Amp Camp Amp Mod - Page 2 - diyAudio
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 21st March 2013, 12:37 AM   #11
diyAudio Member
 
Loudthud's Avatar
 
Join Date: Nov 2007
Location: Near Dallas Texas USA
Yes, Source current for Q4 comes through the 56 ohm feedback resistor. The voltage drop across that resistor gets hidden by the gate-source voltage of Q4 such that the gate and output are at zero volts. R9 has to be adjusted to null the output.
  Reply With Quote
Old 21st March 2013, 12:43 AM   #12
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
I like it, but wonder sbout the influence of the input. Ultimately it does give you more gain for feedback,which is important and helpful.
__________________
...Shape the sound , Man!
  Reply With Quote
Old 21st March 2013, 02:02 AM   #13
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
see buzz - again F5/F6/toob - like feedback

__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 21st March 2013, 02:13 AM   #14
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
Round and round we go.
__________________
...Shape the sound , Man!
  Reply With Quote
Old 21st July 2013, 09:48 PM   #15
diyAudio Member
 
VoltSecond's Avatar
 
Join Date: Mar 2004
Location: USA
Default Why no 10K between R5 and R7

I was browsing around and found this amplifier. I'm curious, Why no 10K between R5 and R7? It looks like the gain from Q3 is completely swamped out by the bypass cap. I only browsed ~30 of the 100+ pages of comments trying to see if this has already been answered. I'll look for a "summary site," off to do yard work!

I like the use of switching supplies for power. A small, damped common mode choke and a small bead on the power results in a very quiet supply. The only problem I've run into with switching supplies is oscillations under certain capacitive loads. This is usually fixable with a zobel (inductor in parallel with a resistor) in the series with the switching supply.
Attached Images
File Type: gif zen DIY AUDIO.GIF (178.5 KB, 583 views)
__________________
Unplug it, discharge it, and measure it (twice) before you touch it.
  Reply With Quote
Old 21st July 2013, 09:51 PM   #16
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
you can try it , and certainly expect different THD spectra , comparing to original

maybe you'll like it , maybe not
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 6th October 2013, 09:51 AM   #17
diyAudio Member
 
dragonweed's Avatar
 
Join Date: Sep 2010
Location: Hungary
Finally....I've tried the suggested 10kohm resistor mod between R5 and R7, the THD value dropped to almost half, but it effectively killed the "magic" of this amp, the speed, dynamics, and punch present with the original circuit is all gone.... So much about the differences between theory and practice. Nevertheless thanks for your suggestion. (I used a switch to bypass the 10k, so the comparision could be made almost immediately)
  Reply With Quote
Old 6th October 2013, 10:29 AM   #18
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
C2 is with reason connected to R7,R5 node - to modulate gate of upper mosfet

introducing resistor in between transforms mu-like operation to common CCS , ACA becoming ordinary SE amp
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 6th October 2013, 10:46 AM   #19
diyAudio Member
 
dragonweed's Avatar
 
Join Date: Sep 2010
Location: Hungary
Yes, I was aware of that fact from other Pass designs..... now I've replaced the 10k resistor with a pot, so you can "transit" between the two modes. For my ears the truth is somewhere midway of the two ends. The shorted version is a bit too "etched", while the 10k setting is too soft, loosing the dynamic impact in regular SE mode. Thanks again for the suggestion.... if you have any other ideas I am glad to try them, this is not my most "familiar" territory.

Last edited by dragonweed; 6th October 2013 at 10:48 AM.
  Reply With Quote
Old 7th October 2013, 12:38 AM   #20
diyAudio Member
 
Loudthud's Avatar
 
Join Date: Nov 2007
Location: Near Dallas Texas USA
Quote:
Originally Posted by Zen Mod View Post
introducing resistor in between transforms mu-like operation to common CCS , ACA becoming ordinary SE amp
It's not a constant current source because the output is tapped between R1 and R3.

Q3 regulates the voltage drop from the Drain of Q1 to the source of Q2, but when output current flows and thus changes the voltage drop across one of the resistors, Q3 tries to make a compensitory change to Q2's current to maintain the Q1 Drain to Q2 Source voltage. If Q1's current is increasing and going to the output, Q2's current will reduce. If the R1, R2 pair are the same value as the R3, R4 pair, the changes in current will be as close as the resistors dictate. Mu stage operation is preserved.

The problem is that R7 and the new resistor are too high resistance to get any bandwidth out of Q2. Try something like 470 of 1K. See the schematic I posted in the ACA thread, reply #149 Link: Amp Camp Amp - ACA

I posted that before I fully understood C2's role in modulating Q2's current.
  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
Amp Camp Amp - ACA flg Pass Labs 1825 26th August 2014 01:39 AM
Amp Camp Kit Jason The diyAudio Store 20 23rd July 2014 06:58 AM
Amp Camp Amp #1 A Pictorial Build Guide N Brock The diyAudio Store 1 28th September 2013 08:23 AM
WTB: Amp Camp Amp PCBs Nisbeth Swap Meet 2 25th December 2012 05:39 PM
Amp Camp! Jason Site Announcements 2 30th June 2012 02:57 PM


New To Site? Need Help?

All times are GMT. The time now is 12:07 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