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Arkless 640P "Dr T Mode"/current input version interest check

Discussion in 'audio' started by Arkless Electronics, Feb 15, 2020.

  1. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    If I was to convert my demo unit to current input who would be interested in trying it?

    It will cost each person £11 postage to send it to the next person on the list by insured, tracked Royal Mail "Special Delivery", as it did when it was originally doing its several tours of the country.

    These will be £255 for the conversion (Cambridge Audio 640P or 651P donor unit required) and I cannot stress strongly enough FOR MC ONLY unlike the MM/MC switchable standard version. The current input concept is only doable for MC's as they work into a "virtual short circuit" and no longer have loading requirements etc. MM's like to see 47K load as standard so completely unsuitable under any circumstances for a current input phono stage.

    Those who already own an Arkless 640P can have it converted to current input for £40 plus postage.

    The only other such units I know of which work in this way are the Dynavector P75 when in "Dr T Mode", the 47 Labs Phono Cube and the recent RSL phono stage.

    If enough people wish to try it then I'll go ahead with it:)
  2. nobeone

    nobeone pfm Member

    Yup, count me in, I have tried the RSL phono stage and liked it very much, would be interested to hear your spin on the Dr T mode.
  3. matt j

    matt j pfm Member

    As an RSL owner I'd be interested to hear it. I wonder what it is about these style of phono stages that always seem to sound good to me, the P75 sounded like nothing special at all on it's MM and regular MC settings but was great in the Dr.T/Current mode. The RSL again was streets ahead of regular MC stages and step-ups into MM stages I'd heard previously, which was quite a few at the time.
    Tarzan and Alex S like this.
  4. suzywong

    suzywong Wot, no electrons?

    Sounds similar to what Meridian did back in the mid ‘80’s with their MC “dual module” for the 101/101B.

  5. Marcus401

    Marcus401 New Member

    Yes for me too.
  6. poco a poco

    poco a poco I'm Jim

    I had (I think I still have it, but can't find it) one of these modules in a 101B used into my Meridian M1's and later M10's. It was a big improvement over a couple of different normal MC modules I had for the 101 when fed by a Linn Asak or Supex 900e.
  7. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    I'm going to need several more people interested in hearing this to make it practical folks...

    I can find no information to suggest that Meridian ever used this technique...
  8. peterm

    peterm pfm Member

  9. Sue Pertwee-Tyr

    Sue Pertwee-Tyr Well, I can dream, can’t I?

    I'd be a potential customer for this. Currently MM only, but looking to a MC option soon and intrigued by what I've heard about the 'Dr T' option.
  10. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

  11. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Hopefully enough people will add their names to the list here for it to happen and that by the time you have an MC it can be your turn:)

    It will be available to order once I've proved it works well in practice (I'm confident it will) but the only way anyone can hear it before purchase will be to add their name to the list here. 'fraid there's no non blunt way of saying this but if anyone is thinking "I'll see what the others say about it and maybe ask to hear it in a few months time" I can say right now the answer will be no. Whilst hopefully a hell of a giant killer, this is a budget phono stage and I ain't paying the postage to send it out to each individual rather than it going "round Robin" from one person to the next. Not unless they want to pay the (£11) postage in each direction anyway! Yes there are vastly cheaper postage options but Royal Mail "special Delivery" gives me assurance that if the unit should disappear then I am compensated for the loss. The tracking and it being "signed for" also adds confidence that it will get safely from one person to the next and thence back to me:)
    misterdog and Sue Pertwee-Tyr like this.
  12. suzywong

    suzywong Wot, no electrons?

    I think those are the schematics for the older units where the 101 used individual modules for different cartridges . When the the Double Module came out, I remember reading about "virtual short circuits" and that it could handle any MC cartridge. Like Poco said above, it was certainly a nice uplift on the Supex module I was using at the time. Still got a couple: a 101 in the loft, and a 101B on-loan to daughter #2.
    poco a poco likes this.
  13. poco a poco

    poco a poco I'm Jim

  14. peterm

    peterm pfm Member

    The "IMCOS" module was how the double mc module was described at its introduction, I think the 101 had been changed from discrete components to ic based construction some time before.

    I had an original 101 with separate mc and equalisation modules feeding a 103 amplifier.

    A few years later I bought a 101B (to go with a pair of M2 speakers) and that had mostly ic circuitry but still used the individual mc input module and equalisation module. the "IMCOS" double module was introduced later as an upgrade, I don't remember it being much of an improvement!
  15. Alex S

    Alex S carbon based lifeform

    Should be able to get enough interested; google ads keeps telling me 10 million have tried Harry’s razors!
  16. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    101 IMCOS (whatever that is) has a 270R noise generator (resistor) at the input. Transimpedance amplifiers (the correct name. Why should "Dr T" get the credit when this is a textbook circuit and used in most IR remote receivers!?) are not in fact compatible with all MC carts as the carts internal resistance sets the gain... Now as, in general, higher output carts have more turns in the coils and hence a higher internal resistance this will tend to self compensate but there are "flyers" such as many Linn carts at one end some Benz carts at the other... Linn Asak etc has pretty high output with quite low internal resistance and will likely blow the doors off with most transimpedance units whereas many Benz carts have a high (for an MC) internal resistance and will likely be rather quiet. That's not to say that necessarily either will not work perfectly well with it but you may have vol down at "2-3" with an Asak but up at "7-8" with the Benz.

    Hence the P75 has IIRC two gain settings and the RSL maybe more. The 47 Labs phono Cube must be ordered as "high" or "low" gain versions.

    I will make the demo version with a gain that makes it usable with the majority of carts, hopefully including the "flyers" noted above but note what I said about likely vol settings. I will make them available for sale as high or low gain in the same way as the 47 Labs units though. Just two gain settings should cover pretty much everything.
    Tim Jones and suzywong like this.
  17. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

  18. eevo1969

    eevo1969 pfm Member

    Yes please. PM sent.
  19. Tim Jones

    Tim Jones pfm Member

    Excellent post Jez, thanks for the explainer. I'd be up for it too, but am committing to an RSL.
  20. Tigerjones

    Tigerjones Bagpuss

    You wouldn’t think they’d need to advertise with 10m customers.

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