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Thread: Inductive Loop Success

  1. #21

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    With the larger amplitude of the audio signal, the LCD noise may be lost in the signal to noise ratio. ???

    Jeff
    250 20/20
    500 25/25
    1000 40/45
    2000 50/55
    4000 60/70
    8000 75/90

    2 X Phonak Naida Q70

  2. #22
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    Aug 2010
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    Central California
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    Quote Originally Posted by jlgreer1 View Post
    With the larger amplitude of the audio signal, the LCD noise may be lost in the signal to noise ratio. ???

    Jeff
    I really don't know the answer to that question, Jeff. I do know that my hearing aids (in the t-coil program) can 'hear' my CRT monitor very well from a couple feet away. I haven't 'listened' to my laptop's screen but it may be an interesting experiment.

    Speaking of such, has anyone besides me used his or her hearing aids to track down sources of electrical noise? I walked the house a while back looking for a source of pulse noise in my ham radio transceiver and found a light dimmer in the bathroom that sounded like a threshing machine.
    Frequency...Left......Right
    250 Hz.......35 dB....50 dB
    500 Hz.......55 dB....60 dB
    1,000 Hz....65 dB....70 dB
    2,000 Hz....70 dB....75 dB
    4,000 Hz....75 dB....70 dB
    8,000 Hz....90 dB....70 dB

  3. #23

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    Hi Geezer,

    Thanks for the tip on rf noise. I just purchased a Jetstream 45 amp switching power supply for my station. I haven't noticed any birdies but I'll have to give it the HA telecoil test.

    I have an appointment with the audi tomorrow. I'll have her activate the coil.

    73, de Jeff
    250 20/20
    500 25/25
    1000 40/45
    2000 50/55
    4000 60/70
    8000 75/90

    2 X Phonak Naida Q70

  4. #24
    Join Date
    Aug 2010
    Location
    Central California
    Posts
    25

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    Quote Originally Posted by jlgreer1 View Post
    Hi Geezer,


    I have an appointment with the audi tomorrow. I'll have her activate the coil.

    73, de Jeff
    You can also use your hearing aids in the t-coil position to troubleshoot sparkplug misfire problems.

    de KD7S
    Frequency...Left......Right
    250 Hz.......35 dB....50 dB
    500 Hz.......55 dB....60 dB
    1,000 Hz....65 dB....70 dB
    2,000 Hz....70 dB....75 dB
    4,000 Hz....75 dB....70 dB
    8,000 Hz....90 dB....70 dB

  5. #25
    Join Date
    May 2010
    Location
    trenton, NJ
    Posts
    120

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    Geezer, I just built a single channel 18 watt amp with the TDA2030A chip. I got the schematic from the data sheet.http://pdf1.alldatasheet.com/datashe.../TDA2030A.html

    As you can see,it has a very low parts count and sounds very good too. I wanted a little more volume out of it so I added a simple J-Fet gain stage and single knob tone control in front of it. I actually used the Strat-o-Blaster clean boost circuit with a trim pot to control the gain. Unlike a guitar, the TV does not sound good when the distortion kicks in. LOL It is now going to be my permanent loop amp. I couldn't see wasting a channel on that new 20 watt mini stereo that I just bought.

    Next up is a hearing aid made with vacuum tubes - talk about warm analog tone! LOL How many 12V batteries needed for 300VDC? LOL!

    Don
    250hz - 15
    500hz - 15
    750hz - 30
    1Khz - 45
    2Khz - 65
    4Khz - 60
    8Khz - 50

    Both ears are the same

  6. #26
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    Aug 2010
    Location
    Central California
    Posts
    25

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    Quote Originally Posted by bigbeck View Post
    As you can see,it has a very low parts count and sounds very good too. I wanted a little more volume out of it so I added a simple J-Fet gain stage and single knob tone control in front of it. I actually used the Strat-o-Blaster clean boost circuit with a trim pot to control the gain. Unlike a guitar, the TV does not sound good when the distortion kicks in. LOL It is now going to be my permanent loop amp. I couldn't see wasting a channel on that new 20 watt mini stereo that I just bought.

    Next up is a hearing aid made with vacuum tubes - talk about warm analog tone! LOL How many 12V batteries needed for 300VDC? LOL!

    Don
    Great project. The data sheet is a bit small for my antique CRT monitor. Does that IC require a gazillion square inches of heat sink?

    As for the vacuum tube hearing aid, just make sure you don't have the B+ feeding the plate of the amp through the phones. Ask me how I know that's a bad idea.

    de KD7S
    Frequency...Left......Right
    250 Hz.......35 dB....50 dB
    500 Hz.......55 dB....60 dB
    1,000 Hz....65 dB....70 dB
    2,000 Hz....70 dB....75 dB
    4,000 Hz....75 dB....70 dB
    8,000 Hz....90 dB....70 dB

  7. #27
    Join Date
    May 2010
    Location
    trenton, NJ
    Posts
    120

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    Quote Originally Posted by OldGeezer View Post
    Great project. The data sheet is a bit small for my antique CRT monitor. Does that IC require a gazillion square inches of heat sink?

    As for the vacuum tube hearing aid, just make sure you don't have the B+ feeding the plate of the amp through the phones. Ask me how I know that's a bad idea.

    de KD7S
    Just kidding about the tube hearing aid but you tried it? LOL! You're a piece of work. :-)

    Right next to that small data sheet is a yellow box that says download. Right next to it is the link that will open it as a PDF file. It's about 15 pages. I used half of a CPU heatsink based on info from DIY Audio forum. If you run it at max voltage you'll need something much larger. Seems like most people run it from 12 to 24 volts

    So you really had 300 Volts running through your head? Did it do any damage? ROFLMAO........................ The things we do,.....just to be able to hear.

    Don
    250hz - 15
    500hz - 15
    750hz - 30
    1Khz - 45
    2Khz - 65
    4Khz - 60
    8Khz - 50

    Both ears are the same

  8. #28
    Join Date
    Aug 2010
    Location
    Central California
    Posts
    25

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    No, I have never experimented with vacuum tube hearing aids although I have seen a couple of them in actual use. They used one or two tiny vacuum tubes powered by 22 1/2 or 30 volt batteries. They were simply audio amplifiers feeding a magnetic or crystal earphone.

    As for the 300 volts stuff, I have been a license ham radio operator for over 55 years. A good number of receivers and transmitters were created on my own workbench. Most of the 50's vintage receivers used high impedance headphones and every once in a while you would see a design that ran the B+ voltage through the coils of wire in the phones. Not a good design.
    Frequency...Left......Right
    250 Hz.......35 dB....50 dB
    500 Hz.......55 dB....60 dB
    1,000 Hz....65 dB....70 dB
    2,000 Hz....70 dB....75 dB
    4,000 Hz....75 dB....70 dB
    8,000 Hz....90 dB....70 dB

  9. #29
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    Aug 2010
    Location
    Central California
    Posts
    25

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    Quote Originally Posted by xiangwang View Post
    There are also some very good technical reasons, the liquid crystal display cycle is not feasible. There are a lot of electrical pulses are generated which cause the display to 'draw' the picture on the screen. A loop will select those most likely a. As a test, switch to your hearing aid T-coil position and location of the screen within a few inches of the head.
    ...
    In a typical setup the loop far removed from the television set itself. I feed audio from the output of the television to the loop located 20+ feet away with shielded microphone cable. While you're correct about the loop being able to pick up impulse noise, that has not been a problem in my case.
    Frequency...Left......Right
    250 Hz.......35 dB....50 dB
    500 Hz.......55 dB....60 dB
    1,000 Hz....65 dB....70 dB
    2,000 Hz....70 dB....75 dB
    4,000 Hz....75 dB....70 dB
    8,000 Hz....90 dB....70 dB

  10. #30
    Join Date
    Mar 2011
    Location
    Western Michigan
    Posts
    125

    Default

    Quote Originally Posted by jlgreer1 View Post
    Hi Geezer,

    Thanks for the tip on rf noise. I just purchased a Jetstream 45 amp switching power supply for my station. I haven't noticed any birdies but I'll have to give it the HA telecoil test.

    I have an appointment with the audi tomorrow. I'll have her activate the coil.

    73, de Jeff
    Wow! I just came across two hams with HAs. I'm a ham who's about to get aids.

    73 de Alan

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