Simplistic NJFET RIAA - Page 791 - 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 27th August 2012, 09:08 AM   #7901
diyAudio Member
 
merlin el mago's Avatar
 
Join Date: Sep 2009
Location: Catalonia - Europe
Quote:
Originally Posted by Salas View Post
Its an experiment I don't recommend it before I test it. Certainly fits best to low MC carts. There can be Jxxx subs for the European BF although noisier, but BF are everywhere. K369 give benefits in the 1/F region and for wide-band 2 are like using 4 K170s. But it can be tried with same IDSS K170s too. Q5 can be used or not to taste. Without Q5, C2 should be 15nF due to more Miller.
Quote:
Originally Posted by Salas View Post
Ok, here it is for classic 4XK170BL. You may relax the matching for the quads since they are degenerated enough to share current at ~0.75*IDSS and the total transconductance (~130mS) will be steady for 7.5-9mA samples at shared ID. But make sure that the sum total of the quads IDSS between channels is nearly the same. So the folded cascodes will be sparing the same drive current to R16 and same gain. No loop feedback here to match the gain if not thorough with JFETs picking in both stages. It should present ~15 Ohm input equivalent noise resistance, not bad. And some better input headroom, adequate for normal MC also. Pick a ~5mA BF245A for Q8 and circa 15mA BF245C for Q5.
Latest design share the possibility to use or note of Q5 & C2 15nF?
  Reply With Quote
Old 27th August 2012, 09:59 AM   #7902
RCruz is online now RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
Quote:
Originally Posted by merlin el mago View Post
Latest design share the possibility to use or note of Q5 & C2 15nF?
Hi Merlin

Using Q5, you reduce miller on second stage so you might need to add some capacitance to C2 (use 16n instead of 15n).

If you do not cascode second stage, use "normal" C2 values.
__________________
RC
  Reply With Quote
Old 27th August 2012, 11:30 AM   #7903
lohk is offline lohk  Europe
diyAudio Member
 
lohk's Avatar
 
Join Date: Apr 2001
Location: Northern Noricum, near the Limes
This is very long thread now, indeed, and very interesting, but not easy to read it all again.
Besides of the missing symmetrical input your preamp should be useful as a high gain/low impedance microphone preamp, isn't it?
If I let out the RIAA network, do I have to leave a resistor between the stages?
__________________
/lohk/
  Reply With Quote
Old 27th August 2012, 12:38 PM   #7904
diyAudio Member
 
merlin el mago's Avatar
 
Join Date: Sep 2009
Location: Catalonia - Europe
Quote:
Originally Posted by RCruz View Post
Hi Merlin

Using Q5, you reduce miller on second stage so you might need to add some capacitance to C2 (use 16n instead of 15n).

If you do not cascode second stage, use "normal" C2 values.
Thanks Ricardo, so it's the same like with 369s
  Reply With Quote
Old 27th August 2012, 01:33 PM   #7905
RCruz is online now RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
Yes
__________________
RC
  Reply With Quote
Old 27th August 2012, 04:45 PM   #7906
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Quote:
Originally Posted by lohk View Post
This is very long thread now, indeed, and very interesting, but not easy to read it all again.
Besides of the missing symmetrical input your preamp should be useful as a high gain/low impedance microphone preamp, isn't it?
If I let out the RIAA network, do I have to leave a resistor between the stages?
It has been used for NAB curve open reel head amplification once but not for microphone. Provide the input level, source impedance and gain needs so we can evaluate if and how it can fit that purpose.
  Reply With Quote
Old 27th August 2012, 04:47 PM   #7907
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Quote:
Originally Posted by RCruz View Post
As load resistor is refered to GND, this means current flows inversely in Q3.

Output impedance of first stage is 2k2r right ?
Yes.
  Reply With Quote
Old 27th August 2012, 08:18 PM   #7908
RCruz is online now RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
I will start to work on it
__________________
RC
  Reply With Quote
Old 27th August 2012, 09:14 PM   #7909
lohk is offline lohk  Europe
diyAudio Member
 
lohk's Avatar
 
Join Date: Apr 2001
Location: Northern Noricum, near the Limes
Quote:
Originally Posted by Salas View Post
It has been used for NAB curve open reel head amplification once but not for microphone. Provide the input level, source impedance and gain needs so we can evaluate if and how it can fit that purpose.
Microphones are very different in out level and impedance, but generally have about 100Ohm source impedance upwards, usually around 200 Ohms. Because level and sound pressure changes the gain needed varies from 50-60db to -say- 20-30db. Real life dynamics exceed the dynamics we know from music productions by far, so the headroom should be very high or the distortion characteristics smooth.

Usually mic preamps have either differential amps as inputs or transformers, also because they are usually balanced.
__________________
/lohk/
  Reply With Quote
Old 27th August 2012, 11:10 PM   #7910
diyAudio Member
 
Bksabath's Avatar
 
Join Date: Dec 2007
Have a look at FDW Balanced Phono stage
I got that on the bench at present
Or you can try INA stile made up with LT1038
30dB gain is easy and not much problem with Jhonson noise
Balanced input all DC coupled RIAA preamp
  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



New To Site? Need Help?

All times are GMT. The time now is 06:45 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