0
\$\begingroup\$

I am building a tube headphone amplifier. I built a AC/DC regulated power supply (220v AC to ~250v DC) but I am not sure about how good is the filter. The filter contains 120uF and 68UF capacitors, in between them there is a 0.4mH inductor. (170uF in total)

But it seems that most schematics use absurd filters - 10H inductors or really big capacitance caps. (1000uF)

Would my filter be good enough for high-end tube headphone amp or do I need to improve it with bigger capacitors?

What results would you get by using 'bad' filters? (More hum, more noise, short tube life..)

\$\endgroup\$
  • \$\begingroup\$ If your filter is inadequate, there will be an audible hum in your headphones. There is no way to predict if you will hear the hum from the little information that you provided. The hum will be the result of ripple, and the amount of ripple will depend on the amount of current the amp draws. How audible the hum will be will also depend on the gain of the amp. \$\endgroup\$ – Mark Jun 14 '16 at 23:43
  • \$\begingroup\$ How did you choose the values you used in your filter? \$\endgroup\$ – uint128_t Jun 15 '16 at 0:42
  • \$\begingroup\$ 1000uF is not 'really big' in solid-state. Most SS preamps use PSU capacitors at least this size. However it is big in vacuum tube circuits. \$\endgroup\$ – user207421 Jun 15 '16 at 0:56
  • 1
    \$\begingroup\$ It depends on the schematic you are using. Some topologies are immune to voltage ripple, some are very sensitive to it. \$\endgroup\$ – greg Jun 15 '16 at 9:07
  • \$\begingroup\$ The inductor is small enough that it might as well not be there (though it won't hurt anything)... if you hear a little hum, then you need to increase the capacitance; if you hear a lot, then you need to consider a regulated supply. \$\endgroup\$ – Brian Drummond Jun 15 '16 at 11:34
1
\$\begingroup\$

The result of inadequate B+ filtering will be injecting hum into the audio path. I would not expect any symptoms like noise (other than hum which is a type of noise) or reduced tube life.

You need adequate filtering to remove (at least >70-80 dB down) hum from the signal path. Dunno exactly what is the definition of "high-end tube amp"? That seems rather subjective and "audiophoolish".

Yes you will see all sorts of over-built circuits which are designed on the notion that "more is better" regardless of any engineering principles or any actual measured or perceived performance benefit. The name for this kind of silly behavior is "audiophoolishness".

\$\endgroup\$
0
\$\begingroup\$

I used to work on tube equipment, TV's and some amplifiers. I build my first tube amplifier (20 watts) when I was in high school. The capacitance you are using is typical of what I had seen. Hum is the most common problem with inadequate power supply filters. The early tube radios used a very large inductor in the speaker as an electromagnet, mid-1940s (Many years before I was...) prior to high powered Alnico magnets. More than likely you will get filament or shielding hum. There are tube hum balancing circuit diagrams on the internet if you have a problem with hum. The hum balancing circuits mostly worked with the filament voltages.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.