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Dynaco ST-70 amp and Klipsch KLF-20 - buzzing sound


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Hi all,

I recently acquired the Dynaco ST-70 set, which was serviced,
power plugs replaced to new, capacitors renewed in preamp.
Amp showed suberb graph on spectrum analizer.
There are original Western Germany made tubes.
(Didn't looks at what exact model number yet).

When I connected it to old speakers Sansui x6700 it worked perfectly
(Sensitivity about 94-96).

After connecting amp with Klipsch KLF-20 with sensitivity 100,
there started constant 'zzzzzzzzzzz' sound.
Like ground sound or I felt it was like sound from tubes buzzing.
Overal sounds amazing, but hum sound is pretty big.

Wondering what it might be and how to fix it.
Do you have any ideas or advices?

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Could be a few different things. First thing I would look into would be a ground issue. If the power cable was replaced with a three prong grounded cable try a three prong to two prong adapter at the wall power outlet, this should help if you have a ground loop going on.

Do you know what the extent of the amp serviceing consisted of? If the filter supply caps were not replaced there is a good chance that is were the noise is coming from and these would need to be replaced.

Good Luck

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No way to know if any of the conditioners you listed will work for you or not without actually trying them in your system.

You need to figure out which item is causing the ground loop and then take care of it at the source, lots of times it will be cable T.V. (dissconnect the cable and see if the hum goes away) could also be your CD player, turntable, etc. If you end up having to use a Ground Isolator Transformer make sure you buy a good one, the cheaper ones will lower frequency response resulting in poor sound.

Here's good article on ground loop problems: http://www.audioholics.com/tweaks/connecting-your-system/ground-loops-eliminating-system-hum-and-buzz

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It might not be a ground loop, but emi/rfi... If you describe it more as a buzz and not a hum, it sounds like 120Hz, the harmonic of your 60Hz line freq. This could be easily be caused by a light dimmer, or other appliance. Fluorescent lights are another possiblity. A line conditioner may help, nonetheless.

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I have the same AMP and since It started buzzing I top shelved it, just like a broken "Woody" w/ a torn arm. Since then I have yet to find a repair service or educate myself to take on the role of EEE. Are there recommended business that refurb/refreshes tube amps? I'd ship but the Northeast is the area I live in..



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