Cascoded LTP input stages - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 7th March 2007, 09:14 AM   #1
diyAudio Member
 
Join Date: Jan 2004
Location: Lithuania Kaunas
Default Cascoded LTP input stages

Has anyone tryied to use it, instead of tradicional ltp, and which advantages this approach has.

I found interesting site and different and interesting input stage approches.

Input stage variants

Now in my power amp, I am using tradicional LTP, but I'm planning to try B example. But I' m concerned about CFP LTP stability.

Maybe someone has more experience . And is it worth cascoding ltp at all.
  Reply With Quote
Old 7th March 2007, 02:14 PM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
I would not call any of those variations cascodes.
They all appear to be complex transistor multiples.

None have the cascoding base/gate referenced to a fixed voltage.
__________________
regards Andrew T.
  Reply With Quote
Old 7th March 2007, 02:51 PM   #3
diyAudio Member
 
Join Date: Jan 2004
Location: Lithuania Kaunas
Default LPT-CFP Input Stage

Hi Andrew,

Thanks for correcting me. Sorry for mistake. I'm interested in LTP-CFP input stage. Is it better than a traditional diff. input stage and why. I used only tradicional diff. input stage in my amp with constant current source and current mirrors.
  Reply With Quote
Old 7th March 2007, 04:12 PM   #4
diyAudio Member
 
Join Date: Aug 2006
Location: Buenos Aires
Send a message via MSN to aguantesoda
hello! how is the functioning in "b" configuration?

*Hola! Como es el funcionamiento en la configuración "b"?
  Reply With Quote
Old 7th March 2007, 06:55 PM   #5
forr is offline forr  France
diyAudio Member
 
forr's Avatar
 
Join Date: Dec 2004
Location: Next door
AndrewT,
C and D are real cascodes, they could be called "cascode followers" (like John Linsley-Hood did) or "floating cascodes" : the bias voltage of the common grid is referenced to the base of the input transistor, it could also be to the emitter.
The aim is to maintain the Vcb and Vce voltage of this input transistor nearly constant, this is all the beauty of this kind of cascodes which is lost when using a fixed voltage referenced to 0V or power supply unless there is no emitter degeneration.
  Reply With Quote
Old 7th March 2007, 07:09 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi Forr,
thanks for the clarification.
I had seen similar but never thought of them as cascodes. They seemed too different from the classic cascode that I was used to.
__________________
regards Andrew T.
  Reply With Quote
Old 7th March 2007, 08:38 PM   #7
forr is offline forr  France
diyAudio Member
 
forr's Avatar
 
Join Date: Dec 2004
Location: Next door
Hi AndrewT,

I must a bit more clear about emitter degeneration : in the case of a LTP pair, as shown in the schematics (which come, I think, from Peufeu's site), the input transistors without emitter degeneration suffer from voltage variations if the common grid transistor has its grid bias referenced to a fixed voltage.
An often seen cascode scheme is bipolar transistors in common base used as outputs of the cascode circuit with their base voltage referenced to the tail of the input pair.
  Reply With Quote
Old 7th March 2007, 10:28 PM   #8
diyAudio Member
 
Join Date: Jan 2002
Location: Silicon Valley, CA, USA
Your figure C is a variant of the usual scheme, where the gates of the FETs are connected to the R7/R8 junction. Biasing the FETs from this point has the advantage of reduced input capacitance. Your scheme trades increased input capacitance (due to Miller effect) for constant Vce on the input bipolars.
  Reply With Quote
Old 8th March 2007, 02:49 AM   #9
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
more diff pair hacks in:

cross-quad and cascomp circuits


Quote:
Originally posted by jcx
http://db.audioasylum.com/cgi/m.mpl?...rophead&n=3169


http://www.analog.com/UploadedFiles/...917MAT04_d.pdf

(fig 6)


Hawksford also explored some related diff pair input linearization techniques

J4 DISTORTION CORRECTION CIRCUITS FOR AUDIO AMPLIFIERS, M.O.J. Hawksford, JAES, vol.29, no.7, 8, July/August 1981

At http://www.essex.ac.uk/ese/research/...lications.html

Somewhere you might also find Gilbert’s “multi-tanh” proposal

Its not clear that these techniques are necessary in audio amplifier design - high loop gain, emitter degen and bootstrapped cascode appear to be enough for super low distortion in audio amp inputs
do you really need to do better than ExtremA's input stage? (or the converse of the question - is the rest of your amp already better than this)
ExtremA, class-A strikes back?
  Reply With Quote
Old 10th April 2007, 09:09 AM   #10
thanh is offline thanh  Viet Nam
diyAudio Member
 
thanh's Avatar
 
Join Date: Jan 2004
Location: ho chi minh city
Send a message via Yahoo to thanh
Default CFP LTP

Hi !
If I can understand Sefl's book, CFP LTP is only good for analysing input stage. In the whole amp, CFP has no any improvement.

A good paragraph
"With the 1mA current chosen for the cfp stage the gain will be increasing with current, and this will add to the distortion from other sources of non-linearity. What we need is a device with either constant current gain at 1mA +/- 10% or even better a reducing gain with increased current so that other non-linearity can be partly cancelled. The best I found so far is the BC650 (or the higher voltage BC651) which has maximum d.c. current gain around 1mA, but unfortunately appears to no longer be available. Another alternative is the 2SC2911 which has an almost flat current gain from under 1mA up to 30mA, but this is a medium power device with lower gain"
(from http://www.angelfire.com/ab3/mjramp/ampdes1.html)

MikeB said that CFP boost gain--> compensate. Oh! I fear it
__________________
Justice for Victims of Agent Orange
http://www.petitiononline.com/AOVN/Thank all of you!
  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
Power amp input stages from National Calvin Solid State 1 14th July 2008 06:18 PM
Differences between this two kind of input stages??? Leolabs Solid State 6 2nd November 2007 02:08 PM
Input stages - to decouple B+ or not? andyjevans Tubes / Valves 1 9th March 2004 10:28 AM
Reduced rails for input stages. K-amps Pass Labs 4 10th February 2004 06:41 PM
Dual-differential input stages Jon T. Pass Labs 14 2nd October 2001 08:53 PM


New To Site? Need Help?

All times are GMT. The time now is 10:39 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