Hi,

This might sound like a silly question but I am trying to figure out how a connector I bought today works and if it is safe to use in the way that I want to. I have bought a phono 2 into 1 converter, so it allows me to place two mono phonos into one side and give me a single mono phono out. Now, I want to put a stereo signal in and get a mono signal out, will this do the job? Is there some circuitry inside to combine the two signals else surely you would short circuit the two live signals out?

Any help would be much appreciated.

If it's just a plain adapter it will be for getting two phono's out of a single input, the other way round to the way you are wanting to use it. If you want to join two outputs just insert a resistor in line with each channel and join their free ends together, 470 ohms 1/4 watt should do fine.

So if you tried to put to live signals in you would short them out?

Can I please ask what this is for?

John Denim.

Joining low-level outputs together without a few ohms of resistance between them is generally not a good idea, but probably won't damage them.

Can you give us a link to the item you bought or describe it more precisely?

It will sound awful trying to just connect the stereo phonos just into one, as the signals will be also going back up into each other's output..as it were.

If you want to combine a stereo feed into a mono then as already stated you need to join them with resistors (so the signal's mixed properly). I'd use 4.7k resistors in each leg in a Y-pattern myself.

http://www.maplin.co.uk/Search.aspx?criter...rce=15&SD=Y

If you look at the bottom FAQ about the DVD player, that is similar to what I want to do but with a minidisc player, I want to convert L & R into one mono output. I wanted to check this with you guys because I am not sure if that is reliable information on their site.

Hmm. That's a plain adapter for two outs from one in. Maplin's advice is a wee bit dodgy. It probably won't hurt your gear but should have resistance added to be electrically correct.

Knowing this I will take the adapter back, if used will the sound quality go drastically down hill? Even used on low level line devices surely this would eventually cause damage?

I had a feeling that the guy in the shop had no idea what he was talking about, thanks guys.

It's quite possible that the resistors will be integeral to this part.

I'd suck it and see, I don't think you will damage anything, if it sounds bad don't do it!

John Denim.

The sound quality might be worse than it need be, hard to say.

Low-level outputs have limited ability to supply current so are not likely to be damaged by being connected together. Also there may be capacitors in the output circuitry which will limit their ability to harm one-another by the worst case possibility of one output going positive while the other goes negative - the caps will stop the resulting direct short between the power supply lines.

If you are at all worried don't use it.


EDIT: I used to feed a laptop headphone output into a radio mic belt pack via a couple of resistors, all assembled on one of those plastic 12-screw strips.

Using a multi meter I tested the live one side against the live on the other and found no resistance, so they can't have put a resistor in the middle.

Unlikely. I think they'd mention the fact if there were and then charge more for it! If you have an ohmmeter you could measure it.


EDIT I feel soooooo redundant LOL

It really isn't a good idea to use it as a combiner.

Hmmm I really dont see the problem with using this adaptor .

We often use similar adaptors to plug the stereo outputs from our cd players in to a mono line input on our mixer.

The sound quality is fine for general PA use.

There are lots of theoretical reasons why this is a bad idea but I've done it hundreds of times (usually doing playback at rehearsals with a stereo backing track into single powered speaker) and not had a problem with the gear yet.

However, there is one theoretical problem which CAN be real, and that's how it sounds. Depending on how the stereo track is mixed, you can quite often get phase cancellation problems when you combine them to a single mono. The person who did the mix should be checking for mono compatibility but this doesn't always happen (read: I forgot to do it on several occasions) and you suddenly find your kick drum or something disappears when you combine to mono.

So long as you're aware of this aspect and watch for it, it shouldn't be a problem.

Bob

I must admit I was sitting there thinking that I've done this before plenty of times and it's been ok. Granted it's technically the correct way to do it, but the quality of the result is fine for the majority of times it is required.

I only ever met one person in Maplin who did know what he was talking about! Needless to say it wasn't one of the staff members.

The sound quality is usually awful doing this. Try it at home. You need to combine (or mix) the L&R together, not create a destructive interference pattern.

Come on - this has been done for years. The resistor version adds a level of security in that if one output dies, the other at least has something available. Both these systems can produce the odd phase cancellations spoken about, but 'destructive interference pattern'??

Sound quality is categorically NOT awful using either of these methods - even going into two mixer channels panned centre will have exactly the same problems with a non mono compatible signal. Most output designs have no electronic issues with combining that I have ever found. In fact, I have never ever had a problem with amp inputs that have been shorted out - far more 'brutal' than a resistor-less merge!

ive done this a few times for plugging into a single monitor for DJing purposes and its been fine

however I dont try and make a habit of it

I agree with Paul on this , Iv used this method for many years on various applications without any problems.

Using professional & domestuc equipment causing NO damage or real problems ,,

Can I ask what application the OP is using this adaptor for ???


Matt

No Paul I must disagree with you. Putting stereo into a desk via two mono channels will mix the signal and give a proper mono effect, just joining them is not the same thing. By 'destructive interference' I mean that if one channel tries to drive the output high and the other is driving it low (for example with a track that has reverb) then the result with the L&R joined will be zero. This can lead to a 'hollow' or tinny sound or attenuated vocals or musical beats, similar to a lost earth. It's unpredictable, as it depends on the output impedance of the line output stage and the impedance of the input, not to mention the production of the musical track. With a proper mixing arrangement, the result will be correct and since a couple of simple in-line resistors will effect this, it's surely better to suggest this as the correct way in a forum which people often use as a means of reference.

I'm not being pedantic or snooty, I come across this problem alot in the cabaret, DJ and Karaoke business where inputs on PA desks are at a premium and amateurs have to use stereo sources eg Minidisc, CD, Karaoke, Laptop into a mono channel. It's not so bad on older mixes but modern productions just swim with reverb and phase effects and the result of incorrect connection is often unintelligible audio.

The use of such adaptor is perfectly acceptable for general PA and sound re-inforcement purposes. The quality of the sound if fine for all but the most fussy and trained ear.

If the OP would tell us his propsed purpose for this adaptor we could advise further.

Matt

I'm afraid I have to disagree with you KevinE. The method of mixing the stereo tracks down to a single mono doesn't matter--it's the content that determines whether there's phase cancellations or not.

As paulears says, putting two stereo tracks together by using two faders on a mixer (both panned centrally) will have exactly the same effect as doing the mixing using a "Y" cable. As I said, if the person who mixed the material hasn't checked for mono compatibility and has the same material moving in a positive direction on one side and a negative direction on the other, you will indeed get destructive cancellations and they'll be there whether you mix with a console or a cable.

Fortunately, most recordings ARE "mono compatible" because they have to be able to be played on cheap transistor radios or whatever, but there CAN be problems.

Bob

I found this out the hard way with a Panasonic DAT recorder that had it's input XLRs connected via one with a reversed connection. For 6 months every single recording I did had no mono compatability.

Let's make sure that we separate electronic reasons for not doing the merge (there really aren't any) and the acoustic results that only rear their head when the source material is not mono compatible.

The fact that this nasty effect is revealed in the cabaret, DJ and karaoke markets is simply because many of their music sources have been produced in home studios where it sounds great in stereo, and my own experience is that very often it is reverb units that make his worse, the returns being out of phase - which sounds reat - but messes up the stereo image. Since my own problem, I have run a phase meter as a plug in and use it all the time. Mono and over wide mixes are very easy to see. Commercial recordings don't normally have this kind of error.

I realise others have already said it - but resistors do not work in the time domain, so using them will only result in level changes, and this has NO impact on mono compatibility whatsoever.

While I agree that there are two different criteria here, I'd disagree that there are no electronic reasons for not doing a simple Y merge. You can get away with it with most modern outputs because the outputs are protected - thanks to the ingenuity of modern IC op-amp designers. Less well protected outputs would still cause problems.

Cheers

James.

Hi

Lots of going round the houses on this - joining two line outputs from a mini disc is not a problem, it used to be recognised that buffer resistors were needed but not nowadays as most outs and ins can handle it!( High Z bridging inputs).

Done all the time on pro installs!

But it won't. Within the innards of an audio mixer there are input buffer resistors and then gain restoration amps to achieve the mixing effect. Not all audio sources have output buffer resistors (save for maybe the odd 10-ohm here and there) and many are DC coupled right back to the final driver.

technical article here


My reasons for my argument were both electrical integrity and sonic quality based on 20 years experience, not on some theoretical whim I dreamt up. But I'm obviously banging my head against a wall here, so I'll withdraw.

I have to say, I do follow Kevin here to a point.

Whilst we know it's possible to do it without any significant audio quality loss on SOME new equipment, from experience, some gear, both old and new doesn't like this at all. Yes we can look at the mono compatibility of things, and yes it's an issue but most pro recorded stuff is fine with this (as has been mentioned previously). However there is alot of stuff out there, namely backing tracks where this IS a problem. A number of acts I work with use backing tracks on minidisc, for the most part I'll just use one channel of this as bringing them both in sounds awful* This is not a case of 1 channel being inverted polarity, it is simply certain parts of the track having differing phase / polarity.


Why don't you just put in some resistors and then it's a universal lead, able to work on any unit without the risk of shorting the outputs, you can get 947,002 resistors for about 16 and a half Yen ad it'll only take a minute per resistor to fix to the lead. That way you can say to yourself, whilst this might have been fine on most stuff, now I can be assured it'll be fine on it all. Of course, as we've already learnt, this wont help audio quality if its not mono compatible, or indeed just plain crap.



Rob

*one channel sounds bad enough, early 90s midi anyone?

I'm with kevin. I was teching a presentation at uni a couple of years ago and the only input to the crestron controlled system to do the sound was a mono XLR intended for a podium mic. I was running a bit short on time, so bodged it using a Y lead, which is basically what you're proposing and some XLR-phono adapters.

It was a very embarrassing moment for me. Nuff said that since we were playing a dvd clip then bad things happened.

Now I propose everyone has a good old read at: http://www.rane.com/note109.html before considering the answer to the question. Funnily enough one of my projects this morning was to build a magic laptop lead (stereo minijack to mono jack combiner) for use when you just don't have enough channels!

M

I'm afraid the problem you created was not related to 'Y or not to Y'. You were driving a line level signal into a mic input which probably had phantom power sitting on it. Mic inputs are for mic level ( -60db to -40db approx) line inputs are for line level( nominally 0db )ie 60db above a dynamic mic output.

Of course, the REAL problem here is that the input was a balanced one, and you were sticking stereo into it. That will react REALLY badly.

I've been hitting a similar problem over the last week with some projector installations. Wall plate has 2x phonos for "AUX" and 3.5mm jack for "PC". Now we all know that your typical AUX is a DVD or VCR with a 10kR impedance and a PCs headphone socket is 600R. Does it work? Nah; not really!

I'm not sure about both your suggestions. If I was driving line into a mic input (the volume pot was tres low at this point) then I'd hear clipping. If there was a phantom power issue then probably I'd have let the smoke out of something somewhere, and phantom would be no more. It was two phonos with their plus wired to pin 2 of an XLR and their minus wired to pin 3 of the XLR. The other tell tale sign was that when I unplugged one side, the sound got a lot better.

M

That's what you'd expect if you had the 2 phono pins connected to 2&3 on the XLR.

I don't want to be too annoying but I'm not sure how this could have happened - I basically used clicky with a couple of these clicky again and then one of these into the laptop?

So you guys are saying that there was a wiring fault, and somehow I'd in effect used a 3.5mm balanced jack to XLR lead in a very very wrong way?

M