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Old 26th December 2010, 07:16 PM   #1
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Default Poor TV audio S/N

My TV is an integral part of my stereo system. I have a Sony Bravia with the analog L/R output connected to a vintage tube amplifier. I also have a BluRay player and a cable box connected to the TV via HDMI. My amplifier alone has an excellent S/N, when disconnected from the TV there is no audible hiss. Hooked to the TV, there is an obvious hiss that one can hear between songs (CD played on the BluRay), the hiss is there even with the TV muted.

My ears are telling me the S/N is somewhere in the 50 dB range. (My ears are somewhat calibrated from 32 years experience in automobile radio design.) I would expect at least 80 dB from HiFi equipment. The level seems to be well matched between the TV and the amplifier (standard line level).

I'm wondering if there is some way I can use the digital audio output of the TV with my vintage tube amplifier. Is there a small, inexpensive DAC device that could interface my TV to my amplifier? (I'm assuming the digital audio would have a better S/N.) What kind of digital audio bus comes out of the TV? (In the automobile radio world we used I2S.)

Bobby Dipole
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Old 27th December 2010, 11:22 AM   #2
AndrewT is offline AndrewT  Scotland
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the TV hiss comes through when you have CD selected !
It continues to hiss when you turn the TV off !

I think you have incorrectly wired the TV to the stereo.
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Old 27th December 2010, 02:23 PM   #3
Pano is offline Pano  United States
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Hmmm... how is the hiss getting to the amp when you are playing CDs? Are you passing everything thru the TV?

This little gadget should do what you need.
Digital to Analog Audio Converter Optical / Coaxial / USB | Parts-Express.com
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Old 27th December 2010, 10:10 PM   #4
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Originally Posted by panomaniac View Post
Hmmm... how is the hiss getting to the amp when you are playing CDs? Are you passing everything thru the TV?

This little gadget should do what you need.
Digital to Analog Audio Converter Optical / Coaxial / USB | Parts-Express.com
Yes, I'm passing everything through the TV. The BluRay player goes through the TV, and I use the BluRay player for CDs. Everything that goes though the TV gets tainted with hiss, otherwise the signal is clean. The hiss is low enough that it's covered up when my furnace runs, but definitely audible when the room is quiet.

Bobby Dipole
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Old 27th December 2010, 10:25 PM   #5
Pano is offline Pano  United States
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OK, then just get a decent DAC. The one I linked to or something fancier, if you wish.
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Old 27th December 2010, 10:49 PM   #6
sandyK is offline sandyK  Australia
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Quote:
Originally Posted by Bobby Dipole View Post
Yes, I'm passing everything through the TV. The BluRay player goes through the TV, and I use the BluRay player for CDs. Everything that goes though the TV gets tainted with hiss, otherwise the signal is clean. The hiss is low enough that it's covered up when my furnace runs, but definitely audible when the room is quiet.

Bobby Dipole
I agree with Michael. Many late model TVs have optical OUT in addition to HDMI ports.
I am using a fairly similar set up to you, with a relatively inexpensive BluRay player , then Toslink cable from the TV to a Silicon Chip (magazine) DAC.
Unless your BluRay player is of the calibre of an Oppo with a Sabre DAC, then forget it for CD playback.My modified Oppo DV981HD SACD/DVD-A player via HDMI EASILY outperforms my BluRay player when playing CDs this way, although I normally use SPDIF Out, directly to the DAC. However the Oppo has been modified in the SMPS by using fast slow recovery BYV26C diodes in the main bridge rectifier section, as well as an 100nF 630V capacitor across the main electrolytic. This alone made a worthwhile improvement via HDMI audio, as well as a glossier picture.
Alex
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Old 27th December 2010, 11:57 PM   #7
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Does the Sony TV hiss when playing a source that also contains a video signal?
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Old 28th December 2010, 12:47 AM   #8
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I would expect nearly no hiss with your setup. I'm doing the cheesy route and using the headphone out of the TV (55" LG LED LCD) into a Technics receiver to a pair of JBL TLX-121 speakers. There is a very small amount of hiss but you need to be very near the speakers to detect it. It's in the -65-70 zone.(estimate by ear.)

G
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Old 30th December 2010, 02:24 AM   #9
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Originally Posted by Speedskater View Post
Does the Sony TV hiss when playing a source that also contains a video signal?
Yes it does. I hauled out my HP audio volt meter and actually measured the unweighed S/N right out of the TV audio output:

Analog out in "Fixed" mode (no TV volume control) - 60 dB S/N

Analog out in "Variable" mode (TV volume control active) - 45 dB S/N @ normal volume level. (Hiss level stays constant regardless of volume setting.) I suspect that the S/N would be the same as "Fixed" mode with the TV volume control turned up all the way.

I'm using the "Variable" mode because I'm actually using the TV as a preamp. My power amp (stereo block), has no controls and only one set of stereo inputs. The TV is doing the source switching and volume control functions. My TV has an optical output. I would buy a DAC, but I don't know if the volume control affects the optical output.

Bobby Dipole
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Old 30th December 2010, 11:14 AM   #10
AndrewT is offline AndrewT  Scotland
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use the TV as a source only.
Do not use it as your pre-amp.

The S/N ratio of your Pre-amp should be better than -100dB and preferably -120dB.
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