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View Full Version : FM Tuners; Not Dead, Apparently!



Dave Cawley
23-06-2009, 08:00
I'm going to did out one of my old FM Tuners and work out what/why/how the " Multipath " meter does. :kiss: Any suggestions on how they really work?

Regards

:bag:

Dave

Alex Nikitin
23-06-2009, 10:50
Hi Dave,

AFAIK, the multipath meter works from the level of noise/interference on HF (there is a bandpass filter with 20 kHz central frequency and 7 kHz BW for the multipath detector), at least in a chip I've worked with for Creek T43 tuner - TEA6822T.

Cheers

Alex

Dave Cawley
23-06-2009, 13:08
Hi Alex

I think they are confusing this with diversity antenna switching or a stereo blend? Or some other noise reduction function.

Multipath as I know it, is when you are at fixed location and your reception is coming from multiple paths, directly and from a hill or building reflection. You can't pinpoint it, but the meter will tell you all is not well? On an analogue TV it would show up as ghosting.

I think the old Multipath term has been replaced by a new one that isn't quite the same? If I wasn't waiting for the Denon rep to call, I would go and get my 80's behemoth tuner and fire it up, and take a photo of the Multipath meter!

Any others out there with some info?

Regards

:bag:

Dave

Alex Nikitin
23-06-2009, 13:25
Multipath as I know it, is when you are at fixed location and your reception is coming from multiple paths, directly and from a hill or building reflection. You can't pinpoint it, but the meter will tell you all is not well? On an analogue TV it would show up as ghosting.

Hi Dave,

This would be my understanding of a multipath effect too. The chip I've mentioned has extensive noise and interference detection/suppression capabilities and "multipath" is only one of these. I suspect that a reception of a delayed signal on top of a main one creates some additional noise in that particular range of frequencies (13-27 kHz), so it is used for indicating the situation.

Cheers

Alex

Dave Cawley
26-07-2009, 09:42
http://www.fmtunerinfo.com/B261.jpg

Alex was of course right!!

The Revox B 261 tuner is simply wonderful, just put up a 3 element yagi in the loft, there was already a good quality downlead buried in the wall in the right place. I never knew Classic FM sounded so good!

Regards

Dave

DSJR
26-07-2009, 10:23
Those tuners could be got for a song once up on a time *if you knew the right person* and that revox was the best of the lot as I remember - performance AND reproduction quality (the earlier ones were more towards performance and could sound a bit sterile when compared with the source fed them).

Classic FM can be a bit compressed, but not as badly as the pap (sorry, pop) stations. Having said that, has radio 1 put some bass back in recent times? Either that or the BC2's are reproducing what the small ATC's weren't... may be due to the over-abundance of those horrid little active screechers made by Dynaudio in the pop studios over-egging the upper mid/lower treble and not reproducing the compression so much......

Dave Cawley
26-07-2009, 10:43
http://www.soundhifi.com/kenwood.jpg

Hi Dave

Revox made some of the best stuff ever, but didn't get the recognition in the UK I believe?

The best tuner I have seen is the Kenwood/Trio KT-9900/KT-8300 with a six gang air spaced variable capacitor, no varicaps, no synthesiser, in fact no logic chips at all! Silky smooth flywheel tuning and the elusive Multiplex Meter! But it isn't as convenient so it's on the way out on eBay sometime? See more at near bottom of this page http://www.fmtunerinfo.com/kenwood.html It also has a switchable narrow filter that extracts weak signal next to strong ones.

Regards

Dave

DSJR
26-07-2009, 10:57
They were lovely.

As I recall, the problem with all these "adjustments" for selectivity and multipath was again - the more you put in the way, the worse it got and i reckon that some of these fancy tuners were bad because of getting a good spec (like many Jap amps of the period were, adding shedloads of global feedback to bring the basic THD down and ignoring other distortions such as TID and the inevitable time-smear (can't remember the tech term for it but it's one area valve amps could be brilliant at)).

At the end of the day, you cannot beat a decent aerial (with a rotator if you're really keen:)) and it's amazing how many FM problems disappear when you use a suitable example of one (Ron Smith anyone?). Ron did all our aerial work (he's an old boy now though) and Naim swore by him - The 01 may have its sonic abberations and its technical spec cannot compare with the best from the far east's best, but it followed good tuner practice I thought in keeping it fairly simple, defaulting to mono when the signal got too weak and muting completely if a listenable signal wasn't available. A good aerial making up for lack of fancy "extras."

True story - when the NAT 01 came out, Martin Colloms "borrowed" our new dem tuner for testing for HiFi Choice. It was a bit of a disaster and Naim had it returned with its tail between its legs for checking. I don't know what they did, but it came back a much better performing and sounding beast. It seems that now elderly examples of this model (twenty plus years old now) need all the fuss and bother they can get to return them to spec. I bet the Revox's, Sansui's, Accuphases and Yamaha's from the classic era don't......

Dave Cawley
26-07-2009, 11:19
The lovely thing about the Kenwood/Trio KT-9900/KT-8300 is that it has two IF chains for each selectivity, so no compromises. Also there is no negative feedback anywhere, not even AFC ! Did you look at the circuit? simplicity and purity.............

But TID on amplifiers, a different subject, and maybe we should start a new thread, that is a different matter and I had a letter published in Hi Fi News in the late 70's about that.

Dave

DSJR
26-07-2009, 14:48
Dave, you're an engineer, I just mop up and assimilate a lot of what I hear and read :)

My current issue about FM in the UK is that the Beeb *apparently* take the (fugged up) DAB feed and convert it to FM for transmission. certainly, the only station that seems to be transmitted "pure" is radio 4, one reason it has such lower volume than the others.

Do you think the next generation will try to restore the quality lost by the current "mejia studies" lot?

Dave Cawley
26-07-2009, 15:23
Oh no!! a DAB feed.............. Is this really true?

I only listed to Classic which did sound OK.

Regards

Dave