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Old 7th Jun 2018, 12:50 pm   #1
mark2collection
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Default Mullard/Philips LP1401S

Hi Folks,

I'm looking for some information on the above stereo decoder.

Ideally, a guide on how you set this up correctly. I've worked out the edge connector connections, but no clues about which potentiometer does what, & I don't fancy blindly twiddling!

Looking on the internet proved fruitless, though the datasheet for the TDA1005 does give some clues. There's a chance this decoder has been setup in the factory, though trying it, you'd never know!

I shall be using the decoder with a Leak Troughline 3, which works great (in mono).

I know I could build a modern decoder using newer IC's/parts etc, but since I have an LP1401S in my hand, makes sense to give it a go(?)

The symptoms we're seeing, flickering stereo beacon (with a good signal), poppy/wooly bass (stereo beacon has been known to flash in time with the beat - whilst this is kinda 'groovy', it's not the look I'm after).

I've tried the tuner with another decoder (which is normally hooked up to a Troughline II), & it works great, so defo an issue with the LP1401S.

Any help/advice gratefully received.

Mark
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Old 7th Jun 2018, 7:34 pm   #2
Biggles
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Default Re: Mullard/Philips LP1401S

There is information about the LP1400. It is possible they follow a similar circuit, but this can't be guaranteed of course. I have an LP1400 module, and a circuit for it, but admit it hasn't been connected so I'm not sure whether they were very good. I just use an MC1310 decoder chip, which is quite old now but performs well and is easy to adjust, being of the PLL type. I think the adjustment is to set the oscillator to 19KHz and that's it. Plenty of info around for circuits too. Try a search on the forum, as I think there was quite a bit of discussion about them on and off. If you would like a copy of the LP1400 circuit let me know.
Alan.
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Old 24th Jun 2018, 12:46 pm   #3
mark2collection
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Default Re: Mullard/Philips LP1401S

Hi Alan, many thanks for the kind offer. Apologies for the delayed reply, family matters ...

Having read various posts on the forum, the decoder had one 'Lokfit' transistor, a BC148, which has now been replaced by a BC548. The odd 'ploppy' noise has gone, & once everything was wired up, I connected my stereo encoder, 'scope & frequency counter.

Everything was way off (according to the TDA1005 data sheet) with huge amounts of crosstalk. Very careful adjustment of the potentiometers & coil soon revealed their purpose, aside from one pot, which appears to make no difference, so set to 'where it was'.

The decoder now sounds the bizzo, very clear, great stereo separation & overall great frequency response.

Well worth the effort.

Mark
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