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Old 19th October 2004, 09:38 AM   #1
mikeks is offline mikeks  United Kingdom
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Default Bear Symphony #1

Hi Bear,

looks interesting....

http://www.bearlabs.com/NEXT/SYMPHONY.html

Perhaps you might enlighten us further in respect of your design philosophy...shematics...etc....?
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Old 19th October 2004, 10:21 AM   #2
Eva is offline Eva  Spain
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After '2,5K VA' and 'half farad' I decided not to spend my time reading further... My mains line peak voltage drops by nearly 25% when loaded with 2,5KW of rectified DC load [about 15KW peak power consumption!!]

People should stop wasting their money in 2K VA toroidal transfoemers and huge capacitors and build regulated SMPS [or linear regulators]. There is no other way to get good regulation since mains line itself is pretty unregulated

Active PFC is also a very interesting option since it reduces peak mains current consumption by up to 70%. It appears as a pure resistive load to mains, produces almost pure 100Hz ripple on its output [much less harmonics than standard rectification] and provides less than half the peak to peak ripple voltage with the same filter capacitance. And it offers average output regulation against mains fluctuations too
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Old 19th October 2004, 11:47 AM   #3
PMA is offline PMA  Europe
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Exactly, Eva. Huge capacitors do only increase RF interference and overload the diodes.
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Old 19th October 2004, 11:58 AM   #4
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Quote:
Originally posted by PMA
Exactly, Eva. Huge capacitors do only increase RF interference and overload the diodes.
NOT if these are after the choke in a PI-filter!

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Old 19th October 2004, 12:11 PM   #5
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These amps would be awesome to weigh down your car with on an icy mountain road.
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Old 19th October 2004, 01:45 PM   #6
Eva is offline Eva  Spain
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In order for a pi filter to not resonate at audio frequencies, capacitor ESR / inductor DCR / capacitance values should be big

Further increasing inductor value in order to get a low enough cutoff causes the DCR/ESR/capacitance values required to tame the resulting third order resonant system to be huge

So pi filters damp ripple and reduce peak mains current value but allways at the expense of additional voltage drop on its output [ie: worse regulation] or resonance at audio frequencies

Pi filters were very useful for tube PSUs since inductor DCR in the range of 100 ohms was practical at values like 500V and 200mA [resulting in no filter resonance], but this is no longer true for solid state values like 50V and 5A
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Old 19th October 2004, 03:41 PM   #7
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Cool Working PI-filter

Quote:
Originally posted by Eva
In order for a pi filter to not resonate at audio frequencies, capacitor ESR / inductor DCR / capacitance values should be big

Further increasing inductor value in order to get a low enough cutoff causes the DCR/ESR/capacitance values required to tame the resulting third order resonant system to be huge

So pi filters damp ripple and reduce peak mains current value but allways at the expense of additional voltage drop on its output [ie: worse regulation] or resonance at audio frequencies

Pi filters were very useful for tube PSUs since inductor DCR in the range of 100 ohms was practical at values like 500V and 200mA [resulting in no filter resonance], but this is no longer true for solid state values like 50V and 5A
Eva,
This is totally wrong.
Some Pass model has indeed a working PI-filter. Maybe Nelson Pass himself can persuade you....
I am sorry I don't remember which Pass model.
For your information I have 2 x15mH and 4x 12000F in my Ampzilla and it is a working circuit even at full power into a 4 ohm load. The DC resistance of the coil is 0.57 Ohm
I still remember Nelson's post: Pi-filter multo bene.
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Old 19th October 2004, 04:24 PM   #8
PMA is offline PMA  Europe
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Elso - she is right and argueing in technical terms (it is very easy to calculate what happens in the LC filter), contrary to you, who argue in terms of audio gods .
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Old 19th October 2004, 04:26 PM   #9
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Oh........so no one has ever built a commercial SS amp with a Pi-input filter.

Wrong!

Jocko
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Old 19th October 2004, 04:42 PM   #10
PMA is offline PMA  Europe
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OK - let's speak about values and behavior of the defined filter.
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