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Completed D3a Phono Stage

Posted by sganti (A) on August 16, 2009 at 16:36:38

Hi All
Just finished a D3a --> RIAA --> D3a phono stage. The D3a's are triode connected and all 4 D3a's share the following op point

Vp = 150V
Ip = 10mA
Vc = 1.8V
Rc = 180 Ohms

Stage-1 has a 10K plate resistor, and Stage-2 has a cascoded IXYS CCS for plate load.

I used Russian Silver Mica's in the RIAA, the coupling cap between stages is VH Audio teflon, and the o/p cap is VH Audio Oil cap.

The power supply uses 80 as the rectifier tube going into a LCLC 25H --> 100uF --> 7.5H --> 200uF going to CCS/ShuntReg combo. There is one Reg per stage. Each Shunt Reg has the o/p set to 250V/30mA -- 10mA per tube, and 10mA of Shunt current. Input to the shunt reg is 320V. There are big heatsinks on these beasts.

The chokes are Hashimoto, Caps are old Cerafine dual 100uF/500V I had lying around, and CCS/ShuntReg is designed by a good friend John Levrault. He helped designed the preamp circuit also.

Filament supply is with Schottky Bridge and is regulated with LM7806, which gives constant 6V o/p. There is one LM7806 per stage.

Fired up the preamp today after finishing it, first impression, it sounds pretty good, nice/wide soundstage, nice HF and Mids. I am going to let it burn in for a few days before doing some critical listening.

My existing setup is a Yamamoto phono/line-stage preamp CA-03L. with a Yamamoto Stepup SUT-03. I have a Shelter 501 Cartridge. Right off the bat, it sounds comparable to the yamamoto preamp, atleast that is a good sign :-). My linestage is a C3o based, and can be seen on the shelf behind the phono

The preamp has little hum, not bad considering my skills and that this is a phonostage.

ganti

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