Aiken Amps Star Grounding Clarification #3 is clear as mud
Xtrchessreal
(3) If you are using non-isolated input jacks,( I am) you can instead
directly connect their shield to chassis ( I did) directly with a
short wire (don't depend on the nut to make contact (I didn't),
because they corrode over time). If you do this, you cannot also
ground the main power supply star node to the chassis, or you will
likely develop massive hum. (huh?)
My question then is where do you ground the main power supply star
node, in this case?
This may be a reason for my hum so I need to test this possibility.
Can I lift the main power supply star node from chassis ground? And
then leave the other preamp stages grounded to chassis. This may be a
good way to see if I am getting the hum from the power supply or not.
If so I should isolate the input jacks and run the shield to a star
node on the chassis but then I will get the hum back as soon as I
connect the node to the other node.
I suspect then if I am getting hum directly from the power supply then
I have a filter issue.
JP
Phil S.
"JP" <J...@AskMeForRealEmailAddy.com> wrote in message
news:uu2nk4tbagoatr92r...@4ax.com...
The link above shows typical buss ground layout. It is well tested and what
many builders, including me, typically follow because it works and it is
relatively easy to implement.
Here is R. G. Keen's take on star grounding. I find Aiken's articles to be
a wealth of information, but they are also dense with technical information,
making it more difficult to take away the "how to".
http://www.geofex.com/Article_Folders/stargnd/stargnd.htm
I won't pretend to be an expert here, but, IMO, you should scrap the metal
jacks and use Cliff's style jacks that are insulated from the chassis. For
a couple of bucks, you will bypass what is the most likely source of a
ground loop. Then, in a star, you tie the inputs together and run one wire
to the star on the chassis.
Like Keen says, the star will get to be quite a rat's nest, as there are so
many wires you need to bring to it. Even a simple amp like a Champ might
have 6 ground wires, and your typical 3 preamp 2 power tube amp might have a
dozen or more grounds.
Back to your original question, where to put the main star? I just took a
minute to read Aiken's paper on star grounding (again). I noted that he
incorporates a discussion of the hybrid buss/star system as the practical
way of building an amp.
I believe Aiken means that once you ground the jacks to the chassis, that is
your one point of contact with the chassis. Incredible as it seems, maybe
the main star is then just a floating ground? Float the star and see what
happens?
Maybe someone here who really knows this stuff will comment.
JP
wrote:
The main "star" point is by the power transformer just like Hoffman
shows in his diagram. Grounds are seperated on 1st filter cap and the
rest of the filter caps. At least this is what I am getting from the
info so far...
Xtrchessreal
> On Fri, 19 Dec 2008 09:11:15 -0500, "Phil S." <psymo...@comcast.net>
Thanks JP and Phil for your input.
I haven't read the el34world links yet but I will when I am done
here.
I do understand the reason you ground a chassis and the various
devices that are attached to the chassis. Its a safety issue first,
at least that is how it came about and the reason devices have a third
conductor attached to ground. It is that issue that has caused so
many different understandings of ground schemes. Regardless of how,
amplifiers need a star ground because of the RFI factor, I should say
EMI because its all EMI.
"Okay I drift away a bit here"
Even in the case there is no Radio Freq Interference measured in the
RF band you can have RFI caused by multiple sources of EMI at much
higher frequencies crossing such that their combination causes an
aliasing at a lower frequency in the RF band. It might sound like
someone turning on or off a motor, or a drill, or even like glass
bottles banging against each other, especially when the sources are in
motion and moving across each other. Cell phones would be a good
example of that but there is momentary things like sun flares and
other universe noise too. I personally hate the Cell phone when it
does that stupid keep alive check with the nearest tower. You know it
as the "morse code sound" pisses me off at the bars, in the middle of
a song and suddenly "di di dee di di dee di di dee dee dee dee di di
dee di di dee" Not my phone but someone has a high powered phone
nearby.
"Back to task"
Anyway universe and sun flares is not the reason its called star
grounding. A buss that has many common grounds attached to it and
then itself is attcahed to a single point inside the device is still a
star ground. It doesn't have to look like a star with all the jumpers
leading from a center. The real and important point is that you do
not have multiple grounds located in various geographical places on
the chassis thus avoiding a ground loop. Any type of ground loop is
an antenna providing signal that does not go to ground and instead has
the potential to be amplified. If you are speaking specifically about
the signal path a ground loop always gets amplified.
I am just rambling at this point. I am leaving to read the info you
provided and then do some work on my amp.
Thanks again
Phil S.
without a hum, you need to organize the various grounds in an audio circuit
in a certain way.
JP
The RF (radio frequencies) in a guitar amp are generated by the
harmonics of the frequencies you want to amplify also. And this
cinversation from here goes into more than I care to try and explain
at this time..and then you can pick up radio signals and amplify them
also...
Xtrchessreal
Keen makes sense too and is a bit more connecting the dots than
Aiken's stuff. Hoffman's notes are good too but he doesn't do the
full monte either. I will continue to go for a complete star and see
where it gets me. The points about grounding the rectifiers with the
first Cap make sense so I will do that as well. My initial scheme
sucks so I am just going to rewire all the grounds to the Keen
suggestions. Then I should be closer, in the least, to a no hum amp.
I'll keep you posted.
BTW Hoffman was the one I was referring to in my ah geez post when I
was stating that one should not do star grounding. And it was helpful
in that it opened up the real issue that I am finally addressing.
Noel Grassy
The initial ground is as close to the point where AC enters your amp
as possible.
Your others grounds wouldn't be[GND] if you lifted this point as your
Mains or Line Voltage.
Ground and hum in general are the alltime bitch when working in High
Gain amps. Follow a
NASA clean wiring layout with wires crossing only at sharp right
angles and no HT lines in the
vicinity of signal lines.
Not dying is the work ethic above all else. I personally would hate to
be found in "browned-out"
pants still clinging to something in an amp's chassis while a loved
one pushed me off it with a wooden stick,
Have fun!
Dave Curtis
wrote:
>The RF (radio frequencies) in a guitar amp are generated by the
>harmonics of the frequencies you want to amplify also.
Huh? ?
JP
<dbaud...@roderunner.com> wrote:
>On Fri, 19 Dec 2008 22:22:47 -0600, JP <J...@AskMeForRealEmailAddy.com>
>wrote:
>
>>The RF (radio frequencies) in a guitar amp are generated by the
>>harmonics of the frequencies you want to amplify also.
>
>Huh? ?
Upper harmonic freqs range into the RF spectrum...
RichL
They get seriously attenuated (mostly by the cable capacitance) before
they even get to the amp input.
Dave Curtis
wrote:
>JP <J...@AskMeForRealEmailAddy.com> wrote:
>> On Sat, 20 Dec 2008 10:44:20 -0500, Dave Curtis
>> <dbaud...@roderunner.com> wrote:
>>
>>> On Fri, 19 Dec 2008 22:22:47 -0600, JP <J...@AskMeForRealEmailAddy.com>
>>> wrote:
>>>
>>>> The RF (radio frequencies) in a guitar amp are generated by the
>>>> harmonics of the frequencies you want to amplify also.
>>>
>>> Huh? ?
>> Upper harmonic freqs range into the RF spectrum...
Radio frequency (RF) is a frequency or rate of oscillation within the
range of about >3 Hz< to 300 GHz.
>They get seriously attenuated (mostly by the cable capacitance) before
>they even get to the amp input.
>
But they aren't "generated by the harmonics of the frequencies you
want to amplify".
RichL
> On Sun, 21 Dec 2008 01:48:23 -0500, "RichL" <rple...@yahoo.com>
> wrote:
>
>> JP <J...@AskMeForRealEmailAddy.com> wrote:
>>> On Sat, 20 Dec 2008 10:44:20 -0500, Dave Curtis
>>> <dbaud...@roderunner.com> wrote:
>>>
>>>> On Fri, 19 Dec 2008 22:22:47 -0600, JP
>>>> <J...@AskMeForRealEmailAddy.com> wrote:
>>>>
>>>>> The RF (radio frequencies) in a guitar amp are generated by the
>>>>> harmonics of the frequencies you want to amplify also.
>>>>
>>>> Huh? ?
>>> Upper harmonic freqs range into the RF spectrum...
>
> Radio frequency (RF) is a frequency or rate of oscillation within the
> range of about >3 Hz< to 300 GHz.
>
>> They get seriously attenuated (mostly by the cable capacitance)
>> before they even get to the amp input.
>>
>
> But they aren't "generated by the harmonics of the frequencies you
> want to amplify".
LOL, I read that as "are the harmonics of the frequencies you want to
amplify", which is true except that they're completely negligible above
~1 MHz.
Maybe I'm too old school but I've always considered RF to include only
frequencies above the audio range.
JP
wrote:
that's right..put that backwards...
>Maybe I'm too old school but I've always considered RF to include only
>frequencies above the audio range.
>
Same here ..everything between audio and microwave frequencies...and I
am not saying you cannot communicate on microwave and above
frequencies but we were not discussing transmitting frequencies. We
were only talking about guitar amplifiers.
Stephen Cowell
"Dave Curtis" <dbaud...@roderunner.com> wrote
> But they aren't "generated by the harmonics of the frequencies you
> want to amplify".
If you clip a stage, they sure can be.
Not saying that JP knew what he was talking about...
he mighta gotten lucky, this time.
__
Steve
.
JP
Already covered that in my 1961 Tube Radio - TV rerpair correspondence
course...but that doesn't mean I know much...I just could not recall
it in the correct context to explain what I meant. But, as far as I
can tell now, harmonics can make or break a good sounding amp.
K Oc's Tut 1 is finally getting interesting. I am on Power Beam
Pentodes now so maybe I'll get some more knowledge soon. Maybe by Tut
5 ...lol But, my education's in the shitter! I can hardly believe that
I have read 6 inches or more of amp books and a whole 60 booklet
correspondence course by reading one sub heading at a time while
taking care of business in the morning. And I don't stay in there for
extra time either.That's over a foot deep of material read in what
otherwise in uncomfortable wasted time...lol..!