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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Re: How do you make a VERY GOOD passive pre posted by AlanC on May 17, 1999 at 19:01:23:
Hi there,>>>>Could you go into more detail on the "simple" Valve Buffer-Stage? <<<<
I can.
I use a single section of a 5687 per Channel. This is biased via a 3V Lithum Battery in the Grid having a 470k Resistor the Grid. There is a ferrite Bead on the Grid-pin of the Valve Socket.
To block the DC on the Input I use a 0.1uF Film & Foil (I use Arcotronics - Hoveland or REL will do nicely).
The Cathode is connected directly to ground, the Anode has a 10k Resistor.
Output Cap according to your taste, 2.2uF minimum (this can be paper/Oil, Film/Foil or whatever you like - this Cap makes the "sound").
The Circuit has a 50uF decoupling Film-Cap (Solen or SCR or Ansar) in the Anode Circuit and needs a well filtered DC (I use a special Regulator Circuit).
Heaters are DC using a Constant Current Source connected LM317T. The negative side of the Heater is grounded....
That's it. Gain is about 18db and Input Impedance is about 470k...
Output Impedance is like a 10k passive Pre....
Later Thorsten
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Follow Ups
- Re: How do you make a VERY GOOD passive pre - Thorsten 05:11:16 05/18/99 (1)
- Since when does +18 db = passive ??? (NT) - Sean 21:57:49 05/21/99 (0)
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