Headphone Testing Help - Page 1
Forum section: electronics / beginners

author: wardenclyffe
author_rank: Contributor
timestamp: May 18, 2011, 02:51:08 pm
content: A friend of mine asked me to repair some headphones the other day. The only problem was general wear where the wires come out from the end of the jack. I cut the jack off and went to add a new one but I couldn't figure out which wires were the left and right channel. I tried to pull the rubber coating off the the old jack to figure out how they were soldered on but goofed it up so badly it was useless.I know very little about audio signals so my question is how I can best test the headphones to figure out which side is left and right. I am assuming I can feed in a sine wave in the audio range and listen for a tone in headphones but I don't want to damage them in the process. Is there an amplitude limit I should stick to? Some other places have suggested putting a 1.5V battery across the terminals and listening for a pop in the headphones, but I am skeptical of that approach. Any suggestions would be much appreciated.

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: May 18, 2011, 03:33:13 pm
content: I've done the 1.5V battery thing many, many times.

author: Zero999
author_rank: Super Contributor
timestamp: May 18, 2011, 04:29:18 pm
content: The 1.5V battery will work but don't do it with the phone in your ear - it's really loud.

author: Simon
author_rank: Unknown
timestamp: May 18, 2011, 04:49:21 pm
content: you can sometimes use you meter in low ohms mode

author: Zero999
author_rank: Super Contributor
timestamp: May 18, 2011, 04:53:01 pm
content: That won't tell you which is left and which is right though.

author: Simon
author_rank: Unknown
timestamp: May 18, 2011, 04:59:24 pm
content: it will if you listen for the crackle ! not sure if it works on digital meters though

author: pmrlondon
author_rank: Contributor
timestamp: May 18, 2011, 06:03:40 pm
content: There's probably no surer way than the ones mentioned. Sometimes the core wire colour is a hint but it is by no means standard. Last pair I had to change the plug on had enamelled wire - that was a bit of a pain, but I think the colours helped there.

author: ziq8tsi
author_rank: Regular Contributor
timestamp: May 18, 2011, 06:04:08 pm
content: Quote from: Simon on May 18, 2011, 04:59:24 pmIt does, but you will probably need to be wearing the cans to hear the low test currents from a DMM.One of the non-intuitive features of unamplified analog meters was that on the lowest ohm range they put a significant fraction of an amp through the device under test, even at only 1.5V. Enough to make an incandescent torch bulb glow dimly for instance, and certainly make loud clicks on a headphone.Whereas on the highest ohm ranges the open-circuit voltage could be 9V, but the short circuit current would be only microamps.

author: Simon
author_rank: Unknown
timestamp: May 18, 2011, 06:12:16 pm
content: you have just elaborated on my point

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 19, 2011, 12:55:05 am
content: you repair earphone and you dont have anything to play from? radio? cd player? pc with sound card? very odd. use a battery then, scratching the wire on it, u'll hear something.

author: Ronnie
author_rank: Regular Contributor
timestamp: June 22, 2011, 01:48:02 am
content: Connect a capacitor in series with the 1.5 V battery to avoid shorting it continuously by the speaker coil. During transient speaker coils like inductors are open circuit but will be short circuit after several µs or ms (depending on the resistance of the circuit).

author: vk6zgo
author_rank: Super Contributor
timestamp: June 22, 2011, 04:00:55 am
content: Do the headphones have markings to show which is physically L or R?If so, just keep trying pairs of wires using the method posted by others above,until you find ,say, the L one.The other pair are the R.But,wait--there's more! The above finds the two sides,but it doesn't necessarily get them phased correctly.The only easy way to do this is if you can somehow see the diaphragms.You then put the two pairs in parallel,& do the ohmmeter test as before.If both diaphragms move in the same direction,they are phased correctly.If not,reverse one connection.The other(harder) way is to use a tone or mono music,again with the earpieces parallelled,& see if you can hear the difference.The wrong way round should subtract,the right way,add,but I think you may need "Golden ears" to notice.VK6ZGO

author: Simon
author_rank: Unknown
timestamp: June 22, 2011, 05:28:46 am
content: Quote from: vk6zgo on June 22, 2011, 04:00:55 amThe common earth is usually quite obvious on gheadphones

author: vk6zgo
author_rank: Super Contributor
timestamp: June 22, 2011, 07:16:42 am
content: You are right,that is the normal configuration.I was led astray by the fact that fact the stereo phones that I set up for mono use for Ham radio are odd ones which use two separate pairs.My first HF receiver was quite happy with the mismatch of two earpieces in parallel,but the transceiver I bought later,wasn't,so I connected them in series.I couldn't have done that if it had one wire always commoned.VK6ZGOPS:- Come to think of it,of course I could have connected them in series, just by ignoring the fixed common!It isn't how I wired them,though as they did have separate pairs.

author: pmrlondon
author_rank: Contributor
timestamp: August 14, 2011, 08:35:35 am
content: Quote from: pmrlondon on May 18, 2011, 06:03:40 pmSelf-followup time:I've forgotten how I stripped the enamel - and the same thing has just cropped up again. Any hints on how to get (soldering-proof) enamel off wires?

author: ciccio
author_rank: Frequent Contributor
timestamp: August 14, 2011, 08:57:32 am
content: Quote from: pmrlondon on August 14, 2011, 08:35:35 amEnamelled wires are hard to solder...sometimes I had success with a VERY short immersion in a VERY hot solder pot, sometimes I was capable of burning the enamel with the flame of a gas lighter, sometimes the VERY hot tip of the soldering iron was enough.

author: Unknown
author_rank: Unknown
timestamp: August 14, 2011, 09:03:49 am
content: Rubbing some fine sandpaper helps a great deal. A lot less messy than burning with flame.

author: Psi
author_rank: Super Contributor
timestamp: August 14, 2011, 11:03:27 am
content: I normally just scrape them carefully with a sharp craft knife or scalpel rotating the wire as i go.You can normally see where you've scraped off the enamel off because the color changes.However if the wire is really thin, (eg lots of strands all enameled separately), then things get tricky.A flame is probably the easiest way.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 15, 2011, 04:56:45 pm
content: [quote author=pmrlondon link=topic=3452.msg59188#msg59188I've forgotten how I stripped the enamel - and the same thing has just cropped up again. Any hints on how to get (soldering-proof) enamel off wires?At home I use a scalpel. At work when I need to strip a long length, or very delicate wires with very tough coatings I use formic acid. Watch out for fumes... it isn't particularly dangerous as chemicals go, but just a whiff is like snorting vinegar.