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.
It's not 15 Ohm, it's 0R15 or 0.15 Ohm and as you said it makes the rc filter. A downside would be the power dissipaded across the resistor. Any other member care to add?
I have been told, that when you add a resistor in series with the caps, you reduce some small "click" sounds, that are caused by the diodes/capacitors, because the diode isn't feed unlimited current to the cap, but a current controlled by the resistor i series 🙂
Others ????
Others ????
I have been told, that when you add a resistor in series with the caps, you reduce some small "click" sounds, that are caused by the diodes/capacitors, because the diode isn't feed unlimited current to the cap, but a current controlled by the resistor i series 🙂
Others ????
Others ????
My reading mistake, ifrythings.
Besides the lost of power, using the series resistor, any other negative effect?
ACD gave another positive effect of using it: then why few schematics uses it? I hope the big guys enlight us!
Besides the lost of power, using the series resistor, any other negative effect?
ACD gave another positive effect of using it: then why few schematics uses it? I hope the big guys enlight us!
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 Chris,
and in which range the resistor should be and why?
Bryston uses 0.15 ohm, Am-Audio 4.9.
and in which range the resistor should be and why?
Bryston uses 0.15 ohm, Am-Audio 4.9.
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
It could also be that the transformer on one is more loosely-coupled, or has higher internal resistance, limiting the current spikes by itself...
Cheers!
Cheers!
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
Hi Claudio,
Metal Oxide are very good. You can get the flame proof variety (recommended!). The wire wound types are inherently better at handling surges also. Keep in mind that you are handling repetitive current surges.
-Chris
Metal Oxide are very good. You can get the flame proof variety (recommended!). The wire wound types are inherently better at handling surges also. Keep in mind that you are handling repetitive current surges.
-Chris
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