Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 13th July 2013, 12:06 PM   #1
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
Default Preamp wanderings.

AS if i didnt have enought going on, I am starting this thread to play with preamp ideas. Here is the first. It use LTP input in order to try to avoid increasingly scarce reistors. THe y are 369's, but are easily bought in large quanitities. It is based on a mix of the Salas folded RIAA and the Pumpkin. Havent decided to keep final stage common drain or switch to buffer. WE will see.
Attached Images
File Type: png CM Preamp.png (125.7 KB, 505 views)
__________________
...Shape the sound , Man!
  Reply With Quote
Old 13th July 2013, 05:15 PM   #2
PKI is offline PKI  United States
diyAudio Member
 
PKI's Avatar
 
Join Date: Aug 2011
Is this mine? ;-)
  Reply With Quote
Old 13th July 2013, 07:10 PM   #3
DUG is offline DUG  Canada
diyAudio Member
 
Join Date: Jan 2003
Location: mississauga ontario canada
Could someone please post a schematic.

Figuring out what it is from a board layout is a bit of a pain.

IMHO

__________________
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
  Reply With Quote
Old 13th July 2013, 07:50 PM   #4
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
I will post the schematic later. I have a tendency to skip that and go straight for the pcb.
@PKI,
You can choose between this and complimentary version. Gonna be one late birthday present
__________________
...Shape the sound , Man!
  Reply With Quote
Old 13th July 2013, 11:59 PM   #5
DUG is offline DUG  Canada
diyAudio Member
 
Join Date: Jan 2003
Location: mississauga ontario canada
"...skip that..."

Sounds like an idea.

Thanks.

__________________
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
  Reply With Quote
Old 14th July 2013, 09:03 AM   #6
Itsmee is offline Itsmee  England
diyAudio Member
 
Itsmee's Avatar
 
Join Date: Feb 2009
Hi Buzz, I know you like playing with circuits, just as a suggestion, why not replace the cascode voltage referance with a TL431, that way you can adjust the voltage with a pot to find the 'sweet spot', you wouldn't need to match the LED's and you could save those JFETs for another project.

You could also replace the LEDs in the output stage with a transistor (or TL431) for an improved current sink, obviously you would then need to match the FETs but I suspect you would do that anyway for minimal differential offset; the LTP current sink would also need the same treatment.
  Reply With Quote
Old 14th July 2013, 10:32 AM   #7
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
All very good ideas. I have the luxury of knowing that these are good operating points as offered in other circuits, but you are right, it would give more freedom.
__________________
...Shape the sound , Man!
  Reply With Quote
Old 19th July 2013, 03:41 PM   #8
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
I need some help with folded cascodes. In a typical cascode circuit, the voltage seen by the gate of the cascode device sets the drain voltage of the gain device. In a folded cascode, the cascode device does not set the drain voltage of the gain device, which is now determines by either CCS or Rl. What purpose does the Vref on the cascode serve? What determines the output of the collector of the folded cascode. If not loaded by a resistor or transistor, isnt it functioning as a transimpedance amplifier.
__________________
...Shape the sound , Man!
  Reply With Quote
Old 19th July 2013, 03:50 PM   #9
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
Found what I thought was a good reference. It confirmed my suspicions.
The Shunt Cascode Driver | Bartola Valves
Will have an updated schemtic soon.
__________________
...Shape the sound , Man!
  Reply With Quote
Old 19th July 2013, 04:16 PM   #10
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
that one originated from our very DiyA , toob forum

it's already implemented in one veeeery secret (still in evaluation phase ) ZM's shebang

however , one need to not confuse it with modulated cascode hints from Pa
__________________
my Papa is smarter than your Nelson !
tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; Mighty ZM's Bloggg;I'm dumb ; Papatreasure
  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
Running a tube preamp into a solid state preamp? Pckid212 Solid State 5 6th January 2013 10:12 PM
Tube Preamp Popping on Source Input Change (?) / 6DJ8 Preamp On Chip Amps MartyM Tubes / Valves 3 16th October 2008 04:52 AM
Guitar Preamp = MIC Preamp = other preamp ,,are they all same? Paswa Solid State 1 12th March 2008 05:16 PM
twisted pear Preamp/other suggestions for Preamp kit LukeDuke Chip Amps 1 1st February 2008 09:57 PM
Electret mic preamp - will phono preamp work? darthmullet Analogue Source 6 12th October 2007 07:32 AM


New To Site? Need Help?

All times are GMT. The time now is 02:08 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