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Guitar "wireless jack" from broken telephone headset

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TaDa

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Hi
I've got a telephone headset on which the speaker does not work and I want to meld the microphone input it to a 1/4" jack plug so I can plug it all into a guitar so I don't have to lug the cable around
I'd do similar at the base station end to plug into the amplifier/speaker.

Is this likely to be practical and will I need to do anything clever to match impedences or somesuch?

I'm wondering if I will _need_ to buy one of those mini oscilloscopes to watch the waveforms :)
 

alec_t

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the microphone input
:confused: Isn't the microphone wire an output to the phone? A headset would normally have a microphone output and mono or stereo inputs for the earpieces (speakers). Whatever, a guitar pickup will probably require a high-impedance pre-amp to get the signal level up somewhere near that of the phone audio signal level.
 
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TaDa

Member
Hmm I was hoping that the output from the microphone would be comparable to that of the guitar (maybe they'd both need a preamp or the transmitter in the headset would work with the lower signal levels without pre amplification)
 

dr pepper

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Theres a chance it will work, the o/p of the guitar pickup and a condenser mic probably arent that far apart, assuming it is a condenser mic.
You'd need a decoupling cap, say 1u from the pickup to the xmitter, as condenser mic's are dc powered.
And you'll need a attenuator at the rx end, depending on what o/p it has, if it drives a speaker then you will need an attenuator, a 1k pot might do the trick.
Guitar pickup impedances tend to be low, as are loudspeaker outputs so I dont think you'll need to match impedances, you only need to do that if your going from high impedance to low, or if your operating at radio freq's.
 

TaDa

Member
Thanks for that but now I'm going to show my electronic naivety...
Do I simply wire the the 1u cap in series?
Hmm do I do the same with the pot too? (The base unit of the telephone headset would normally feed into the back of a telephone not a speaker)
Lastly do I need the mini oscilloscope to check the signals - I don't want to knacker either the amp or the guitar (and I do have a hankering for one if you'd not guessed)
 

dr pepper

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The pickup connects in place of the mic capsule, ground to ground and signal from the pickup through a 1u cap to the mic signal i/p on the tx.
The rx end, one end of the 1k pot track goes to the signal o/p from the rx, the other end of the track to ground, and the wiper of the pot to the amp i/p signal, and obviously amp ground to rx ground, chances are if you look there will allready be a cap in series with the o/p on the rx board.
The 'scope wouldnt show you a great deal here, I spose you'd get an idea of o/p signal level.
 

audioguru

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The output from a magnetic guitar pickup is at a level much higher than a microphone. A mic input on an amplifier has way too much gain and an impedance that is much too low for a magnetic guitar pickup. The guitar pickup is usually fed into a Jfet that has a very high input impedance and low gain so that the "twang" 4kHz resonance is boosted like this:
 

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TaDa

Member
The output from a magnetic guitar pickup is at a level much higher than a microphone. A mic input on an amplifier has way too much gain and an impedance that is much too low for a magnetic guitar pickup. The guitar pickup is usually fed into a Jfet that has a very high input impedance and low gain so that the "twang" 4kHz resonance is boosted like this:
Ah, I feared this, I guess it makes sense that the guitar output requires a high impedance preamp - after all the guitar has no internal power supply.

I've not yet managed to dismantle the headset - it has some tiny tiny torx screws and I want to progress slowly lest I need to be able to put some of it back together - so I've not rushed into this yet.

Could I drive the transmitter's mic input from the guitar if I insert a new Jfet miniature preamp?
(driven by the headset's battery - well, it hasn't got a speaker or microphone to drive!)

Would the trick of using the pot on the base station's output be sufficient to drive the amp - or do I need to do something clever there too.

I'm beginning to wonder if the components I will need will cost more than the commercial wireless jack I am hoping not to buy :)
 

Mikebits

Well-Known Member
The output from a magnetic guitar pickup is at a level much higher than a microphone. A mic input on an amplifier has way too much gain and an impedance that is much too low for a magnetic guitar pickup. The guitar pickup is usually fed into a Jfet that has a very high input impedance and low gain so that the "twang" 4kHz resonance is boosted like this:
According to your graph, it looks like a 47K load would be best. That peaky response at 1Mohm input looks icky to me.
 

audioguru

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Why does your headset have a battery? Its earphones are driven from the phone and its Jfet in the electret mic is powered by the phone.
Two series resistors make an attenuator to reduce the preamp output level to mic level.

Transmitter? Base station? Amp? What transmitter and receiver arte you planning to use?
 

audioguru

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According to your graph, it looks like a 47K load would be best. That peaky response at 1Mohm input looks icky to me.
Players and listeners of electric geetars want the sound to be as BAAAD as possible with lots of fuzz (distortion). The loud sounds of their band has deafened their hearing so they like to hear the 4kHz peak.
The cheap speakers on a geetar amplifier also have a resonant peak at about 4kHz.
 

TaDa

Member
Why does your headset have a battery? Its earphones are driven from the phone and its Jfet in the electret mic is powered by the phone.
Two series resistors make an attenuator to reduce the preamp output level to mic level.

Transmitter? Base station? Amp? What transmitter and receiver arte you planning to use?
It's a wireless headset made by jabra normally the base station plugs into the back of a desk phone
Base station has audio io into the phone and the headset has a mic on a boom and a speaker that sits next to the ear

I know I can just buy a wireless guitar setup but I want to make one from this headset - it might look a bit steampunk too :)
 

TaDa

Member
Players and listeners of electric geetars want the sound to be as BAAAD as possible with lots of fuzz (distortion). The loud sounds of their band has deafened their hearing so they like to hear the 4kHz peak.
The cheap speakers on a geetar amplifier also have a resonant peak at about 4kHz.
I love this! When we bought the guitar for our daughter I didn't get as honest an explanation as that! I'd asked why the amp had all the different distortion effects-specifically why I would want my 2015 guitar to sound as rough as an early electric guitar- man I must've looked and sounded so 'square' :)
 

audioguru

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I never liked to hear "acid rock" with its terrible distortion. Instead I liked "high fidelity" and I still do.
 

dr pepper

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One thing you might want to consider is range, a wireless headset will probably only have a range of a few feet, as usually your sat right next to the 'phone.
Jabra are a reasonable make, once done you's have something better than a bargain basement music shop item.
 

TaDa

Member
So do I need to mount a preamp between the guitar and the transmitter?

And can I simply use the pot to limit the signal from the base station to the amp?
 

audioguru

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The transmitter probably uses a voltage to power an electret microphone. Then a coupling capacitor must be used to block the DC from going into a 100k logarithmic (volume control) pot, try 2.2uF.
Try it, but the guitar will sound muffled without a high impedance preamp. Connect the few parts like this:


Why doesn't your amp have a volume control? Or use the pot in between the guitar and the transmitter instead.
 

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audioguru

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I dont think so.
The very high input impedance of the Jfet preamp I showed allows the inductance of the magnetic pickup to resonate with cable capacitance producing the peak in the frequency response at about 4kHz as I showed to allow the guitar to produce the electric guitar "twang" sound. When the peak is reduced then the sound is muffled but is fine for a bass guitar. An acoustic guitar does not need the peak.
 
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