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Old 28th October 2014, 01:05 PM   #1
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Default AUDIO RESAERCH Regulated PSU

Hi !

I have a SP14 preamp and I noticed that the chemical capacitor after the diode bridge was connected on + to a resistance with a small coil on it. It's a RL circuit.
This resistance is not on the diagram of the SP14 but I noticed it on a schematic of the Audio research LS5.
Does anyone know what exactly is the coil resistance and what is his interest?

thanks

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Old 29th October 2014, 02:04 AM   #2
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Inrush current limiter. You'll either need to look up the ESR in the inductor's datasheet, measure it, or make reasonable guesses from context. Its contribution to the source impedance to the load is likely minor or negligible compared to R81 and I'd be surprised if it does much that's meaningful to the supply's line interactions after startup.
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Old 29th October 2014, 02:26 AM   #3
rayma is offline rayma  United States
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Quote:
Originally Posted by killmister View Post
Hi !

I have a SP14 preamp and I noticed that the chemical capacitor after the diode bridge was connected on + to a resistance with a small coil on it. It's a RL circuit.
This resistance is not on the diagram of the SP14 but I noticed it on a schematic of the Audio research LS5.
This is a patented circuit to improve the capacitor's impedance.

Patent US5036292 - Decoupled electrolytic capacitor - Google Patents
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Old 29th October 2014, 07:05 AM   #4
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Thank you to you for your answers. It is clearer to me now.
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Old 3rd November 2014, 12:34 AM   #5
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It doesn't improve the capacitors impedance, it lets the film capacitor work alone at high frequencies where it's lower dielectric absorbtion provides better performance.
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Old 3rd November 2014, 01:22 AM   #6
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At high frequencies the output impedance of the cap bank is that of the capacitor's ESLs in parallel, including layout. Adding more inductance to one of them increases the impedance per Kirchoff's laws as usual, which is not significant in supplying the regulator normal operation with four smaller caps paralleled closer in (particularly in a circuit like this with a 100 ohm series resistor). It is significant at startup for managing the power pulled through the trafo.

DA is negligible in this; you can see for yourself if you like by sweeping the parallel resistances in Spice.
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Old 3rd November 2014, 02:45 AM   #7
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The caps have staggered values to cover different frequency bands when the series chokes are figured in, 470uf in parallel with 120uf isn't exactly a killer load for the diode bridge and transformer

Last edited by ticknpop; 3rd November 2014 at 02:47 AM.
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