws on a terminal strip supplying the flood. I heard a click. What was that?
Carried on and completed the re-wire. Inserted the fuse and "no light".
Oh! the RCCB has fired.
Ahh. The click was when the insulated screw driver had touched the neutral screw terminal. The RCB has detected the current from my body passing to the neutral in the RCCB and it measured the unbalanced return current (there was no Live current because the fuse was pulled) and said "fault" and switched off. I was impressed. Since then I have always specified RCCBs on each of my power rings around the house.- Status
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