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Thread: DC offset question.

  1. #61
    Join Date: Oct 2012

    Location: The Black Country

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    I'm Alan.

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    1.7 mV, positive or negative is very low and should be no problem for any amp.

    The ground doesn't carry a voltage.

  2. #62
    Join Date: Dec 2015

    Location: Alicante. Spain.

    Posts: 1,692
    I'm Adrian.

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    Quote Originally Posted by Firebottle View Post
    1.7 mV, positive or negative is very low and should be no problem for any amp.

    The ground doesn't carry a voltage.
    Thank you, I just don't get why the volume/voltage pushes the meter from null into a negative reading when increased (it powers the led).

    But I agree 1.7mv is tiny.
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  3. #63
    Join Date: Jan 2009

    Location: Essex

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    I'm openingabottleofwine.

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    Quote Originally Posted by farflungstar View Post
    Thank you, I just don't get why the volume/voltage pushes the meter from null into a negative reading when increased (it powers the led).

    But I agree 1.7mv is tiny.
    Without seeing the circuit diagram for the Truth, it is difficult to say for sure, but I suspect the LED and the buffer amps might share the same power
    supply, which is not, IMO, a good idea.
    Have you listened to this month's choice in the Album Club?

    Barry

  4. #64
    Join Date: Dec 2015

    Location: Alicante. Spain.

    Posts: 1,692
    I'm Adrian.

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    I have emailed Audio Research about compatability whey the Truth and the jfets input stages of the ref 75. The Truth is measuring perfectly but ARC's topology may be an issue - let's see what they say.

    Meanwhile I've bought and am waiting for a Luxman AT3000 TVC to replace the Truth, so I can finally switch on the newly returned 75 without worry.
    Technics SP10 mk2
    Jan Allaerts MC 1 Boron mk1 cart
    Miyajima Shilabe cart
    Hashimoto HM-X SUT
    Siggwan (gimballed not unipivot) Cocobola 12"
    Aurorasound Vida LCR Phonostage
    The Truth linestage
    Dave Slagle Autoformer Volume Controller
    Cary 805c SET amps
    Audio Note ANe-SPX speakers
    Townshend Isolda speaker cables
    Cardas Golden Presence interconnects

  5. #65
    Join Date: Apr 2012

    Location: London

    Posts: 322
    I'm james.

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    Very nice! And good move IMHO

    Sent from my GT-I9195 using Tapatalk

  6. #66
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 1,142
    I'm Andrew.

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    Quote Originally Posted by Barry View Post
    It's difficult to find much technical information about the Truth, but their claim that the input impedance is 'near infinite' does suggest the use of op-amps.
    Quote Originally Posted by farflungstar View Post
    There are no opamps in the box.
    From what I can gather, The Truth uses video buffer amps before and after an LDR volume control. The video buffers are op-amps with a specialised purpose. Because they're designed to work at video rather than audio frequencies I would expect they need extra care to make sure they don't go into ultrasonic oscillation.

  7. #67
    Join Date: Jan 2009

    Location: Essex

    Posts: 17,441
    I'm openingabottleofwine.

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    Quote Originally Posted by RothwellAudio View Post
    From what I can gather, The Truth uses video buffer amps before and after an LDR volume control. The video buffers are op-amps with a specialised purpose. Because they're designed to work at video rather than audio frequencies I would expect they need extra care to make sure they don't go into ultrasonic oscillation.
    My thoughts exactly, though my knowledge of electronic circuitry is insufficient to make specific suggestions.
    Have you listened to this month's choice in the Album Club?

    Barry

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