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 Post subject: What is the 'best sounding' simple solid state AM detector?
PostPosted: Dec Tue 05, 2017 2:18 am 
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Joined: Sep Sun 04, 2016 9:26 am
Posts: 35
Location: North Queensland, Australia.
G'day all, please forgive my hi fi AM indulgences for a moment. I'm always looking for the nicest sounding/lowest distortion AM detectors that I can build and I'm trying to arrive at a definitive answer purely on the basis of listening.

All my DIY AM detectors sound good patched into a good audio system including my various diode and infinite impedance designs but trying to find the best sounding is a bit like 'splitting hairs'! So far I put my 'voltage doubler' two diode detector as the best sounding in terms of general clarity, but there isn't much between all of them! Any thoughts or comments. Regards, Felix.


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 Post subject: Re: What is the 'best sounding' simple solid state AM detect
PostPosted: Dec Tue 05, 2017 6:40 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 28943
Location: SoCal, 91387
What Diodes are you using? I've found the best to be a 1N64.

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 Post subject: Re: What is the 'best sounding' simple solid state AM detect
PostPosted: Dec Tue 05, 2017 10:06 am 
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Joined: Sep Sun 04, 2016 9:26 am
Posts: 35
Location: North Queensland, Australia.
G'day mate, mostly BAT-46 Schottky diode 'germanium diode equivalents'. Regards, Felix.


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 Post subject: Re: What is the 'best sounding' simple solid state AM detect
PostPosted: Dec Thu 07, 2017 7:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2200
Location: Saskatoon
There is a whole range of linear detectors from simple passive circuits at the low end, to precision rectifiers, to synchronous detectors at the high end. Since you specified simple, here's a diode linearization scheme that uses two diodes and two resistors.

Attachment:
LinearDetector.png
LinearDetector.png [ 23.29 KiB | Viewed 1117 times ]


It forms a voltage divider with identical components on each leg. Since the components are identical (assuming the diodes are matched), the output must be exactly half of the input voltage when forward biased. Thus the diode nonlinearities cancel out. So you get linearity at the expense of having the signal attenuated by half. For this to work properly, the output impedance of the IF should be much lower than the 4.7k resistors, and the input impedance of the audio amplifier stage should be much higher than the 4.7 k resistors.


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 Post subject: Re: What is the 'best sounding' simple solid state AM detect
PostPosted: Dec Tue 26, 2017 9:36 am 
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Joined: Sep Sun 04, 2016 9:26 am
Posts: 35
Location: North Queensland, Australia.
G'day all and Season's Greetings! Just a bit of an update. More listening to my various DIY AM detectors and I think that the infinite impedance detector based on a bipolar transistor is pretty good and sounds great with very low audio distortion and a wide audio bandwidth.

Interestingly enough the FET based infinite impedance detector although very selective, sounds rather dull in comparison, indicating considerable treble roll off. The reasons for this may be rather complex resulting from tuned circuit 'Q' considerations, but in any case the bipolar transistor version 'may be' lower distortion and generally more pleasant to the ear patched into a good audio system. Regards, Felix (vk4fuq).


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 Post subject: Re: What is the 'best sounding' simple solid state AM detect
PostPosted: Dec Tue 26, 2017 2:54 pm 
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Joined: Jul Mon 26, 2010 8:30 pm
Posts: 23579
Location: Annapolis, MD
"AM Hi-Fi" strikes me as being the ultimate oxymoron.....

But, if you must:
You have to use a synchronous detector which uses something like a MOSFET switch that goes cleanly from on to off. I think you can also use regular diodes back to back.

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 Post subject: Re: What is the 'best sounding' simple solid state AM detect
PostPosted: Dec Wed 27, 2017 12:27 am 
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Joined: Sep Sun 04, 2016 9:26 am
Posts: 35
Location: North Queensland, Australia.
G'day mate, at least here in Australia, AM broadcasters transmit an audio bandwidth out to at least 9 KHz and if fully reproduced in a low distortion detector/audio system, it actually sounds pretty good, almost comparable to high quality FM broadcasting. Regards, Felix (vk4fuq).


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 Post subject: Re: What is the 'best sounding' simple solid state AM detect
PostPosted: Dec Thu 28, 2017 2:19 am 
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Joined: Jun Wed 08, 2011 2:33 am
Posts: 7239
Location: Ohio 45177
Quite happy for you that you have the quality of AM broadcasting that motivates one to seek out the best sounding detector! Those seem to be uncommon here, based upon the complaints I read on these forums regularly. Many of the inmates here have gone totally to home broadcasting, that is, obtaining a very low power transmitter to broadcast within the confines of one's home, and therefore choose the content. And if you construct such a device, you may have the capability to extend the audio bandwidth somewhat beyond what they typical station can send out. And enjoy the full potential of the medium. Building and adjusting a device to have excellent fidelity and linearity is probably no mean feat, as I suspect a lot of the simpler circuits are merely a novelty device and performance might disappoint for good music.


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