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KPA500 hum

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wayne burdick

KPA500 hum

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A low level of AC hum is normal with products like the KPA500 that use
a high-power linear supply.

Nearly all reports of KPA500 hum have come from kit builders. So we
did some reverse engineering of our kit building process to see how to
make the normal hum worse. In the process we found three ways to make
it better:

1. Hum is proportional to supply voltage. Using the yellow (lowest
voltage) tap, there's little or no hum. The red tap increases it a
bit, and the green tap a bit more. Per the assembly manual, the
rectifier block should use the lowest-voltage winding that produces
60V key down at 500W of output.

2. Loose hardware definitely increases hum. To minimize it, make sure
your transformer mounting bolts and chassis hardware are all tight.

3. Make sure the transformer wires and other wires inside the KPA500
are not in close contact with the top, bottom and side covers.
Vibration of these covers against the wires can cause louder hum,
especially when in transmit.

Of course we'll work with any customer who still has an obvious hum
after trying the above.

Other possible hum causes (or not):

We've tested the toroidal transformers extensively, and have confirmed
that they do not generate hum internally. Replacing the transformer
has no impact on how much hum an amplifier produces.

You could also have hum due to DC on the AC line or by bad AC line
waveforms. For example, the KPA500 will operate with the "modified
sine-wave" output of a low-cost DC to AC inverter. But like other
transformer-operated devices it will hum loudly when presented with
harmonic-rich input.

With reasonable AC input waveforms, the proper transformer tap
selected, and all the mounting hardware tightened properly, the normal
audible hum from the KPA500 is lower than the combined hum and blower
noise from nearly any AC-powered amplifier.

The KPA500 is a lot quieter than most amplifiers, in general, thanks
to its thermostatically-controlled multispeed fan and diode-switched
keying. However, it is not always *completely* silent. It is not
library-approved.

>

73,

Wayne
N6KR

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Johnny Siu

KPA500 hum

Hello Wayne,

I suggest you also post your message somewhere on the Elecraft website. The hum in my KPA500 has been much reduced by using your suggestion solution as previously advised by Gary.

TNX & 73,

Johnny VR2XMC

________________________________
從︰ Wayne Burdick <[hidden email]>
收件人︰ Elecraft Reflector <[hidden email]>
傳送日期︰ 2011年09月29日 (週四) 7:40 AM
主題︰ [Elecraft] KPA500 hum

A low level of AC hum is normal with products like the KPA500 that use
a high-power linear supply.

Nearly all reports of KPA500 hum have come from kit builders. So we
did some reverse engineering of our kit building process to see how to
make the normal hum worse. In the process we found three ways to make
it better:

1. Hum is proportional to supply voltage. Using the yellow (lowest
voltage) tap, there's little or no hum. The red tap increases it a
bit, and the green tap a bit more. Per the assembly manual, the
rectifier block should use the lowest-voltage winding that produces
60V key down at 500W of output.

2. Loose hardware definitely increases hum. To minimize it, make sure
your transformer mounting bolts and chassis hardware are all tight.

3. Make sure the transformer wires and other wires inside the KPA500
are not in close contact with the top, bottom and side covers.
Vibration of these covers against the wires can cause louder hum,
especially when in transmit.

Of course we'll work with any customer who still has an obvious hum
after trying the above.

Other possible hum causes (or not):

We've tested the toroidal transformers extensively, and have confirmed
that they do not generate hum internally. Replacing the transformer
has no impact on how much hum an amplifier produces.

You could also have hum due to DC on the AC line or by bad AC line
waveforms. For example, the KPA500 will operate with the "modified
sine-wave" output of a low-cost DC to AC inverter. But like other
transformer-operated devices it will hum loudly when presented with
harmonic-rich input.

With reasonable AC input waveforms, the proper transformer tap
selected, and all the mounting hardware tightened properly, the normal
audible hum from the KPA500 is lower than the combined hum and blower
noise from nearly any AC-powered amplifier.

The KPA500 is a lot quieter than most amplifiers, in general, thanks
to its thermostatically-controlled multispeed fan and diode-switched
keying. However, it is not always *completely* silent. It is not
library-approved.

>

73,

Wayne
N6KR

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Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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______________________________________________________________
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Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Phil Hystad-3

Re: KPA500 hum

In reply to this post by wayne burdick

Wayne,

I have not purchased my KPA500 yet but I do want to understand anything you
say. Now, I don't understand item (1) below about using the yellow (lowest
voltage) tap.

I think my problem is possibly perspective but in reading the manual, the yellow
tap is associated with the highest primary voltage. Why is it that you are calling
it lowest voltage?

73, phil, K7PEH

On Sep 28, 2011, at 4:40 PM, Wayne Burdick wrote:

> A low level of AC hum is normal with products like the KPA500 that use
> a high-power linear supply.
>
> Nearly all reports of KPA500 hum have come from kit builders. So we
> did some reverse engineering of our kit building process to see how to
> make the normal hum worse. In the process we found three ways to make
> it better:
>
> 1. Hum is proportional to supply voltage. Using the yellow (lowest
> voltage) tap, there's little or no hum. The red tap increases it a
> bit, and the green tap a bit more. Per the assembly manual, the
> rectifier block should use the lowest-voltage winding that produces
> 60V key down at 500W of output.
>
> 2. Loose hardware definitely increases hum. To minimize it, make sure
> your transformer mounting bolts and chassis hardware are all tight.
>
> 3. Make sure the transformer wires and other wires inside the KPA500
> are not in close contact with the top, bottom and side covers.
> Vibration of these covers against the wires can cause louder hum,
> especially when in transmit.
>
> Of course we'll work with any customer who still has an obvious hum
> after trying the above.
>
> Other possible hum causes (or not):
>
> We've tested the toroidal transformers extensively, and have confirmed
> that they do not generate hum internally. Replacing the transformer
> has no impact on how much hum an amplifier produces.
>
> You could also have hum due to DC on the AC line or by bad AC line
> waveforms. For example, the KPA500 will operate with the "modified
> sine-wave" output of a low-cost DC to AC inverter. But like other
> transformer-operated devices it will hum loudly when presented with
> harmonic-rich input.
>
> With reasonable AC input waveforms, the proper transformer tap
> selected, and all the mounting hardware tightened properly, the normal
> audible hum from the KPA500 is lower than the combined hum and blower
> noise from nearly any AC-powered amplifier.
>
> The KPA500 is a lot quieter than most amplifiers, in general, thanks
> to its thermostatically-controlled multispeed fan and diode-switched
> keying. However, it is not always *completely* silent. It is not
> library-approved.
>
>>
>
> 73,
>
> Wayne
> N6KR
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Robert Friess

Re: KPA500 hum

Hi Phil,

Wayne was referring to the highest supply voltage internal to the amplifier
which increases in steps when moving from the yellow to the red, to the
green tap. It is a bit confusing because the "highest voltage tap" would be
used with the lowest AC mains voltage to maintain the operating voltage for
the PA module around 60 volts under load.

73,
Bob, N6CM

On Wed, Sep 28, 2011 at 8:56 PM, Phil Hystad <[hidden email]> wrote:

> Wayne,
>
> I have not purchased my KPA500 yet but I do want to understand anything you
> say. Now, I don't understand item (1) below about using the yellow (lowest
> voltage) tap.
>
> I think my problem is possibly perspective but in reading the manual, the
> yellow
> tap is associated with the highest primary voltage. Why is it that you are
> calling
> it lowest voltage?
>
> 73, phil, K7PEH
>
>
> On Sep 28, 2011, at 4:40 PM, Wayne Burdick wrote:
>
> > A low level of AC hum is normal with products like the KPA500 that use
> > a high-power linear supply.
> >
> > Nearly all reports of KPA500 hum have come from kit builders. So we
> > did some reverse engineering of our kit building process to see how to
> > make the normal hum worse. In the process we found three ways to make
> > it better:
> >
> > 1. Hum is proportional to supply voltage. Using the yellow (lowest
> > voltage) tap, there's little or no hum. The red tap increases it a
> > bit, and the green tap a bit more. Per the assembly manual, the
> > rectifier block should use the lowest-voltage winding that produces
> > 60V key down at 500W of output.
> >
> > 2. Loose hardware definitely increases hum. To minimize it, make sure
> > your transformer mounting bolts and chassis hardware are all tight.
> >
> > 3. Make sure the transformer wires and other wires inside the KPA500
> > are not in close contact with the top, bottom and side covers.
> > Vibration of these covers against the wires can cause louder hum,
> > especially when in transmit.
> >
> > Of course we'll work with any customer who still has an obvious hum
> > after trying the above.
> >
> > Other possible hum causes (or not):
> >
> > We've tested the toroidal transformers extensively, and have confirmed
> > that they do not generate hum internally. Replacing the transformer
> > has no impact on how much hum an amplifier produces.
> >
> > You could also have hum due to DC on the AC line or by bad AC line
> > waveforms. For example, the KPA500 will operate with the "modified
> > sine-wave" output of a low-cost DC to AC inverter. But like other
> > transformer-operated devices it will hum loudly when presented with
> > harmonic-rich input.
> >
> > With reasonable AC input waveforms, the proper transformer tap
> > selected, and all the mounting hardware tightened properly, the normal
> > audible hum from the KPA500 is lower than the combined hum and blower
> > noise from nearly any AC-powered amplifier.
> >
> > The KPA500 is a lot quieter than most amplifiers, in general, thanks
> > to its thermostatically-controlled multispeed fan and diode-switched
> > keying. However, it is not always *completely* silent. It is not
> > library-approved.
> >
> >>
> >
> > 73,
> >
> > Wayne
> > N6KR
> >
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Johnny Siu

KPA500 hum

In reply to this post by Phil Hystad-3

Hello Phil,

The line voltage in Hong Kong is 220v 50Hz. I measured the AC socket at my QTH with a Fluke DMM at 218v. Initially, I chose the Green tap and got quite a noticeable hum. After that, I switched to Red tap and the hum was much reduced.

The amount of hum had been further reduced after the installation of additional hard wares mentioned on P.32 Fig.46 of the latest KPA500 kit assembly manual.
http://www.elecraft.com/manual/KPA500%20Kit%20Assembly%20Manual%20Rev%20D.pdf

Now, my KPA500 is very quiet on my shack even at full 500W. The only noise noticed is the fan noise.

Elecraft radios are not the only gears on my shack because I am also an Icom user. I also do not always clap my hands towards Elecraft but I am very happy with my KPA500. I used ICPW1 in the past and the 5 fans in the ICPW1 running together could be fairly noisy.

TNX & 73,

Johnny VR2XMC

________________________________
從︰ Phil Hystad <[hidden email]>
收件人︰ Wayne Burdick <[hidden email]>
副本(CC)︰ Elecraft Reflector <[hidden email]>
傳送日期︰ 2011年09月29日 (週四) 11:56 AM
主題︰ Re: [Elecraft] KPA500 hum

Wayne,

I have not purchased my KPA500 yet but I do want to understand anything you
say. Now, I don't understand item (1) below about using the yellow (lowest
voltage) tap.

I think my problem is possibly perspective but in reading the manual, the yellow
tap is associated with the highest primary voltage. Why is it that you are calling
it lowest voltage?

73, phil, K7PEH

On Sep 28, 2011, at 4:40 PM, Wayne Burdick wrote:

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html