Line-out vs earphone?

[nbtv]

Hello. I'm new here.

I'm building a Televisor, based on the Mindset kit which really is super, but with a few refinements of my own.

I would like to know the difference between head-phone audio output and the line-out the circuit needs. Is there some way of converting? Otherwise I will have to find a second-hand CD player.

Best wishes, Edmund-Paul

[kareno]

First of all, welcome nbtv

I assume your CD player lacks a line out socket?

Don't worry, it is not ideal but you can use the headphone socket as a line out socket.

Start with the volume quite low and turn it up until your televisor responds. It is unlikely that you will do damage with the volume turned up high but the signal will be distorted on high volume.

CD players vary a lot in the output level on their line out sockets (as does the earphone output) but with a little experimentation we usually get things working.

When you do get things working you might find that the picture you get is negative i.e. black where it should be white and vice versa. If that happens there are solutions so just post again and you'll get plenty of help to fix that.

[Steve Anderson]

Again, welcome...

Karen's post above is totally correct and with domestic equipment there is a 50:50 chance you'll get inverted video, i.e. the incorrect polarity. There are a number of fixes for this...

If it's a battery-powered player, just swap the input leads to the televisor. This though is a bodge just to get you going, there's a good chance of picking up mains hum even though it's running off batteries.

If it's mains-powered and earthed/grounded...no way, but if it isn't (a two-core power lead) it's more than likely a 'no way' as you'll pick up hum through the internal power transformer whether it uses a linear or switched-mode power supply.

The fix, whatever the source is a simple one-transistor inverter circuit to put the video up the right way. Somewhere on this forum there's a thread devoted to this, but it was a while back. I still have the circuits I posted all that time ago, just ask and I'll post them here again. They are quite simple.

Steve A.

[Viewmaster]

Steve, the thread and your circuits.........

http://www.taswegian.com/NBTV/forum/vie ... er+circuit

[Steve Anderson]

Steve, the thread and your circuits........

Albert, thanks very much, I really couldn't be bothered to wade through what is now a large database of information on this forum. I must admit I forgot about the search function, I so rarely use it....must remember that in future...

Steve A.

[kareno]

I even have one cheap Tesco MP3 player that crosses over the left and right channels!!!

Had it not been for the fact that it can play WAVs it would now be rotting at the bottom of a desk drawer. Instead I made a special crossover cable so that I could use it with my NBTV stuff.

[Steve Anderson]

I even have one cheap Tesco MP3 player that crosses over the left and right channels!!!

A Left-Right swap? Now that is inexcusable! Next thing will be someone will pop-up and say there's a 180 phase difference between channels on such and such piece of gear...how do these guys get away with it? In fact for a 180 degree phase inversion between channels, is it possible to get that wrong? However, I'm sure out there somewhere there is an example.

...the easiest manner would be audio transformers in tube/valve gear...it could be a design or production error...mind you it would tend to bugger up the negative feedback (if used)!!

...anyway...getting a bit OT...

Steve A.

[nbtv]

Thank you all very much for the help. I'll have a go with various outputs and see what happens. Then report back here!

[Klaas Robers]

My MP3-player crosses the channels now and then, not always. It looks that it is not so easy to define the R-L difference if you start an MP3-file somewhere in the middle, because it mostly crosses when I paused a track and restart it again. In the beginning of the track the difference looks to be better visible.
For a .wav file it is easy. Each "frame" starts with the left sample.

Well, anyway MP3 is too bad for NBTV, and I don't know if my MP3 player plays back also .wav

[Roland]

On the subject of line output levels - I've been going through my pile of personal CD players seeing what sort of line out level I get. If I understand my little portable oscilloscope properly - then I seem to be getting about 0.8v peak to peak - a little less when running off batteries. About half of the units I've tried have had inverted outputs.

I've not really experimented with headphone output though I seem to get much lower voltages out of them as far as the 'scope is concerned.

Roland.

[Lowtone]

Well, anyway MP3 is too bad for NBTV, and I don't know if my MP3 player plays back also .wav

FLAC could be an interesting format.

[Steve Anderson]

...About half of the units I've tried have had inverted outputs.....Roland.

Yep, that's about par for course. I did a similar survey a few years back, and I also found about 50% of the units had inverted outputs. There is a polarity standard but few domestic equipment manufacturers follow it.

Amongst professional equipment with balanced inputs and outputs on XLR connectors they usually get it right, but then there's the question of level. The audio CD has all but vanished in professional circles having been replaced by servers and an AES digital bit-stream. (Very similar to SPDIF but balanced when on copper at 110Ω)

Here there's a choice of line-up levels, five at least that I'm aware of, from -16dbFS to -24dbFS. So if the professionals can't get their act together....Oh! Not only but also...dare not mention sampling rates....Oh heck! I just did!

Steve A.

Did I mention bit-depth?

[kareno]

On the subject of signal level standards, might I point out that NONE of my various CD and MP3 players can achieve the club level of 1V peak-to-peak! Only my laptop can produce 1V, and that's with the mixer settings at maximum. And when I can get a 1V signal, the audio amp is overwhelmed and a very low volume setting is necessary.

I always include some gain (typically three) in my monitor front ends (except my club monitor of course) so as to be able to work from these sources.

Where did the idea arise that domestic audio equipment puts out 1V peak-to-peak? In my experience it rarely does.

[Steve Anderson]

Karen, I can only assume that the 1V p/p 'standard' was a reflection from 405/525/625 TV where the composite signal is a maximum of 1V p/p at 75Ω circuit impedance...ignoring colour subcarrier effects for the moment. However the NBTV circuit impedance wasn't specified and in today's world assumed a zero Z source and an open-circuit load...as near as damn it....much like domestic audio gear.

As for domestic audio gear line levels, somewhere between 100-300mv RMS (say 300-900mv p/p) is most usual....very roughly...very roughly. A deliberate repeat there.

There is a reason for this. As a minimum, a real minimum, you need at least 10db above this line-up level which in professional audio gear is 0.775V RMS (1mW into 600Ω...the 600Ω bit is these days ignored and quoted in dbu or dbv). This means 0.775V RMS at +10db = 2.45V RMS or 6.93V p/p. Now there's the start of the problem. If your gear runs off two dry cells it's kinda difficult to do.

Any decent and respectable professional audio gear 'should' be able to output +24dbu and accept an input at the same level without distortion...hence my mention of +16dbFS and +24dbFS earlier.

+24dbu = 12.3V RMS or 34.7V p/p....get the idea? Domestic equipment manufacturers DO NOT want to provide this level of 'headroom' and the costly power supplies involved. Hence the drop in line levels we're all used to...and the varying 'standards' that are seen.

Mr. Joe Public will never notice the drop in sig/noise ratio with his air-con or heating system running, so we'll design this Audiophool gear around 12V and we'll get away with it....and generally they do, and do I give a damn about sig/noise after a few beers? No! All I want to hear is the MUSIC!

Steve A.

OK, I'll step down from my soap-box now.

[M3DVQ]

Something in the murkier recesses of my memory makes me associate the value 200mV with line output level on computer sound cards. Now, was that 200mV peak, or p-p...?