Headphone jack install in turntable...need help

[Kroensburg]

I bought a Crosley CR249 Keepsake USB Turntable a little while ago and I love it. The cabinet is all self contained; it has speakers built in. A major downside is that it doesn't have a headphone jack. I'm interested in installing one but I'm not too knowledgeable about circuits or anything. I have a basic knowledge and I can read a schematic fairly well, and I know how to solder, so if anyone can help me out, I'd love it. I figured I could just install a headphone jack that would bypass the speakers when it was plugged in, but I don't know how exactly to go about doing that (where to attach it in the circuit, what resistors I'd need to use, etc.) If you need pictures or anything, I can get them up here, too. Again, I would love any help I can get.

More information: the power consumption of the whole device is 12 watts. There are two speakers, each of which says 3 watts and 8 Ω. I thought they may be some useful information...

 

[MrAl]

Hi,

Adding a headphone jack isnt that hard but you have to decide if you want to switch the speakers out when you use the headphones or not. The best way seems to use a switch to disconnect the speakers when you are going to use the headphones. Sometimes you have to switch in a dummy load too though to take the place of the speaker (one per channel) because the headphone impedance is usually much higher than the speaker.

A double pole switch will suffice to turn off the speakers, one pole per channel. The headphone jack should be stereo, one jack channel to each stereo channel.

It's sometimes good to provide some electrical isolation between the circuit and headphones, and for that you need a transformer or for two channels two transformers. This might not be needed if you dont expect any problems.

 

[audioguru]

A solid-state amplifier does not need a dummy load. A vacuum tubes (valves) amplifier must have its rated load all the time.

For low impedance headphones (8 ohms) a 120 ohm series resistor was used to reduce the level but newer headphones are 32 ohms or 600 ohms so might burn out and blow your ears off.

 

[Kroensburg]

Thank you both very much for your help. I can't imagine it would but does it matter if I use a 1/4" vs a 1/8" jack? It's a retro-looking turntable so I wanted to stay in line with that and 1/4" seemed more 60s/70s than 1/8" (maybe I'm just making that up, though...)

Can't I do it without a switch, though? Don't most headphone jacks cut the circuit that would go to the speakers when headphones are plugged in?

Also, like I said, I'm fairly new to this whole game; would the jack come with a diagram as to what should be hooked up where or is it pretty self explanatory?

 

[audioguru]

You can buy a stereo 1/4" jack with built-in switches.
The jack does not come with a diagram. A diagram is available on the manufacture's website but it shows the jack and its switches, not how to connect it.

 

[Kroensburg]

Alright, so just trial and error? Would i harm anything if I initially got the connections wrong?

And is there any way someone could send me a link of the jack I'd be looking for? I've come across a couple different kinds and I'm not sure which is the one I want.

 

[audioguru]

If wrong connections cause a short-circuit to the outputs of the amplifier then the amplifier will probably blow up.

 

[Kroensburg]

Ok, so I pulled this headphone jack out of an old stereo (who plays CDs these days anyway?) and was fairly easily able to establish which connections did what, as I mapped out in the attachment 1.

The two speaker disconnects (I don't know the technical term for it) are in contact, but when a headphone plug is inserted, one of the pair on each side has a lever, so it disconnects from its complementary connection, thereby cutting the signal to the speaker.

My question with that is: does it matter which one I have coming from the circuit board and which one I have going to the speaker when I connect the wires? I can't imagine it would since they don't touch any other part but themselves.

Also, since the speakers' wires need to be attached there, do I need to route another wire to attach to the ring and tip connections? (attachment 2)

 

[MrAl]

Hi again,


Yes you can use a jack with switches on it to auto disconnect the speakers when the headphones are plugged in, if that's what you prefer.
I had preferred to use a small switch on my TV back when i had to install one, as i felt it would last longer and it was not hard to click because it was installed right next to the headphone jack. Depending also on power rating, you may want to use a switch anyway if the power of the system is rather high.

 

[audioguru]

Your headphones jack has a single sleeve that is the ground for both channels on headphones.
But make certain the stereo has a single ground for both speakers.

Sometimes a speaker is driven at both wires from a bridged amplifier that is actually two amplifiers. Then the speakers have no common ground.

 

[Kroensburg]

It's a common ground, they're soldered together at the circuit board. I think I've figured it out but I just wanted to get some last bits of advice before I try it out and potentially kill my record player. If one (or a couple) of you could look at my makeshift diagram and tell me if I have it right or not, that'd be excellent and I'd be eternally grateful.

 

[MrAl]

Hi again,


That looks right although you should make sure you know where the switch contacts are by using an ohm meter to test the jack with.

You also dont need two wires to go to the jack from each channel, just one each and then jump two of the jack terminals.