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reg power supply isolation

Audiolab 6000CDT Dedicated CD Transport

sarathssca

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Hello,

i am thinking of using common power supply for main power amp and pre amp ie. both will be powered from same DC power supply source.

Heard people talking about requirement of isolation between power supply of two stages. Can't we power both the stages taking power lines from same DC power supply?

Also once we connect the pre amp to the main amp input, will both have same ground?

Also how about using isolated dc-dc converter for the preamp power supply?

thanks and regards
S Sarath
 

sarathssca

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hello,

Please suggest, if powering both preamp and amp from same DC power supply, Do we need to use isolated DC-DC converter for preamp or can we have normal non-isolated dc-dc converter?

When we connect output of preamp to input of main amp, doesn't both will share common ground? Will it cause any ground loop problem?

note: amp will be using 19v dc power supply, and preamp needs +/-9v to +/-15v. So thinking to use a dc-dc converter for preamp from the main amp power supply

thanks and regards
S Sarath
 

omishra

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Are they - pre and power housed in same box?
ground wiring is important as it may lead to ground loop.
But it wsould work.
 

sarathssca

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Are they - pre and power housed in same box?
ground wiring is important as it may lead to ground loop.
But it wsould work.

Hi O Mishra,

Not yet decided whether to have both preamp and main amp in same box, but thinking if we could use the same power supply rather than again building separate power supply. Currently using 19.5v laptop power supply for main amp (2 amps: one class d TPA3116 based board and another is class A ACA amp)

I have read people using isolated dc-dc converter for powering additional circuits with main amp to avoid ground loop issues. But i am not able to understand that as when we connect the output of preamp and input of main amp , then the both the grounds of the preamp and main amp will be connected and be the same. So what is the role of isolated dc-dc converter, when we are connecting both the grounds.

thanks and regards
S Sarath
 

omishra

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In proposed solution, I can see two ground paths - one through power rail return path and other one through pre amp output L/R channel return path. Electronically both are same but flowing different return currents. Hence chances of loop if ground legs are longer than 10". I am using same strategy of sharing power between my phono (separate box) and B1 preamp ( another box). But its dead silent.
DC-DC isolator is good option unless noisy or adding noise to audio. Because DC DC convertors are nothing but small SMPS with transformer isolation. Primary side is driven by some oscillator and secondary side drives load after DC conversion. But it separates ground effectively.
 
Last edited:

demir

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sarathssca, using similar power supply is generally not a very catastrophic idea and if one has sufficient knowledge of noise, filtering and isolation, it might work in ones favour. Please note that there might still be some grounding paths that you might need to keep separate so that the noise doesnt get shared between both amps. I hope you wont have any issues in using a single supply, if you do, please let us know; if you dont please still do let us know.

Regards,
Demir C.
Blog - Bittele Electronics
 

omishra

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you could also use a crc or crcrc filter to reduce the voltage.
In that case R is dependent of current, how much voltage you need to drop. Smaller R wont serve purpose of reducing voltage. Also this bigger 'R' adds to PS impedance which plays role of changing sound signature of preAmp, mostly brightness.
 

doors666

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In that case R is dependent of current, how much voltage you need to drop. Smaller R wont serve purpose of reducing voltage. Also this bigger 'R' adds to PS impedance which plays role of changing sound signature of preAmp, mostly brightness.

thats the whole point of the filter design, to drop the voltage. it also squashes any ripple like a bug. Not sure why you would say it adds brightness, most of the tube preamps use crc (or crcrc or clc) filters and they are not really known for their brightness.
 

omishra

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IMO tube amps are high voltage and low current devices or use significantly large caps as power bank after resistance.
 
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