Poor TV audio S/N

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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
 
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
 

sandyK

Member
2007-04-27 12:54 am
Sydney
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
 
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.)

 
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. :confused:

Bobby Dipole
 
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.

Hi Andrew: I think you hit the nail on the head, I need a pre-amp. (Sony should still be horse whipped for the poor S/N of their analog output! :mad: I wonder if Sony intentionally designed the S/N to be that bad! How did they even find an audio IC with a S/N of 45 dB? :eek:)

My problem now is finding a pre-amp that doesn't break the bank. (I want to keep my vintage tube power amplifier, I put a lot of work into it.) I want a remote control, so that means something modern. I don't need anything esoteric, but unfortunately, just the word "pre-amp" puts you into the high-end spectrum. You can buy a whole integrated SS amp for $100, but pre-amps start at $600.

Bobby Dipole
 

Pano

Administrator
Paid Member
2004-10-07 6:05 am
I have not seen an optical out that was affected by the volume, so I doubt.
I use my TV has the preamp, and it's not noisy as far as I can tell.

It may be time for you to get a decent HT receiver and use that as the preamp. Most have preamp outputs.
 
low buck hifi

See this thread. http://www.diyaudio.com/forums/anal...improving-disco-mixer-mid-fi-performance.html I paid $15 for the disco mixer, and have another $10 in op amp upgrade, sockets,electrolytic caps, $1 wall transformer. Everything else I salvaged from old dead PC power supplies. I've got hiss down to as low as the tube PAS2 with new metal film resistors. Hum is good if you have a power amp that will take 5V pp signals. The reason it needs to be a disco mixer is I use LP's and magnetic phono cartridge. Regular PA mixers hum less than this disco mixer, but also need a hiss upgrade usually. Putting in better op amps means more power supply decoupling, disc capacitors around the feedback resistors. All cheap stuff. I picked up a Peavey mixer to use on the TV. I have separate HDTV tuner, which doesn't hiss much out of the RCA jacks. The barrier is buying a bunch of Y's for the RCA's so I can watch the news without powering the big amp-PA on. The plus of a mixer is the HDTV tuner, the MDTV converter box, DVD recorder, DVD player, VHS player, all have different output levels and I'm always messing with the volume. The mixer should fix that. Tons of used band mixers on craiglist music thread. Many of them will need slider pot repair. Still not $100. The disco mixer is tiny, 6"x10"x6", fits nicely on top of the piano. PA mixers have a big panel.
Also I have a $59 RCA CD player(1985), a $15 memorex CD player (2005), a $5 used Sony CD player, all have a lot less hiss than any LP's- and good LP's are about 55 db down. (Colombia, RCA red seal dynagroove, Mobil Fidelity- Capitol, Atco, Rhino are a lot worse)
 
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Hi Andrew: I think you hit the nail on the head, I need a pre-amp. (Sony should still be horse whipped for the poor S/N of their analog output! :mad: I wonder if Sony intentionally designed the S/N to be that bad! How did they even find an audio IC with a S/N of 45 dB? :eek:)

My problem now is finding a pre-amp that doesn't break the bank. (I want to keep my vintage tube power amplifier, I put a lot of work into it.) I want a remote control, so that means something modern. I don't need anything esoteric, but unfortunately, just the word "pre-amp" puts you into the high-end spectrum. You can buy a whole integrated SS amp for $100, but pre-amps start at $600.

Bobby Dipole

OK, I just found an economical pre-amp on eBay called "HLLY AMK-II". It's only $100. I couldn't find any specs on it, but how bad could it be? If it makes at least 80 dB S/N, I will be happy. I'll report back to this thread after I've had a chance to try it out.

Bobby Dipole
 
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