His Master's Noise: A Thoroughly Modern Tube Phono Preamp - Page 10

21st April 2010, 12:00 PM
SY On Hiatus Join Date: Oct 2002 Location: Chicagoland	His Master's Noise: A Thoroughly Modern Tube Phono Preamp After more than 25 years of faithful service, it seemed that it might be time to redo my phono system. After all, I like to think that I've picked up a few tricks in the intervening years... The old system consisted of a VPI HW17-II, a Linn Ittok LVII tonearm, and a Troika cartridge. The Troika was... Click here to read the entire article Last edited by Variac; 2nd April 2011 at 12:17 AM.

19th December 2010

d to the g

wildburro audio

diyAudio Member

Quote:

Yes. It does make the sound more "high end," though.

Sounds dangerously close to a *gasp* tone control!

20th December 2010

jackinnj

diyAudio Member

I was reading the Sowter 8055 datasheet -- it's been changed a bit to include some recommendations for a Zobel. The Denon cartridge I use has a 40 ohm impedance, so I added 20 ohms to the output of my generator (it has 20 ohms output impedance). I used a 740pF variable cab and 2.4K resistor (in parallel with the 6.8K) to look at the input at the grid of the D3a. The 190pF +2.4K reduces the bandwidth 0.4dB @22kHz.

Why, silly hare, are you fleeing from the fierce jaws of the lion now grown tame?

23rd December 2010

jackinnj

diyAudio Member

here are some more charts -- i took a look at the frequency response with the zobel -- using a 40-740pF variable cap and 2.4k, and 3.18uS compensation:

and a comparison of the different D3a's I have -- the baseline is the preamp connected to the power line and analyzer, with no power. The 60Hz bump is =140DbV. Input was 400uV and 63dB gain.

Why, silly hare, are you fleeing from the fierce jaws of the lion now grown tame?

23rd December 2010

On Hiatus

Just curious- were the D3a burned in first? I had a lot of current noise with a few samples for the first several hours, but with time, the noise dropped considerably as the getter did its thing.

"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."

24th December 2010

jackinnj

diyAudio Member

Yes, they were all burned in. Only one tube is problematic as I see it. This pre is in its temporary house -- no umbilical connecting the power supply to the pre so things will improve when that bit of business is being attended to -- in the next couple of days.

My THD% measurements, with the 400Hz HPF are pretty consistently in the 0.03% to 0.04% range and the sound is just great!

Boards came in the other day but I can't solder one up until after Christmas.

Why, silly hare, are you fleeing from the fierce jaws of the lion now grown tame?

24th December 2010