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Many vacuum tube phono preamplifiers are designed using the 12AX7 and the 6SL7. These are high gain tubes but high internal resistance so it is necessary to have 3 tubes on the signal path to reduce output impedance or use circuit topologies like SRPP (totem pole).
There are few tubes with high gain and low internal resistance like the pentode D3A. The D3A it is easy to find on the market and the performances in triode connection are fantastic. In my PF2007 and in my new cheap 2A3 PSE it is possible see some results.
|The sound of
this simple phone preampl. is incredible and I suggest it with
9580 Sowter MC transformer and DL103 Denon
cartridge.9580 1:12.5 High Z Cartridge
The 9580 is a very high performance transformer for use with cartridges with an impedance in the range 25 to 100 ohms. Bandwidth 5 Hz to 60 kHz. Suitable for Denon DL - 304 and DL - 103.
To calculate the RIAA network I have used the spreadsheet of Fabrizio Marignoni
The operation point of the D3A has been the result of many measurement with the Clio system by Audiomatica.
To get the max sonic performances has been used a slow turn on power supply for the filaments with a common LM317 and a virtual battery operation power supply for the anodic with a power mosfet.
For this power supply I have used the R-CORE model R26-90 by DiyClub.Biz with primaries 2 x 115v and seconaries 0-150v(0.2A) + 2 x 0-9v (1.1A).
A good capacitor must be connect on anodic voltage output, 100uF or 220uF Blackgate or Jensen electr. or ELNA Cerafine.
Some measurement with the Clio system by Audiomatica with 3mV input.