NFB for push pull guitar amp - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

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 23rd May 2011, 01:12 PM   #1
diyAudio Member
 
Join Date: Feb 2011
Default NFB for push pull guitar amp

Hello...

Could someone give me a run down of the advantages and disadvantages or having negative feedback on a push pull guitar power amp? What about sonic performance?

thanks a lot
  Reply With Quote
Old 23rd May 2011, 02:18 PM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Broadly speaking, global NFB reduces gain, distortion and output impedance. In a sound reproducer these are often seen as good things. For an instrument it all depends on what sound you want. NFB in a guitar amp can be used to turn low-order distortion into smaller amounts of high-order distortion, or to introduce frequency reponse anomalies. NFB will harden the effect of clipping, which may or may not be what you want.
  Reply With Quote
Old 23rd May 2011, 02:27 PM   #3
diyAudio Member
 
Join Date: Feb 2011
Thanks for the reply. To tell you the truth, i am not too sure what i want...I want an amp with character. Basically i would like to understand what i should expect from an amp with NFB and without (sonicwise) and then base my choice. that's mroe or less what you wrote. Would you have some references on the web i could look up about this matter? Specifically what NFB does to sound?
Also, could explain a little further what you mean harden the effect of clipping?

Thanks a lot
  Reply With Quote
Old 23rd May 2011, 02:49 PM   #4
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
There are others on here far more knowledgeable than I when it comes to guitars and their amps. I just listen to them; they play them.

When an amp with NFB begins to clip the NFB will push it further into clipping, so if you look at the waveform it has sharper edges and a flatter top. This means more high-order components, which sounds harder or harsher. However, below the clipping threshold the amp may sound cleaner.
  Reply With Quote
Old 24th May 2011, 10:45 AM   #5
Ian444 is offline Ian444  Australia
diyAudio Member
 
Join Date: Nov 2008
Location: Brisbane QLD
+1 what DF96 said.
More reading follow the link in the 2nd post:
The Amp Garage :: View topic - Negative feedback - How much?

If you want character, forget the NFB IMO, guitar amps have no need of it, don't know why they ever used it ever.

Like a clean guitar amp cannot be designed "clean enough" without NFB? What were they thinking????

Last edited by Ian444; 24th May 2011 at 10:48 AM.
  Reply With Quote
Old 24th May 2011, 11:52 AM   #6
Trout is offline Trout  United States
diyAudio Member
 
Trout's Avatar
 
Join Date: Nov 2004
Location: Midwest Madman
If you want an amp known for its character you might consider something like the 50's tweed Deluxe 5E3 circuit.

It has no NFB as well as being one of the simplest designs ever. Many variations have emerged over the years, but the original is one of the most loved amps to ever come along.
YMMV

Edit,
A lot has to do with your target tone. You will not get Marshall tones out of a tweed deluxe easily, but if you are wanting some very raw bluesy tone, its tough to top a well built 5E3.

Last edited by Trout; 24th May 2011 at 11:54 AM.
  Reply With Quote
Old 24th May 2011, 12:37 PM   #7
teemuk is offline teemuk  Finland
diyAudio Member
 
Join Date: Nov 2004
Location: Suomi, Finland
Quote:
Originally Posted by Ian444 View Post
If you want character, forget the NFB IMO, guitar amps have no need of it, don't know why they ever used it ever.
-cough- Fender Bassman -cough- all classic Marshall amps -cough- all classic Hiwatt amps -cough - Soldano SLO100 and the countless derivates of the design -cough, cough...


Negative feedback is a "tool" just like any other circuit topology. You can use it to increase headroom and linearity of both amplification and frequency response, naturally at the cost of overall "smoothness" of clipping. Some find those characteristics favourable and many, many classic designs are based on them. Not to mention you can introduce feedback -controlled tone shaping like resonance and presence controls, or in rarer cases a "damping" control that alters the magnitude of negative feedback.

Last edited by teemuk; 24th May 2011 at 12:43 PM.
  Reply With Quote
Old 24th May 2011, 01:04 PM   #8
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
High Gain Overdrive guitar amps use GNFB (in moderate amounts) to achieve rapid transition from clean to mean.

Combined with the feedback you get when the strings pick up the output of the amp, you get a low level trem effect to a greater extent with GNFB than without it as well as slightly more sustain.
  Reply With Quote
Old 24th May 2011, 01:15 PM   #9
Doz is offline Doz  United Kingdom
diyAudio Member
 
Doz's Avatar
 
Join Date: Jul 2010
Location: Sat Down
Why not make it variable? Then tweek to suit..
__________________
"To err is human.. to make a real balls-up requires a computer"
  Reply With Quote
Old 24th May 2011, 01:25 PM   #10
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
A guitar amp is a circuit where a user control knob for variable feedback may make sense.
  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
6v6 push pull guitar amp schematic sought guitar_joe Tubes / Valves 40 12th April 2013 06:26 AM
50c5 push-pull for guitar? freefallingegg Tubes / Valves 33 18th October 2010 09:27 PM
6V6GT push pull NFB resistor value jetbat Tubes / Valves 2 11th April 2009 07:06 PM
simple guitar push pull amp dan _s Tubes / Valves 8 12th August 2008 01:02 AM
Guitar amp, push pull dan _s Instruments and Amps 4 8th August 2008 09:26 AM


New To Site? Need Help?

All times are GMT. The time now is 03:05 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