Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki 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

Active LRC EQ
Active LRC EQ
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 July 2018, 03:11 PM   #1
mashaffer is offline mashaffer  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Default Active LRC EQ

My apologies, I have searched and the only hits I found were full of dead links.

I understand the basic passive LRC notch filter and could probably work out a passive cut only graphic EQ but I am struggling at trying to figure out how to incorporate it into a FB loop for active boost cut EQ.

Any help would be appreciated.
__________________
The only reason I drive the 91 Colony Park is that I can't afford a 65. Me old school? Couldn't be.
  Reply With Quote
Old 8th July 2018, 04:57 AM   #2
mashaffer is offline mashaffer  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
OK, Using an op-amp tapping Rf works but when using tubes it works great for boost but almost no cut. certainly it cant be an impedance issue can it? Does it need to be a differential input for some reason?
Attached Images
File Type: png NIopamp.png (44.8 KB, 251 views)
File Type: png NItube.png (92.0 KB, 248 views)
__________________
The only reason I drive the 91 Colony Park is that I can't afford a 65. Me old school? Couldn't be.

Last edited by mashaffer; 8th July 2018 at 05:05 AM.
  Reply With Quote
Old 8th July 2018, 06:38 AM   #3
ruairi is offline ruairi
diyAudio Member
 
Join Date: Jun 2010
Check out this useful doc from Fred Forssell, it doesn't seem to be on his website anymore.
Attached Files
File Type: pdf Forsell Passive eq.pdf (130.4 KB, 41 views)
File Type: pdf EQ1A pass eq sch.pdf (7.2 KB, 34 views)
  Reply With Quote
Old 8th July 2018, 12:50 PM   #4
mashaffer is offline mashaffer  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Quote:
Originally Posted by ruairi View Post
Check out this useful doc from Fred Forssell, it doesn't seem to be on his website anymore.

Thank you. I will check them out but I was looking at active.

Perhaps the follower has insufficient current drive or too high of Zout for the chosen values. A SS follower may help. I will follow up on that possibility later today.

BTW I realize I have not accounted for the paralleled pots of the other bands but I put in a parallel 5k in the feedback loop and it of course reduced overall closed loop gain but the limited cut (about 1dB) remained.
__________________
The only reason I drive the 91 Colony Park is that I can't afford a 65. Me old school? Couldn't be.

Last edited by mashaffer; 8th July 2018 at 12:54 PM.
  Reply With Quote
Old 8th July 2018, 08:44 PM   #5
mashaffer is offline mashaffer  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Ok. This is the unit I am basing this on. In fact I hope to be able to use the filter board directly. I will be honest, these complex SS circuits confuse me.

SSII_filters.png
I figure I can build a differential amp something like this but I am at a loss as how the filters are integrated.
DiffAmp.png
__________________
The only reason I drive the 91 Colony Park is that I can't afford a 65. Me old school? Couldn't be.
  Reply With Quote
Old 9th July 2018, 12:25 AM   #6
mashaffer is offline mashaffer  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
This seems to work. I couldn't figure out how to step the resistances together so ignore the middle lines. The BW seems to be pretty constant but it takes a log pot to make it work.
Attached Images
File Type: png SEpentode.png (110.7 KB, 130 views)
File Type: png SEpentodeOutput.png (33.4 KB, 123 views)
__________________
The only reason I drive the 91 Colony Park is that I can't afford a 65. Me old school? Couldn't be.
  Reply With Quote
Old 9th July 2018, 12:37 AM   #7
mashaffer is offline mashaffer  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Figured it out...use an expression for the second resistance.
Attached Images
File Type: png SEpentodeOutput.png (59.7 KB, 130 views)
__________________
The only reason I drive the 91 Colony Park is that I can't afford a 65. Me old school? Couldn't be.
  Reply With Quote
Old 9th July 2018, 05:23 AM   #8
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
I do not understand your plans. Maybe cuz I'm not sure where in and out are, and you should use a proper pot part?

The "complex solid state" plan is obvious, once you get past the very bad drawing. Signal come in through a 3.3K resistor. Output comes back through a same-value 3.3K. Pots are hung across the two opamp inputs. LC networks hang off the pot wipers.

Please find R.G. Keen's page on parametric EQ. The truth is out there.

Steve Dove calls this "Swinging Inputs". A mirror-world version is "swinging outputs". Ampeg used this in some tube amps. Again we have matched resistors (except for some reason fudged to slight mismatch), but on the output. Pots across. LC networks from wipers to ground. One side goes to next stage, other side goes back to input as NFB.
Attached Images
File Type: gif BasicSwingingInputsEQ.gif (20.8 KB, 30 views)
File Type: gif VT40-EQ.gif (58.2 KB, 37 views)
  Reply With Quote
Old 9th July 2018, 05:47 AM   #9
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
And then there is the old-old cathode follower output swinger:
Attached Images
File Type: gif CF-LRC-boost-cut.gif (20.1 KB, 42 views)
  Reply With Quote
Old 9th July 2018, 12:26 PM   #10
mashaffer is offline mashaffer  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Thank you. I like the looks of the cathodyne... Nice and simple.

I don't quite understand this one. What is Vb? If the 150k input resistor were tied to the top and in+ was grounded it would look like an inverting amp but the input goes to in+ like a non-inverting amp but there is no corrisponding feedback resistor to ground. I could see the array as part of the input resiator of an inverting amp if it wasn't also connected to in+. I suppose the key lies in my first question about Vb.
Attached Images
File Type: gif greq.gif (8.0 KB, 77 views)
__________________
The only reason I drive the 91 Colony Park is that I can't afford a 65. Me old school? Couldn't be.
  Reply With Quote

Reply


Active LRC EQHide 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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Help/recommendation - Presonus 2.0 active Monitors and active sub setup *photos Goremans Subwoofers 0 18th July 2016 01:20 AM
The Totem of Tone, an active 3-way dipole and active subwoofer Gerrit Boers Multi-Way 61 23rd May 2016 10:59 AM
Active 3-ways with solen active loudspeaker module soundemon Multi-Way 14 19th March 2009 11:17 AM
Behringer DCX2496 I want to try active biamping using it as the active xover. georgehifi Digital Line Level 3 15th August 2006 07:46 AM
XVR1 active crossover, discrete active stage promitheus Pass Labs 18 22nd July 2002 01:29 AM


New To Site? Need Help?

All times are GMT. The time now is 10:47 AM.


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