Go Back   Home > Forums > Design & Build > Equipment & Tools

Equipment & Tools From test equipment to hand tools

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 27th September 2012, 01:33 AM   #491
EssB is offline EssB  United Kingdom
diyAudio Member
 
Join Date: Jan 2009
Looks like a Wien bridge to me, just configured a bit differently.

I'd agree with Richiem, Victor's design looks better.

I can never understand how a LDR + PI controller can work properly, seeing as the LDR is a PI control element in itself, or at least a leaky integrator. Everytime I've simulated one it's very difficult to get them to stabilise. By the time I got that AN43 design to work the distortion looked poor.

Does anybody have a spice model for the VTL5C10 ?
I only have Thomas Gootee's VTL5C2 model, the 5C10 is a low slope type.
  Reply With Quote
Old 27th September 2012, 02:11 AM   #492
richiem is offline richiem  United States
diyAudio Member
 
richiem's Avatar
 
Join Date: Sep 2010
Location: Grapeview, WA
It's a Wien bridge -- series elements in the input leg and parallel elements in the feedback leg. This is however an all-inverting design, which eliminates a serious obstacle to low distortion in feedback oscillators -- common-mode errors. Jim Williams attempted an apparently successful fix for this in the oscillator from app note AN43.

Victor's circuit (I hope I looked at the right schematic) solves this in a different way by keeping the amps in inverting mode. Huge benefit. A state-variable design does this too, except for the summing stage, but not having any non-inverting amps in the oscillator proper really helps.
__________________
...................
Dick Moore
  Reply With Quote
Old 27th September 2012, 02:20 AM   #493
EssB is offline EssB  United Kingdom
diyAudio Member
 
Join Date: Jan 2009
I knew I'd seen the all inverter config before:
Low distortion oscillator tests measurement circuits | TMW
  Reply With Quote
Old 27th September 2012, 03:15 AM   #494
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Has anyone tried using the Linear Tech RMS-DC converters in the detector/AGC loop? Williams wrote an application note (AN-106) and there was another little squib using the LTC1966 or LTC1968.

With respect to the VTL5C10, you can take the values off the data sheet and use Eurequa to determine the spice parameters.
  Reply With Quote
Old 27th September 2012, 03:24 AM   #495
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by EssB View Post
Looks like a Wien bridge to me, just configured a bit differently.

I'd agree with Richiem, Victor's design looks better.

I can never understand how a LDR + PI controller can work properly, seeing as the LDR is a PI control element in itself, or at least a leaky integrator. Everytime I've simulated one it's very difficult to get them to stabilise. By the time I got that AN43 design to work the distortion looked poor.

Does anybody have a spice model for the VTL5C10 ?
I only have Thomas Gootee's VTL5C2 model, the 5C10 is a low slope type.
I think I do but I've never tried it. I'll dig it up and post it here.

David.
__________________
David.
  Reply With Quote
Old 27th September 2012, 03:31 AM   #496
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by jackinnj View Post
Has anyone tried using the Linear Tech RMS-DC converters in the detector/AGC loop? Williams wrote an application note (AN-106) and there was another little squib using the LTC1966 or LTC1968.

With respect to the VTL5C10, you can take the values off the data sheet and use Eurequa to determine the spice parameters.
I tried the LT RMS-DC converter. I had to filter the output of the convertor so heavily it was only good for 1KHz down. Not suitable for a full range oscillator unless noise is not an issue.

The output looks like a full wave rectifier but with a wave form shape that averages RMS with an LP filter.

I discovered a trick with the 1968. Since the output is switched capacitor, two convertors can have their outputs parallel. One of the two convertors fed from the quadrature. The output wave form is symmetrically overlapped reducing the ripple buy about 80%.



David.
__________________
David.

Last edited by davada; 27th September 2012 at 03:41 AM.
  Reply With Quote
Old 27th September 2012, 04:01 AM   #497
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by EssB View Post
Looks like a Wien bridge to me, just configured a bit differently.

I'd agree with Richiem, Victor's design looks better.

I can never understand how a LDR + PI controller can work properly, seeing as the LDR is a PI control element in itself, or at least a leaky integrator. Everytime I've simulated one it's very difficult to get them to stabilise. By the time I got that AN43 design to work the distortion looked poor.

Does anybody have a spice model for the VTL5C10 ?
I only have Thomas Gootee's VTL5C2 model, the 5C10 is a low slope type.
I found it.

Oh maybe you have this already.

David.
Attached Files
File Type: zip VTL5C.zip (7.4 KB, 35 views)
__________________
David.

Last edited by davada; 27th September 2012 at 04:20 AM.
  Reply With Quote
Old 27th September 2012, 11:17 AM   #498
EssB is offline EssB  United Kingdom
diyAudio Member
 
Join Date: Jan 2009
Quote:
Originally Posted by jackinnj View Post
Has anyone tried using the Linear Tech RMS-DC converters in the detector/AGC loop? Williams wrote an application note (AN-106) and there was another little squib using the LTC1966 or LTC1968.

With respect to the VTL5C10, you can take the values off the data sheet and use Eurequa to determine the spice parameters.
The 'little squib', was this it ? http://cds.linear.com/docs/LT%20Jour...TC1968-Pei.pdf

Yes, I expected I'd have to modify or create a VTL5C10 model, I thought I'd ask here first.
  Reply With Quote
Old 27th September 2012, 11:17 AM   #499
diyAudio Member
 
dirkwright's Avatar
 
Join Date: May 2011
Location: Virginia
Quote:
Originally Posted by richiem View Post
It's a Wien bridge -- series elements in the input leg and parallel elements in the feedback leg. This is however an all-inverting design, which eliminates a serious obstacle to low distortion in feedback oscillators -- common-mode errors. Jim Williams attempted an apparently successful fix for this in the oscillator from app note AN43.

Victor's circuit (I hope I looked at the right schematic) solves this in a different way by keeping the amps in inverting mode. Huge benefit. A state-variable design does this too, except for the summing stage, but not having any non-inverting amps in the oscillator proper really helps.
OK, please be patient with my ignorance. I do not see the series and parallel elements in Victor's schematic. There are supposed to be two capacitors and two resistors of equal value. I can't even identify the input leg and the feedback leg. Are the resistors in the Wein bridge R17+R18 and R10+jfet? I don't get it.
  Reply With Quote
Old 27th September 2012, 11:18 AM   #500
EssB is offline EssB  United Kingdom
diyAudio Member
 
Join Date: Jan 2009
Quote:
Originally Posted by davada View Post
I found it.

Oh maybe you have this already.

David.
Thanks David, that looks like a different model - I'll give it a go.
  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
Radford Low Distortion Oscillator Series 2 audiomik Equipment & Tools 21 19th February 2014 10:46 AM
ultra-low distortion audio oscillator geekysuavo Analog Line Level 16 26th March 2013 03:04 PM
Low distortion oscillator? rjm Equipment & Tools 30 4th May 2011 10:45 PM
Can we improve this low distortion sine oscillator ? gaetan8888 Solid State 22 29th March 2009 12:30 PM
Simple, low distortion 1kHz oscillator jackinnj Solid State 4 6th October 2003 03:58 AM


New To Site? Need Help?

All times are GMT. The time now is 12:00 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