Phone Jacks/Audio Jacks Beginner Questions - Page 1
Forum section: electronics / beginners

author: otpowell
author_rank: Regular Contributor
timestamp: January 02, 2016, 06:25:04 pm
content: Hello, I have a few stupid questions, couldn't find the answers searching online, I figured it would be easier to ask the EE experts.1. Can someone tell me why these are called phone jacks and not audio jacks? I mean, it's not for a phone, is it? Phone lines are usually RS-232 I think. I noticed the audio input on a audio receiver is called phono for some reason too.2. These are mono plugs, can I input a stereo signal and get a mono output on two speakers? I can, correct? This takes the stereo and turns it into one channel but I can still get a two speaker output right? I guess that would depend on how my output is wired, but it should work, I think. Hope that question makes sense. Maybe it doesn't.3. I noticed when I was at Radio Shack buying their overpriced crap, they have two different types of audio panel mounts. They have "open circuit" and a "closed circuit." What's the difference? The closed circuit keeps the circuit working with no audio input, and the open circuit keeps the circuit open with no audio input?Sent from my iPhone using Tapatalk

author: Simon
author_rank: Unknown
timestamp: January 02, 2016, 06:42:42 pm
content: I don't know if phone is a regugitation by some sales twit of "phono" that refers to a record player input.You can connect L and R to one input and get the resulting mono that can play on as many speakers as you like, but connect them through resistors so avoid any damage.Panel sockets are often put on things that have a speaker and the speaker automatically gets cut out when the headphone plug goes in, it could be they are refering to the built in switch to the cocket as being nomarlly open or closed. Can you provide more information ?

author: helius
author_rank: Super Contributor
timestamp: January 02, 2016, 06:56:50 pm
content: They are called "phone jacks" because, um, they were used first by the phone company. Many decades before the modular jacks and plugs that you connect your (land line) phone to today. There is even a miniature form called TT for "Tiny Telephone" used in recording studio plugboards.Phono is shortened from phonograph, i.e. a record player. It doesn't mean this type of plug, in fact most record players connect with RCA plugs.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 02, 2016, 07:17:47 pm
content: Quote from: otpowell on January 02, 2016, 06:25:04 pmBecause back 100 years ago they were originally used for telephone switch-boards. See the photo posted by @helius.If you used the term "audio jack" nobody would know what you are talking about. There are literally dozens of different connectors used for audio.QuoteNo, its not for a phone. But there are dozens of examples of things whose common names don't correlate with their current use.QuoteNo, phone lines are not "RS-232" That is the old,original name for the standard for old-school serial communication, originally used by TeleType machines, etc. And later adapted for use by computers.QuoteThe word "phono" could refer to two different things. The first could be what we commonly refer to as "RCA" connectors, aka "Cinch" in Europe. The other meaning of "phono" is the abbreviation for "phonograph" which was a method of recording and distributing sound recordings on plastic disks with physical grooves to reproduce the waveform of the audio. Perhaps you have seen one.QuoteYour question depends ENTIRELY on how the connector is used. i.e. how it is wired into whatever gear you are asking about. As a generic question, it fails completely. Unanswerable.QuoteAn "open circuit" jack is simply a straightforward connector. A "closed circuit" jack includes SWITCHING contacts which change when you insert a plug. The most common example of this was a transistor radio where inserting the earbud plug would automatically disconnect the internal speaker.There are several other common uses of this technique. Another is audio mixing consoles which have an "insert" jack. When nothing is plugged in, the audio continues through the mixer to the fader control. But if you plug something into the "insert" jack, it interrupts the audio flow (via the switching contacts) to send the audio signal out to some external gear, and then returns it back into the mixing console to the fader control.And many effects boxes used by electric guitar players use the switching contact to automatically connect the battery when you insert the audio plug, and then automatically disconnect (and save) the battery when you disconnect the audio plug.Ref:https://en.wikipedia.org/wiki/Phone_connector_(audio)https://en.wikipedia.org/wiki/Telephone_switchboardhttps://en.wikipedia.org/wiki/RCA_connectorhttps://en.wikipedia.org/wiki/Phonographhttps://en.wikipedia.org/wiki/Audio_and_video_interfaces_and_connectorshttps://en.wikipedia.org/wiki/Plain_old_telephone_servicehttps://en.wikipedia.org/wiki/RS-232https://en.wikipedia.org/wiki/Phone_connector_(audio)#Switch_contacts

author: Brumby
author_rank: Unknown
timestamp: January 03, 2016, 02:53:54 am
content: To help you understand what happens when you use mono and stereo 'phone' connectors.....

author: Audioguru
author_rank: Super Contributor
timestamp: January 03, 2016, 03:27:12 am
content: Never short circuit amplifier outputs together. To make mono from stereo then mix together the amplifier inputs with series resistors to make mono.

author: otpowell
author_rank: Regular Contributor
timestamp: January 03, 2016, 02:43:53 pm
content: Quote from: Simon on January 02, 2016, 06:42:42 pmThanks Simon, unfortunately I don't have any more info on the closed/open circuit. The package is all I have. The back of the package doesn't have any information.Sent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 03, 2016, 02:45:18 pm
content: Quote from: helius on January 02, 2016, 06:56:50 pmInteresting! Ok, I guess radio shack is just old school. Thank you!Sent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 03, 2016, 02:50:21 pm
content: Quote from: Richard Crowley on January 02, 2016, 07:17:47 pm

author: IanB
author_rank: Super Contributor
timestamp: January 03, 2016, 02:53:02 pm
content: Quote from: otpowell on January 03, 2016, 02:43:53 pmIf you have the package containing the connector you have all possible information. Simply examine the connector and find out how it is configured.

author: otpowell
author_rank: Regular Contributor
timestamp: January 03, 2016, 02:53:21 pm
content: Quote from: Richard Crowley on January 02, 2016, 07:17:47 pmThanks Richard, I do appreciate all he the information and links, totally makes sense now!Sent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 03, 2016, 02:58:58 pm
content: Quote from: Audioguru on January 03, 2016, 03:27:12 amThank you sir, should I use an arbitrary High value resistorto connect the outputs? Like say 100K or 1M? What is the risk associated with shorting them together?Sent from my iPhone using Tapatalk

author: Simon
author_rank: Unknown
timestamp: January 03, 2016, 03:22:30 pm
content: Quote from: otpowell on January 03, 2016, 02:58:58 pmNo 100 to 1K is fine. The resistors just create a load because you don't want one channel negative with the other positive creating a short but most of the signal needs to get through so they need to be lower than the input impedence to the AMP or a bit higher than the expected load on the device supplying the signal. Basically make them no less than twice the load usually driven and you will be fine. So say it's a headphone out put usually drives 32 ohm headphones, then 100R will be fine but as the amp input will be high impedence up to 1K or even 10K may be fine but 1M is a bit much.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 03, 2016, 05:46:16 pm
content: Quote from: otpowell on January 03, 2016, 02:58:58 pmIt depends entirely on where the audio signal is going to. And specifically the input impedance of the destination.For example, if you were passively combining two audio signals to go into a modern ~10K line-level audio input, then resistors of 5-10K would be appropriate.But if you are passively combining the output of two power amplifiers into an 8 ohm speaker, then you would use perhaps 4-8 ohm resistors.As you can see there is a HUGE difference in resistor values depending on the larger picture of what you are trying to do. That is why I said you question cannot be answered as an isolated generic example.The risk from directly connecting outputs also depends on what outputs you are talking about. Many "line-level" outputs use "build-out" resistors that protect them from dead short to ground. They would probably not be permanently damaged by shorting them together. But it would force them to work harder (and heat up more) and it is not recommended.However, if you are talking about outputs from a POWER AMPLIFIER driving a low impedance load (like a speaker), then shorting the outputs together could quite possibly damage the amplifier in a way that is expensive to repair (i.e. blowing many of the high-power output transistors, etc.)

author: Audioguru
author_rank: Super Contributor
timestamp: January 03, 2016, 06:21:24 pm
content: A modern power amplifier designed to drive a speaker or an opamp is perfectly happy when driving a load that is many times higher than a speaker. Oh, but not an old vacuum tubes amplifier that always needs a load for its output transformer.Use two 1k or 10k resistors, one from each channel and join together their outputs to make mono to feed a mono amplifier. Use a third lower value resistor to ground as an attenuator if it is needed.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 03, 2016, 06:31:47 pm
content: @otpowell, we are shooting in the dark here trying to answer your question #2 about "input a stereo signal and get a mono output on two speakers". If you can give us the details of exactly what you are trying to do, we can offer specific suggestions. Otherwise, you will continue to get very conflicting advice because none of us know what you are trying to do here.

author: tooki
author_rank: Super Contributor
timestamp: January 04, 2016, 01:19:41 am
content: Quote from: helius on January 02, 2016, 06:56:50 pmIndeed. Just a little clarification: Phone plugs wereonlyused at telephone switchboards, because they were designed to be plugged and unplugged constantly. They were never used at the station (end-user) end. There, phones were originally hard-wired, then later used various chunky multi-pin connectors, and eventually settled on the modular jacks. (They were also not used anywhere in a telephone exchange except the switchboard. All the permanent connections were soldered, wire-wrapped, crimped, or punched down.)Quote from: helius on January 02, 2016, 06:56:50 pmRight. The thing about the phono input is that despite using the same RCA ("cinch" to Europeans) jacks as the various line inputs, it's electrically different. You do sometimes see the RCA connector type referred to as "phono jacks", presumably because they were often the connectors used for the phono input.Quote from: otpowell on January 03, 2016, 02:45:18 pmNothing to do with being old-school. It's just what they're called. Seehttps://en.wikipedia.org/wiki/Phone_connector_(audio)By the way, all this discussion of telephone switchboards and exchanges provides the perfect context to link a couple of videos that I've been meaning to post here for a while.The most relevant are these, showing exactly how manual switchboards — the place where phone plugs were originally designed for — worked:This one shows the manufacturing of a 1970s telephone switch. Absolutely fascinating production processes of every component.The AT&T Archives they're from has provided me with hours upon hours of learning!

author: helius
author_rank: Super Contributor
timestamp: January 05, 2016, 02:03:15 am
content: Nice videos, thanks for the links.You may also enjoy some historical recordings from "the outside", viz. the amateur phone phreaks.https://soundcloud.com/evan-doorbell/howbphreak4?in=evan-doorbell/sets/group-1Most of these are taken from early step-by-step exchanges and crossbars, and include recordings of very odd activities like "tandem stacking" which later became (in)famous.It's also correct that the "phone" plugs, more often called Quarter-Inch today, were only used by the phone company for operator switchboards, and also I think for some diagnostic connections. Nowadays they are most commonly used in audio equipment, both for line-level connections (as in patchbays) and for headphones. The stereo version is also called the TRS connector.The modular connectors used for terminal (user) equipment are also different in different countries: The US Western Electric modular series uses the RJ or "registered jack" nomenclature. There are different series used in the UK and Germany:Left: BS 6312 British plug; Right: US RJ-11 plugGerman TAE plug

author: IanB
author_rank: Super Contributor
timestamp: January 05, 2016, 02:19:54 am
content: The UK also used a phone style jack plug for movable telephones before the current modular plug was introduced. It was like a large stereo jack plug with four connections on it:

author: helius
author_rank: Super Contributor
timestamp: January 05, 2016, 05:16:45 am
content: Yes, the old-style connectors are very pretty in their own way. Much more expensive and laborious to terminate.These are still found in some US homes:(the number four appears often in telephone circuits, although a single pair("tip" and "ring")is enough for a basic subscriber line. Four-wire lines were used for long-distance, and for assorted other functions.)

author: RobertBG
author_rank: Regular Contributor
timestamp: January 05, 2016, 03:29:17 pm
content: They are some neat videos,thanks for sharing.My father was from Mi and I remember him talking about the old switchboard there and how it was one of the last ones around.It's nice to see a video that confirms some old storiesI was always told years ago that "phone jacks" where the same size as the ones used on switchboards and that "phono plugs or jacks" where the smaller versions.One source said the name was taken from phone and stereo while another said a similar thing but they called them Phono plugs due to the operators headphones using the smaller plugs.Both stories came from people who worked for Bell Atlantic and coincided with each other so I never really questioned it.These things have been around for years though and I'm sure they've had different names in different regions over the years but it really doesn't matter a whole lot to be honest as we all know what they are.

author: dmills
author_rank: Super Contributor
timestamp: January 05, 2016, 04:40:25 pm
content: There is a lovely gotcha with 1/4 inch jacks in that there are two different (and incompatible) types....The 'A' gage is seen in use as a large headphone plug, and in these sockets the contact springs are short and come in from the side (Meaning inserting the jack does not clean the normalling contacts, which tend to become unreliable over time).The 'B' gauge (sometimes called a 'long frame') jack is what was used on the phone switchboards and is still sometimes used in broadcast and studio audio patch bays, this connector has a different tip profile and the contact springs come in from the back of the connector (meaning they are longer hence the name) with the normalling contacts wiped by the action of inserting the plug.The gotcha is that inserting an 'A' gauge plug into a 'B' gauge socket will force the contact springs too far apart, damaging them.73 Dan.