Hello,
I just wondering filament parallel capacitor act like high pass filter?
I added capacitor in ECC88 tube for reduce ripple voltage.
I thought:
Filament is also cathode.
Then filament parallel capacitor is same as cathode bypass capacitor.
Am i right?
I just wondering filament parallel capacitor act like high pass filter?
I added capacitor in ECC88 tube for reduce ripple voltage.
I thought:
Filament is also cathode.
Then filament parallel capacitor is same as cathode bypass capacitor.
Am i right?
In indirectly heated tubes as the ECC88 the heaters are isolated from the cathodes.
Best regards!
Best regards!
Thanks to your reply.
I added 220uF capacitor to ECC88's heater.
After that i get reduced bass.
What theory can explain this situation?
Unlikely, unless the capacitor changes the filament rms voltage.
This is schematic based on sijosae's Multi-Hybrid Headphone Amplifier(MHHA).
I modified that combine both LM317 CCS to achieve ECC88 heater current.
I added electrolytic capacitor 220uF to ECC88 heater in parallel.
Why is a current source connected from the audio output to the filament?
That can't be right.
I cant see how the 220uF could change the frequency response. Not in any other case either, but I was suspecting some bad construction or concept.
The current source is the load for the source follower (highish current, headphone amplifier), and they smartly use part of the dissipated power to heat the valve.
The current source is the load for the source follower (highish current, headphone amplifier), and they smartly use part of the dissipated power to heat the valve.
It just changed source follower's load by LM317 CCS + filament's resistance instead of resistor.
That's not problem.
I heard this from someone I knew at a local amplifier DIY club and tried the same thing, and got the same result.
He experienced the same bass reduction as I did in replicas of famous circuits.
In my circuit I assume the filament is the load of the source follower and I can understand that the capacitor can affect the frequency response, but in his circuit it doesn't make sense to power the heater with a constant voltage.
What PS voltage do you use (Vcc) ? 24V like in original is not enough with your component values. Need 48V at least ...
When circuits show unexpected behaviour change I always smell oscillation.
Mosfets can develop parasitic oscillation.
You need gate stopper: 1 kohm resistor soldered directky to gate pin as short as possible, no wire.
When circuits show unexpected behaviour change I always smell oscillation.
Mosfets can develop parasitic oscillation.
You need gate stopper: 1 kohm resistor soldered directky to gate pin as short as possible, no wire.
It can "work". There is precedent.
The Source Follower needs a heavy DC drain current. The tube needs a heavy current and DC is less hum. We find similar tricks on old Hi-Fi: cathode current of four 6V6 dumped to phono stage heaters. While it looks like feedback the thermal time-constant in the middle, sized to nix 60Hz hum, assures hardly-any audio effect.
I would expect a cap in that place to give an insignificant bass LIFT, not drop. But if this seems to reduce bass then take the cap out. I can't see it doing any good.
As Sorento says: MOSFETs oscillate, which can make unexplainable audio problems.
Thought it was just a preamp circuit, but this fad for low B+ voltage headphone amplifiers seems odd.
Why not a low power, single ended amp with a more normal HV, and a different output transformer design
optimized for 32R loads?
Why not a low power, single ended amp with a more normal HV, and a different output transformer design
optimized for 32R loads?
I saw this; but not until post #7.
"This is schematic based on sijosae's Multi-Hybrid Headphone Amplifier(MHHA)."
I've known sijosae's work for decades so I guess it was osmosis.
Many builders are afraid of transformers. Does not help that there are few good choices, most of these cost real money, and it is not clear which is best.
A side note: Heater current as provided by both paralleled CCS's is about 280 mA. The ECC88 needs to be fed with 365 mA, though. Hence, I'd replace it by a PCC88 (and both 9R1 resistors by 8R2 ones to get even closer to 300 mA).
I suspect the uneven frequency response might result from the LM317 properties as a not so good CCS in terms of AF performance.
Best regards!
I suspect the uneven frequency response might result from the LM317 properties as a not so good CCS in terms of AF performance.
Best regards!