Needed: input impedance of FET-VALVE preamp (built late 1993)

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KHashmi316

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    • Gamma Electronics
In order to adjust the capacitor values on my Toshiba CD player (see: http://johnswenson1.home.comcast.net/3950_mod/Toshiba_3950_3960_mod_intro.html) I need the input impedance value for a FET-VALVE preamp I purchased from AVA in late 1993.

Thx,
-KH
« Last Edit: 22 Oct 2006, 07:16 am by KHashmi316 »

avahifi

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The line level input impedance of all AVA preamplifiers is 47,000 ohms, set with precision resistors.  The phono input impedance is also 47,000 ohms, again set with precision resistors.  We suggest that adding capacitance to the input load is bad idea, as this will provide a difficult load for your source to drive.

Frank Van Alstine

KHashmi316

  • Jr. Member
  • Posts: 9
    • Gamma Electronics
We suggest that adding capacitance to the input load is bad idea, as this will provide a difficult load for your source to drive.

Frank Van Alstine

That's not what was suggested.

Please re-read the orig message carefully. Preamp-end capacitance is not being moded. Rather, the output of CD player and/or DAC is being tweaked .

Quoting from the article linked in the orig. message: "[One needs to add:] Two high quality coupling capacitors. The type and brand is up to you. Each system and person will do best with a different type. This is the most critical part of the mod so don't use the cheapest part available. But you don't need the $50 caps either. I used Vitamin Q caps, I like the sound in my system.

"If you are feeding a preamp with a 50k input impedance a 0.47uf cap works well. If you are feeding a 10k preamp use a 4uf cap. For in-between input impedances choose a cap somewhere between 4 and 0.47

"[One also needs to add:] Two 300pf [bypass] caps. High quality ceramic, silver mica or film will do. These caps cut down on residual high frequency noise from the DAC."