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Preventing Hum/Noise in Amplifiers
Preventing Hum/Noise in Amplifiers
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Old 11th April 2017, 11:33 AM   #11
Bonsai is online now Bonsai  Europe
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Thanks

Yes - I have gone over to returning the speaker 0V to the amplifier PCB and not directly to the central ground - neater and you also get a smaller loop area. I might commrnt further on this in later updates - it will remain a 'living' document no doubt.
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Old 11th April 2017, 12:01 PM   #12
Nico Ras is offline Nico Ras  South Africa
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Hi Russel, thanks. Never had a problem with your site.
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Old 11th April 2017, 06:31 PM   #13
Bonsai is online now Bonsai  Europe
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Thank you!
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Old 11th April 2017, 11:36 PM   #14
PRR is offline PRR  United States
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>> Your IP address (XXX.XXX.XXX.XXX) has been blocked for security reasons.
Probably your IP address has been used for violation of server security rules before.
> I think you've been hacked or have a malware issue.


No; Bonsai's server has a feature that monitors for way-excessive activity from a single IP, and blocks it.

https://doc.bitninja.io/
https://doc.bitninja.io/concepts.html#user-greylist

As I doubt Art did any such thing, his IP is most likely a "dynamic IP" which gets re-assigned occasionally. Maybe someone who had the IP last year was running a scanner or crack-hack software, and BitNinja cut them off. Through IP lease renewals, that hacker has since got another IP and Art now has the "tarnished" IP. BitNinja has no way to know the IP has gone to a different user. Doing the Capcha (prove you are human) is the simple way to be un-blocked.
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Old 12th April 2017, 11:53 AM   #15
Walkalone is offline Walkalone  Viet Nam
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Thanks Bonsai, great grounding guide.

I wonder if i have front-end board that is separately power output board, so where to connect HBR (Hum Breaking Resistor)? It will be connected to local decoupling ground of front-end board (point 3 at pic below) or it should be connect to decoupling ground of power output board (point 4)?!
Please note that point 3 connected to 4 by a short wire.
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Old 12th April 2017, 07:38 PM   #16
AndrewT is offline AndrewT  Scotland
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the 5.6ohm shown between 2 & 3 is the HBR.
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Old 13th April 2017, 12:39 AM   #17
Walkalone is offline Walkalone  Viet Nam
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Yes, i know that is HBR. I mean where to correctly connect HBR if i have separately front-end board and output board. I think it must be connected to (3) to keep loop area smallest. Is it right?!
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Old 13th April 2017, 06:36 AM   #18
Mark Whitney is offline Mark Whitney  Netherlands
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I would change the output board. Move 4 to connect between 6 and 7 to improve the feedback loop.
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Old 13th April 2017, 08:45 AM   #19
Walkalone is offline Walkalone  Viet Nam
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Thanks Mark,

This is another issue i'm wondering too. There is something wrong with that diagram. speaker & Zobel return should be conneted after local decoupling caps.
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Old 13th April 2017, 09:03 AM   #20
AndrewT is offline AndrewT  Scotland
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Disconnect both the "3" connections, disconnect the 4, & 6 connections.
You now have 5r6 going to 5, speaker return. This is a dedicated line that only carries the speaker return current and some very small return currents flowing in the NFB route. Oh and a tiny DC current if the voltage amplifier stage is not exactly current balanced for +ve and -ve flows. The tiny DC current cannot create any emi. You can safely ignore it. Except it confuses output offset measurements. If you compare speaker output offset to one side of the 5r6 to the measurement to the other side of 5r6 they will be different. Which is correct? Setting the net DC error to exactly zero will make the two measurements of output offset to be equal.

That arrangement keeps the "audio" side separate from the power side, no sharing of current routes.

Now connect the two 3s to 4. Connect the Zobel 6 to 4.
Connect 4 to 7
"7" has become the Main Audio Ground. It's where all the circuits resolve their currents

7 is connected as a "star of stars" (or buss if you prefer) to 8, 4, 5, 5r6 (this is the first star).
4 is connected to 3+3 & 6 (this is the second star).

Once you have corrected the sch to show the correct connections you then analyse the current loops. Find each source and the route that source uses to send current out into the load and where it comes back. Every source+current route must be arranged to have low LOOP AREA. you can "SEE" three source current routes from the input.
1.) The loop going into the coax.
2.) The loop around the RF cap and back to the coax.
3.) The loop from the RFcap/LTPbase across the LTP to the NFB lower leg R+C to "2" to "1" and up the cap back to the input base.
4.) The missing loop for the Rin resistor at the input base. This returns to the coax alongside the RF cap.

Do the same for the speaker leads.
Do the same for each decoupling capacitor, there are four decoupling capsa and each has a current route AREA that needs to be minimised.
Do the same for the Zobel current route.
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Last edited by AndrewT; 13th April 2017 at 09:21 AM.
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