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    PRE-AMP HUM

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    RMG

    Posts : 16
    Join date : 2010-06-13

    PRE-AMP HUM

    Post by RMG on Sun Jun 13, 2010 8:29 am

    Hello all. I know this topic has been discussed somewhat but I have no resolution. I have a ST70 that is totally quiet with the inputs shorted. There is a hum with the inputs not shorted. When using a PAS3 as a preamp the ST70 is quiet. However when I tried to use a Mcintosh MX112 as my preamp I get the same hum from the ST70 as if the inputs were not shorted. I have tried using a two prong AC adapter and the hum is diminished but still present. Any ideas? Thanks.

    Bob Latino
    Admin

    Posts : 2414
    Join date : 2008-11-26
    Location : Massachusetts

    Re: PRE-AMP HUM

    Post by Bob Latino on Sun Jun 13, 2010 10:12 am

    RMG wrote:Hello all. I know this topic has been discussed somewhat but I have no resolution. I have a ST70 that is totally quiet with the inputs shorted. There is a hum with the inputs not shorted. When using a PAS3 as a preamp the ST70 is quiet. However when I tried to use a Mcintosh MX112 as my preamp I get the same hum from the ST70 as if the inputs were not shorted. I have tried using a two prong AC adapter and the hum is diminished but still present. Any ideas? Thanks.

    Hi,

    Are you absolutely sure that your McIntosh MX112 does not have a hum issue ? Have you used the MX112 with another amp to verify that this tuner/preamp is hum free?

    Bob

    RMG

    Posts : 16
    Join date : 2010-06-13

    Re: PRE-AMP HUM

    Post by RMG on Sun Jun 13, 2010 1:08 pm

    I haven't but I think it may have just been a coincindce. I now have a hum in just the left channel. I'll have to check my tubes. Thanks for the quick reply Bob.

    Bob Latino
    Admin

    Posts : 2414
    Join date : 2008-11-26
    Location : Massachusetts

    Re: PRE-AMP HUM

    Post by Bob Latino on Sun Jun 13, 2010 1:42 pm

    RMG wrote:I haven't but I think it may have just been a coincindce. I now have a hum in just the left channel. I'll have to check my tubes. Thanks for the quick reply Bob.

    The general rule (and you have mentioned above that you have already done this) is that if your Dynaco ST-70 does not hum with the inputs shorted then the amp is exonerated as a source of the hum. Check out your MX112 with another amp to see if it hums with an amp other than your ST-70.

    Bob

    RMG

    Posts : 16
    Join date : 2010-06-13

    Re: PRE-AMP HUM

    Post by RMG on Sun Jun 13, 2010 2:40 pm

    Thanks Bob.

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