Hi tube friends. I have question about how to tackle small hum problem in aer834 clone. Its ebay kit, works great, sounds sweet, but it has ~12 mV hum, looks like 60hz on output. I use 12 Vdc on heaters, well filtered. I use ~200 Vdc to power it, two sets of filters, each channel separate. When i touch the grouning connector, the one you use to ground the wire from turntable, hum is lower, but still there. I am only testing it with cheap sony ttable, no separate ground wire. Preamp is not in box, just on the floor. What should i try to eliminate hum?
Btw i built shure m-65 tube riaa preamp, ebay kit, and it works great, sounds great, no hiss, no hum, no box, just testing. No hum whatsoever.
Thank's for suggestions.
Btw i built shure m-65 tube riaa preamp, ebay kit, and it works great, sounds great, no hiss, no hum, no box, just testing. No hum whatsoever.
Thank's for suggestions.
I was able to get rid of the hum. I placed the tube preamp in sub-enclosure (from old tube preamp/headphone amp project) and grounded it to the preamps input. There is no hum now. I placed this in the bigger case (top cover from old receiver), which is another shielding, but its not grounded. Was not needed. I went overboard with filtration. Separate 12V dc wallwart with extra filtration. RCRCRC...on the high voltage power supply, separate for each channel. No hum no noise. Excellent sound.
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Seems that when the kit was "cloned", they left some loose ends. In my case, the solution to the strong hum was grounding each HR point (filament) through a 47 ohm 1 W resistor. It's also recommended to isolate the PS from the preamp, preferably in separate metal boxes. It gets more expensive, but an audiophile would spend another X dollars to get X/100 improvement...
This is the most important step to be able to say whether the hum is caused by inadequate shielding or by an issue with the power supply or its transformer.