Rane 4th order SVF - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 10th June 2004, 11:32 PM   #1
nuppe is offline nuppe  Sweden
diyAudio Member
 
nuppe's Avatar
 
Join Date: Aug 2003
Location: Gothenburg
Default Rane 4th order SVF

Hi
I was just wondering, has anyone built an active filter based on the design in this Rane article?

I've smacked together a quick test setup (with R=10k). I played around with a scope and a tone generator, and the filter seems to work, but theres alot of (really) high frequency noise at the LP out (thats not at the input to start with).

I used the schematic as pictured on page 4 with L-R alignment. It's a breadboard setup, so i didn't expect miracles, but the noise really swamps the LP. I'm a newbie at electronics, so i don't know what to do about it, but i guess i've builtin an antenna or an oscillator somewhere in the circuit.


Could someone either give me a clue about how to correct it, or maybe point me to some info i could read up on?
Would a buffer at the input and outputs help?

Any suggestion is welcomed.

/Andreas
  Reply With Quote
Old 11th June 2004, 12:50 AM   #2
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
This seems like a parastitistic oscillation and/or a wiring mistake issue

I've been using this state-variable 4th-order circuit in the custom crossover of my 3-way all-horn-loaded experimental system for several years and it works just fine. Even with 105-108dB/W efficiencies, noise is barely audible at 1m from the tweeter with about 27dB amplifier gain applied to crossover outputs. As opamps I used LM833 [not outstanding but with good specs/price relationship] and R values are around 10K

I never had parasitistic oscillation problems but from the beginning I included : A simple RC lowpass filter on the input, 150 ohm decoupling series resistors on the outputs and 68pF capacitors from IN- to OUT on the first op-amps in order to reduce gain at RF. I included also 100nF supply decoupling capacitors every 5cm or so
  Reply With Quote
Old 11th June 2004, 09:23 AM   #3
nuppe is offline nuppe  Sweden
diyAudio Member
 
nuppe's Avatar
 
Join Date: Aug 2003
Location: Gothenburg
Default Thanks!

I'll try some of your suggestions later today. I suspect RF-oscillation as you say, but i have no experience, so i thought i'd better get a second opinion.

I'll also check the ground returns, i'm not sure i have star grounded everywhere.

If i can get it right, then i'll try the setup with mulitplexers, so i can vary the frequency. Btw, i'm using lm837 amps, these are similar to lm833 but quads if i understand correctly?

Thanks again!

/Andreas
  Reply With Quote
Old 12th June 2004, 07:46 PM   #4
nuppe is offline nuppe  Sweden
diyAudio Member
 
nuppe's Avatar
 
Join Date: Aug 2003
Location: Gothenburg
I tried some more, but i have no clue really...

The 68pF you mentioned, this was from inverting in to output on the leftmost opamp in the schematic right? I put that in but it made no difference. I measured the supply lines at the chips and they look clean.

I did some more measuring, grounded the input, the picture below shows the LP out (yeah, i know, the scope's an antique...). The scope was set to 0.2 V/cm and 0.1 s/cm.
(edit: that would make the wave something like 3MHz, 0.3v peak, right? )

I get approximately the same waveform on all of the four rightmost amp outputs, the first amp output is clean. All of the last four amps are in the same package, the first is in a separate quad. Is the quad busted?

/Andreas
Attached Images
File Type: jpg scope.jpg (16.3 KB, 51 views)
  Reply With Quote
Old 12th June 2004, 08:54 PM   #5
nuppe is offline nuppe  Sweden
diyAudio Member
 
nuppe's Avatar
 
Join Date: Aug 2003
Location: Gothenburg
Default update

Well, i switched the quad i thought was busted, no difference...
I decoupled the supply lines at the chips to ground with 10nF, no difference... (well the wave changed slightly, but that might have been me touching something when i put the caps in)
I rerouted the ground so that it would be as close to star ground as possible (can't get a real star ground with breadboard), no diference...

I'm at a loss, have no clue where to start...

Should i add a load at the output? Am i measuring things right?

/Andreas
  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
FS: Rane AC23B active balanced x-over (4th order LR) taloyd Swap Meet 0 20th July 2009 11:04 PM
WTB: Rane Pe-17 Cloth Ears Swap Meet 0 29th October 2008 02:15 AM
1st order Passive Line Level Crossover + 2nd order Highpass? alexclaber Multi-Way 11 4th January 2008 07:15 PM
deceptive perception ? 1st order-2nd order question poldus Multi-Way 4 10th April 2007 11:58 PM
Rane AC23b bjackson Swap Meet 2 7th October 2005 12:08 PM


New To Site? Need Help?

All times are GMT. The time now is 10:11 AM.


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