Need Help: Noisy output (Pin 14) of BB PCM 1704-based DAC - diyAudio
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Old 2nd December 2010, 10:37 PM   #1
dtm1962 is offline dtm1962  Canada
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Join Date: Apr 2003
Location: Sarnia, Ontario, Canada
Default Need Help: Noisy output (Pin 14) of BB PCM 1704-based DAC

I have a Lite 60 DAC that uses a PCM1704 (Current Output) DAC & passive I/V stage that feeds a SRPP tube stage.
I am getting noise DC voltage of 46mV (0.046V) on the right output (Pin 14 is current output) of the PCM 1704. The left channel works normal and has no DC voltage or static. All the main power supplies are common and each DAC has local PS Decoupling caps at all the PS pins of each DAC.

The result is the noise is equally as strong & mixed with the music. The 0.046V gets amplified by a factor of 27 (gain of the tube stage).

The power supply voltages are shown below (except the I output:

Left right
pin 15/16 (AGN) 0.000 v 0.000v
# 17 (Servo DC) -1.975 -1.806
# 6 (+VDD) 4.949 4.946
# 11 (+VCC) 4.946 4.946
# 4 (-VDD) -4.864 -4.865
# 20 (-VCC) -4.864 -4.866
# 5 (DGND) 0.000 0.000
# 12 (BPO DC) 1.820 1.987

# 14 ( I Output) 0.046 0.000


Is this PCM1704 damaged?

Or is there a bad PS decoupling cap or?

Let me know what you think as any help would be appreciated

Thanks in advance.
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