Hello,
I was looking at 2 preamplifier from Bryston and AM Audio, where both uses after the rectification diodes a resistor (4.7 ohm for AM Audio and 15 for Bryston) in series, and then the electrolitic caps. The Bryston schematic is at this address: http://www.bryston.ca/BrystonSite05/pdfs/PREAmplifiers/BP26+MPS2_SCHEMATICS_2005-01-17.pdf
Since it is uncommon to use a series resistor before the filter caps, I would like to ask which are the negative sides of doing so. The positive side should be the resulting RC filter.
I was looking at 2 preamplifier from Bryston and AM Audio, where both uses after the rectification diodes a resistor (4.7 ohm for AM Audio and 15 for Bryston) in series, and then the electrolitic caps. The Bryston schematic is at this address: http://www.bryston.ca/BrystonSite05/pdfs/PREAmplifiers/BP26+MPS2_SCHEMATICS_2005-01-17.pdf
Since it is uncommon to use a series resistor before the filter caps, I would like to ask which are the negative sides of doing so. The positive side should be the resulting RC filter.
Hi Claudio,
The resistor does reduce the current spikes, and also the peak inrush current to the caps. This reduces the higher frequency noise on the supplies where three terminal regulators have trouble. It results in a quieter supply.
Consider these are low power supplies, the power lost is not great. I can't see many downsides to doing this.
-Chris
The resistor does reduce the current spikes, and also the peak inrush current to the caps. This reduces the higher frequency noise on the supplies where three terminal regulators have trouble. It results in a quieter supply.
Consider these are low power supplies, the power lost is not great. I can't see many downsides to doing this.
-Chris
Hi Claudio,
It depends on the current draw and what the designer is happy with. In other words, the designers whim.
The higher value will result in a little lower voltage (could be intentional) and lower supply noise. The transformer then lives an easy life.
These resistors may also become part of the overcurrent protection.
-Chris
It depends on the current draw and what the designer is happy with. In other words, the designers whim.
The higher value will result in a little lower voltage (could be intentional) and lower supply noise. The transformer then lives an easy life.
These resistors may also become part of the overcurrent protection.
-Chris
The transfomer winding itself is 'full of inductance' so using a non-inductive resistor isn't going to be of any benefit.
Metal or carbon... well maybe the experts can tell us... less noise on metal than carbon, but is that significant here? I don't think so, since it's swamped by the filter capacitors...
Cheers
Metal or carbon... well maybe the experts can tell us... less noise on metal than carbon, but is that significant here? I don't think so, since it's swamped by the filter capacitors...
Cheers
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