The best preamplifier

[quanghao]

Hi All
This is a design I did in 5 years!
It has been many favorite friend. Especially in 2011 I have improved dramatically! To me this is my best pre tube using 6H30Pi or 6Dj8 ...
I opened the topic here, because this is the place to discuss all matters of Audio uses tube!

Sounds very realistic detail, balance!

[Luke]

Hello Quanghao,

whats the bias and why is the gain so high for a linestage? I thought you said somewhere it was less than unity gain?

[DF96]

Miller effect? It would need to be driven from a low impedance source, otherwise some HF cut is likely - it could sound smooth (i.e. inaccurate).

[SY]

Originally Posted by DF96

Miller effect? It would need to be driven from a low impedance source, otherwise some HF cut is likely - it could sound smooth (i.e. inaccurate).

Presumably, it will have a level control, which will allow the sound to change spectral balance at different volume settings.

[suntechnik]

Actually tubes input capacitance is less than most semi-insulators especially if talking about something like FE86 or KT88.

However personally I would prefer mu-followers for triodes like 6N6P -30P, 6DJ8

[quanghao]

Originally Posted by DF96

Miller effect? It would need to be driven from a low impedance source, otherwise some HF cut is likely - it could sound smooth (i.e. inaccurate).

Yes!
This cap Miller = 10pF!
Output impedance about 500R

[quanghao]

Originally Posted by Luke

Hello Quanghao,

whats the bias and why is the gain so high for a linestage? I thought you said somewhere it was less than unity gain?

+ B= 160V
One Tube = 17.5 mA
One channel need ~35mA

[SY]

Originally Posted by quanghao

Yes!
This cap Miller = 10pF!

How do you arrive at that number? From the datasheet values, one would expect about 12-15 times higher.

[quanghao]

Originally Posted by SY

How do you arrive at that number? From the datasheet values, one would expect about 12-15 times higher.

Hi!
By practical experience!
I practice many times and found that the best results!

[SY]

OK, so no measurement or calculation, just assertion from the seller.

Using a more conventional engineering approach, one should expect 120-150pF, maybe somewhat more, depending on strays from wiring (which can be considerable with four paralleled sections) and how optimistic the datasheets are.