You want coloration, at this supply voltage you will get it. But the output coupling cap is necessary. Then the tube's grid is centered voltagewise between + and - and you need no input coupling cap. Hook the anode of the tube to the + rail and the lower end of Rk to the - rail. You already have tried out that the 12AU7 works fine at 20V supply, so 30V will do better. So you want this cathode follower produce tube sound, tube coloration for you, right?Īssuming so, in contrary to my former recommendations i recommend to use low operating voltages, you can use your SS preamp's +/ supply of say +/15V (the higher the better, but 2x15 will do.) Slowlyslowly am realizing what you want to achieve (correct me if i am wrong).Īs i understood it, you want to feed a cathode follower by opamp or SS devices and this cathode follower feeds another opamp. Me being a tube person striving for freedom of coloration, i If there is too much voltage across the CCS, put it in series with a resistor. Then the tube and the CCS forms a voltage divider, each having about the same quiescent voltage across it and the whole assembly can swing easily to both sides with lots of headrooms. (For that you need the input coupling cap) Have the grid biased at a voltage that ensures that the tube has atleast, say, 150V, better 175 or 200 across it when no input signal is there. Have a constant current source as "load resistor" for your cathode follower and adjust it to exactly the current the tube is meant to run with. If you run this stage as an insulated additional linestage, you will need an input coupling cap and also an output coupling cap. It runs at 10.5 mA with 250V= supply and -8.5V bias at the grid. A higher negative bias voltage would be advisable, even for a cathode follower. You may want to have more headroom at the input. Of course it is a follower and will follow the input voltage, but for a very short period it will draw grid current if the signal swings too fast and too high. As the tube has high amplification (µ=100), its bias at this current is only -2V. The 12AX7 is meant to run at 1.2 mA with a plate supply of 250V=. OTOH, the 12AX7 is one of the best sounding tubes for gain stages, provided the input capacity doesn't hurt. But this tube is the last i would choose for that purpose. If you insist on using a ECC83 / 12AX7 for a cathode follwer, then please do it. A cathode follower has the highest local negative feedback possible.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |