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Speaker for the headset jack?

Steve Crewdog

Steve Crewdog

Well Known Member
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Chasing our tail with a squelch problem, the GTR-200 does not have a speaker option so whenever I want to check for the noise I have to pick up my headset. Sure would be easier if there was a small speaker I could plug into the headset jack, do they make such a thing?


TIA
 
bjdecker said:
Need a transformer to match the impedance. IIRC the GTR 200 is looking for 150 - 300ohm, and your typical replacement paper cone speaker is 8ohms.
Click to expand...
Adding a transformer will not provide the required energy to drive a speaker. A simpler and effective solution is a small audio amp. It will provide the high impedance input and low impedance output for the speaker while adding the energy to drive the speaker.

This one from Amazon will work fine: https://www.amazon.com/HiLetgo-LM386-Audio-Amplifier-Module/dp/B00LNACGTY

You will have to also connect aircraft 12V to the amp, or just use a 9v battery if only needed occasionally.
 
CN_airhead said:
Adding a transformer will not provide the required energy to drive a speaker. A simpler and effective solution is a small audio amp. It will provide the high impedance input and low impedance output for the speaker while adding the energy to drive the speaker.

This one from Amazon will work fine: https://www.amazon.com/HiLetgo-LM386-Audio-Amplifier-Module/dp/B00LNACGTY

You will have to also connect aircraft 12V to the amp, or just use a 9v battery if only needed occasionally.
Click to expand...
Even simpler might be an amplified laptop speaker which would be a speaker and amplifier in an attractive case. You'd need to use a plug adapter to go from 1/4" headphone jack to the 1/8" used by the speaker and still have to provide a power source, in this case a USB power bank will do.
 
CN_airhead said:
Adding a transformer will not provide the required energy to drive a speaker. A simpler and effective solution is a small audio amp. It will provide the high impedance input and low impedance output for the speaker while adding the energy to drive the speaker.

This one from Amazon will work fine: https://www.amazon.com/HiLetgo-LM386-Audio-Amplifier-Module/dp/B00LNACGTY

You will have to also connect aircraft 12V to the amp, or just use a 9v battery if only needed occasionally.
Click to expand...
CN_airhead said:
Even simpler might be an amplified laptop speaker which would be a speaker and amplifier in an attractive case. You'd need to use a plug adapter to go from 1/4" headphone jack to the 1/8" used by the speaker and still have to provide a power source, in this case a USB power bank will do.
Click to expand...

Maybe I've done something wrong - but the math says something different:

The GTR 200 specifications are thus, 60mW minimum into a 150ohm load. Using these numbers to calculate amps and volts produced by the radios output stage gives you 20mA @ 3V. ( I = (P/R)^1/2 and V = (P*R)^1/2 ).

The audio transformer I spec'd has a 200 Ohm input (Zin) and 8 Ohm output (Zout).

To calculate the voltage change through this particular transformer, use Vout = Vsource*(Zin / ( Zin + Zout)) => Vout = 3*(200/208) => 2.88v.
...and the available power to the 8 ohm speaker => P = (V^2)/R => 8.2944/8 => 1.0368W

The speaker that I spec'd is capable of 1W.

Since the calculated output of the transformer is just a "hair" more than the speaker, there shouldn't need to be any amplification.

Where did I go wrong?
 
bjdecker said:
Maybe I've done something wrong - but the math says something different:

The GTR 200 specifications are thus, 60mW minimum into a 150ohm load. Using these numbers to calculate amps and volts produced by the radios output stage gives you 20mA @ 3V. ( I = (P/R)^1/2 and V = (P*R)^1/2 ).

The audio transformer I spec'd has a 200 Ohm input (Zin) and 8 Ohm output (Zout).

To calculate the voltage change through this particular transformer, use Vout = Vsource*(Zin / ( Zin + Zout)) => Vout = 3*(200/208) => 2.88v.
...and the available power to the 8 ohm speaker => P = (V^2)/R => 8.2944/8 => 1.0368W

The speaker that I spec'd is capable of 1W.

Since the calculated output of the transformer is just a "hair" more than the speaker, there shouldn't need to be any amplification.

Where did I go wrong?
Click to expand...
Well, wrong formula.
But, fundamentally, a transformer is a passive device that can change voltages but always conserves energy and power. It cannot magically change 60 mW into 1 W! Your 200 ohm:8 ohm transformer will change 3 volts/20 ma into 0.6 volts/100 ma (still 60 mW). How loud will that sound in that speaker? I have no idea.
 
BobTurner said:
Well, wrong formula.
But, fundamentally, a transformer is a passive device that can change voltages but always conserves energy and power. It cannot magically change 60 mW into 1 W! Your 200 ohm:8 ohm transformer will change 3 volts/20 ma into 0.6 volts/100 ma (still 60 mW). How loud will that sound in that speaker? I have no idea.
Click to expand...
hmmm...back to the board :(

So the "turns" formula is more appropriate to the voltage reduction Vs = Vp * (Ns/Np) => 3 * (1/5)

I wonder where the Zin / Zin + Zout came from?

I guess I can spec a smaller 8 ohm speaker -- something in a 100mW version. Like https://www.mouser.com/datasheet/3/360/1/specs_AS05008PR_R.pdf

Also, I noticed the GTR 200 output power is a minimum number (60mW). Can the L-pad handle more?
 
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