Convert stereo to mono

I used 23 ohm resistors on each channel, but the volume is to low. I shorted them to check the level, still to low. I wanted to drive a pillow speaker from the headphone jack. The radio has a line out and a headphone jack, but unless I open the radio and modify the wiring to the internal speaker, I don't think I'll have the power I need for a pillow speaker. The internal speaker has good sound and volume. I have the Tangent Quattro MKII internet radio. I've only had it a few days but it is pretty neat to have 10,000 radio stations available with no static. Mikek

What is the impedance of the speaker? Headphones range from around 30 ohms to around 600 ohms, but loudspeakers can be way less. Is there a published minimum impedance that can be driven by this device's headphone jack?

It could.

If the amplifiers are playing nearly the same signal, there won't be an issue because the output transistors will be at the same voltage. This situation of tracking almost exactly the same voltage means that the left output looks like a high impedance to the right one, and vice versa.

The correct stress test for this is: what if the left and right signal is quite different? For instance, complete silence in one channel and loud music in the other. In this situation, the output device with signal swings sees the silent one as a low impedance. This is like asking it to drive a near-zero-ohm speaker. (Basic electronics: a voltage source is a low impedance, and a perfect voltage source is a zero impedance!)

So, in essence the common mode signal should mix to the speaker nicely, but any differential signal faces a short circuit between the two different voltages.

Even if this doesn't damage the output device, are you okay not hearing much of the differential signal out of the speaker?

It's not a bad idea just from the consideration of the possible low impedance of the speaker compared to headphones.

Both outputs should be separated from each other by at least the minimum required load resistance so that means idnvidually coupling them to the speaker through resistors which are at least half that resistance.

But remember since R will shunt any differential signal, but not common mode signal, your differential signal is attenuated. The common mode signal goes through R and the speaker, but the differential signal goes through R, and then another R in parallel with the speaker. This will work best if R is significantly larger than the speaker load, in which case you take a lot of loss of volume across R.

The best approach is to feed the channels to another device which can properly mix them, and re-amplify to a single speaker.

Probably not harm (usually the power output to a headphone is limited internally) but: if you connect the outputs in parallel, the amplifiers 'fight' each other, creating distortion (not good). If, on the other hand, you connect them in series (speaker from L_out to R_out, leaving the 'ground' unconnected), the occasional mono signal that comes out of the radio will result in zero speaker output.

Usually, a 'blend' function of some sort is used to convert stereo to mono, or one simply uses the L_output channel and disregards the other. Check the controls or menus on the radio to see if there's a 'mono output' option.

Why not get two pillow speakers, and just set them next to each other?

Good Luck! Rich

The output clearly has no power to drive these speakers. The power dissipation may be there on paper, but what you need is efficiency: to move air. That speaker is not converting enough of the electrical energy into sound decibels. Headphones also don't, but they are right next to your ear!

That's silly; why don't you get two pillow speakers and have stereo.

Don't there exist powered pillow speakers?

There are all kinds of power speakers that are form-factored to work off

Don't you have some old wall-wart-powered computer speakers lying around? The might not fit under a pillow very well, but some positioning arrangement could be negotiated with them.

It's very likely that there is a separate amplifier for that speaker.

Also, according to the specs on the website, the speaker is a neodymium driver. A stronger magnet translates to a more sensitive speaker.

No static? Sure, if you don't count compression artifacts as "static".

Most sites will not provide quality, high bit rate streams, unless you pay for a subscription, or you are willing to listen to tons of embedded ads.

sometimes. Sometimes they take feedback from the output terminal and if you tie the two channels together you'll get distortion

do you feel lucky.

Nope, I wasn't lucky, not enough power to drive an 8 ohm speaker at (quite low) pillow speaker level.

I'll need to open it up and add a switched 1/8" mini plug jack to the existing speaker circuit. In the process voiding my 2 year parts and labor warranty. :-) Would be nice to be able to shut the display light off too. It is menu adjustable, but even the lowest level is more light than I want, during my beauty rest. Mikek

Thanks Rich, but one speaker is enough to deal with, 99% of what I listen to at night is talk radio, so a stereo signal is not real important. Mikek

I'm used to listening to AM stations at night with static and fading as a constant, varying with the season. This audio is beautiful, to me! Regarding ads, so far everything I have programed in are commercial broadcast stations, so yes tons of embedded ads, ideal bathroom breaks. Mikek

Okay, let's compare digital with ... AM. :)

Oh, heck! If it's just talk, then just use one channel and ignore the other one - no parts, done. (Use a stereo plug, and just connect up one of the active lines. The other one will have no load, so draw only standby current.)

Cheers! Rich

Masking tape? ;-)

Have Fun! Rich

I made a cardboard flap with a magnet embedded between layers. The magnet holds the flap to the speaker grill on the top of the radio, and it hangs down over the display. I can lift and slide it a bit when I want use the display. Not the the first one I've made, did this for my Icom R-71A also. Hmm.. also a Chrysler car radio, is it silly to have three radios at your bedside? :-) Don't ask my wife! I have now installed a (switched) speaker output jack, on the internet radio (Quattro Tangent) and all is good. I see a lack of motivation to build AM Band antennas in my future :-( Mikek

Tune one to Myron Floren music, the second one to Dick Contino music, and the third to Florian ZaBach music; play them simultaneously while making love. =:-O

Have Fun! Rich