hum problem, please help

I encounter hum problem now, that is my normal connection, no hum

CD analog(RCA) -＞ pre-amp(CD) -＞ poweramp
CD digital(COX) -＞ DAC -＞ pre-amp(Tuner) -＞ power-amp

after I add one more digital out from CD to same DAC

CD digital(XLR) -＞ DAC -＞ pre-amp(DAT) -＞ power-amp

Then I got hum nosie, the only solution is remove CD analog connection

my CD has three digital out (TOS/COX/XLR) and two analog out (XLR/RCA)

may I to know you CD palyer brand name
thx

CEC CD3300

are you tube amp used, what brand name DAC

are you tube amp used
tube pre-amp + tube power amp

what brand name DAC
Assemblage DAC 2.6 + Lite MODEL-1 upsampler

connect both or DAC only, problem still happen

without DAC without  problem

do you try to switch ground on/off for both.

[quote:5b92f10880="DUALXEON"]without DAC without  problem

do you try to switch ground on/off for both.[/quote]

you mean DAC or CDP ground, I try to float power cable ground at DAC or CDP, same result: hum with XLR digital connect

I mean try to switch float ground for you tube pre/pow amp.did you try that.

my power amp is already float ground, but pre-amp always with ground, but one thing I have notice, if the power phase is same at CDP and Pre-amp, then the hum noise will reduce, but if not the hum noise will very loud

sorry do not understand (if the power phase is same at CDP and Pre-amp,)

"power phase same" mean the L and N wire connect position is same in CDP and Pre-amp,

L -N        L-N

"not" mean

L-N         N-L

O, I see

do you bring you DAC to you tube amp fried home

do you try to float ground and float chassis etc.

problem is solved after remove the ground pin (1) from upsampler AES/EBU input jack

anyway thanks for your help

you are welcome

finally find out that is the internal headphone amp problem, after disconnect it, no noise anymore :roll:  :roll:  :roll:  :roll:  :roll:  :roll: