Bob Cordell Interview: Power Supplies - Page 15 - diyAudio
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Old 28th November 2006, 09:01 PM   #141
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Were'nt two diode bridges used in some Mark Levinson amplifiers ?

MIKEB
--- no advantage in using 2 bridge rectifiers, in the contrary, additionally to the doubled diode drop you also get double the diode ringing...---

To me, this seems a good argument against the twin bridge approach.
However, it could imply that for circuits with low dissipated wattage like preamplifiers, it would be an advantage, in the aim to minimise diode HF garbage, to use a twin diode rectifier and a transformer without a center tap instead of the ubiquitous bridge scheme.
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Old 28th November 2006, 09:17 PM   #142
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Default Re: Re: Re: Re: Re: Actual example

Quote:
Originally posted by mikeks



I have never seen rational grounds for this either.

Good thing you brought it up; perhaps someone will come up with a good explanation.

Here

See also post #s 2, 16 and 48 in this thread.
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Old 28th November 2006, 09:21 PM   #143
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Default Re: Re: Re: Re: Actual example

Quote:
Originally posted by Bob Cordell
There are two popular ways of connecting the transformer-rectifier-reservoir capacitors to provide the pos and neg rails for a power amplifier. In the first, a center-tapped transformer has its center tap grounded, and its two arms go to the a.c. inputs of a single bridge rectifier, whose + and - outputs go to a pair of reservoir capacitors whose common node goes to ground. This is the most common and popular setup.

In the second, a transformer with two isolated secondaries is used (no center tap). Each secondary goes to a bridge rectifier. The pos and neg outputs of each bridge connect to a reservoir capacitor. The two reservoir capacitors then share a common node connected to ground.

Some claim that the second approach, which uses two bridge rectifiers, is superior. However, I have never seen a clear explanation of why it is superior. Indeed, the second arrangement appears to suffer an extra diode drop in the rectification process.

Is the second approach superior?

If so, why?

What are the tradeoffs?
Most customers want total silence from the amplifier, including
mechanical noise. If there is not complete matching between the
secondary coils and only 1 rectifier bridge, any net DC imbalance
between the current of the + supply and the - will tend to
saturate the core of the transformer and create noise. This is
seen for quite low current differences and can also show up with
low frequency output. Using two bridges eliminates the problem.

In the eyes of a manufacturer, any other subtle differences
pale in comparison to the cost of having to replace a transformer
in the field due to mechanical noise.

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Old 28th November 2006, 09:32 PM   #144
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Quote:
Originally posted by Ultima Thule
the "blip" is coupled through the magnetic field.
Option No 3:
1 transformer + 1 rect. bridge for 1 capacitor bank ?

(i'll save the usual amp listing for the history channel)
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Old 28th November 2006, 09:55 PM   #145
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Default Re: Re: Re: Re: Re: Actual example

Quote:
Originally posted by Nelson Pass


Most customers want total silence from the amplifier, including
mechanical noise. If there is not complete matching between the
secondary coils and only 1 rectifier bridge, any net DC imbalance
between the current of the + supply and the - will tend to
saturate the core of the transformer and create noise. This is
seen for quite low current differences and can also show up with
low frequency output. Using two bridges eliminates the problem.

In the eyes of a manufacturer, any other subtle differences
pale in comparison to the cost of having to replace a transformer
in the field due to mechanical noise.


Thanks, Nelson! Great insight.

Bob
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Old 28th November 2006, 10:51 PM   #146
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Default Re: Re: Re: Re: Re: Actual example

Quote:
Originally posted by Nelson Pass


Most customers want total silence from the amplifier, including
mechanical noise. If there is not complete matching between the
secondary coils and only 1 rectifier bridge, any net DC imbalance
between the current of the + supply and the - will tend to
saturate the core of the transformer and create noise. This is
seen for quite low current differences and can also show up with
low frequency output. Using two bridges eliminates the problem.

In the eyes of a manufacturer, any other subtle differences
pale in comparison to the cost of having to replace a transformer
in the field due to mechanical noise.
Yes, that may be very well a truth I admittedly was not aware of though I know the importance of pure AC balanced voltage supply on the primary where small DC imbalance can easily saturate the transformer.
I understand very well the equation that must be fullfilled as stated by NP for the saturation to occure, eg. BOTH the secondary windings AND + and - supply must be in imbalance. Only either of the imbalances will not create a saturation as far as I see then.

Thanks NP!

Cheers Michael
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Old 28th November 2006, 10:57 PM   #147
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Quote:
Originally posted by jacco vermeulen


Option No 3:
the "Blip" sensation?
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Old 28th November 2006, 11:21 PM   #148
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Talking Re: Re: Re: Re: Re: Actual example

Quote:
Originally posted by Nelson Pass


Most customers want total silence from the amplifier, including
mechanical noise. If there is not complete matching between the
secondary coils and only 1 rectifier bridge, any net DC imbalance
between the current of the + supply and the - will tend to
saturate the core of the transformer and create noise. This is
seen for quite low current differences and can also show up with
low frequency output. Using two bridges eliminates the problem.

This must be what I meant by friendly flux!
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Old 29th November 2006, 12:29 AM   #149
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Oh Dear,

They released Mr Dynamic,....again.
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Old 29th November 2006, 12:32 AM   #150
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Quote:
Originally posted by abc11
... which is the best is obvious...
I quite often find the things that people say are obvious are not. Could you ellucidate please?
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