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Old 6th January 2012, 08:02 PM   #1
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Question humbuster schematic

I have an Usher power amp that has a singing transformer,James Bongiorno of Ampzilla fame had an article in a recent TAS re: singing amplfiers and offered his solution in the form of a schematic for the ultimate humbuster. My knowledge of electronics is pretty basic and I was wondering if there is anyone out there that could translate this schematic into a more basic diagram? (see attached).
Thanks, David
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File Type: pdf Humbuster.pdf (27.3 KB, 328 views)
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Old 7th January 2012, 12:14 AM   #2
Enzo is offline Enzo  United States
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I could totally be wrong here, but that circuit looks to me like something to "bust" ground loops. If I understand your problem, you are hearing the music coming from the amp power transformer itself. The transformer mechanically acting a little like a speaker. A ground loop would cause some low mains frequency hum in your signal chain. Totally different phenomenon from a transformer with vibrations in the laminations from the current variations.

I don;t see how a mains filter of any kind would prevent that. And if it does, I am eager to learn how.
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Old 7th January 2012, 03:01 AM   #3
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That circuit removes some DC from the AC. It can be that un removed DC can drive the mains transformer into saturation and then a mechanical hum can be heard.
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Old 8th January 2012, 09:58 AM   #4
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Quote:
Originally Posted by dafdesign View Post
I have an Usher power amp that has a singing transformer,James Bongiorno of Ampzilla fame had an article in a recent TAS re: singing amplfiers and offered his solution in the form of a schematic for the ultimate humbuster. My knowledge of electronics is pretty basic and I was wondering if there is anyone out there that could translate this schematic into a more basic diagram? (see attached).
Thanks, David
As I understand your question the mains transformer is "singing"
due to the mains frequency and its overtones.

The diagram as shown revoves traces of DC from the mains by
insertion of the diode bridges. Especially toroidal transformers are
sensitive to this. For each half wave of ac four diodes are connected
in series. Additional caps provide some means of filtering or noise
suppression. The resistor is for discharge with open leads.

I have seen simpler arrangements with only two diodes. But JB
probably knows why he recommends this one.

Last edited by as_audio; 8th January 2012 at 10:04 AM.
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Old 11th January 2012, 07:05 PM   #5
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Me again, I would like to build this, to see if it will solve the noise problem (not sure of the cost of parts?). I was wondering if there is someone out there that would like to take the time to turn the schematic into a somewhat simpler diagram with parts list for an inexperienced diyer. Please see my original post for attached "Humbuster" schematic
Thanks David

Last edited by dafdesign; 11th January 2012 at 07:07 PM.
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Old 11th January 2012, 07:32 PM   #6
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Quote:
Originally Posted by dafdesign View Post
I was wondering if there is someone out there that would like to take the time to turn the schematic into a somewhat simpler diagram with parts list for an inexperienced diyer.
Just omit all caps and the resistor for a first try
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Old 11th January 2012, 07:38 PM   #7
DF96 is offline DF96  England
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I'm not certain that circuit will remove DC, unless there is no AC present. All it does is remove about 2.8V of the mains waveform. This might create switching noise, so the capacitors are added to filter this out.

To remove DC you need some back-to-back fat capacitors, with diodes to stop reverse bias.
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Old 11th January 2012, 07:49 PM   #8
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Small amounts of dc less than 2.8 volts will be removed,
thats the idea. Some manufacturers use circuits like this
on their toroidal transformers.
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Old 11th January 2012, 07:57 PM   #9
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Default DC OFF SET

How's This

DC sigle bridge.png
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Old 12th January 2012, 04:26 PM   #10
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Dhrab,
Much simpler, so I am just running one side of the AC (-) thru this?
Would you know what size Capacitors are needed and Rectifier? Parts list I can take to Radioshack etc..
Thanks for you help
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