Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

The Frugalamp by OS
The Frugalamp by OS
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 22nd November 2008, 02:48 AM   #141
andy_c is offline andy_c  United States
Banned
 
Join Date: Apr 2003
Looking much more like a single pole response now. Good stuff. Try right-clicking on the V(b)/V(a) expression at the top of the graph, and putting a minus sign in front of it in the expression editor dialog. Then click OK. Left-click on the -V(b)/V(a) expression. That will activate the measurement cursor. Move it until you find the frequency at which the magnitude is as close to 0 dB as possible. What is this frequency? And what is the phase shift at that frequency?
  Reply With Quote
Old 22nd November 2008, 02:53 AM   #142
ostripper is offline ostripper  United States
diyAudio Member
 
ostripper's Avatar
 
Join Date: May 2008
Location: Smoky Mountains , Tennessee
Andy, freq. is 344khz , and phase is -96dB.
  Reply With Quote
Old 22nd November 2008, 02:55 AM   #143
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
ostripper
just one little detail: R3 10k in long tail pair
BC546 can take 60 Volt, so you need no such resistor.
It does not do any good.
Probably does things a bit worse

As Douglas Self tells us:
Quote:
Originally posted by DouglasSelf
http://www.siliconchip.com.au/cms/A_110797/article.html
is a copy of the Blameless design,
carefully including a mistake I made.
(putting a resistor in the input tail - bad move)
Attached Images
File Type: jpg d_self_mistake.jpg (17.3 KB, 526 views)
__________________
lineup
  Reply With Quote
Old 22nd November 2008, 03:01 AM   #144
ostripper is offline ostripper  United States
diyAudio Member
 
ostripper's Avatar
 
Join Date: May 2008
Location: Smoky Mountains , Tennessee
Line up, there are 50 volts across R3, even when I reduce it to
8.2 k I get 4+ma in each differential , so removing it would
fry my LTP.!!!

I see your point, as you would have to modify the CCS to
take the place of R3...
  Reply With Quote
Old 22nd November 2008, 03:06 AM   #145
andy_c is offline andy_c  United States
Banned
 
Join Date: Apr 2003
Quote:
Originally posted by ostripper
Andy, freq. is 344khz , and phase is -96dB.
Looks like the amp is a bit overcompensated.

Try finding the frequency at which the phase shift of the loop gain is -100 deg. This will be a frequency larger than 344 kHz. That's what you want to be your new unity loop gain frequency. To increase the unity loop gain frequency, you can decrease the input stage emitter degeneration. Try decreasing it in the same ratio that you're increasing the unity loop gain frequency. That is, if the new unity loop gain frequency is e.g. 500 kHz, the new input stage emitter degeneration resistor should be 344/500 times the old one. Replace 500 by the actual frequency in kHz at which the phase of the loop gain is -100 deg.
  Reply With Quote
Old 22nd November 2008, 03:09 AM   #146
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
50 volts, so what

the ccs transistor (BC546) can take 60 volt,
so taking 50 volts from R3 and let BC546 have it
is no problem

And if you need higher, you can use 2N5551 (160 Volt C-E) or some other
for constant current source transistor
__________________
lineup
  Reply With Quote
Old 22nd November 2008, 03:12 AM   #147
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
To change CCS current in input you use R8, 220 Ohm

Increase R8 will lower current in LTP
Decrease R8 will give higher current in LTP

get away with R3, as D.Self says: it was a mistake (bad move)
__________________
lineup
  Reply With Quote
Old 22nd November 2008, 03:19 AM   #148
ostripper is offline ostripper  United States
diyAudio Member
 
ostripper's Avatar
 
Join Date: May 2008
Location: Smoky Mountains , Tennessee
Hey, this is fun...At unity gain freq. is 536khz and phase is
EXACTLY -100.39db.. good guess.
  Reply With Quote
Old 22nd November 2008, 03:23 AM   #149
andy_c is offline andy_c  United States
Banned
 
Join Date: Apr 2003
I'm confused. At 536 kHz, the gain should be less than 0 dB right? Which means you'd like to decrease the emitter resistors in the input stage to get it back to 0 dB there. Or did you already tweak the input stage emitter degeneration?
  Reply With Quote
Old 22nd November 2008, 03:32 AM   #150
ostripper is offline ostripper  United States
diyAudio Member
 
ostripper's Avatar
 
Join Date: May 2008
Location: Smoky Mountains , Tennessee
Quote:
By lineup - To change CCS current in input you use R8, 220 Ohm
Mr. self has said other things ,too but do we always listen to him?? he said a balanced VAS was too much trouble, but I'm
not listening.

One thing at a time. your idea is good but the load on my LPT
is in the uA's (EF'ed VAS's)balanced as well. With a different amp, like frugal 1, I will try this.

BTW , I figured out how to import .models and made my own
LTspice libraries (custom)..thanks
OS
  Reply With Quote

Reply


The Frugalamp by OSHide 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

Forum Jump


New To Site? Need Help?

All times are GMT. The time now is 09:00 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki