[Elecraft] KPA500 Noise While Off

[Bob McGraw K4TAX]

Yes that is the magnetization current of the transformer core. 
Doesn't happen when powered up at the zero voltage crossing point. 

One person advised to always turn on equipment at the zero crossing point.  Seems like a good idea.  Now if I could only get my finger timed correctly to do this. 

Bob, K4TAX


Sent from my iPhone

> On Jun 27, 2018, at 2:42 PM, hawley, charles j jr <c-hawley at illinois.edu> wrote:
> 
> I’ve only noticed a thump with a piece of equipment which has a power supply when it turns on at a line voltage peak. On the occasion that it turns on at a line voltage zero crossing, it makes no noise at all.
> 
> Chuck 
> KE9UW
> 
> Sent from my iPhone, cjack 
> 
>> On Jun 27, 2018, at 2:10 PM, Bob McGraw K4TAX <rmcgraw at blomand.net> wrote:
>> 
>> Seems that the AC line supplying the equipment has a rather high impedance thus allowing the voltage to suddenly drop under the dynamic load and then surge to a higher than normal value. 
>> 
>> A dedicated 120V and/or 240V service should be considered for the station power. 
>> 
>> Laser printers do draw considerable power when they start. 
>> 
>> Bob, K4TAX
>> 
>> 
>> Sent from my iPhone
>> 
>>> On Jun 27, 2018, at 2:00 PM, John Simmons <jasimmons at pinewooddata.com> wrote:
>>> 
>>> My Astron RS35 does the same thing under the same conditions.
>>> 
>>> -John NI0K
>>> 
>>> Matt NQ6N wrote on 6/27/2018 1:20 PM:
>>>> My KPA500 makes a noticeable hum/thump when the laser printer that is on
>>>> the same circuit draws a lot of current.
>>>> 
>>>> 73,
>>>> Matt NQ6N
>>>> 
>>>> On Wed, Jun 27, 2018 at 12:58 PM Jim Brown <jim at audiosystemsgroup.com>
>>>> wrote:
>>>> 
>>>>>> On 6/27/2018 10:37 AM, Richard Wade wrote:
>>>>>> If I had to venture a guess, I would say that somehow the unpowered
>>>>> KPA500
>>>>>> was picking up noise on the shack wiring.  Very strange. Is that
>>>>> possible??
>>>>> 
>>>>> It is if equipment in your shack is not properly bonded together, and to
>>>>> house grounds that are also properly bonded together. Study N0AX's
>>>>> recent ARRL book on the topic, to which I contributed, or the slides for
>>>>> a tutorial talk I've done at several hamfests.
>>>>> 
>>>>> http://k9yc.com/GroundingAndAudio.pdf
>>>>> 
>>>>> 73, Jim K9YC
>>>>> 
>>>>> 
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