Can you get high quality sound from an AM tuner?

Can you get high quality or "better then average" sound out of the AM tuner of a hifi system.. Typically speaking something like an AM/FM tuner going through an amplifier and such?

Reply to
John
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Depends on the tuner and the station. Back before we switched down to

9kHz spacing, local ABC RN (2CN in CBR) was very respectable using an AWA AM3, or on the Pik Synchrodyne circuit published in Electronics Aust. in 1975. As a gerneal rule, AM/FM tuners have crap AM stages.

AWA AM3's turn up from time to time on Ebay (au).

There's a HiFi AM group on Yahoo groups:

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DN

Reply to
David Nicholls

Make that 2CY.

DN

Reply to
David Nicholls

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Many AM tuners give only 2 kHz of audio bandwidth. Yup, 2 kHz. Its usally because of the RF and IF bandwidth in the set which is also only 4 kHz, hence the audio bw is limited to 2 kHz. Tubed tuners gave slightly more on average, about 3 khz, and with speakers used on old radios with a rising response above 400Hz the AF bw was perhaps

6 kHz. But tubed tuners with an RF amp input stage will usually also have poor AF bw. They gave "mellow" sound, ie, distorted with 5%+ of mainly 2H and perhaps 2.5kHz of audio bw.

But I have two tubed AM tuners good for 9kHz due to careful over coupling in the IF transformers and these sound very nice indeed compared to much solid state crap, or the typical older tube radio. The older sets were tailored to be selective allowing socially isolated ppl in the bush to enjoy stations far away despite the crakles and noises. Very few AM radios or dedicated tuners were made for good reception of local stations to suit hi-fi afficionardos in the major cities.

By the time ppl woke up to hi-fi in a big way, FM radio was with us. People didn't need the cricket scores or horse racing to be announced in hi-fi, and for many years live music broadcasts from Sydney Town Hall was via AM from

2FC, and ppl enjoyed it although much programme was missing, ie, all above about 5 kHz.

Some old AM tubed radios can have the first IF altered to include a tertiary winding of about 8 turns wound over the primary of IFT No1, and then placed in series with the secondary winding and able to be switched in or out. Thus you tune using the narrow 5kHz bw if there is that much, then when tuned you switch to extend the bw of the IFT, and avoid the imprecise tuning with the tertiary switched in.

6BE6 F converter, 6BA6 intermediate F amp, and a pair of cathode followers using 12AU7 plus silicon diodes will make a nice linear detector, and the sound will be very clean.

Patrick Turner.

Reply to
Patrick Turner

**Except for interference, there is no technical reasons why AM cannot equal or surpass the performance of FM. Many years ago, I built what is known as a TRF (Tuned Radio Frequency) AM tuner. TRF radios suffer from a number of problems, compared to the more usual Superheterodyne tuners. TRFs are more complex to build, more complex to adjust and generally a PITA. They do, however, offer excellent sound quality. I recall calling up the local radio station to advise them that one of their turntables had a worn stylus. The difference between turntables was easy to pick on my old TRF. There is a 'gotcha' however. AM radio stations have restricted their transmission bandwidth, such that high fidelity reproduction is pretty much impossible nowadays.
--
Trevor Wilson
www.rageaudio.com.au
Reply to
Trevor Wilson

Second time lucky

part of the reason (apart from bandwidth) is a diode is used to take the sound off the IF for a sound detector, a diode is a non-linear device and that is were you get the problems like distortion

for better quality AM take a closer look at "am stereo" receiver even if "your" radio station does not boardcast in "am stereo" the mono sound will sound a lot better than a radio receiver made with just a (crappie) diode for the sound detector.

for more on "am stereo" plug it into google and do a bit of reading.

take my word for it I have made a "am stereo" using the Harris system, it will never sound as good as FM (well we know that already) bit it sound heaps better than a standard AM radio. From EA magazine many years ago, I believe Dick Smith had the kit, also Silicon Chip, (or was the Australian electronics magazine before that ETI) come to think of it, it was ETI just a little bit before SC time.

Reply to
Eric

Build yourself a crystal set. (Seriously). Due to the small number of components there is little to limit the audio bandwidth. The downside is that you must have a strong incoming signal and will probably need an outdoor antenna. Take the audio from where the headphones would normally connect.

This works. You will be pleasantly surprised.

Reply to
Sir Nigel Puke-Fuui

Diode plus RC circuits can produce negligible distortion if the voltage being detected is high, and the diode is forward biased. Perhaps you know nothing about making such circuits, and making them as linear as need be.

Stereo AM can have the same distortion as mono AM if the detector and the rest of the set is poor quality.

No such kits are available now, and a DIYer has to think about all aspects of AM detection himself now if he wants to build anything.

But there is little AM programme worth real hi-fi tuners except the ABC amd print hadicapped stations. Commercials playing music play mostly MP3 and processed music to allow poor radios to get slightly better reception.

Patrick Turner.

Reply to
Patrick Turner

The audio bandwidth of any AM tuner is 1/2 the RF bandwidth of the tuned circuits, so that if you have a 1MHz tuned circuit with a Q of 100, then the RF bw =

10kHz, and the Af that can be recovered is -3dB at 5 kHz.

Any transmitted AM wave actually consists of the carrier tone at say 1,053 kHz, and the upper and lower sideband produced by the modulation, so if there is a

5 kHz tone used to modulate the amplitude of a 1,053 kHz carrier, then in fact there are frequencies of 1,048 kHz and 1,058 kHz present as well as the carrier of 1,053 kHz. A tuned circuit which has a bw which is -3dB at +/- 5 kHz will attenuate the two sidebands by 3dB in the above case, and if the af modulation F was 10kHz, the attenuation of the sidebands and hence the af modulation is a lot more, maybe 12dB.

With several cascaded tubned circuits, the sideband attentuation slope is quite steep, and the af bw will roll off quite steeply, and no amount of treble boost from a tone control can compensate for the losses caused by the poor RF or IF bw. Such low RF or IF bw is good for long distance listening, but who would bother, since noise and dull programme content defeats anyone interested in DX.

In a TRF set the problem is that you may well need 3 or 4 tuned circuits all cascaded, and tunable and which track each other, which thus prevents wide RF bw, maybe 2 kHz if you are lucky if the Q of each of the circuits is above 50.

The reasons are listed above. Also the skirt selectivity is poor so that stations only 50hHz away may only be -50dB, and audible when tuned to a weak local.

Most stations that are able to transmit 9kHz, will do so, and this usually sounds very heathy for speach and most music. Its far better than 2.5kHz.

There is no reason why a superhet with an IF channel cannot sound equally good and measure well compared to any TRF you may like to build. The af bandwidth can be arranged to be 10kHz by juggling the IF coil distances and using a tertiary on IFT no1, which was done on many japanese imported tubed am/fm recievers.

Such a set has usally got a total of 5 tuned circuits, one RF and 4 IF, with the 4 IF having two each and critically coupled to get a wide IF pass band to thus get wide band af despite the LC circuits having a high Q if measured separately. Nobody could ever achieve the skirt selectivity that you can get with such a superhet with a TRF.

-60dB is easily possible at 45kHz away from a wanted station.

There were several kits produced in the past for solid state tuners which could make

10kHz af bw and at low thd but one cannot obtain the special parts, so if anyone wants to build a decent AM tuner tomorrow, they must learn all about superhets and IT tranny construction and DIY a tuner or revise an old tube set, and hope the plate voltages don't kill them in the attempt.

And setting up variable µ tubes to work properly without distorting much and setting up a distortion free diode detector is an art and the product of a keen mind indeed.

So in a nutshell, good AM is not available to the ordinary punter unless you buy

something special already made.

And indeed it can sound very well.

Patrick Turner.

Reply to
Patrick Turner

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I will NOT be pleasantly surprised.

To get 10kHz of audio bw, the RF bw of the crystal set LC must be 20kHz, so the Q will have to be only 50, and sure the fidelity of a wanted station will be ok but all the other stations will be anle to be heard in the background.

Crystal sets are only good for kids to learn basics.

And the distortion from the low signals at low currents into diodes isn't too good either.

Patrick Turner.

Reply to
Patrick Turner

What you wrote proves you have never listened to a AM stereo receiver even if it was in mono mode,

if you cant get your facts right dont reply! get some experience first.

Eric wrote:

Diode plus RC circuits can produce negligible distortion if the voltage being detected is high, and the diode is forward biased. Perhaps you know nothing about making such circuits, and making them as linear as need be.

Stereo AM can have the same distortion as mono AM if the detector and the rest of the set is poor quality.

it

a

No such kits are available now, and a DIYer has to think about all aspects of AM detection himself now if he wants to build anything.

But there is little AM programme worth real hi-fi tuners except the ABC amd print hadicapped stations. Commercials playing music play mostly MP3 and processed music to allow poor radios to get slightly better reception.

Patrick Turner.

tuner

Reply to
Eric

I think you are a funny guy Sir

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through

Build yourself a crystal set. (Seriously). Due to the small number of components there is little to limit the audio bandwidth. The downside is that you must have a strong incoming signal and will probably need an outdoor antenna. Take the audio from where the headphones would normally connect.

This works. You will be pleasantly surprised.

Reply to
Eric

sorry I can not give you the magazine PCB number, but Dick Smith PCB number is/was ZA1699 the PCB measures about 110mm * 145mm it has 3 IC's to it part from the regulator HCF4016, UAF774 but the heart of the decoder was a MC13020 (I am sure it was a Electronics Australia project.)

I purchased the blank PCB from a sale when Dick Smith had there head office in Newmarket, corner of Khyber pass Road & Park Road it must be about 15 years ago (about 1990) give or take a few years

I converted a old AM receiver, latter on I went to buy a AM-FM (Hi-fi looking type) tuner to add on to my stereo, switching the amplifier input from my new AM-FM tuner to my old converted AM receiver there was a noticeable difference in sound quality.

Eric wrote:

Diode plus RC circuits can produce negligible distortion if the voltage being detected is high, and the diode is forward biased. Perhaps you know nothing about making such circuits, and making them as linear as need be.

Stereo AM can have the same distortion as mono AM if the detector and the rest of the set is poor quality.

it

a

No such kits are available now, and a DIYer has to think about all aspects of AM detection himself now if he wants to build anything.

But there is little AM programme worth real hi-fi tuners except the ABC amd print hadicapped stations. Commercials playing music play mostly MP3 and processed music to allow poor radios to get slightly better reception.

Patrick Turner.

tuner

Reply to
Eric

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Well that wa rather comical..........

My original question was serious as a topic of interest. I have a Realistic branded AM/FM tuner fed through an Akai amplifier and 2 speakers. I'm reasonably happy with the performance and was asking out of interest if AM can be improved.......

But thankyou for the comical response Sir Nigel

Reply to
John

This sounds like splendid fun. I am aware of the kits and have the schematics for most that were relaesed in Oz by EA and others.

One was even a synchrodyne using tubes in about 1955, another later one was also a synchronous type using a chip.

Was the switch to the converted AM receiver an improvement? I am not sure.

Patrick Turner.

Reply to
Patrick Turner

Hi John, As one or more people indicated, the audio bandwidth and distortion level of a typical "hifi" tuner/receiver is pretty poor. The manufacturers assume that people are only interested in getting good performance from the FM section. And that's probably true most of the time. :)

Bob

Reply to
Bob Parker

I can recall an Electronics Australia project called the Homodyne Tuner (now that will get Phil all fired up). Built one of these tuners (circa 1973 ?) as a kit. Sounded quite a bit better than many commercial AM tuners of the day. The only thing I hated about it was the method of tuning. It used variable inductance coils (similar to those used in car radios of the era) which IMHO was a bit cumbersome. Demodulation was based around a Motorola IC and sensitivity was adequate.

The only drawback was the due to it's wide bandwidth and low selectivity, listening at nights occasionally resulted in some distant station crosstalk and interference. Other than that, the sound was very respectable for a

70's kit job.

Cheers, Alan

Reply to
Alan Rutlidge

I remember that technique- also known as a synchronous receiver in which the local oscillator is on the same frequency and in phase with the carrier. So instead of the mixer stage producing an intermediate frequency, the output is the original audio. Many years ago I experimented with a very simple version of that idea, and I was surprised by the quality of the audio. Unfortunately the difficulties of tuning this kind of circuit and keeping the LO in phase with the carrier so it doesn't lose lock and cause a horrendous audio squeal seem to have been what stopped it from ever being popular. Bob

On Sat, 3 Dec 2005 17:49:59 +0800, "Alan Rutlidge" listening at nights occasionally resulted in some distant station crosstalk

Reply to
Bob Parker

OK I am sorry,

I get sick of some of the people to shoot their mouth off without learning the fact, I did it, I got the experience, even tonight as I switch from one tuner to the other I can see the better quality from the tuner in the set I modified,

By the way, a diode is NOT a linear device, never has been, look at the volt - current graph

Eric wrote:

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This sounds like splendid fun. I am aware of the kits and have the schematics for most that were relaesed in Oz by EA and others.

One was even a synchrodyne using tubes in about 1955, another later one was also a synchronous type using a chip.

Was the switch to the converted AM receiver an improvement? I am not sure.

Patrick Turner.

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sound

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Reply to
Eric

That was the Philip Pik synchrodyne circuit. It wasn't your typical kit circuit (a lot more skill required to build and tune, and you had to source all the parts yourself), but I agree with your point about the slug tuning. The demodulation didn't involve a standard "demodulator" chip but a couple of CMOS chips (4016 quad switch, 4013 dual D flip flop) and some comparators and op-amps. The original papers are are available on the hifi-am Yahoo group in the files section. EA June 1975 and Proc. IREE, Sept 1975.

As for sound, it avoided the bandwidth problem PT referred to (bandwidth determined by the audio bandwidth, with a TRF front end with 60kHz bandwidth) and sounded very close to FM (although mono) in quality, provided you listened to local ABC. The AWA AM3 was sold in the US as the McKay Dymek AM3, but it wasn't a patch on the Pik circuit for audio quality.

DN

Reply to
David Nicholls

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