Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: chuggy on April 18, 2010, 06:15:43 pm
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My 5f6a clone has a voltage divider line out (2.2k/100k) that carries objectionable hum. The amp has minimal hum. Any suggestions for hum reduction?
Thanks-
Jim R
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My first guess would be that it is not caused by your amp.
I would tend to believe it may be your cabling between the DI and whst ever you are plugging it into.
other causes may be impedance miss match and ground loops.
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> miss match
I dated her once.
Actually what you want is a LOW impedance. But not so low that it drags on the source. What is the source? If it is a 4/8/16 ohm speaker feed, you could go down to 100 ohms total divider impedance without affecting the speaker. Then if 100K:2.2K was giving a good voltage, your new values could be 100:2.2 ohms. 2 ohms is an awkward value; also I suspect 100:2 or 50:1 is too steep a ratio for even a 5F6A. Try 220 ohms and 10 ohms. Or 2.2K and 100 ohms.
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Source is a 2 ohm output transformer.
Hum has persisted despite isolating the line out jack.
PRR et al- Why will the lower splitter resistor values suggested reduce hum?
Thanks-
Jim R
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Why will the lower splitter resistor values suggested reduce hum?
Hum is due to a current, and current time big resistors equals big hum voltage. If there is a somewhat small hum current and you're using large resistors, lowering them will unleash a lot more signal current and drown out the hum. It will seem smaller by comparison. Or seen another way, it will result in a smaller hum voltage across smaller resistors.