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Old 6th January 2003, 07:39 AM   #1
Rarkov is offline Rarkov  England
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Default Transformer Hum?! STOP IT!

Hi,
A while ago I completed my "Optimos" amps. The PSU in them are:

500VA
Single BR
4x6800uF (2 per rail)
+-68.1V

If you want any more details about the setup, just ask...

The problem is that the amps hum...Not through the speakers, but if I'm sat next to them, they make an irregular pulsing humming noise.

I haven't got snubbing caps on the BR or HF caps after the large ones, but I didn't thing they would cause these problems. It is a torodial xformer. The only other thing is that I don't have the Earth wired in...All grounds are wired to a HQG point...

Thanks in advance for any help!

Gaz
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Old 6th January 2003, 07:52 AM   #2
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If you get uneven and unregular hum from the transformer itself you probely have DC on the mains. Maybe you shuold get a DC trap?

Two anti parallel diodes 5 A plus a capacitors 2200-10000 µF across them. Put this gadget in series with one of the primary wires.

If people uses hairdryers with halfwave rectification DC is created OUT from the hairdryer. (is it dryer or drier BTW)
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Old 6th January 2003, 08:04 AM   #3
Rarkov is offline Rarkov  England
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Hi,
Thanks for your reply Peranders...

I think your first spelling was right, but don't quote me on it!
English never was my strong point!

I have never heard of a DC trap, is that basically a cap inline with the mains? I was thinking I should do this anyway...

If it is just a cap, what type should I use?
1uF 450V?

Thanks,
Gaz
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Old 6th January 2003, 09:09 AM   #4
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Quote:
Originally posted by Rarkov
If it is just a cap, what type should I use?
1uF 450V?
No! A couple of thousands of µF and low voltage (is enough) but you must protect the caps with diodes. The diodes must withstand the inrush currents of the transformer.

AND!!! In SERIES with one of the primary wires.
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Old 6th January 2003, 09:41 AM   #5
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Default DC - block / filter

Something like this? (Pic).

Arne K
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Old 6th January 2003, 10:21 AM   #6
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Arne,

Isnt there a small mistake in your picture. It says that C1 and C2 must be AC rated but IMHO that must be C2 and C3

Ralph
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Old 6th January 2003, 10:28 AM   #7
Rarkov is offline Rarkov  England
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Wow!
I don't have that much room in my Monoblocks' Chassis!
The other thing is that I am (maybe wrongly) skeptical about feeding a 35V (assuming >16V anyway) capactior with 240V from the UK mains...

Am I missing somthing? Thanks,

Also, can I simplify that as much as possible to take up as little room as possible?

Gaz
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Old 6th January 2003, 10:49 AM   #8
Freddie is offline Freddie  Sweden
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I have built built the circuit posted above. It works good, no hum from the transformer anymore.

/Freddie
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Old 6th January 2003, 11:16 AM   #9
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"I have built built the circuit posted above. It works good, no hum from the transformer anymore."

Hi Freddie, any change in sonics of the system ?. (apart from no transformer buzz)

Eric.
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Old 6th January 2003, 11:34 AM   #10
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Default Different Hum Problem

I have two large monobloc tube amps...the power supply transformer on one of them is emitting a 60 Hz hum..real annoying at low levels..any suggestions. I don't think it's dc on the mains because..as I said...only one amp does it.

thanx
rt
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