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Thread: DC offset question.

  1. #11
    Join Date: Apr 2012

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    I'm james.

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    No! The cap goes in series with the output.

    Edit: not aimed at Firebottle
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  2. #12
    Join Date: Dec 2015

    Location: Alicante. Spain.

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    I'm Adrian.

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    Quote Originally Posted by Firebottle View Post
    Put it on 2000m and see what it reads.

    What did you use to adjust internally to zero?
    If it is showing 0.02 on the 200m range that is more than likely the expected error of the multimeter and is nothing to worry about.

    Though to put your mind fully to rest (we are all behind you in this) report what the 2000m range reads.
    Hang on....
    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
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  3. #13
    Join Date: Dec 2015

    Location: Alicante. Spain.

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    I'm Adrian.

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    Quote Originally Posted by farflungstar View Post
    Hang on....
    Ok - on 2000 both channels read the same - they fluctuate (maybe the probes) between 000 and -000.......

    Oh, there are small pots to adjust DC internally.
    Last edited by farflungstar; 03-05-2018 at 21:18.
    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

  4. #14
    Join Date: Apr 2012

    Location: London

    Posts: 370
    I'm james.

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    Sounds like the pre is behaving itself. Panic over

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  5. #15
    Join Date: Oct 2012

    Location: The Black Country

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    I'm Alan.

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    I concur, good to go Adrian

  6. #16
    Join Date: Oct 2016

    Location: Bolton, England

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    I'm Andrew.

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    Quote Originally Posted by Jazid View Post
    Sounds like the pre is behaving itself. Panic over
    Quote Originally Posted by Firebottle View Post
    I concur, good to go Adrian
    I would be more cautious. How did the amp get damaged in the first place? It's a very expensive repair to go through again. Why won't connecting and using the same equipment as before give the same results as before - ie a blown power amp?
    It would worry me.
    Maybe the fault wasn't caused by a DC offset from the pre-amp but by ultrasonic oscillation.
    I'm just advising caution, that's all.

  7. #17
    Join Date: Apr 2012

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    It might indeed! It would help to know what pre it is, otherwise we all go round in circles. Also do the Jfets occur after the input tube, or is it a driver? If the former I'd be inclined to look at the 6H30P tubes, in my experience they can misbehave if stressed.

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  8. #18
    Join Date: Dec 2015

    Location: Alicante. Spain.

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    I'm Adrian.

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    Quote Originally Posted by RothwellAudio View Post
    I would be more cautious. How did the amp get damaged in the first place? It's a very expensive repair to go through again. Why won't connecting and using the same equipment as before give the same results as before - ie a blown power amp?
    It would worry me.
    Maybe the fault wasn't caused by a DC offset from the pre-amp but by ultrasonic oscillation.
    I'm just advising caution, that's all.
    This is my worry. I really can't say for absolutely sure what caused it (the techie said it was DC at the input) - but what other equipment did it? The problem came up (or was very apparent) when I bought that ill fated CDP and connected it direct to the amp using its inbuilt volume. That was returned but I cannot be 100% sure it was the cause.

    I checked the DC at the outputs of the truth pre after the techie told me about the DC - one channel (at the 200m setting) was 00.2 the other 01.7 - but had I checked it at the 2000 setting I don't know what that would have been. For this reason I contacted the maker (who said it was negligible and not likely to cause any issue) and adjusted the input buffers and output buffers to 0 on both channels using the 200m setting on the meter. In theory there is no DC in the circuit except perhaps the anomoly of bad probe contacts on the outputs when measuring.

    The truth is never switched off and I never connect or disconnect stuff when things are switched on. The only components are the cart, Vida, hashimoto, truth, ref 75, Tannoys.

    Is there a possibility that the small input tubes in the 75 could have an effect? It was soak tested using them at the centre without a problem but I have a brand new set of power and signal tubes.

    It's silly but I still haven't switched the amp on - I just dare not.

    The truth has caused no problems with the Hiraga amp but of course it's a different animal to the ARC.
    Last edited by farflungstar; 04-05-2018 at 12:41.
    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

  9. #19
    Join Date: Aug 2008

    Location: Suffolk, UK

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    I'm Paul.

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    Can you advise your setup, is it the same as in your signature? It looks like your Truth phono amp is connected via the poweramp via a transformer based volume control/preamp? If this is the case any DC on the output of the Truth will effectively be blocked by the volume control as transformers do not pass DC. However, out of hearing band oscillation could be passed on to the poweramp.

    Many multimeters dont tend to be good at measuring at the frequency extremes but you could try measuring the Truth’s outputs with the lowest AC volts setting with and without the inputs grounded.
    ~Paul~

  10. #20
    Join Date: Dec 2015

    Location: Alicante. Spain.

    Posts: 1,700
    I'm Adrian.

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    It's simple - Vida phono stage into hashimoto sut into Truth ldr pre into amp - no transformers. Though now I wish I still had the old slagle autoformers....
    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

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