[OT] 3.5mm stereo to mono adapter with switch?

[Carlos E.R.]

Exactly.

[Carlos E.R.]

I'm an electronics engineer. It is against my ethics to recommend such a system.

It should be a button in the audio mixer.

[Dave Plowman (News)]

One of the first use of headphones etc was with telephone lines. And apart from the use in a telephone itself, the ability to listen across a telephone line without loading it noticeably. Hence the high impedance. Obviously, these were made in relatively large quantities, so got used for other things too, like early crystal sets.

Once they became primarily a domestic device fed from a sound system, etc, it was likely easier and cheaper to make them low impedance since they were now being driven by an amplifier designed for this job. And easier to get high levels from a low voltage supply.

[pamela]

I suspect the reason no one makes a mono switched adapter is lack of demand.

[Dave Plowman (News)]

Indeed. Adaptors to use stereo headphones from a mono outlet where once quite common - but not the other way round since headphones are essentially stereo.

[micky]

If you have to unplug it anyhow, why not get a stereo to mono adapter with no switch? This will be hard enough to find because most of them will be designed for a mono-plug. I seem to remember seeing one but maybe I'm thinking of a Y-connector that does this.

iirc monoprice.com sells a wide range of adapters, they're very low priced and shipping for a small amount is very cheap. While you're on the site you may find other things you want, like a long amplified usb cable. Who knew?

But even here, it's not that much trouble to plug the adapter in between the two things, especially if it's a different stereo source from usual.

I say this because I'm an adapter addict, and woould have had every adapter there was 40 years ago if I could have. But now there are thousands of kinnds and it's impossible, and I've never seen one with a switch, and if it had a switch, it would be 3 times the size of one without a switch!

[micky]

Yes, the switch used to be there, but you don't mean that the adapter used to be sold, do you?

You might try sci.elecronics.repair

Months ago in computer ng's I tried to find a PC audio player which would combine L and R. I had a pair of v. good PC speakers but one is broken, and I have a friend who wants to play music from his laptop through the wall into the kitchen. He wanted only one speaker, which worked, out great, but I wanted him to get both channels. I coudln't find the software, and so far he hasn't even thought of the problem. I was over there a couple days ago and the speaker light was on, though no sound was coming out.

[micky]

So instead of what you're using, use the Y connector and the stereo plug he refers to and instead of plugging and unplugging it, run a

2-conductor wire from the L hot and R hot to a switch. For inlilne switch recommendations, especially the second one, see my post closer to the start of this thread.

[micky]

That's true.

The Bilderberg Group, the World Alliance for Progress, and the Ladies Decency Society decided about 20 years ago to abolish mono, so as to be able to say one thing in one of our ears and something else, something more sinister from a free person's point of view. It took them 4 years to organize and start implementation but they 've been at it for 16 years now.

The Ladies Decency Society was originally about propriety, morality, the quality of public speech, etc. just as the name implies, but it was taken over by drug-using pot-smoking hippies and now its goals are entirely different.

[pamela]

I didn't realise that was an active group. I'll bear that group in mind in future. Thanks.

[micky]

A lof ot what they talk about is way over my head, but they will deign to talk to civilians too.

[The Natural Philosopher]

Well that's Corbyn's labour party for you.

[Carlos E.R.]

You are right, it is not a short circuit, but for lack of better words...

Say that the L side tries to send 1 volt. Say the right side tries to send 2 volts. What do you get? Well, undefined, you have to calculate on each case. With resistive internal loads you might get the average voltage, but output amplifiers would not typically have a resistor in series with the load.

Because you have a voltage source trying to impose its voltage on another voltage source. If the output circuitry is weak... yes, it might be damaged.

At best, you get sound degradation. Distortion.

[Dave Plowman (News)]

A decent power amplifier will have an output impedance very much lower than the nominal load. Say 0.1 ohm. Paralleling two power amps means each one is effectively trying to drive into a dead short.

Of course if it's a cheap amplifier just for low quality headphones, it may well have a series resistor in the output to protect it from a short circuit.

[Carlos E.R.]

No.

[micky]

I wasnt' objecting to the use of "shorting" except to using it to reach conclusions which might not apply to this "kind of shorting", and which afaik are usually about actual shorting. **

I find other, possibly similar, situations where people categorize what they see and then relate to what they see as if has all of the charateristics of the category, mabye the worst examples of the category.

For example, one kid will do something with or to another kid, or an adult to another, and it's labeled "bullying" and then the discussion becomes about bullying, even when supposedly they're still discussing the individual occurrence, whether it was bad, how bad was it, and what to do about it. Not every thing about bullying will apply.

Or "discrimination". Things are called discrimation as if all discrim. is invidious discrim. And a firmly planted label just confuses things. "Is this invidious discrimination" is worth asking at the end of a discussion .

I'm sure there are many other examples about all facets of our lives.

**BTW, everyone on alt.home.repair told me you can't use a light dimmer to control the speed of a table fan, but I've been doing it with 1 fan for 30 years and a couple others for 20 years with no problem. (I always test first. For about one out of 6 or 8 of my fans it wouldn't work at all, and if it works I let it run for an hour while I'm watching.). And I never let the speed get down to zero, but they can run all ight and all day without getting hotter than normal or any other problem. I lower the speed until I can't hear it, and I like that much better.

[micky]

Let us know if it works, and if there is distortion or worse for any of the devices you plan to do this with.

The dictating machine is monaural to begin with iiuc.

When I was just out of college, I worked in a poltiical campaign for Congress, and there were two small cities in the district (and two smaller ones). The first two were where most of the votes were and when I got there there already was a direct, local line to the second city from the first (where the hq were and the candidate lived.) But anyone who wanted to call had to go to the HQ. This was before 3-way calling. I took the toll-free phone and a local-only phone and connected t hem in parallel, so that anyone could call in on the local only line and anyone there could call the other city, flip the switch and connect everyone. It worked but the volume was low.

Another thing I did was that every day they (I) called every radio station in the district with 30 seconds of a speech the candidate made** that day or the previous day. I held the speaker of the cassette player to the mouthpiece of the phone. The radio stations would play it*** but fidelity was bad. After I had the job for a couple day, I just connected a 1/8" plug across the mouthpiece of the phone and plugged it into the speaker jack of the cassette player, and when I heard it on the radio the fidelity was perfect. Not only that, we could talk while we were playing it and the radio station didn't hear that. (Not secrets but we didn't want to garble the recording either.)

**Or had made some other day. He didn't actually have an event every day, not even a coffee.

***They also printed our press releases for the same events, which we sent to every newspaper in the district, and often it read like they had a reporter there, even though they were just printing word for word our press release. Apparenly this is standard in the industry for papers with few reporters.

[Johnny B Good]

Herein lies the problem of using a simple (switched) bridging circuit to link the left and right channels together in a simple mono source to stereo phones adapter when used the 'wrong way round' to downmix a stereo source into dual channel mono. It may or may not work to an acceptable quality standard depending on the nature of the stereo source being so abused.

In the case of older generation HiFi amplifiers using a simple resistive attenuator to allow the main amplifier outputs to safely drive a set of 8 or 16 ohm stereo headphones without having to choose a lower volume setting (and the secondary benefit gained of allowing attenuation of the fixed noise level in the speaker driving amps), simply bridging the left and right contacts of the headphone socket to collapse the stereo down to mono was an effective and distortion free solution.

However, with modern portable music players (often relying on a single AA or AAA cell to power the digital processing as well as the final analogue stage of the headphone driver typically designed to drive 35 Ohm earbuds and earphones, this cheap trick is more or less guaranteed to cause unwanted distortions.

Although it's reasonably straightforward, if slightly more complex, to use a combination of both voltage and current negative feedback in an analogue amplifier to endow its output with an impedance other than almost zero ohms (or almost infinite ohms in special cases) without resorting to fitting actual resistors of the desired impedance in series with the amplifier outputs, there is no real benefit in designing in a defined output impedance characteristic of, let's say 35 ohms as a match to the expected load, compared to the use of 35 ohm series resistors with a low Z output amp using simple voltage negative feedback to achieve both a desired voltage gain and low impedance characteristics.

At least there isn't when you don't have the luxury of amplifier biasing voltages a good 6dB in excess of requirements. With portable players running off a single AA cell, you don't have a lot of voltage swing for the amplifier to work with. For a start, assuming a perfect PowerFET based amplifier design, the peak to peak voltage swing is a mere 1500mV, corresponding to 750mV peak amplitude which corresponds to 530.3mV rms. which corresponds to a maximum level of +9dBmW into a 35 ohm earbud load.

+9dBmW into a reasonably sensitive 35 ohm earbud or closed back heaphone is likely to be quite loud which may cause some to think that trimming this back by 6 dB to a mere +3dBmW/35 ohms will be an acceptable loss in performance[1] just to allow the headphone terminals to be bridged into mono without distortion effects using either 35 ohm series resistors or else designing the amp to look like a 35 ohm source (it matters not which method is used - you'll lose 6dB 'head room' off a given amplifier voltage supply regardless).

Since the requirement to bridge the headphone driver amplifier's outputs into mono is the very last thing to cross the designer's mind when developing such portable audio kit designed to be run from a single cheap and readily available galvanic cell (aka the AA and AAA Carbon/Zinc "battery" or its alkaline non-leak equivalent), you can bet your life that the driving amp's output will be as low an impedance as possible so as not to needlessly squander what miserly peak to peak voltage swing is available to a practical single ended analogue amplifier powered from a mere 1.5 volt supply. IOW, you can guarantee distortion products (quite possibly severe distortion products) when you bridge the two channels with a simple shorting link when using such a gadget or 'appliance'.

If you want to keep it distortion free and as compact and as simple as possible (and can accept a 5 to 6 dB reduction in output level when using

35 ohm earphones), just wire a couple of 33 ohm resistors between the input and output sockets on a small adapter box containing the mono/ stereo switch and wire said switch across the headphone socket contacts (you could eliminate a separate input socket by using a suitable stereo plug equipped fly-lead wired to the adapter box - your choice).

Incidentally, a quick and dirty way to audition the effects of bridging the left and right channels of a headphone socket on such gadgets is to playback audio material that has been hard panned to one or the other channel such that the other channel is totally silent. You can then more readily detect any changes due to distortion when you flick the switch from stereo to mono.

[1] Squandering a hard won +6dB additional clipping margin is never a good idea (unless you only ever audition "popular" music limited to little more than 3 to 10 dB's worth of dynamic range), when listening to recordings of actual musical performances where you need a decent audio level without risking transient peaks (percusson instruments) becoming unduly clipped. When it comes to recordings of music, you can never have too much clipping head room in your replay system. :-)

[Johnny B Good]

There's no reason why a standard TS&R 3.5mm stereo jack plug can't be used to deliver a mono source into a stereo headphone adapter where the ring contact is left unconnected and the tip is wired to the T&S contacts of the stereo headphone jack socket of the adapter.

[tabbypurr]

Using feedback to give the output impedance does not reduce available output swing.

NT