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Old 5th July 2012, 05:28 AM   #1
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Default Questions about a vintage tuner

Hello

I've found a vintage Radio-Shack TM-101 tuner, I lnow that there is better one today, but I would like to use it.

I Have the schematic.

Anybody can suggest me simples modifications to made it sound better and more sensitive ?

And where can I connect a small meter to see the signal strength wen I tune for a station ?

Here's the link to the schematic:

View image: Realistic TM 101 Schematic 1

Thank

Bye

Gaetan

Last edited by gaetan8888; 5th July 2012 at 05:31 AM.
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Old 5th July 2012, 11:18 AM   #2
oshifis is offline oshifis  Hungary
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I had a Luxman tuner very similar to this one. Actually it looks and should sound better than many digital tuners. I like the variable capacitor tuning. Varicaps cause distortion. Perhaps you could add another ceramic IF filter, and replace the diode in the PSU to a bridge rectifier (lifting the bottom end of the transformer from GND). The tuning indicator can be put across the capacitor C139. I upgraded my tuner with 2x TOKO BBR3132A 6-pole LC flter, but I am not sure if it is still available. Anyway "if is not broke, don't fix it"...
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Old 5th July 2012, 11:53 AM   #3
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What do you want the meter do? Normally, it indicates some form of signal intensity in AM and the center frequency in FM. Or also want signal strengt in FM?
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Old 5th July 2012, 11:59 AM   #4
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Quote:
Originally Posted by oshifis View Post
Varicaps cause distortion.
Something new for me. In FM receivers input signal is deliberately distorted in the limiter stage to cut AM signals.

Augmenting IF filtering implies reduce bandwidth, so increases high frequency distortion and in FM, they cut the L-R signal, so receiving FM Stereo signals in worse.
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Old 6th July 2012, 10:12 PM   #5
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Quote:
Originally Posted by Osvaldo de Banfield View Post
What do you want the meter do? Normally, it indicates some form of signal intensity in AM and the center frequency in FM. Or also want signal strengt in FM?
Hello

I was meaning a FM tuning indicator.

Thank

Bye

Gaetan
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Old 7th July 2012, 01:46 PM   #6
DF96 is offline DF96  England
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Varicaps, if used badly, can cause RF intermodulation. BJTs, as used in this tuner, are likely to be much worse. Fortunately RF IM does not directly translate to audio IM so provided you keep signal levels from the antenna high enough but not too high you should be OK.

For an FM tuning indicator you need to monitor the voltage at TP1 across C142. This is the output from the ratio detector. You may need a buffer, such as an opamp, to avoid any meter from loading the circuit. The meter needs to be a centre-zero type.

An FM signal strength is not really possible as there is no point in the circuit where a suitable voltage is available.

This tuner is not intended for serious hi-fi listening, just normal domestic radio reception. It is basically a Japanese AM/FM portable, with the audio output stage replaced by a stereo decoder chip.
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Old 7th July 2012, 03:53 PM   #7
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Hello

Ok, it's not hi-fi.

So, is there any one chip fm tuner with a hi-fi sound ?

My two fm tuner with fm syntetiser tuning are dead, maby I could made a diy
hi-fi fm tuner using the minimum number of Ic's chips.

Thank you

Bye

Gaetan

Last edited by gaetan8888; 7th July 2012 at 03:56 PM.
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Old 7th July 2012, 05:30 PM   #8
DF96 is offline DF96  England
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One-chip tuners are unlikely to be hi-fi. DIY tuner designs are rare nowadays, as the RF front end requires knowledge and test equipment not normally associated with audio DIYers, while RF DIYers are not always so interested in audio quality. I designed and built an FM tuner but I guess I am unusual! Before you ask, I don't have a full circuit diagram for it and most of the chips in it are probably obsolete by now.
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Old 7th July 2012, 05:36 PM   #9
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There are an enormous quantity of true Hi-Fi FM receivers on E-Bay going for silly money. It's equivalent to the end of the Vinyl age.

One day people will realise that FM is better than DAB, the same as they did with vinyl vs CD.

The ones for sale are those built at the pinnacle of the FM age. Grab a bargain.
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Old 30th October 2012, 11:05 AM   #10
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What do you think about to bring back to life all those Hi Fi analog fm receivers with their fine workmanship ,high selectivity etc etc?
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