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Leak TL which decoder?

Discussion in 'classic' started by Linnovice, Jan 26, 2021.

  1. Linnovice

    Linnovice pfm Member

    Good afternoon all. It's lockdown time and I, like I expect most of you, am bored. In this case the brain starts wandering and wondering what can be done to fettle with the kit.

    I have a small collection of FM tuners, one of which is a Leak Troughline Stereo. It was faithfully refurbished last year by a friend of mine who is steeped in tradition with valve technology. All valves were replaced along with capacitors and resistors as necessary. I primarily listen to R3 during the day and specifically when they broadcast a live concert. It sounds good overall, I prefer it to my Linn Kudos in many ways. Trouble is the sound is very soft. I don't mean in volume, I mean in details. All the instruments are there but they seem to be playing through a veil. ie. as mentioned in other threads it 'sounds like granny's radiogram'.

    Doing some homework on this forum it appears that the problem lies with the stereo decoder. So my question is, how can I go about changing the decoder. As I said earlier. My friend is steeped in tradition so when I broached the subject his reaction was that you shouldn't meddle with the original design. I understand his perspective but times change and if its possible for me to update it and improve its performance I'd like to give it a try. I'm not an electronics engineer, just a muppet who knows which end of the soldering Iron to hold. I don't mind fixing tape decks when I'm tracing out 24V. I don't fancy frying myself with 240V! Is there any easy route to update the original onboard decoder.

    Any advice would be very gratefully received.

    Incidentally, I also have a Leak Stereofetic that has been refurbished and that sounds very good. It's just nice to ring the changes occasionally.

    Thanks, Mike.
     
  2. Radfordman

    Radfordman pfm Member

  3. Vinny

    Vinny pfm Member

  4. Linnovice

    Linnovice pfm Member

    Hi, thanks for the suggestions. I was hoping there may be an off the shelf solution but, it would be quite an achievement for me to build it myself. Would the components be readily available from somewhere like RS?
     
  5. Radfordman

    Radfordman pfm Member

    RS possibly, ebay, Cricklewood Electronics are good.
     
  6. Vinny

    Vinny pfm Member

    LM1310 may be obsolete - RS and CPC do not list it, but EPay has them for sale - buying components from EPay neeeds experienced help as it is stuffed with fakes.

    Same goes for MC1310
     
  7. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    There are many equivalents to the MC1310P and also several better more modern ones but many are getting difficult to obtain these days. Try TCA4500 for example. It needs to be a separate unit with its own PSU whatever you do and then there is the circuitry to interface it properly...

    The Stereofetic is a much better tuner than the Troughline even after getting a good stereo decoder though. I know from experience as I've built many decoders for Troughlines over the years....
     
  8. Linnovice

    Linnovice pfm Member

    So, Arkless, are you saying I should leave the Troughline as is and keep it as an example of 60’s British valve technology and settle on the Stereofetic. At present to my inexperienced ear it seems as though I’ll have to use a hammer to crack the nut. The Stereofetic sounds better anyway but even that is not really as good as the Kudos IMHO.
     
  9. davidsrsb

    davidsrsb pfm Member

    So far as I know, none of the "analogue" stereo decoder ICs are in current production from a reputable supplier.
    Cricklewood do the MC1310, they may do others and they generally don't sell fakes
    Don't waste your time with eBay.
     
  10. Radfordman

    Radfordman pfm Member

    I used Cricklewood for decades, very good. many years ago they changed their name from Markshalls to Cricklewood Electronics, I still have a Marshalls catalogue!
     
  11. Radfordman

    Radfordman pfm Member

    A vintage British tuner that is very good and usually cheap is the Rogers Ravensbourne 2 FET. I prefer this to the Stereofetic.

    Watch out though, there was an earlier version of the Ravensbourne tuner that was not as sensitive. I had both, the later version is still with me.
     
  12. toprepairman

    toprepairman pfm Member

    Definitely agree with Jez (Arkless), leave the Troughline as it is.
    It could be that it's performance is reduced by being fed into too low an input impedance. Are you using a transistor preamp?
     
  13. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    The Troughline Stereo sounds like a quilt has been thrown over the speakers no matter what it is driving!

    I can confirm Radforman's thought's on the Rogers Ravensbourne also. Very good yes. Avoid the Ravensbrook.
    I had one once many years ago. IIRC there were loads of fully screened separate modules that made up most of the circuitry.
     
  14. Linnovice

    Linnovice pfm Member

    Hi, my pre amp is a Linn AV5103, would that effect the Troughline? The Stereofetic sound fine, not quite as detailed as the Kudos.

    What would the opinions of a Quad FM4 be. I know the brand by name have no experience of them.

    I’m looking to listen to quality broadcasts on R3 primarily and R2/R4 occasionally. I like to record live concerts to tape (Studer) so sound quality is paramount. The Kudos is good but a little hard (almost digital) but that is how it was designed to compare with CD.

    I’m disappointed in the Troughline, the rave reviews given on the internet don’t actually appear to match the the output. Perhaps it’s a hang up on valves?
     
  15. Radfordman

    Radfordman pfm Member

    In my opinion the Quad FM4 is good, watch out for leaking battery though and it also needs a high input impedance otherwise bass is reduced. I have one of these, to me the Ravensbourne is just as good though, lovely flywheel tuning.
     
  16. Linnovice

    Linnovice pfm Member

    Ahh, that sounds good. I like a flywheel also
     
  17. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    FWIW it is incorrect to ascribe any "valve sound" to the Troughline (esp when used with external decoder) as at the point where the RF (IF in fact) is demodulated into audio (using SS diodes in the Foster Seeley discriminator) it is then fed to the multiplex socket without passing through any valves. In a mono one used via it's own mono output there is a cathode follower valve present and same between tuner and decoder in the stereo one but a cathode follower is intrinsically pretty low distortion and neutral sounding.
    It makes no difference to sound quality if transistors, valves, mosfets whatever are used before the discriminator as the signal is at this point a deliberately massively distorted "square wave" at about 12MHz (yes not standard 10.7MHz IF frequency!) carrying the "audio" in the form of frequency modulation (FM).

    Edit: IMHO any difference in sound from a TL is likely to be from the use of a Foster-Seeley discriminator to convert IF to audio rather than a quadrature discriminator as used in virtually all tuners from around '73-ish onward. FWIW there was also the ratio detector which was the most popular between about '65 and then.
     
    Last edited: Jan 27, 2021
  18. Linnovice

    Linnovice pfm Member

    Thanks for the explanation Jez, I just had a very loud whoosh sound pass right over my head
     
    Arkless Electronics likes this.
  19. toprepairman

    toprepairman pfm Member

    The specifications page for the pre does not specify the input impedance, which is really stupid. In any case it is unlikely to be much above 100 Kohm.
    The Tuner wants at least 1 Meg ohm input impedance.
     
  20. Linnovice

    Linnovice pfm Member

    I’m afraid that’s all part of the Linn philosophy of ‘keep em in the dark and feed them horse***t’. It’s frustrating at times but they do make good kit.

    I’m going right off course now, based on what I’ve read, heard and seen I think that me making the effort to build a modern decoder, as a challenge, would in practice be a waste of time.

    So, as I do like FM as a medium, I think I will start looking for an alternative/additional tuner.

    Sony ST3950?
    Kenwood KT-8005?
    Rogers Ravensbourne?

    Being likely contenders.

    Any opinions or users of the Kenwood?
     

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