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Old 1st October 2005, 05:09 PM   #1
Bgt is offline Bgt  Netherlands
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AMP1B and an UCD400

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BTW the 500VA toroid of Farnell is quieter than the Hypex 1. Maybe bad luck?

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Old 1st October 2005, 05:50 PM   #2
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Default Amp 1 question

I notice you are using one of the electronic transformers for power. Did you rewind the transformer to get the voltages you need? Is it dual output so you can generate +/- power?
Toroidal transformers have an inherent limitation in that their cores with no gaps can saturate easily. With input DC resistance less than one ohm it doesn't take much DC to cause a lot of current flow and saturation. When this occurs the draw from the line will skyrocket to 10's of amps and this is what causes the buzzing. Some transformers are a lot worse than others due to the way they are made, like not wound as tight. The main factor seems to be input winding resistance. For noise higher is better and this doesn't seem to have much of an effect sonically other than to reduce the buzz. Of course you can always add a small amount of resistance to equalize things. Another factor is the basic design parameters of the transformer and how high of flux density they use. Some are nearly at saturation with normal line voltage and will easily saturate with just a little high line voltage. This is a cost factor in the design with the lower flux density requiring a larger core and more wire to fill. If you have a good volt meter and read the residual DC on your power line you will be surprised how high it can get. Another thing that can be done is to buy a surplus kilowatt toroidal transformer and connect it across the line in another room so you donít have to listen to it buzzing. This will appear as an almost dead short to any DC and will greatly reduce it.
Roger
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Old 1st October 2005, 05:50 PM   #3
t. is offline t.  United Kingdom
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Very nice
Thank you for sharing
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Old 1st October 2005, 06:50 PM   #4
Bgt is offline Bgt  Netherlands
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Default Re: Amp 1 question

Quote:
Originally posted by sx881663
I notice you are using one of the electronic transformers for power. Did you rewind the transformer to get the voltages you need? Is it dual output so you can generate +/- power?
Toroidal transformers have an inherent limitation in that their cores with no gaps can saturate easily. With input DC resistance less than one ohm it doesn't take much DC to cause a lot of current flow and saturation. When this occurs the draw from the line will skyrocket to 10's of amps and this is what causes the buzzing. Some transformers are a lot worse than others due to the way they are made, like not wound as tight. The main factor seems to be input winding resistance. For noise higher is better and this doesn't seem to have much of an effect sonically other than to reduce the buzz. Of course you can always add a small amount of resistance to equalize things. Another factor is the basic design parameters of the transformer and how high of flux density they use. Some are nearly at saturation with normal line voltage and will easily saturate with just a little high line voltage. This is a cost factor in the design with the lower flux density requiring a larger core and more wire to fill. If you have a good volt meter and read the residual DC on your power line you will be surprised how high it can get. Another thing that can be done is to buy a surplus kilowatt toroidal transformer and connect it across the line in another room so you donít have to listen to it buzzing. This will appear as an almost dead short to any DC and will greatly reduce it.
Roger
The Farnell toroid is always quiet. If I for a moment put the volume up to very loud the Hypex transformer immediately starts humming while the Farnell stays dead quiet. The same amps. Just bad luck I guess. Maybe tolerance. Never had a humming toroid.
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Old 1st October 2005, 07:06 PM   #5
t. is offline t.  United Kingdom
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Hi Bert,

Does the voltage from the Hypex one drop more than the Farnell one when you crank the volume up?
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Old 1st October 2005, 07:09 PM   #6
Bgt is offline Bgt  Netherlands
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Quote:
Originally posted by t.
Hi Bert,

Does the voltage from the Hypex one drop more than the Farnell one when you crank the volume up?
Hi T., no it has exactly the same power output. About 150W per channel both channels driven at 8 ohms.
T., thanx
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Old 1st October 2005, 07:19 PM   #7
t. is offline t.  United Kingdom
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Quote:
Originally posted by Bgt

Hi T., no it has exactly the same power output. About 150W per channel both channels driven at 8 ohms.
T., thanx
Well it is a shame Bert, a buzzing transformer can be annoying
Rogers probably spot on whats causing the buz, would it be worth telling Jan about it?
BTW I've used some of the Farnell toroidals before and they do seem good quality, I have also not had many toroidals that buz, its mainly EI types that are worse for higher current needs
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Old 1st October 2005, 08:02 PM   #8
Bgt is offline Bgt  Netherlands
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Quote:
Originally posted by t.


Well it is a shame Bert, a buzzing transformer can be annoying
Rogers probably spot on whats causing the buz, would it be worth telling Jan about it?
BTW I've used some of the Farnell toroidals before and they do seem good quality, I have also not had many toroidals that buz, its mainly EI types that are worse for higher current needs
Well, maybe I just had bad luck, does not matter. Will exchange it in time. To cheap to send back. Heavy transport costs.
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