DC Voltage on RCA Output - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th January 2009, 03:14 AM   #1
baxtr is offline baxtr  United States
diyAudio Member
 
Join Date: Jan 2009
Default DC Voltage on RCA Output

I just bought a new Super Pro DAC707 and I noticed something odd. The RCA outputs have about 9V off DC current on them. This doesn't seem normal, shouldn't a output on have a few millivolts of DC? Can this high amount of DC current damage my equipment?

http://www.diykits.com.hk/dac_super_pro_dac707.htm

Thanks,
Dan
  Reply With Quote
Old 16th January 2009, 04:41 AM   #2
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Default Re: DC Voltage on RCA Output

Hi,

Quote:
Originally posted by baxtr
I just bought a new Super Pro DAC707 and I noticed something odd. The RCA outputs have about 9V off DC current on them. This doesn't seem normal, shouldn't a output on have a few millivolts of DC?
Plenty of equipment has DC on the output. Output coupling caps being considered either 1) "not audiophile" or 2) too expensive of a luxury.


Quote:
Originally posted by baxtr
ICan this high amount of DC current damage my equipment?
Absolutely!

I personally consider a source switchbox that uses DC blocking caps essential.

Cheers!
  Reply With Quote
Old 16th January 2009, 06:26 AM   #3
baxtr is offline baxtr  United States
diyAudio Member
 
Join Date: Jan 2009
What is a normal amount of DC offset for most line outs? Also what would you consider to be unsafe for my preamp? Thanks.
  Reply With Quote
Old 16th January 2009, 08:15 AM   #4
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
"Normal" DC offset is zero.

If your preamp is AC coupled on the input (blocking cap), no worries. Not all of them are, like tube equipment is often DC in to the volume control.

Cheers!
  Reply With Quote
Old 16th January 2009, 08:40 AM   #5
sandyK is offline sandyK  Australia
diyAudio Member
 
Join Date: Apr 2007
Location: Sydney
Default DC Voltage on RCA Output

baxtr

It is highly unusual to have even 30mV DC out of a piece of equipment such as a DAC or CD/DVD player etc. Even most power amplifiers would not have any higher than 30mV DC offset.
This DAC either has a fault or is poorly designed .
If the potentiometer of the preamp/amplifier is before the preamp/amplifier's input coupling capacitor, this will lead to noise with movement of the volume control, even with 50mV DC, let alone 9V DC. I would check with the seller of the item, as it does appear to have a problem.

SandyK
  Reply With Quote
Old 16th January 2009, 12:35 PM   #6
oshifis is offline oshifis  Hungary
diyAudio Member
 
Join Date: Mar 2004
Location: Budapest, Hungary
I can imagine the output DC coupling capacitor is floating because it has no resistor to GND. Measure the voltage with a 100k resistor between the RCA hot and sleeve. If that solves the problem, finish the manufacturing process...
  Reply With Quote
Old 16th January 2009, 10:20 PM   #7
baxtr is offline baxtr  United States
diyAudio Member
 
Join Date: Jan 2009
What type of damage could DC do to a preamp? I'm going to send the DAC back, does anyone else have a Super DAC 707 they could test?

Thanks
Dan
  Reply With Quote
Old 16th January 2009, 11:37 PM   #8
sandyK is offline sandyK  Australia
diyAudio Member
 
Join Date: Apr 2007
Location: Sydney
Default DC Voltage on RCA Output

baxtr
Try Oshifis suggestion first about testing with a 100K terminating resistor, before sending it back. I could imagine a small voltage via capacitor leakage if the output side of the capacitor did not have a high value (e.g.100K) resistor to earth, but not 9V due to the small loading effect (10M ?)of the measuring meter.
SandyK
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Can An Output Transformer Change A Voltage Amp's Output Impedance From 0.1 To 47 Ohms kelticwizard Everything Else 11 25th March 2007 06:17 AM
eqt with low output voltage marko Car Audio 6 2nd January 2007 01:19 AM
use D1 I/V with voltage output dac poolorpond Pass Labs 6 11th June 2006 08:47 PM
DC voltage on output durxter Chip Amps 20 6th March 2005 07:25 PM
P27 Output Voltage rayban68 Solid State 0 6th October 2004 07:19 PM


New To Site? Need Help?

All times are GMT. The time now is 05:56 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2