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    Hum issue in PAS Aikido

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    mjock3

    Posts : 10
    Join date : 2013-05-14

    Hum issue in PAS Aikido

    Post by mjock3 on Fri May 17, 2013 5:43 pm

    Wondering if anyone could give me a hand in tracking down a low level hum in a recent PAS Aikido build? It does increase with volume. How do I go about tracking down the culprit?

    Thanks,
    Mark

    Bob Latino
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    Join date : 2008-11-26
    Location : Massachusetts

    Re: Hum issue in PAS Aikido

    Post by Bob Latino on Fri May 17, 2013 7:07 pm

    If you could post a photo of the wiring on the forum here, it might be helpful. In general, if the hum DOES (as you said) increase with volume it is probably NOT related to the power supply of your preamp. Have you tried different tubes on the board to see if the hum is tube related ?

    Bob

    mjock3

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    Join date : 2013-05-14

    Re: Hum issue in PAS Aikido

    Post by mjock3 on Fri May 17, 2013 7:31 pm

    I have not tried other tubes yet, I will try that on Monday. I will try to post pictures tomorrow.

    Thanks,

    Mark


    Last edited by mjock3 on Fri May 17, 2013 7:49 pm; edited 1 time in total (Reason for editing : change pics date)

    mjock3

    Posts : 10
    Join date : 2013-05-14

    Re: Hum issue in PAS Aikido

    Post by mjock3 on Sat May 18, 2013 1:01 am

    I think this will give you the pictures.


    Not sure why this isn't working.


    Last edited by mjock3 on Sat May 18, 2013 8:19 pm; edited 1 time in total

    tubes4hifi
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    Re: Hum issue in PAS Aikido

    Post by tubes4hifi on Sat May 18, 2013 8:04 pm

    email me a photo at info@tubes4hifi.com

    mjock3

    Posts : 10
    Join date : 2013-05-14

    have sent pictures

    Post by mjock3 on Sun May 19, 2013 12:12 am

    I have emailed the pictures.

    Side note the hum seems to vary in how loud it is. Sometimes relatively quiet then suddenly it increases for 10-20 minutes then gets relatively quiet again. Does that likely indicate a tube issue?

    Thanks,
    Mark

    peterh

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    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Hum issue in PAS Aikido

    Post by peterh on Sun May 19, 2013 3:10 am

    Are all covers installed and screwed ?

    mjock3

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    Join date : 2013-05-14

    Re: Hum issue in PAS Aikido

    Post by mjock3 on Sun May 19, 2013 12:55 pm

    Yes, all covers installed and screwed in place.

    tubes4hifi
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    Re: Hum issue in PAS Aikido

    Post by tubes4hifi on Sun May 19, 2013 2:03 pm

    from your note I would suspect bad tubes

    mjock3

    Posts : 10
    Join date : 2013-05-14

    Re: Hum issue in PAS Aikido

    Post by mjock3 on Tue May 21, 2013 4:41 pm

    Swapped all 12au7's and it is the same. Hum variable to what volume is and at times louder than other times.

    I have 7 days and still cannot post pictures.

    tubes4hifi
    Admin

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    Re: Hum issue in PAS Aikido

    Post by tubes4hifi on Fri May 24, 2013 12:33 pm

    did you try the filament mod that I sent you via email?

    mjock3

    Posts : 10
    Join date : 2013-05-14

    Re: Hum issue in PAS Aikido

    Post by mjock3 on Fri May 24, 2013 12:40 pm

    Yes I did. And it helped but did not get rid of it.

    mjock3

    Posts : 10
    Join date : 2013-05-14

    UpDate

    Post by mjock3 on Tue May 28, 2013 2:32 pm

    Someone suggested that I short the inputs to the preamp. In order to show it was the preamp or something else. I had disconnected them while working on this but that is not good enough. Shorting them stopped the hum. So evidently the hum is before the preamp.

    Mark

    mjock3

    Posts : 10
    Join date : 2013-05-14

    Update problem found and fixed

    Post by mjock3 on Wed Jun 12, 2013 4:09 pm

    I to do an update for the sake of others that may have a hum problem as well as for Roy's name sake.

    After doing the shorting of the inputs to eliminate the preamp from the equation, I came to find out at least part of the hum problem was caused by a CAPS 2 music server I had put together. When I unplugged the USB from music server to DAC  the hum stopped. After a period of time I narrowed it down a bit more. I had hooked up a digital antenna to the CAPS server for recording some TV. (That is a no no but I did it anyway) When I disconnected the antenna the hum decreased but was still there on a low level. So I came to find out there is an isolation transformer that is used for cable TV. I bought one and hooked it up and all hum is gone!!

    Hope this might help someone digging to find out how to solve a hum issue. Smile

    hificanada

    Posts : 6
    Join date : 2010-11-07

    had that same problem with a Heathkit AA-151, hum would increase when the volume is increased. You will find the problem using a Heathkit signal tracer, hovering the prob over the negative side of the electrolytic capacitors.

    Post by hificanada on Wed Jun 12, 2013 5:41 pm

    mjock3 wrote:I to do an update for the sake of others that may have a hum problem as well as for Roy's name sake.

    After doing the shorting of the inputs to eliminate the preamp from the equation, I came to find out at least part of the hum problem was caused by a CAPS 2 music server I had put together. When I unplugged the USB from music server to DAC  the hum stopped. After a period of time I narrowed it down a bit more. I had hooked up a digital antenna to the CAPS server for recording some TV. (That is a no no but I did it anyway) When I disconnected the antenna the hum decreased but was still there on a low level. So I came to find out there is an isolation transformer that is used for cable TV. I bought one and hooked it up and all hum is gone!!

    Hope this might help someone digging to find out how to solve a hum issue. Smile

    hificanada

    Posts : 6
    Join date : 2010-11-07

    Re: Hum issue in PAS Aikido

    Post by hificanada on Wed Jun 12, 2013 5:45 pm

    had that same problem with a Heathkit AA-151, hum would increase when the volume is increased. You will find the problem using a Heathkit signal tracer, hovering the prob over the negative side of the electrolytic capacitors.
    If you don't have a signal tracer, I would start grounding the negative side of the electrolytic capacitors to chassis ground, using heavy stranded wire like number 14 or 16 gauge wire. Solder one end of the 14 gauge to the negative side of the cap or it's grounding lug and and the other to ground on the chassis.
    If this unit was recapped by you or someone else that has replaced the cap cans with individual electrolytic capacitors, that is when hum will usually start to be a problem. I guarantee that this will solve your problem.
    Remember that the original cap cans have a very short distance to ground and they are usually grounded well and hum is not at all a problem.
     
    In some cases, adding other components increases the hum,is because the original path to ground in your amplifier is not good and the problem becomes much worse.
    Inline Issolation transformers are perfect when connecting a laptop audiocard to your amplifier which can cause severe hum, this will totally issolate both ccomponents and the hum will totally dissapear and is dead quite.

    mjock3

    Posts : 10
    Join date : 2013-05-14

    Re: Hum issue in PAS Aikido

    Post by mjock3 on Wed Jun 12, 2013 7:12 pm

    May I ask what model signal tracer you used? Just curious.

    hificanada

    Posts : 6
    Join date : 2010-11-07

    Re: Hum issue in PAS Aikido

    Post by hificanada on Thu Jun 13, 2013 2:53 am

    Heathkit IT-12.

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