Info on machine output jack wiring

[Goodrat]

Moved my question to top.
I'd like some info on various machine output jack wiring.
For example, most machines use a stereo jack with tip and ring shorted, then the phones may connect to tip or ring then return to ground. (A mono headphone jack would short the output).
I assume others use the T and R and no sleeve (ground) needing headphones to accomodate this output. Then there are those machines that use the T and R as seperate stereo channels with the sleeve ground common.
Are there others? does someone want to share what machines use what configuration? Or a few examples?

[bbsailor]

Re: Info on machine output jack wiring

The Sovereign XS (series) uses only the Tip and Ring. This puts the signal through each headphone element in series (assuming you are using a typical stereo headset).

Those handy with a solvering iron can wire up their MD headphones to provide a wiring configuration (meaning series or parallel headphone elements) that provides the most audio volume.

Those familiar with Timberwolf (and other) headhones will find a SPDT switch that allows these headphones to work with those Metal Detectors (MD) that only use the tip and ring or use the ground and tip connections. This low tech solution makes these Timberwolf and other similiar MD headphones compatible with most single channel MD output configurations.

bbsailor

[Goodrat]

Fisher

I heard there are Fishers that have various configurations also.
On the tip and ring only machines, do you think the tip is always positive? Not that it typically matters, but I have some ideas.

[bbsailor]

Tip Positive Does Not Matter

In headphones with isolated transducer elements against your hear, phase is not as important as it would be if the speakers were in free air. Then low frequency cancellation can occur when the speakers are out of phase. With headphones, this would not be an issue when each element is in a separate closed environment.

The more important issues are headphone impedance, headphone element sensitivity and the value of the current limiting resistor in the metal detector. Then a simple switch between series and parallel connections can provide a quick, rough test as to which way is louder. In a series connection, the speaker elements are in series and the power is cut in half. This is at least a 3 db reduction in output.

bbsailor

[Goodrat]

Re: Tip Positive

Ah, but with the circuit I got cooked up, tip positive will matter I've got some ideas about compatibility and switching.

I've worked out a few spread sheets working out impedances and power with the limiting resistor in mind, so that is all figured.

Getting a list of what machines have what configuration, that is the challenge.

[Goodrat]

Re: Tip and ring machines...

These machines that use only Tip and Ring, there is no connection to sleeve? This would be good because a mono plug could then be used. The long sleeve of the mono plug will contact the ring contact in the machine jack. As long as the sleeve/ground connection does not connect to anything in the machine.

[Goodrat]

Then again....

If the machine is just connected to tip and ring, and the headphones have one speaker on tip and the other on ring, all that would do is connect the speakers in series. The other typical machines would connect the speakers in parallel. Now if these T/R machines sound OK with the impedance doubled (series speakers) there is not really an issue.
So why all the headphones with switches?

[Goodrat]

Speadsheet




It can confusing how the manufacturers spec their phones. "150 ohm nominal" often means that they are actually 75 ohm phones.