His Master's Noise: A Thoroughly Modern Tube Phono Preamp - Page 6

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.

22nd October 2010

jackinnj

diyAudio Member

I am taking the HMN to the New Jersey Audio Society meeting this Sunday -- along with several other RIAA pre-pre's.

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

22nd October 2010

luvdunhill

diyAudio Member

Thanks SY. Not my design, but I have played around with it a bit and like it. f you have a chance, move all those jumpers you can find (4) over to the other position, which will setup the amp for a WE connection.

Also, Doug is working on a new bias scheme:

There's more info here:

Prototypers wanted

23rd October 2010

jackinnj

diyAudio Member

Here's some measurements -- these are rough and dirty -- with 500uV 1kHz in the 2nd harmonic is down 62dB and the 3rd harmonic is down 95db. There are no other harmonics. Gain on one channel is 53dB, the other is 55dB.

the blister on my thumb disappeared -- I really hotted up the 1.8K resistors for a few moments.

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

23rd October 2010

Salas

diyAudio Chief Moderator

What is the noise floor level at 20,300,5000Hz?

23rd October 2010

jackinnj

diyAudio Member

Will measure more accurately in the morning -- I haven't used my good cables and it's out of the cabinet -- looks like 197uV @20Hz, 23uV@300Hz and 700nV@5kHz. These were with the front end shorted.

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

23rd October 2010

Salas

diyAudio Chief Moderator

Thanks. Better post a 20Hz-20KHz FFT 0dB=1VRMS, signal -10dB, when ready if you may. I wanna see something about the en we calculate for such trioded pentodes, the secondary's Rn, 1/f etc.

23rd October 2010

On Hiatus

Which ECC88s did you use? I found that to be the single biggest influence on distortion.

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

23rd October 2010

jackinnj

diyAudio Member

Here are two charts. Indeed the ECC88 plays the dominant role -- the ElectroHarmonix 2nd Harmonic is down 89 dB -- Also got the gain in both channels within a fraction of a dB -- had to resolder the trim resistors on the depletion MOSFETs. Further -- it is much quieter from an electrical noise standpoint at 7:00 in the morning.

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

23rd October 2010

Salas

diyAudio Chief Moderator

Thanks, enlightening. What is 0dB on the charts? 1V RMS or 0.3V RMS?

23rd October 2010

jackinnj

diyAudio Member

0dBV = 1V in this case.

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