EMRFD Message Archive 13700
Message Date From Subject 13700 2017-03-13 14:56:15 jwolczanski headphones
I've got a box of various old headphones and have been trying them in this XCVR as well as my other rigs (a K2, and a home-brew 40 meter XCVR) and I was quite surprised to find dramatic differences in the headphones. Some pick up hum, some are very sensitive, some not. Some allow a lot of high frequency "hiss", some don't. The most sensitive of the lot: A pair of C. Brandes with a weird metal head-band that, according to the Internet, might be almost 100 years old.
I started swapping headphones because the XCVR had what I thought was low audio output. I pondered a new audio amplifier...then I started swapping headphones. Eureka!
I guess I should have known all this.
Two questions:
1) What does the EMRFD gang regard as the best modern headset for CW?
2) When designing a receiver, is there a target number for amplification in dBs, to get one from the antenna spigot to the earphones. What does wanting a speaker add to this number?
Out of my junk-box came a cheesy pair of headphones labeled "RH-20 Japan" with a metal head-band. They are not very sensitive and they seem to be easily over-driven, but I'm finding they seem to have a sweet spot around 600Hz and are totally devoid of hiss/hum. They are quiet. I'm trying to get used to the quietness - but quietness aside, they seem to give my ears the best signal-to-noise (if I can use that phrase in this context) of any of my phones.
Jerry
KI4IO
Warrenton, VA
13701 2017-03-13 16:54:06 Nick Kennedy Re: headphones 13702 2017-03-13 18:32:45 bob_ledoux Re: headphones
8 ohm ear buds? I normally see these in the 16 to 32 ohm range and they seem to work fine on the output of op-amps. When you select ear buds, be sure to look for ones with at least 104 dB spl/mW. The best I have seen are up to 112 dB spl/mW. The only ones that I have seen higher than this were actually specified xxx dB spl/***1 V*** which is not at all the same thing and seems to be designed to hide the lack of sensitivity.
106 to 112 dB spl (sound pressure level) per mW is a ton of volume for a tiny 0.5v pk-pk signal. I normally find 50 mV pk-pk a comfortable listening level on these ear buds and use diode limiting across the feedback resistors of the output op-amps to limit the amplitude of sudden large signals to something less than hearing damage levels.
bob-N7SUR13703 2017-03-13 19:53:09 John Marshall Re: headphones
I think this is a lesson lesson on the danger in using "voltage dB". Decibel rule one is that it always expresses a power ratio so 20logV1/V2 is only valid when the impedances are equal.
Let's look at it this way: 1 uV into a receiver with a 50 ohm input is V^2 /50 or 2E-14 Watts. The gain needed is 10log(1E-3 / 2E-14) or 107 dB. Power in, power out, impedances not involved.
John, KU4AF
Pittsboro, NC
13704 2017-03-13 20:12:45 Nick Kennedy Re: headphones 13705 2017-03-13 21:47:36 Tayloe, Dan (Noki... Re: headphones
Speaker would like to see another 20 DB of gain. To my mind this meant plugging in amplified computer speakers which are readily available.
- Dan, N7VE
Sent from my Galaxy Tab® A
-------- Original message --------13708 2017-03-14 15:45:16 Czech-Iowan Hugue... headphones
a young lad building Crystal Radios. They were given to
me by a neighbor who was an Engineer at Collins Radio
in Cedar Rapids, Iowa.
Their impedance was 2000 Ohms when used together
series connected via the headband. When used
individually each impedance was 1000 Ohms.
They were very, very sensitive and worked exceptionally
well with Crystal Sets. On some stations I could place
a headphone in a bucket and hear the broadcast as
if it was a loudspeaker.
Headphones available at Army Navy Surplus stores
back in the 50s looked very similar in construct but
had an impedance of 600 Ohms.
Thanks for the memories!
- - - - - - - - - - - - - - -
headphones
Mon Mar 13, 2017 2:56 pm (PDT)
Posted by: jwolczanski
So I made a neat DC transceiver for 20 meters. It uses the "discrete component version of the Gilbert cell mixer described in EMRFD and, among other circuits, an audio amplifier circuit (figure 9-74) also from EMRFD.
I've got a box of various old headphones and have been trying them in this XCVR as well as my other rigs (a K2, and a home-brew 40 meter XCVR) and I was quite surprised to find dramatic differences in the headphones. Some pick up hum, some are very sensitive, some not. Some allow a lot of high frequency "hiss" , some don't. The most sensitive of the lot: A pair of C. Brandes with a weird metal head-band that, according to the Internet, might be almost 100 years old.
I started swapping headphones because the XCVR had what I thought was low audio output. I pondered a new audio amplifier... then I started swapping headphones. Eureka!
I guess I should have known all this.
Two questions:
1) What does the EMRFD gang regard as the best modern headset for CW?
2) When designing a receiver, is there a target number for amplification in dBs, to get one from the antenna spigot to the earphones. What does wanting a speaker add to this number?
Out of my junk-box came a cheesy pair of headphones labeled "RH-20 Japan" with a metal head-band. They are not very sensitive and they seem to be easily over-driven, but I'm finding they seem to have a sweet spot around 600Hz and are totally devoid of hiss/hum. They are quiet. I'm trying to get used to the quietness - but quietness aside, they seem to give my ears the best signal-to-noise (if I can use that phrase in this context) of any of my phones.13709 2017-03-14 16:50:49 Bill Meara Re: headphones