sher@bbn.com (Lawrence D. Sher) (08/27/90)
I have a new Sony Stereo TV (Model 20TX11). On the back are
a) 2 RCA phono plugs labeled "Audio Output (Variable)" for R and L channels
b) a "Speaker On/off" switch
c) no "Headphones" output
With the TV's speaker shut off and stereo headphones (Sony Model MDRS101
II) plugged into the R and L channel outputs for private listening, the
audio volume is very low, although usable if the TV volume is cranked
way up (80-90% of maximum in a quiet room).
Sony's customer assistance line ((800) 222 SONY) says "You can't use
headphones with that TV." (Hard to believe, isn't it.)
The problem appears to be the mismatch between the TV's output impedance
(manual says 10k ohms) vs the headphones' probably-much-lower input
impedance (like 32 ohms). I've tried other headphones; the results are
expectedly similar.
Questions:
1. Will I damage the TV by running it with the volume cranked way up
and the internal speakers shut off?
2. Are there any modestly priced headphones that *would* be suitable?
3. Is there a simple fix? (Buying a stereo amp just to drive
the headphones seems crazy as well as expensive.)
Your help is very much appreciated.
.----------------------------------------------------------------
/Internet email: sher@bbn.com
Larry Sher < US Mail: BBN, MS 6/5A, 10 Moulton St., Cambridge, MA 02138
\ Telephone: (617) 873 3426 FAX: (617) 873 3776
`----------------------------------------------------------------rhaar@rcsrlh.tmc.edu (Bob Haar CS50) (08/27/90)
In article <59154@bbn.BBN.COM> sher@BBN.COM (Lawrence D. Sher) writes: >I have a new Sony Stereo TV (Model 20TX11). On the back are > a) 2 RCA phono plugs labeled "Audio Output (Variable)" for R and L channels > b) a "Speaker On/off" switch > c) no "Headphones" output ... text deleted >Sony's customer assistance line ((800) 222 SONY) says "You can't use >headphones with that TV." (Hard to believe, isn't it.) ^^^^^^^^^^^^^^^ why? You buy a TV set with no headphone jack and expect to be able to use headphones? Why is this Sony's fault. Seems to me that you bought the wrong set. That isn't Sony's fault. Did the salesman tell you that you could plug headphones into it? If so, then you have a valid complaint against the store, but not Sony. They output on the "audio" jacks is designed to be suitable for input to a sterio amplifier so that you can the better sound quality that is possible by using the speakers in one's standard stereo system. For many people (including me), a stereo TV is a waste without this capability. I think that Sony understands the market pretty well and decided that few people would wish to use headphones unless they also had a stereo system. -- Bob Haar CSNET: HAAR@GMR.COM UUCP: uunet!edsews!rphroy!rcsac1!rhaar Computer Science Dept., G.M. Research Laboratories DISCLAIMER: Unless indicated otherwise, everything in this note is personal opinion, not an official statement of General Motors Corp.
clarke@acheron.uucp (Ed Clarke/10240000) (08/28/90)
From article <59154@bbn.BBN.COM>, by sher@bbn.com (Lawrence D. Sher): > Questions: > 1. Will I damage the TV by running it with the volume cranked way up > and the internal speakers shut off? No. > 2. Are there any modestly priced headphones that *would* be suitable? I haven't seen any. > 3. Is there a simple fix? (Buying a stereo amp just to drive > the headphones seems crazy as well as expensive.) Yes. Buy a couple of audio transformers and use them. Try Radio Shack. Microphone input transformers will probably work ok. Just run 'em in reverse. -- | "Pain, n. An uncomfortable frame of mind that may have Ed Clarke | a physical basis in something that is being done to the acheron!clarke | body, or may be purely mental, caused by the good fortune | of another." - Ambrose Bierce
wolfgang@wsrcc (Wolfgang S. Rupprecht) (08/28/90)
In article <59154@bbn.BBN.COM> sher@BBN.COM (Lawrence D. Sher) writes: >I have a new Sony Stereo TV (Model 20TX11). On the back are > a) 2 RCA phono plugs labeled "Audio Output (Variable)" for R a >nd L channels > >The problem appears to be the mismatch between the TV's output impedance >(manual says 10k ohms) vs the headphones' probably-much-lower input >impedance (like 32 ohms). I've tried other headphones; the results are >expectedly similar. Try a pair of high impedence headphones. The Senheiser 414's are very decent and are over 1k impedence. You can easily drive them off of low power op-amps and the like. I just plug mine into the 600 ohm output line of tape decks when I queue up tapes etc. -wolfgang -- Wolfgang Rupprecht uunet!nancy!wsrcc!wolfgang Internet: nancy!wsrcc!wolfgang@uunet.uu.net Snail Mail Address: Box 6524, Alexandria, VA 22306-0524
jgk@osc.COM (Joe Keane) (08/30/90)
A line-level output is high impedance, and just isn't designed to put out lots of power. You shouldn't be drawing more than a milliwatt. That's not to say you can't, but if you push it you'll get some distortion. A transformer may shift the impedance, but it won't change the power situation. What to do? Many op-amps drive headphones just fine. Not just any random one, you want `high output' so check the specs for output power. You probably want some voltage scaling, so you need two resistors too. If you want to get fancy, one can be a pot, and you get a volume control. Total parts cost could be under a buck, assuming you hook into the TV's power supply.