Build -- Active Twin-T notch filter for distortion analysis - Page 18 - diyAudio
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 12th August 2013, 04:04 PM   #171
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Quote:
Originally Posted by Triodethom View Post
What is the value of the coupling cap that is producing the 2rd H ?
There are several and they are electrolytics. However, the single-ended transistor topology is perhaps a worse offender. Together it is not going to easily serve my needs. Too bad, because it is wonderfully built and reliable work-horse. it still beats the published specs by 50% !!
[if only the 339A had been made as well :-( ]


Thx-RNMarsh
  Reply With Quote
Old 12th August 2013, 06:17 PM   #172
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by RNMarsh View Post
There are several and they are electrolytics. However, the single-ended transistor topology is perhaps a worse offender. Together it is not going to easily serve my needs. Too bad, because it is wonderfully built and reliable work-horse. it still beats the published specs by 50% !!
[if only the 339A had been made as well :-( ]


Thx-RNMarsh

Hi Rick,

Bob's SV auto null notch filter from his analyzer might be worth looking into.
And there is the SYS1 as well.
__________________
David.
  Reply With Quote
Old 12th August 2013, 08:40 PM   #173
diyAudio Member
 
Triodethom's Avatar
 
Join Date: Dec 2009
Location: Newnan GA
Quote:
Originally Posted by RNMarsh View Post
There are several and they are electrolytics. However, the single-ended transistor topology is perhaps a worse offender. Together it is not going to easily serve my needs. Too bad, because it is wonderfully built and reliable work-horse. it still beats the published specs by 50% !!
[if only the 339A had been made as well :-( ]


Thx-RNMarsh
I have a 331a and was going to look in to it . Thanks
  Reply With Quote
Old 13th August 2013, 12:22 AM   #174
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Quote:
Originally Posted by davada View Post
Hi Rick,

Bob's SV auto null notch filter from his analyzer might be worth looking into.
And there is the SYS1 as well.
I loaned (gave away, probably) my dual domain SYS 1 to friends in Thailand. But that reminds me, there are a lot of SYS One's on eBay now and they are a good deal for anyone.

Still looking for the quick and easy way out... an auto-null notch I (and other's) can buy and use or modify. Not into scratch building test equipment anymore. But maybe I could stand it if I had to just stuff a pcb, perhaps.

The IMD option just arrived today for the new Audio-Precision 2722. That will occupy some time for awhile, then read the manuals and load the software and start to see how to run the beast. Then I'll use it and the ShibaSoku to characterize the QA400 and others for accuracy etc at low levels of distortion. Then we'll have some idea of how trust worthy they are <-100dB and under what conditions or limitations.

Then do it with the notch filter I have on a pcb from Larry (the good guy) and check it all again.

Thx-RNMarsh










Thx-RNMarsh
  Reply With Quote
Old 13th August 2013, 02:01 AM   #175
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Default B&K 1607 Activated -

Here is a variable notch filter which is passive (no distortion) and made switchable to active (very tiny distortion) which eliminates the need for correction or fudge-factoring the 2H by increasing Q of the notch filter. The low output Z helps interfacing as well. This is shown in more detail on the short B&K 1607 discussion.

Battery powered and switchable active/passive and a ten turn balance control for even finer tuning.

Now, how do I apply that auto-tune circuit to it?

THX-RNMarsh

B&K1607 Mod3.jpg [BTW - all 1607's wiring is solid silver and all tuning/null caps are Polystyrene film and variable air cap. Very High Q and low distortion.]

B&K1607 Mod2.jpg

Last edited by RNMarsh; 13th August 2013 at 02:10 AM. Reason: Notch filter mod -
  Reply With Quote
Old 13th August 2013, 02:48 AM   #176
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Blog Entries: 3
I don't think the wire is silver, its missing the tarnish that would be there if it were. And if the word got out they would all be stripped for the silver. I believe its tinned copper buss wire.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 13th August 2013, 04:04 AM   #177
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by RNMarsh View Post
Here is a variable notch filter which is passive (no distortion) and made switchable to active (very tiny distortion) which eliminates the need for correction or fudge-factoring the 2H by increasing Q of the notch filter. The low output Z helps interfacing as well. This is shown in more detail on the short B&K 1607 discussion.

Battery powered and switchable active/passive and a ten turn balance control for even finer tuning.

Now, how do I apply that auto-tune circuit to it?

THX-RNMarsh

Attachment 365533 [BTW - all 1607's wiring is solid silver and all tuning/null caps are Polystyrene film and variable air cap. Very High Q and low distortion.]

Attachment 365534
The least intrusive would be to use a mechanical servo on the tuning cap. But you still need to measure the relative phase. I'm just reading up on phase measurement. It's clunky but wouldn't add to the distortion. You could take the output of a vector voltmeter to drive the servo. This would work very well if you don't mind a lot of outboard gear. If you want a neat little package then never mind.

Lot's of vector voltmeters on Ebay for cheep.
__________________
David.
  Reply With Quote
Old 13th August 2013, 04:59 AM   #178
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Blog Entries: 3
I'm not sure you really need the "afc" to get value from the filter. The oscllator will drift and the filter will drift but you are not using it as a classic distortion analyzer to remove the fundamental, just to reduce it 20-40 dB to extend the useful range of an FFT.

It practice a few manually tuned notch filter modules matched to a few of Victor's oscillators could be all that is necessary to get SOTA measurements from a QA400. The Twin T plus feedback and 20 dB of gain should be ideal for the task. 40 dB of post filter gain and an HP333 or HP334 may be able to see that deep? (I think we went down this road a year ago?) if we limit the actual notch depth to 40 dB w/ 40 dB of gain it become usable with almost any distortion analyzer.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 13th August 2013, 07:19 AM   #179
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Yes, i believe this to be trrue as well. I have a variety of source/generators however and find the flexibility useful for a variety of tests and apps. It can be applied in many other areas of T&M. I think the B&K 1607 with the active mod is just fine for me. Guilding the lilly with auto-tune, I suppose.

Next, i have a chassis here that I am about to drill and mount several of Vicktor's generators in it. Just in case my 'loaner friend' takes back his great ShibaSoku source so generously lent -- becoming a long term loan. Thanks Demian for the loan.

THX-RNMarsh
  Reply With Quote
Old 17th August 2013, 06:07 AM   #180
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
I think I'll test the idea that I can increase the open-loop gain of the amps in the HP-334A with active loads - replacing the gain stage load resistor(s). Curious how much imrovement is found that way... easier and simpler than whole redesign/replacement.

-RM

Last edited by RNMarsh; 17th August 2013 at 06:09 AM. Reason: increse the open-loop gain -
  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
need help wana change 60-Hz twin-T notch filter to 279 Hz filter prorms Solid State 0 9th February 2008 11:38 PM
Active Notch Filter design needed Vikash Multi-Way 63 21st May 2007 05:14 PM
Twin-T Lowpass Filter Analysis gmikol Parts 4 17th May 2007 08:16 PM
Noise out of active notch filter reins Multi-Way 0 6th July 2006 07:34 PM
Active notch filter 5th element Solid State 7 6th February 2004 10:06 PM


New To Site? Need Help?

All times are GMT. The time now is 03:26 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