Headphone Signal Into Wireless Transmitter

[Lucas Cheadle]

I was shooting an event earlier today and I tried to connect a 1/8" headphone line to my Sennheiser G2 bodypack. The headphone jack was the only way to get a signal from the house PA system. It sounded horribly weak and noisy through the wireless into my camera. I tested the line by plugging my headphones directly into the PA and it sounded great. Is there a line balancing/phantom power thing happening? What adapter could make that connection usable?

[Brian P. Reynolds]

From what I recall the 'ring' of the 3.5mm TX input connector is the line level connection where as the 'tip' of the connector is the mic level connection for the Sennheiser G2 system.

I would think the connections between the H/P o/p and the TX would be the problem. I would doubt if you could buy one off the shelf, it would probably need to be a custom made cable.

[Chris Harding]

Hi Lucas

Normal bodypack inputs are at microphone level so you more than likely overloaded the input something horrible!! Headphone outputs are normally higher than even line outputs so the internal limiter on the bodypack just couldn't cope....impedence matching would have been quite a lot out as well....!!

I'm not too sure what sort of level the PA would put out for headphones but for line out to transmitter input you would need at least a -40dba attenuator ...Radio shack have these and they are useful indeed!!! If you are handy with a soldering iron you can also make one up with just two resistors!!

Mics are in the order of - 40db sensitivity (or even lower) and line out from mixers are typically 0db....headphones could be a lot higher so it's not a good idea..the PA should always have a line out at least!

Chris

[Rick Reineke]

Brian is correct, you need a custom cable for inputting line-level (-10dB) to a G series Sennheiser body pack transmitter. In this case the 1/8" TRS plug's Ring is hot (+) and the tip is tied to ground/shield. Some attenuation may still be needed for +4 dB output. Most consoles these days have -10dB RCA outs, so an adapter is handy. So is a 1/4" for taking a pre or post send auxiliary output (sometimes referred to as Mon. Foldback, Effects or FX send) which are usually in abundance. I would only use a HP out as a last resort. A DI is real handy to have as well.

[Paul R Johnson]

Might be simpler to use a DI box to convert the audio down to mic level.

However - the headphones outputs from most mixers are often compromised for recording - on my own mixers, the headphone output is usually used for pal of the input sources - which appear loud and VERY clear in the headphone output. Without a PFL button selected, then audio output of the mix is often very low - which would produce the noisy signal you experienced - so by luck, the wiring was probably ok - but as the main headphone amp follows the main output, it could be that the gain structure for the show was such that the output meters of the mixer hardly moved. This is quite common - my own system has the amplifiers and overall gain set so that in say a rock and roll show, the desk shows full output, but the amplifiers, after the crossovers still have some headroom to cope with heavy handed engineers. If the next show is a dance show with tracks and perhaps somebody with a microphone, then the levels are so much lower that the output hardly tickles the meters. My headphone output would be totally useless for a quality output. Virtually all mixers have more suitable ways of getting a proper output at a suitable level. If the mixer did not have this facility, then it could be a bit compromised in the quality department too!

Last thing - I would NEVER give somebody my headphone output. PFL is pretty essential in a live situation - losing the facility seems pretty odd?

[Lucas Cheadle]

Thanks everyone. All of your input helps. I'm a videographer stepping up my run-and-gun audio equipment, skills and understanding. Paul: I agree with you that any decent PA would have something other than a headphone output, however this system I encountered absolutely didn't. It was mounted on the wall with no access to the back of the components and all the speakers were elevated way too high to put a wireless mic (shure 58 type) in front of which is normally how I capture live audio. Next time...

[John Willett]

Brian is correct and what you wanted to do would have worked if you had used the proper Sennheiser CL2 line-input cable and a cable that terminated in an XLR.

The CL1 should also have worked, but would have shorted the right channel of the headphone socket to earth.