What about adding a slight "presence" boost RC network fixed in the amplifier. - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 28th November 2016, 06:52 AM   #1
ygg-it is offline ygg-it  Italy
diyAudio Member
 
ygg-it's Avatar
 
Join Date: Feb 2008
Default What about adding a slight "presence" boost RC network fixed in the amplifier.

According to vintage guitar schematics I have added a "presence filer" to my amplifier for music that alters the response of the amp by boosting of 0.5dB the high frequency range (2~10 KHz). The result is a brighter sound with greater clarity and "presence".

It is implemented as a low pass filter inside the global negative feedback loop and is simply an RC network at the cathode of the triode (15nF + 8.2KOhm with pole at 1.3KHz).

At the beginning I thought to use a switch to exclude it if necessary, but at the end the sound was so amazing (overall with voices) that I leave it fixed forever.

I know to break in this way the most important rule of an hi-fi machine (i.e. having a flat response), so let me know what you think about this unusual choice.
Attached Images
File Type: jpg presence white noise.jpg (190.0 KB, 169 views)
File Type: jpg presence.jpg (29.2 KB, 167 views)
File Type: jpg presencecurve.jpg (176.5 KB, 166 views)
  Reply With Quote
Old 28th November 2016, 07:09 AM   #2
diyAudio Member
 
Join Date: Jul 2015
Location: gothenburg,sweden
Braun ( german hifi brand from the 70 ) did this, they had a switch marked "presens" that
elevated mid frequencys. I know i had several, and the abstinence when i finally abandomed
braun was there :-)
Have a search for CSV 13 amp and identify the "presense" switch.
__________________
My home is at www.tubular-well.se
  Reply With Quote
Old 28th November 2016, 07:53 AM   #3
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
My experience with tone controls is that I can not hear 0,5 dB difference and I am quite sure I am not the only one.
I can detect the difference in tone when treble (Baxandall type) is adjusted to some 2...3 dB.

How did you ended up to 0,5 dB ? Is 1 dB too presence ?
  Reply With Quote
Old 28th November 2016, 08:39 AM   #4
ygg-it is offline ygg-it  Italy
diyAudio Member
 
ygg-it's Avatar
 
Join Date: Feb 2008
Quote:
Originally Posted by artosalo View Post
My experience with tone controls is that I can not hear 0,5 dB difference and I am quite sure I am not the only one.
I can detect the difference in tone when treble (Baxandall type) is adjusted to some 2...3 dB.

How did you ended up to 0,5 dB ? Is 1 dB too presence ?

Hello, the +0.5dB means boost 5-6% the upper mid-range and this is both visible in the simulation and White Noise measurement even if it is very light.

There are two reasons why I choose this:

1) I didn't want to break too much the hi-fi rule to have a "flat response"

2) I tried by "ear" several combination of RC components for several hours and that was the best trade-off between airy-realistic sound and have a metallic, too much bright sound. As soon I experienced synthetic, grainy, or dry character I stopped.

As I told before this is a fixed RC filter: if I put a rotary switch, of course I would have enlarged the range by few decibels as you said.

I found a lot of commercial amplifier with presence switch but never one with a fixed RC one.
  Reply With Quote
Old 28th November 2016, 02:37 PM   #5
EmRR is offline EmRR  United States
diyAudio Member
 
Join Date: Mar 2016
Location: NC, USA
A half dB step can frequently be a huge step in a recording studio situation, quite audible. The basic circuit you show is very common in vintage broadcast/recording gear as transformer droop compensation, with some manufacturers giving different values depending on the input impedance taps to be used. In amps lacking overall NFB you also see series R between plate and grid with a bypass C.
  Reply With Quote
Old 28th November 2016, 11:30 PM   #6
diyAudio Member
 
BinaryMike's Avatar
 
Join Date: Apr 2010
Location: Oregon
Quote:
Originally Posted by ygg-it View Post
I know to break in this way the most important rule of an hi-fi machine (i.e. having a flat response), so let me know what you think about this unusual choice.
I find it oddly refreshing for any audiophile to openly admit that tonal coloration is a principal goal. This uncomfortable truth is usually just an unspoken undercurrent, always plausibly deniable, carefully hidden under layers of bushwa and propaganda extolling the sonic virtues of overpriced components and mystical circuit design features. Yay for diyAudio!
  Reply With Quote
Old 29th November 2016, 12:23 AM   #7
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Coloration is a principal goal of cargo-cult audiophiles who heard sound of some naturally sounding systems that have some drawbacks. They assume drawbacks to be the main quality and go for it. For example, high output resistance driving some speakers cause lower speaker distortions. But it also causes uneven frequency response that is a side effect. Adding uneven frequency response can be regarded as a "high end signature" by cargo-cult audiophiles.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 29th November 2016, 05:06 AM   #8
ygg-it is offline ygg-it  Italy
diyAudio Member
 
ygg-it's Avatar
 
Join Date: Feb 2008
Quote:
Originally Posted by EmRR View Post
A half dB step can frequently be a huge step in a recording studio situation, quite audible. The basic circuit you show is very common in vintage broadcast/recording gear as transformer droop compensation, with some manufacturers giving different values depending on the input impedance taps to be used. In amps lacking overall NFB you also see series R between plate and grid with a bypass C.

Many thanks for this important evidence.
Should be great to have the schematics of such machines, or at least the label. Are those filters fixed or swithchable?

Regarding RC on the cathode (with C << 1uF), I think it acts just as "tonal adjustment" by changing the bandwidth gain of the triode and so the frequency response: a gain boost in just the highs

On the other side the "presence" control always acts on the NFB as it should change the "dynamic" too, as the damping factor produced by the negative feedback loop will be reduced at Mid-Hi frequency (less NFB at those frequencies).

Is damping factor important? Maybe. For more vintage tones less damping is typically desirable.

In my schema it probably works on both side: increase the triode gain freq and reduce the NFB at Mid-Hi frequencies.
  Reply With Quote
Old 29th November 2016, 09:09 PM   #9
diyAudio Member
 
Join Date: Jul 2015
Location: gothenburg,sweden
Consider tone-controls as an asset, provided they do not distort. Many recordings are
already manipulated in some way, too often in a way that actually removes part of the
natural sound.
Add to that the speakers used ( that always colours sound) and room, then i see lots of
instances that even a audiophile would turn the buttons.
At's all about the musical experience (?)
__________________
My home is at www.tubular-well.se
  Reply With Quote
Old 29th November 2016, 10:17 PM   #10
20to20 is offline 20to20  United States
diyAudio Member
 
20to20's Avatar
 
Join Date: Jun 2010
Location: W-S, NC
Quote:
Originally Posted by ygg-it View Post
Many thanks for this important evidence.
Should be great to have the schematics of such machines, or at least the label. Are those filters fixed or swithchable?
Why moddify the amp? This is the perfect case for using a 10 channel equalizer to customize your sound.
  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
Zobel RC network and stability of GNF SE amplifier ygg-it Tubes / Valves 7 2nd January 2016 04:21 AM
Need a Zobel Network (or RC shunt) in tube amplifier? ygg-it Tubes / Valves 37 10th January 2015 02:52 PM
RC network for 5" fullrange weiyan Full Range 2 24th August 2012 04:32 PM
Adding "home style" I/O to a "Pro" Amp Soldermizer Class D 2 13th March 2012 04:17 AM
What makes an amplifier "bright", "warm", or "neutral"? JohnS Solid State 51 13th December 2009 07:42 PM


New To Site? Need Help?

All times are GMT. The time now is 05:17 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki