This doesn´t make any sense to me. I was brought up with crystal sets and minimal receivers, now all I want is a a receiver that will find a signal being broadcast by my Sennheiser head phones (or Sony phones in the cupboard) being plugged into my tv or audio machine. What is this talk about the cost of a car or a house? Are you mad ? All want is a simple bit of circuitry that will receive a signal in my sitting room and output it to a 3.5mm jack which I can plug into an amp. What in the hell is the problem ??

 

The short answer is it'll be something you buy premade. How big is your budget?
Here's a Monoprice wireless speaker extender with a 30W amp for your speakers for $89 they may have a line-level version but I didn't see one. BestBuy also makes a similar device.
http://www.monoprice.com/Product?c_id=109&cp_id=10110&cs_id=1011011&p_id=10601&seq=1&format=2

 

This doesn´t make any sense to me. I was brought up with crystal sets and minimal receivers, now all I want is a a receiver that will find a signal being broadcast by my Sennheiser head phones (or Sony phones in the cupboard) being plugged into my tv or audio machine. What is this talk about the cost of a car or a house? Are you mad ? All want is a simple bit of circuitry that will receive a signal in my sitting room and output it to a 3.5mm jack which I can plug into an amp. What in the hell is the problem ??

Perhaps you missed my response where I directly answered your question:

The thing to understand is that designing a custom radio-frequency receiver is a pretty major undertaking, particularly if it is to work with the signal from an undocumented transmitter (and by "documented", that would mean detailed documentation of the modulation scheme, the symbol encoding scheme, the media-access control scheme, the data packaging protocol, the data encoding scheme, and on and on). You could expect to spend $10,000 to $100,000 for such a design. Now, if you are going to make a million units, then you can spread that cost out at something between one cent and ten cents per unit. But if you only want one of them, then that unit is going to be prohibitively expensive.

Why do you think that "a simple bit of circuitry" is all that is needed to detect, receive, demodulate, and decode a complex, proprietary digital signal waveform?

How well did those "crystal sets and minimal receivers" work? Not very well. And they were working with waveforms that were specifically intended to be received by such simple receivers. Did you every try using such simple receivers on an FM waveform? Required a bit more complexity, didn't it? Yet, again, it was a waveform specifically designed to be received by very simple receivers. That simply is not the case with those head phones you are trying to interface to. The manufacturer doesn't give a rip about whether a simple receiver can receive the signal. It is designed for an entirely different purpose.

This is not the first time that (and it won't be the last time) that someone has come here who doesn't understand the first thing about electronics but who thinks that it must be just so simple to do anything in electronics and therefore someone here should design and build something custom for them for free.

 

This doesn´t make any sense to me. I was brought up with crystal sets and minimal receivers, now all I want is a a receiver that will find a signal being broadcast by my Sennheiser head phones (or Sony phones in the cupboard) being plugged into my tv or audio machine. What is this talk about the cost of a car or a house? Are you mad ? All want is a simple bit of circuitry that will receive a signal in my sitting room and output it to a 3.5mm jack which I can plug into an amp. What in the hell is the problem ??

And you can supply the full detailed technical specification of the Sennheiser transmitter?

You know how the signal is modulated?

You know how the channels are encoded?

Why don't you buy the sennheiser receiver?
It's too expensive, right?

You think someone will custom design and build one for you for less than the cost of an off-the-shelf unit from Sennheiser? Can you tell us, in which universe, is that ever the case?

The fact is; it's not a crystal set and a "simple bit of circuitry" won't do the job.

And to answer your last question; You are the problem.