Proper grounding method... - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 10th August 2007, 02:22 PM   #1
diyAudio Member
 
Join Date: Jan 2006
Location: Central Ohio
Default Proper grounding method...

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!
  Reply With Quote
Old 10th August 2007, 02:35 PM   #2
Zibi is offline Zibi  Poland
diyAudio Member
 
Join Date: Jan 2006
Location: Bialystok
http://www.aikenamps.com/StarGround.html
http://www.geofex.com/Article_Folder...nd/stargnd.htm
  Reply With Quote
Old 10th August 2007, 02:37 PM   #3
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
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.
__________________
regards Andrew T.
  Reply With Quote
Old 10th August 2007, 03:11 PM   #4
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Quote:
Originally posted by AndrewT
For the moment let's ignore the safety ground.
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).
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 10th August 2007, 03:33 PM   #5
diyAudio Member
 
Join Date: Jan 2006
Location: Central Ohio
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.
  Reply With Quote
Old 10th August 2007, 10:47 PM   #6
diyAudio Member
 
Join Date: Oct 2006
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
  Reply With Quote
Old 10th August 2007, 11:34 PM   #7
Jeb-D. is offline Jeb-D.  United States
diyAudio Member
 
Jeb-D.'s Avatar
 
Join Date: Nov 2005
Location: SoCal
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.
  Reply With Quote
Old 11th August 2007, 06:04 AM   #8
dejanm is offline dejanm  Austria
diyAudio Member
 
Join Date: Jul 2005
Location: Vienna
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 ?
  Reply With Quote
Old 11th August 2007, 06:11 AM   #9
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Hi,

An hour or so in the local library with the CSA or UL reference texts for consumer electronic equipment certification standards can provide a wealth of information on safe grounding practises and minimum distances between HV bearing points

Cheers!
  Reply With Quote
Old 11th August 2007, 10:08 AM   #10
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Quote:
Originally posted by cbutterworth
I cannot think of any DIY projects that use double insulation...
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.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Check my layout pls. for proper grounding (6 channel opamp pre) Groundloops Solid State 9 17th February 2008 08:35 PM
best grounding method Leolabs Solid State 0 20th October 2006 01:21 AM
Proper Grounding Scheme PaulHilgeman Parts 38 14th October 2003 05:00 PM


New To Site? Need Help?

All times are GMT. The time now is 07:32 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2