Bipolars for low noise input - Alternatives to 2SC2240 - 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 6th February 2011, 09:52 AM   #11
diyAudio Member
 
Join Date: Jan 2011
Location: Shropshire
Quote:
Originally Posted by 5th element View Post
There's always the KSC1845/KSA992 from fairchild. These come in both through hole and SMD packages and are inexpensive too.
I just searched on these little fellas and can find nothing other than the Fairchild data sheet with very brief info and certainly nothing relating to rbb or noise.. Do you have a link to info?.
  Reply With Quote
Old 6th February 2011, 01:59 PM   #12
diyAudio Member
 
Join Date: Oct 2001
Location: Munich, Germany
Default Balanced zero impedance MC stage

This stage is 12 components, just 5 components more than the well known Hiraga LePrepre.

Of course, because of both floating inputs being on the same voltage level, one could dispense the trimmer. But I feel safer, when both inputs are really on 0.000V level, in case of the cartridge leads getting contact to ground.

This is my first sketch, and I will try to build it later in the evening. I consider replacing the output cap with a simple servo later.

HartmutIMG_7903_MCstage1.jpg

Last edited by hifidaddy; 6th February 2011 at 02:03 PM. Reason: expanding the notes, btw why does the pic disappear when editing ...
  Reply With Quote
Old 6th February 2011, 03:25 PM   #13
diyAudio Member
 
5th element's Avatar
 
Join Date: Oct 2002
Location: England
Quote:
Originally Posted by Blackjack8635 View Post
I just searched on these little fellas and can find nothing other than the Fairchild data sheet with very brief info and certainly nothing relating to rbb or noise.. Do you have a link to info?.
The noise specification is quoted on the first page of the data sheet. Only it's expressed as a voltage so would have to be evaluated with regards to a specific design, as the Toshiba figures are.
__________________
What the hell are you screamin' for? Every five minutes there's a bomb or somethin'! I'm leavin! bzzzz!
  Reply With Quote
Old 6th February 2011, 03:41 PM   #14
diyAudio Member
 
Workhorse's Avatar
 
Join Date: Dec 2004
Hi Hifidaddy,

My take is BC860/850C low noise pairs, they work best in my dynamic mic preamps.





Kanwar
  Reply With Quote
Old 6th February 2011, 04:03 PM   #15
diyAudio Member
 
Join Date: Jan 2011
Location: Shropshire
Quote:
Originally Posted by 5th element View Post
The noise specification is quoted on the first page of the data sheet. Only it's expressed as a voltage so would have to be evaluated with regards to a specific design, as the Toshiba figures are.
Thank you found it! I wasn't looking for mV's!


That will take a little while to calculate back, A bandwidth of 1KHz incorporating all the low frequency flicker. A source impedance of 100K and referenced to an 80dB gain. That won't be much of a guide to a MC phono amp with an Rg of 3 ohm.

On one sheet the operating parameters were missing!

NV Noise Voltage V
CE = -5.0V, IC = -1.0mA,
R
G =100KW, GV = 80dB,
f = 10Hz to 1.0KHz

25 mV typ. 40 mV max

  Reply With Quote
Old 6th February 2011, 05:32 PM   #16
diyAudio Member
 
Join Date: Sep 2004
Location: virginia
Could somebody explain the meaning of this noise specification? I don't understand it. Probably Rg is a source resistance of 100k, not 100kw. Is gv the voltage gain so you have to divide the specified noise level by the gain to reference it to the transistor input?
http://www.fairchildsemi.com/ds/KS/KSA992.pdf
  Reply With Quote
Old 6th February 2011, 06:11 PM   #17
diyAudio Member
 
Join Date: Jan 2011
Location: Shropshire
Quote:
Originally Posted by rayfutrell View Post
Could somebody explain the meaning of this noise specification? I don't understand it. Probably Rg is a source resistance of 100k, not 100kw. Is gv the voltage gain so you have to divide the specified noise level by the gain to reference it to the transistor input?
http://www.fairchildsemi.com/ds/KS/KSA992.pdf

My own interpretation is the same as your own, the datasheets are actually incompetently written. On the other one, the 1845, the test conditions are not mentioned.
It is very bad practice to use the data of a specific test in a data sheet. Data sheet info should be referred back to inputs and generalised into a useable format. But... Hey transistor manufacturers never ever bothered to do that.
  Reply With Quote
Old 6th February 2011, 08:58 PM   #18
MRupp is offline MRupp  Germany
diyAudio Member
 
MRupp's Avatar
 
Join Date: Dec 2003
Location: Frankfurt area
Hello Hartmut,

could you possibly elaborate on what exactly you dislike about the sound of these transistors? I have a bunch of 2SC2545E/2SA1085E that I have not tried yet but that I wanted to use in the future, so I am really curious.

From what I have seen in circuits so far they were usually biased at ca. 3-4mA, which is supposedly optimal from a noise perspective, so maybe if you parallel to fit your current needs? Also, did you play with load and voltage across the transistors? NP has an interesting article "The Sweet Spot" where he shows how much optimising the operating point effects distortion. Re. BJTs: "The reduction in distortion is less dramatic, but it's still about 7 or 8 dB better ...". So maybe a different operating point would help?

Btw. Sanyo 2SC3504/2SA1433 and 2SC3601/2SA1407 should have a similarly low Rbb. Syn08 posted some measurements some time ago (should still be in his WEB site).
__________________
Martin Rupp

Last edited by MRupp; 6th February 2011 at 09:14 PM.
  Reply With Quote
Old 6th February 2011, 09:45 PM   #19
diyAudio Member
 
Join Date: Jul 2001
Location: Orleans, France
Quote:
Originally Posted by rayfutrell View Post
Could somebody explain the meaning of this noise specification? I don't understand it. Probably Rg is a source resistance of 100k, not 100kw. Is gv the voltage gain so you have to divide the specified noise level by the gain to reference it to the transistor input?
http://www.fairchildsemi.com/ds/KS/KSA992.pdf

Yes, 100kohm. W is very frequent mistake for (omega) see :

http://www.datasheetcatalog.org/data...nec/2SA992.pdf
  Reply With Quote
Old 7th February 2011, 07:05 AM   #20
diyAudio Member
 
Join Date: Oct 2001
Location: Munich, Germany
Quote:
Originally Posted by MRupp View Post
Hello Hartmut,

could you possibly elaborate on what exactly you dislike about the sound of these transistors? I have a bunch of 2SC2545E/2SA1085E that I have not tried yet but that I wanted to use in the future, so I am really curious.

...
Martin,

I had tried them in discrete opamps, Mark Levinson style and the like, biased at 50uA to 125uA, but this was about 20 years ago. So my experiences don't apply to this case, where they are to be used at 3..6mA in a non-feedback configurtion.

BTW, the Swiss producer DNM uses exactly these transistors in their preamps.

Hartmut
  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
Low noise, low microphony, low hum valves MarcelvdG Tubes / Valves 38 28th January 2013 08:42 PM
Low noise transistor and noise figure Real_Macgyver Solid State 28 27th July 2012 09:42 AM
preamp supply LOW power LOW noise LOW cost drdagor Power Supplies 1 13th September 2010 11:39 PM
Low noise input? MikeW Pass Labs 11 21st September 2005 11:57 PM
Low noise, high voltage input trannies... Shaun Onverwacht Solid State 5 9th May 2001 05:36 AM


New To Site? Need Help?

All times are GMT. The time now is 09:10 AM.


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