Mr. Marsh's neat MC preamplifier - Page 2 - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 15th March 2013, 11:58 PM   #11
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
The MPSA18 is a very poor choice as an example, you shouls at least pick a transitor intended for ultra-low noise operation like the MAT-02 or the THAT Corp equivalents.
__________________
Silence is so accurate.
  Reply With Quote
Old 16th March 2013, 07:06 PM   #12
diyAudio Member
 
Join Date: Sep 2004
Location: virginia
This 2N5087 spec sheet gives a better example of what I am suggesting. See figure 12 of En vs Ic.
http://www.fairchildsemi.com/ds/MM/MMBT5087.pdf

I think the calculated MPSA18 Rbb is about right. I have some measured data I will try to find. I recall that the MPSA18 Rbb was not very low for a supposed low noise transistor.
  Reply With Quote
Old 16th March 2013, 07:39 PM   #13
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
FWIW, there's an error in equation 5.11 of "The Sound of Silence" -- Boltzmann's constant should be squared in the first term.
  Reply With Quote
Old 17th March 2013, 01:56 AM   #14
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Here is a circuit that biases in input common base stage in a different way :
Patent US6069534 - Balance photo-receiver with complementary HBT common-base push pull pre ... - Google Patente
Here you can run the input transistors on more current then the base current of the second stage.
  Reply With Quote
Old 17th March 2013, 03:39 AM   #15
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Here is another way to set the input idle independently.
Attached Files
File Type: pdf Rosi.TSC - TINA.pdf (77.2 KB, 113 views)
  Reply With Quote
Old 17th March 2013, 12:10 PM   #16
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
Originally Posted by Joachim Gerhard View Post
I would run at least 5mA, better 10mA in the input stage and use low Rbb transistors.
This is just part of the equation -- summing square of kernel, current and thermal noise. So is there such a big difference between 5mA and 10mA?

Click the image to open in full size.
  Reply With Quote
Old 17th March 2013, 12:37 PM   #17
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
I have a cartridge with 4 Ohm impedance so yes, i say 10mA makes a difference.
It may not be big but even in your graph you can see the difference at lower impedances.
Is that 1 or 2dB ?
Also when you make an open loop phono stage the higher Gm on higher idle can be an advantage.
  Reply With Quote
Old 17th March 2013, 05:23 PM   #18
diyAudio Member
 
Join Date: Sep 2004
Location: virginia
I found the data on the MPSA18. It took awhile because I was looking for MPSA18 but the data is for both the 2N4101 and MPSA18 transistors. Apparently they are similar transistors. The measured Rbb is given as 900 Ohms.
  Reply With Quote
Old 17th March 2013, 05:26 PM   #19
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
and very close to
Quote:
same estimate of Rbb, 810 ohms
__________________
regards Andrew T.
  Reply With Quote
Old 17th March 2013, 07:15 PM   #20
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
Originally Posted by Joachim Gerhard View Post
I have a cartridge with 4 Ohm impedance so yes, i say 10mA makes a difference.
It may not be big but even in your graph you can see the difference at lower impedances.
Is that 1 or 2dB ?
Also when you make an open loop phono stage the higher Gm on higher idle can be an advantage.
If you optimize Noise with respect to I(collector) -- this visual should demonstrate how much there is (or is not) gained:

Click the image to open in full size.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
"...the best preamplifier ever made" says Mr. David Price, Hi-Fi- World tiefbassuebertr Analog Line Level 72 10th April 2013 07:50 PM
Musical Surroundings MM/MC Phonomena Phono Preamplifier kp93300 Analogue Source 0 11th October 2009 01:15 PM
HQ Balanced Phono Preamplifier for MC Cartridges using OPA2604 BiepBiep Analog Line Level 5 1st November 2008 05:27 AM
John Curl Mc Kinnie phono pre-preamplifier Antoni Rende Solid State 13 28th July 2008 10:54 PM


New To Site? Need Help?

All times are GMT. The time now is 05:04 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2