Post by thread:[EE:] Gorund loop?

As those following might have guessed I am building an in car mp3 player. A computer powered by an inverter, into a graphic eq/booster. I finally got everything connected yesterday, however, there is a horrendous humming, regardless of engine running. I have tamed that a little by connecting the PC chassis to the inverter 0v with 4 strands of 18 guage (I didn't have anything heavier) but it is still fairly obnoxious. It is nearly eliminated when I unplug the audio from the PC. I am about out of ideas, could anyone please offer some hints and tips how to eliminate (or nearly) this hum? The gritty details... I have the PC output plugged into my EQ using some shielded stereo cable (20 or 18 guage I think) The 12v and 0v line for the inverter are 10 guage. The 12v comes from the battery post through a relay switched by the accessory line The inverter is in the trunk and grounded under a bolt in the trunk. The EQ is hooked up in front, power comes from the stock radio connectors. Using the supplied cabling (looks like 18-20 guage) Thanks, Anthony -- Anthony Toft <spam_OUTtoftatTakeThisOuTcowshed.8m.com> -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

Is the PC in the trunk or close to the EQ? It may be just a matter of the cable being too long and picking EMI from someting along it's path in the car. I'm no expert, but that's what I would check first. I'm currently working on a switchmode PC power supply that runs from the cars battery directly and outputs around 5-10A on the +5v and +12v lines, which should be enough for a basic PC with a hard drive and cd-rom. I plan to build it into an AT power supply housing and use screw terminals on the back to connect the battery supply. If you're interested, take a look on google for car mp3 player power supplies, there's tons of schematics and good stuff to make one of these power supplies. The MAX787 looks like a condidate. I'm sure the efficiency of a battery powered switching power supply would blow away the traditional Inverter setup. Anyways, good luck...cheers -- Matthew J. Brush Lead Developer/Owner mbrushKILLspamleftclick.ca http://www.leftclick.ca LeftClick.ca Internet Media Services -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam.....mitvma.mit.edu

> > As those following might have guessed I am building an in car mp3 > player. A computer powered by an inverter, into a graphic eq/booster. I > finally got everything connected yesterday, however, there is a > horrendous humming, regardless of engine running. I have tamed that a > little by connecting the PC chassis to the inverter 0v with 4 > strands of > 18 guage (I didn't have anything heavier) but it is still fairly > obnoxious. It is nearly eliminated when I unplug the audio from the PC. > > I am about out of ideas, could anyone please offer some hints and tips > how to eliminate (or nearly) this hum? Isolation transfomers in the audio lines to/from the PC will break up the grounds and should solve the problem. Carey Fisher, K8VZ -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu

At 04:45 PM 7/24/2004 -0400, you wrote: {Quote hidden}>As those following might have guessed I am building an in car mp3 >player. A computer powered by an inverter, into a graphic eq/booster. I >finally got everything connected yesterday, however, there is a >horrendous humming, regardless of engine running. I have tamed that a >little by connecting the PC chassis to the inverter 0v with 4 strands of >18 guage (I didn't have anything heavier) but it is still fairly >obnoxious. It is nearly eliminated when I unplug the audio from the PC. > >I am about out of ideas, could anyone please offer some hints and tips >how to eliminate (or nearly) this hum? > >The gritty details... > I have the PC output plugged into my EQ using some shielded > stereo cable (20 or 18 guage I think) > The 12v and 0v line for the inverter are 10 guage. > The 12v comes from the battery post through a relay switched by > the accessory line > The inverter is in the trunk and grounded under a bolt in the > trunk. > > The EQ is hooked up in front, power comes from the stock radio > connectors. Using the supplied cabling (looks like 18-20 > guage) > >Thanks, > >Anthony Is the PC case intentionally or accidentally connected to chassis ground on the car? If so, get rid of that. Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" speffspam_OUTinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com hint: To leave the PICList @spam@piclist-unsubscribe-requestKILLspammitvma.mit.edu

At 06:55 PM 7/24/2004 -0400, you wrote: > > Is the PC case intentionally or accidentally connected to chassis ground on > > the car? > >Intentionally, it reduced the noise a bit (from unable to hear music to >able to hear with annoying hum) Then you probably need an audio isolation transformer as someone else said. Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" spamBeGonespeffspamBeGoneinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com hint: To leave the PICList TakeThisOuTpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu

It'd be interesting to listen to the audio output of the PC on a floating device (headphones, battery powered amplifier, etc.) where the only ground connection is that plugged into the PC sound card. If the hum goes away, the audio isolation transformer suggested by others should work. If the hum is still there, the transformer will probably not do much. In that case, it's probably a problem with the square wave out of the inverter getting into everything. Good luck! Harold {Quote hidden}> As those following might have guessed I am building an in car mp3 > player. A computer powered by an inverter, into a graphic eq/booster. I > finally got everything connected yesterday, however, there is a > horrendous humming, regardless of engine running. I have tamed that a > little by connecting the PC chassis to the inverter 0v with 4 strands of > 18 guage (I didn't have anything heavier) but it is still fairly > obnoxious. It is nearly eliminated when I unplug the audio from the PC. > > I am about out of ideas, could anyone please offer some hints and tips > how to eliminate (or nearly) this hum? > > The gritty details... > I have the PC output plugged into my EQ using some shielded > stereo cable (20 or 18 guage I think) > The 12v and 0v line for the inverter are 10 guage. > The 12v comes from the battery post through a relay switched by > the accessory line > The inverter is in the trunk and grounded under a bolt in the > trunk. > > The EQ is hooked up in front, power comes from the stock radio > connectors. Using the supplied cabling (looks like 18-20 > guage) > > Thanks, > > Anthony > > > -- > Anthony Toft <EraseMEtoftatcowshed.8m.com> > > -- > http://www.piclist.com hint: To leave the PICList > RemoveMEpiclist-unsubscribe-requestEraseMEEraseMEmitvma.mit.edu > -- FCC Rules Online at http://www.hallikainen.com -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestspam_OUTKILLspammitvma.mit.edu

At 07:10 PM 7/24/2004 -0400, you wrote: > > Then you probably need an audio isolation transformer as someone else said. > >Radio Shack have them, will it be OK to recombine the grounds after the >device? I assume there is a ground in the amplifier already (or you wouldn't be having the problem), so you should not put an extra ground in there, unless you want to bring the problem back again. ;-) IOW, the primary of the isolation transformer is grounded by the PC. The secondary of the isolation transformer is grounded to a different point by the amplifier. The two grounds have an AC noise signal between them. Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" RemoveMEspeffTakeThisOuTspaminterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspamspamBeGonemitvma.mit.edu

> IOW, the primary of the isolation transformer is grounded by the PC. > The secondary of the isolation transformer is grounded to a different point > by the amplifier. This I understand! I guess I will have to get some cables and keep the signals and returns separate after the transformers. Thanks for the assistance and the explanation, I am enlightened (think 10W bulbs here:)) BTW a test with the headphones rendered NO noise at all, I think this device will fix it! -- Anthony Toft <RemoveMEtoftatKILLspamcowshed.8m.com> -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestSTOPspamspam_OUTmitvma.mit.edu

> the cable being too long and picking EMI from someting along it's path > in the car. I'm no expert, but that's what I would check first. Well, I have tried the cable unplugged, and there was minimal hum, even less when I moved the audio cable from under the inverter :) > cars battery directly and outputs around 5-10A on the +5v and +12v > lines, which should be enough for a basic PC with a hard drive and > cd-rom. I plan to build it into an AT power supply housing and use The problem with this is that this PC is ATX, and needs 3.3 volts and the negatives. A future design is based around the AMI Indium board which takes +5 and +12v only. For which I am slowly putting the PSU design together (it's not ready for a sanity check yet) > interested, take a look on google for car mp3 player power supplies, > there's tons of schematics and good stuff to make one of these power > supplies. The MAX787 looks like a condidate. I'm sure the efficiency Yes, I have 2 of these, 5A, 5v. the big problem I have found is the 12v rail, National have a nice buck boost solution that will deliver 1.2A at 12v, with 8-16v input. The current stack (indium and drive) draws 0.8A running and about 3A starting, so I have to figure out the LC values for it. > of a battery powered switching power supply would blow away the > traditional Inverter setup. Yes, it would, except that in the car, being efficient isn't such a big deal, there is LOADS of 12v floating around, you might trade efficiency for simplicity which is what I did last year. > Anyways, good luck...cheers Thanks, I'm going to get the rat shack isolator probably tomorrow, I'll let you know how it works out. -- Anthony Toft <spamBeGonetoftatSTOPspamEraseMEcowshed.8m.com> -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestspamBeGonemitvma.mit.edu

----- Original Message ----- From: "Anthony Toft" <EraseMEtoftatEraseMECOWSHED.8M.COM> To: <@spam@PICLIST@spam@spam_OUTMITVMA.MIT.EDU> Sent: Sunday, July 25, 2004 1:03 AM Subject: Re: [EE:] Gorund loop? > Thanks, I'm going to get the rat shack isolator probably tomorrow, I'll > let you know how it works out. > Another way to do this, apart from using isolation transformers, is by using ballanced inputs. You can do a fairly easy electronically balanced input using a decent quality op-amp ie NE5534. If you connect the earth side or ground to one input and the hot side to the other that should work OK. The action in both cases (transformer or ballanced input) is to get rid of common mode signals, which is what your hum is. Cheers......Mike. --- Outgoing mail is certified as Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.723 / Virus Database: 479 - Release Date: 19/07/2004 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Anthony, I would suggest purchasing two 1:1 audio transformers and using them in the cable to the equalizer. Almost everything else will cause trouble. Car "grounds" (notice the quotes), aren't really. From the audio or rf point of view, a couple of meters of thin sheet steel spot welded here and there is not ground. Since you are playing mp3 $10 (each) audio transformers should have good enough quality <g>. Peter -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads