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Exposure VII Pre-Amp

Discussion in 'audio' started by Puffin, Jun 27, 2010.

  1. Puffin

    Puffin pfm Member

    Has anybody had one of these, or still use one. What are they like?
     
  2. colasblue

    colasblue pfm Member

    I have had one

    It now lives across the road with oe of my neighbours.

    They are absolutely first class and if you run them on suitable power supplies will easily see off any naim shoebox.

    The one I had was within a hair's breadth of my tweaked 82 2xHC , and it only had a single VI to power it. If you had two VI's or a IX or XII tthen it would probably equal anything naim have ever made.

    They surely must be the most undiscovered bargain in the whole second user world.

    In terms of overall character they are almost identical to Naim, which shouldn't surprise anyone since they have quite a lot of components in common.
     
  3. Puffin

    Puffin pfm Member

    Thanks Colasblue. I picked one up from an audiojumble minus cover for £25. The rest of it is in very good nick. All the screen printing on the front is pristine. No PS, but no problem to make one or two split rail supplies.

    I will make the PS(s) with TeddyRegs.

    What would they go for these days? Mine is dated 1982.
     
  4. colasblue

    colasblue pfm Member

    They're a bit of a dark horse on ebay.

    Recently a fully working and in decent conditin VI/VII went for £130 ish.

    I forgot to put a snipe on otherwise I'd have had it.

    A more normal pice would be north of £150 for the pre on its own and about the same for the PS.

    Even at those prices they are staggering bargains.

    At £25 you should be laughing all the way home!

    FWIW I doubt there's actually much point in shelling out for STR's or TR's unless you intend to remove the second stage of regulation done on each amp board using a 317/337 pair.

    Expo seem to have invented dual stage regulation long before Avondale, Neil Mcide or any of the subsequent lot.

    I'd go with a reasonable size traffo with a pair of 22000uf caps running +/- 35 V into a 317/337 pair.

    If you're feeling decadent make two of those PS's and hook each preamp board up to its own one.

    Also if you feel like doing a bit of servicing Expo recommend changing the tants for bc/vishay small radial electrolytics.

    I can dig out the correct part No if you're interested.
     
  5. stackowax

    stackowax pfm Member

    I'd be interested in this...
     
  6. Puffin

    Puffin pfm Member

    Thanks for all the info and yes please.

    Rob.
     
  7. lindsayt

    lindsayt pfm Member

    Congratulations Puffin. You've just bought the best £25 pre-amp in the world. I think you'll have a big smile on your face when you fire it up.
     
  8. Puffin

    Puffin pfm Member

    I am assuming it works! Time will tell. Depite the lack of a lid, it is pristine with no smell of previously smoked boards!
     
  9. ipity

    ipity pfm Member

    There are two derivatives of the SEVEN pre-amp: the SEVEN Standard and SEVEN Dual. The latter is significantly superior.

    The SEVEN Standard can use a single power supply from a power amp such as the EIGHT Standard. However, the SEVEN Dual has separate circuit boards for left and right channels, and needs two power supplies, typically from either one or (preferably) two SIX power supply units. I believe you can also combine a TWELVE power supply with the SEVEN Dual, which is better than two SIX units. The SEVEN Dual was replaced by the ELEVEN around 1990.

    You can tell if it's a Standard or Dual version by the number of 12 volt DC power supply inputs on the rear. If it has one input, with the other clearly blanked off, then it's a standard version. The Dual has two separate 12 Volt DC inputs.

    I've seen SEVEN Standard pre-amps being sold as DUAL versions on Ebay, so beware!
     
  10. Puffin

    Puffin pfm Member

    Mine is the dual. It has two DIN syle sockets for the PS IN. I had intended to use one PS and connect both boards. I assuem the dual PS arrangement was done for superior SQ reasons?
     
  11. Dowser

    Dowser Learning to bodge again..

  12. Puffin

    Puffin pfm Member

    Yes I saw that at the weekend. I could not aspire to build anything as brilliant as that!
     
  13. Puffin

    Puffin pfm Member

    [​IMG]

    It lives!

    I have tested using only one PS. I will plumb it in to my main system and see how it is. Then I will make a second PS and change the DIN sockets to XLR for each connection.

    [​IMG]
     
  14. colasblue

    colasblue pfm Member

    This is in fact mostly complete tosh, there is one version which can be configured either way by the factory and is easily changed by any competent DIY'er.

    The only difference is that the single has both amp boards power supply rails connected to a single 5 pin domino din and the dual has a separate din for each board.

    To change single to dual you just install a second din in the pre punched hole and solder up the wiring appropriately.

    PS what item of cambridge audio equipment had to be sacrificed for the new cover??

    PPS This is the 10uF cap they use

    http://uk.farnell.com/vishay-bc-components/mal209758109e6/capacitor-10uf-63v/dp/1165532

    They also use the 5uf 63V and 47uF 63V cap from the same series in a couple of places.

    The axial decoupling caps are these though there may be little benefit to changing them

    http://uk.farnell.com/vishay-bc-components/mal203136151e3/capacitor-150uf-25v/dp/1165424
     
  15. Gromit

    Gromit Plasticine Dog

    What he said - I had a Single VII myself which the factory converted to a Dual in less time than it took to drink a cuppa.

    Fantastic little pre-amp with a great phonostage to boot. :)
     
  16. Puffin

    Puffin pfm Member

    Colasblue. I had a couple of DiscMagic's and I broke one of them, so the case was saved for a rainy day!. Thanks for the cap info.

    Rob.
     
  17. richgilb

    richgilb Admonishtrator

    I have managed to source a vii, which I have had recapped. I infer from the above posts that adding a further power supply may increase sound quality. What do I need to do to the vii to enable this upgrade?
     
  18. cromodora

    cromodora foshfishfie

    This may be five years too late but the "Dual" version has an extra pair (being split rail) of onboard regulators to serve the phono section.

    But yes, this too can be easily changed by a competent diy'er.
     
  19. colasblue

    colasblue pfm Member

    Not quite true

    Having looked at various eBay internal shots over the years the VII board actually went through a few evolutions (At least 3 but possibly more)

    The earliest ones had a single 317/337 pair and very little in the way of internal decoupling.

    Mid period ones like I had had the same single 317/337 pair and quite a lot more of those 150uF decoupling caps.

    That design crossed the boundary between the round edge and square case style.

    Very late ones lost the two power on LED's and the balance switches and lost a few of the decoupling caps in favour of additional 317/337 pairs. I saw one variant with 3 pairs.

    Irrespective of the board iteration they could be single or dual solely on the basis of the PSU connectivity.

    I'd really like to get my hands on one of those later ones with the three pairs of regs!
     
  20. cromodora

    cromodora foshfishfie

    That would be true if the board below is not specifically for Dual version as marked.

    [​IMG]
     

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