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Kenwood Basic M2 Amplifier

Discussion in 'Troubleshooting and Repair' started by Neal, Dec 23, 2009.

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  1. Neal


    Dec 23, 2009
    Picked up the amp @ garage sale for $5 and works great.
    Have a question, there are 2 outputs (R & L), next to the channel A speaker output.
    They are labeled sensor, anyone have any idea what they are for?


    Found out what sensor is, It's a sense line for long runs. Much the same as a sense line on a long pwr supply run.
    Last edited: Dec 27, 2009
    Rick Eiselt likes this.
  2. niftynev


    Mar 20, 2010
    interesting neal about the 'sense' terminal ay!

    i've only ever heard of them used when measuring high currents. not in amplifiers.

    what would that terminal actually do?
  3. restorerjohn


    May 3, 2012
    These are the 'sigma drive' sensor inputs.

    Essentially, kenwood tried to put the speaker cable into the feedback loop and tighten up damping factor by a factor of 10.
    The problem was it was unreliable and caused trouble when the main connection became intermittent.
    By all means give it a go, it makes quite a difference. Just more cables running across the room!
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    What is it? A Kelvin connection for your speakers?
  5. restorerjohn


    May 3, 2012
    Kenwood named it 'sigma drive' for marketing and it was quite the 'thing' on their mid-upper range integrated and power amplifiers for a few years. It disappeared due to reports of amps blowing up due to incorrectly wired or dropped contacts. I have seen a few M2s which blew up for no reason and I blame incorrect sigma drive wiring. The M2 also had a commutating supply with an HV rail for high powered transients which didn't help stability either.
    Back to Sigma Drive, it is a great concept and something I messed with several years ago too. The goal was to remove the speaker cable effects; resistance particularly, from the output equation as the speaker cable represents a significant proportion of the overall impedance particularly if the cable is long and thin. By essentially putting the speaker cable partially in the negative feedback loop, you can create a 'negative impedance' to cancel the cable's resistance/impedance.
    Yamaha did a similar thing in the late 80s with AST (active servo technology) where they coined 'negative impedance drive' which took the characteristics of AST labelled speakers and used a matching plastic cartridge (fit into the back of AST amplifiers) which had a network inside to offset the resistance and compensate for frequency response anomalies in order to have a small speaker reproduce a flat response. Clever and effective.
    Sigma Drive is, and was a valid concept for improving damping factor, just misunderstood.
  6. sb001


    Jun 27, 2012
    New to this board, was doing a google search for Kenwood Basic M2 after recently finding one at a pawn shop and buying. Thanks to all for the explanation of the Sigma Drive on this amp-- can someone explain to me exactly how to properly connect this to take advantage of the Full Sigma Drive mode? I just don't want to blow anything! (Amp sounds great BTW just running in normal mode.) Thanks!!
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