19-08-2017, 08:43 AM
Hi.
Yesterday I decided to go back and use ALD110900 chip and see if I could get an improvement this time. Firstly I wound a new coil on the toroid but this time to just give me isolation from hand tuning effects and a better match to the chip.
Results were disappointing and I was about to give up on the chip. Using my old toroid and OA90 I can get 10mv DC across the high impedance phones off my local, I only got 1mv using the chip from the toroid, no matter how I did the turns ratio no real improvement could be gained.
I then decided to strip a little of the insulation off each of the 7 turn winding on the frame at the middle of the lowest point near the tuning cap. there are three connections going to the chip used in a normal crystal set so I deduced that the two which goes to the opposite ends of the tuning coil should be across the outermost connections of the frame aerial and the remaining one to one of the turns, hence the reason for stripping off the insulation off each turn to attach a crock clip. on the third turn from the the "earthy" end of the windings gave by far the best results I have had. On my local the DC volts across the phones is now up to 22mv with 5ua current volume is greatly increased. I am somewhat deaf and up to now not used my hearing aids along with the phones but with them on the quiet stations now are readable, I also asked my 12 year old grand daughter to try and she could hear more than I could even with the aids on. According to her the two strongest stations are quite loud.
I'll draw out a circuit later on and post it here.
The only disadvantage is the length of the headphone lead and hand capacitance effect performance and tuning, perhaps a 1:1 audio transformer may help.
Yesterday I decided to go back and use ALD110900 chip and see if I could get an improvement this time. Firstly I wound a new coil on the toroid but this time to just give me isolation from hand tuning effects and a better match to the chip.
Results were disappointing and I was about to give up on the chip. Using my old toroid and OA90 I can get 10mv DC across the high impedance phones off my local, I only got 1mv using the chip from the toroid, no matter how I did the turns ratio no real improvement could be gained.
I then decided to strip a little of the insulation off each of the 7 turn winding on the frame at the middle of the lowest point near the tuning cap. there are three connections going to the chip used in a normal crystal set so I deduced that the two which goes to the opposite ends of the tuning coil should be across the outermost connections of the frame aerial and the remaining one to one of the turns, hence the reason for stripping off the insulation off each turn to attach a crock clip. on the third turn from the the "earthy" end of the windings gave by far the best results I have had. On my local the DC volts across the phones is now up to 22mv with 5ua current volume is greatly increased. I am somewhat deaf and up to now not used my hearing aids along with the phones but with them on the quiet stations now are readable, I also asked my 12 year old grand daughter to try and she could hear more than I could even with the aids on. According to her the two strongest stations are quite loud.
I'll draw out a circuit later on and post it here.
The only disadvantage is the length of the headphone lead and hand capacitance effect performance and tuning, perhaps a 1:1 audio transformer may help.
