Hi Frederico,
No post 28 I can understand. Actually, I was referring to post 26, where you show the output voltage (I missed the legends on the graph the first time). I was surprised at the big delta (-12dB) because with the 470uF ps cap one would expect only a very small delta, resulting from the less than perfect decoupling of the B+, although I know that tube ps's are generally worse than ss in this respect. But -12dB is what, a factor of 1/4 the 'normal' output. That's BIG! What is the signal level at the B+?
Jan Didden
No post 28 I can understand. Actually, I was referring to post 26, where you show the output voltage (I missed the legends on the graph the first time). I was surprised at the big delta (-12dB) because with the 470uF ps cap one would expect only a very small delta, resulting from the less than perfect decoupling of the B+, although I know that tube ps's are generally worse than ss in this respect. But -12dB is what, a factor of 1/4 the 'normal' output. That's BIG! What is the signal level at the B+?
Jan Didden
Hi Jan
-12db is the ratio between cir #1 and cir#2 noise (noise from PSU)
it is not an absolute value. When I augment the value of C2 ( and C5)
the noise decreases in both circuits but the ratio remains the same. It practically depends only on the gain of the tube.
That is, in cir #2 there is an injection of noise in the catode
The noise is amplified and appears at the anode about (1+A)
times the original. Part of this noise is cancelled by that coming
directly from B+ ( at top) since they are in phase. So the result
is a noise A time greater in cir #2 than in cir #1.
All this happens irrespective of the value of PSU cap.
At least, I think.
ciao
Federico
-12db is the ratio between cir #1 and cir#2 noise (noise from PSU)
it is not an absolute value. When I augment the value of C2 ( and C5)
the noise decreases in both circuits but the ratio remains the same. It practically depends only on the gain of the tube.
That is, in cir #2 there is an injection of noise in the catode
The noise is amplified and appears at the anode about (1+A)
times the original. Part of this noise is cancelled by that coming
directly from B+ ( at top) since they are in phase. So the result
is a noise A time greater in cir #2 than in cir #1.
All this happens irrespective of the value of PSU cap.
At least, I think.
ciao
Federico
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