possible ground loop

R

Ralph E. Dodd

Guest
Hello all,

I am trying to power an Atari 2600 video computer system and an audio
amplifier from the same 9 volt wall wart. I've applied a stereo
modification to the 2600 and mounted the amplifier and speakers from a
Sony SRS-48 powered speaker system in the Atari case. The Atari came
with a 300ma supply and the Sony had a 600ma supply, both 9 volt. I'm
using a 9V 1 amp wall wart but if I power both from the same supply, I
get a loud hum. I'm assuming that this is a ground loop. If I power
them from separate supplies, I don't get any hum. Is there a simple
cure for this or should I just mount another power connector in the case
and use 2 wall warts? Thanks a lot.

Ralph
 
On 2012-04-05, Ralph E. Dodd <redodd@REMOVETHIScomcast.net> wrote:
Hello all,

I am trying to power an Atari 2600 video computer system and an audio
amplifier from the same 9 volt wall wart. I've applied a stereo
modification to the 2600 and mounted the amplifier and speakers from a
Sony SRS-48 powered speaker system in the Atari case. The Atari came
with a 300ma supply and the Sony had a 600ma supply, both 9 volt. I'm
using a 9V 1 amp wall wart but if I power both from the same supply, I
get a loud hum. I'm assuming that this is a ground loop. If I power
them from separate supplies, I don't get any hum. Is there a simple
cure for this or should I just mount another power connector in the case
and use 2 wall warts? Thanks a lot.
Click to expand...
you could try an audio isolating transformer between the computer and
the amplifier, These are often found in the car audio section of the
store.

If the hum is flowing over the 9V power bus that won't help, check for
this first by disconnecting the amplifier inputs from the computer and
shorting them to ground at the amp end, if the hum persists you have a
powersupply decoupling or conducted RFI problem, or it could just be
that your powersupply is poorly regulated.




--
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On 4/5/2012 8:56 PM, Jasen Betts wrote:
On 2012-04-05, Ralph E. Dodd<redodd@REMOVETHIScomcast.net> wrote:
Hello all,

I am trying to power an Atari 2600 video computer system and an audio
amplifier from the same 9 volt wall wart. I've applied a stereo
modification to the 2600 and mounted the amplifier and speakers from a
Sony SRS-48 powered speaker system in the Atari case. The Atari came
with a 300ma supply and the Sony had a 600ma supply, both 9 volt. I'm
using a 9V 1 amp wall wart but if I power both from the same supply, I
get a loud hum. I'm assuming that this is a ground loop. If I power
them from separate supplies, I don't get any hum. Is there a simple
cure for this or should I just mount another power connector in the case
and use 2 wall warts? Thanks a lot.
you could try an audio isolating transformer between the computer and
the amplifier, These are often found in the car audio section of the
store.

If the hum is flowing over the 9V power bus that won't help, check for
this first by disconnecting the amplifier inputs from the computer and
shorting them to ground at the amp end, if the hum persists you have a
powersupply decoupling or conducted RFI problem, or it could just be
that your powersupply is poorly regulated.




Thanks for the response. I'm going to take the easy way out and use 2
Click to expand...
wall warts. I'll be at VCF East 8.0 with a bunch of modifed Atari stuff
and there are other issues that I have to straighten out before the show
(May 5-6).
http://www.vintage.org/2012/east/

Ralph
 
On 4/7/2012 7:59 AM, Ralph E. Dodd wrote:
On 4/5/2012 8:56 PM, Jasen Betts wrote:

or it could just be
that your powersupply is poorly regulated.




Thanks for the response. I'm going to take the easy way out and use 2
wall warts. I'll be at VCF East 8.0 with a bunch of modifed Atari stuff
and there are other issues that I have to straighten out before the show
(May 5-6).
http://www.vintage.org/2012/east/

Ralph
Click to expand...
I'll bet regulation - or more accurately, filtering, or the lack thereof.

Maybe add a filter inside the case, a few larger electrolytics of 16V to
25V (say a 4,700/25V electrolytic) across it? I bet that 9V supply is
barely filtered, or not filtered at all, and the smaller one for the amp
IS filtered.

Just a suggestion if you wish to keep it to one wall wart.

RwP
 
On 4/7/2012 10:47 AM, Ralph Wade Phillips wrote:
On 4/7/2012 7:59 AM, Ralph E. Dodd wrote:
On 4/5/2012 8:56 PM, Jasen Betts wrote:

or it could just be
that your powersupply is poorly regulated.




Thanks for the response. I'm going to take the easy way out and use 2
wall warts. I'll be at VCF East 8.0 with a bunch of modifed Atari stuff
and there are other issues that I have to straighten out before the show
(May 5-6).
http://www.vintage.org/2012/east/

Ralph


I'll bet regulation - or more accurately, filtering, or the lack thereof.

Maybe add a filter inside the case, a few larger electrolytics of 16V
to 25V (say a 4,700/25V electrolytic) across it? I bet that 9V supply
is barely filtered, or not filtered at all, and the smaller one for
the amp IS filtered.

Just a suggestion if you wish to keep it to one wall wart.

RwP
RwP,
Click to expand...

I'll try this right away. Nice easy fix if it works. Thanks.

Ralph
 
Ralph Wade Phillips <news@philent.biz> wrote:
On 4/7/2012 7:59 AM, Ralph E. Dodd wrote:
On 4/5/2012 8:56 PM, Jasen Betts wrote:

or it could just be
that your powersupply is poorly regulated.




Thanks for the response. I'm going to take the easy way out and use 2
wall warts. I'll be at VCF East 8.0 with a bunch of modifed Atari stuff
and there are other issues that I have to straighten out before the show
(May 5-6).
http://www.vintage.org/2012/east/

Ralph


I'll bet regulation - or more accurately, filtering, or the lack thereof.

Maybe add a filter inside the case, a few larger electrolytics of 16V to
25V (say a 4,700/25V electrolytic) across it? I bet that 9V supply is
barely filtered, or not filtered at all, and the smaller one for the amp
IS filtered.
Click to expand...
25+ year old caps probably don't help at all either.
 
Hello again,

I got distracted from this for a while but now I've finished it up. I
put an additional 2200mfd 16v. cap across the wall wart input and it had
no change at all. I tried using the Sony supply that is quiet with just
the amp connected, but it made the same noise. I mounted another 1/8"
phone jack on the Atari and put an 1/8" plug on the Sony supply so I
using 2 warts and I have crystal clear audio. Thanks for all you help.

Ralph

On 4/5/2012 4:26 PM, Ralph E. Dodd wrote:
Hello all,

I am trying to power an Atari 2600 video computer system and an audio
amplifier from the same 9 volt wall wart. I've applied a stereo
modification to the 2600 and mounted the amplifier and speakers from a
Sony SRS-48 powered speaker system in the Atari case. The Atari came
with a 300ma supply and the Sony had a 600ma supply, both 9 volt. I'm
using a 9V 1 amp wall wart but if I power both from the same supply, I
get a loud hum. I'm assuming that this is a ground loop. If I power
them from separate supplies, I don't get any hum. Is there a simple
cure for this or should I just mount another power connector in the
case and use 2 wall warts? Thanks a lot.

Ralph
Click to expand...
 
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