Hi all, I was experiencing a very small amount of hum but only when certain 6SN7 tubes are in place, I read that if I placed 2 x 220uf capacitors as cathode bypass capacitors the hum would stop, which is has but it now seems that there is less bass and more clarity but it doesn't seem to matter what 6SN7 tube that I use they all sound the same, where as before they all had slight differences, could this be possible or is it my imagination.
Also my mate Mal hums too but I'm guessing there is nothing that we can do about that little problem.
Thanks in advance Ian
Also my mate Mal hums too but I'm guessing there is nothing that we can do about that little problem.
Thanks in advance Ian
A lot of people say the bypass capacitor becomes the dominant sound. Show a schematic?
FWIW I built a phono stage where some 12SN7 tubes were fine, but there were 4 Westinghouse tubes made in Japan that acted like a radio detector. I was hearing 99.9MHz FM through it! Nothing I did short of using different tubes solved it. It's since been scrapped, and the chassis turned into a power supply...
FWIW I built a phono stage where some 12SN7 tubes were fine, but there were 4 Westinghouse tubes made in Japan that acted like a radio detector. I was hearing 99.9MHz FM through it! Nothing I did short of using different tubes solved it. It's since been scrapped, and the chassis turned into a power supply...
Try using a different cathode load, like LEDs. They are lower impedance which makes them less susceptible to hum pickup, and they function like a bypassed resistor without that capacitor dominant sound.
Post up pictures of the layout, or maybe a schematic or description of the circuit, we might could help improve it in other ways to prevent hum.
Thanks, the hum really isn't bad and it's only certain tubes so if I remove the caps it doesn't matter, after all the most important thing is the sound and what's the point of tube rolling if they all sound the same, I will try the leds though.
My $0.03 guess is:
You have an unbypassed cathode on the 6SN7, and the tubes that are causing your higher level of hum have filament to cathode leakage.
An SRPP would be especially sensitive to such leakage.
A cathode follower that has a grid that is biased up in order to be able to have a large cathode voltage swing.
Just an unbypassed common cathode stage could also have hum caused by cathode to filament leakage.
In terms of fixing hum that is due to cathode to filament leakage, using LEDs from the cathode to ground of a common cathode stage, acts similar to a self bias resistor that has a large bypass capacitor across it.
If a particular tube causes hum, it may also have other problems (that will probably still be there even though you fix the hum on that 'bad' tube).
With out a schematic, it is like pointing a shotgun in the general direction, and hoping to hit something.
You have an unbypassed cathode on the 6SN7, and the tubes that are causing your higher level of hum have filament to cathode leakage.
An SRPP would be especially sensitive to such leakage.
A cathode follower that has a grid that is biased up in order to be able to have a large cathode voltage swing.
Just an unbypassed common cathode stage could also have hum caused by cathode to filament leakage.
In terms of fixing hum that is due to cathode to filament leakage, using LEDs from the cathode to ground of a common cathode stage, acts similar to a self bias resistor that has a large bypass capacitor across it.
If a particular tube causes hum, it may also have other problems (that will probably still be there even though you fix the hum on that 'bad' tube).
With out a schematic, it is like pointing a shotgun in the general direction, and hoping to hit something.
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Unfortunately it's not an amp that I built myself, it's the darkvoice 336se, so I don't have a schematic, it's definitely not my imagination that there is less bass so I will probably just remove the caps, the tube that has most hum is a sovtek one and I have better sounding tubes that don't produce any hum so I will just stick with those, in truth I only done it because lots of others said it makes the amp sound better but I truly disagree, serves me right for being sheep and following others, perhaps I'm wrong and my ears are broken.
If there is less bass with the bypass caps make them a larger value. I usually use 1000uf bipolar Nichicon audio caps. Here is a calculator. Judging by the values 220uf should be fine but without knowing exactly what the load of the 6080 grid as a DC coupled cathode follower I can only guess.
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B+ 300V is too high, 30uF is too low as output cap for headphones, attached schematic used for Senns HD600 300 ohms load. Design courtesy of Artosalo (Diyaudio member).
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Sorry, I was mixed up the Hartung amp is 300v but I'm not sure about the darkvoice as I didn't build it. Have you built and used the above amp merlin, if so could I see a picture please.
Harmonic distortion
Could anyone please tell me if there is a magic way to reduce harmonic distortion in a tube headphone amplifier.
Thanks in advance Ian
Could anyone please tell me if there is a magic way to reduce harmonic distortion in a tube headphone amplifier.
Thanks in advance Ian
Negative feedback, different operating point, different load, different, topology, different tube...
Depends on the amp in question really.
Depends on the amp in question really.
@Ian Mason - please do not start multiple threads on the same project/topic.
Headphone amplifier
Hi all, could someone please point me in the right direction for a schematic for a hi end headphone amplifier which is suitable for headphones of 250ohms or more, I would definitely prefer a tube amp if possible please and if anyone has built one could you show some photos please.
Once again thanks in advance Ian
Hi all, could someone please point me in the right direction for a schematic for a hi end headphone amplifier which is suitable for headphones of 250ohms or more, I would definitely prefer a tube amp if possible please and if anyone has built one could you show some photos please.
Once again thanks in advance Ian
