Low-distortion Audio-range Oscillator - Page 128 - 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 21st December 2012, 11:43 PM   #1271
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
As a point of reference for this pro-ject: The "Victor" 1KHz fixed frequency oscillator measures in at .000125% THD+N. That's about -118-119dB
Compare that with my forum #1215 test data on my modded 339A. Thx-RNMarsh

[I finally did the output buffer change -- LME49710 -- only got 2-3dB better. But it adds up once the big drops in THD are done.]

Last edited by RNMarsh; 22nd December 2012 at 12:02 AM.
  Reply With Quote
Old 21st December 2012, 11:49 PM   #1272
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by RNMarsh View Post
As a point of reference for this pro-ject: The "victor" 1KHz fixed frequency oscillator measures in at .000125% THD+N. -RNMarsh
Thanks Rick.

I have some new trick up my sleeve that dramatically reduces the distortion of the oscillator.
But I need to get a handle on all of it before sharing the magic.
Stay tuned.

Cheers,
__________________
David.
  Reply With Quote
Old 22nd December 2012, 12:05 AM   #1273
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
Thanks Rick.

I have some new trick up my sleeve that dramatically reduces the distortion of the oscillator.
But I need to get a handle on all of it before sharing the magic.
Stay tuned.

Cheers,
  Reply With Quote
Old 22nd December 2012, 12:45 AM   #1274
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Here's a quick summary, I found that series connected JFET's with gates all connected together can dramatically improve THD. I didn't show this but you get the idea. The two 100k's could include a pot to trim seconds. The second plot shows a 100 Ohm sense resistor for the LED and 100K resistor on the PV array this gives 1000 to 1 or 1 to 1 on the output. The speed looks like it should not be a problem.
Attached Images
File Type: jpg pv.jpg (105.3 KB, 180 views)
File Type: jpg pv2.jpg (129.9 KB, 181 views)
__________________
Silence is so accurate.
  Reply With Quote
Old 22nd December 2012, 06:20 AM   #1275
richiem is offline richiem  United States
diyAudio Member
 
richiem's Avatar
 
Join Date: Sep 2010
Location: Grapeview, WA
@Richard, David and any others interested: Here are two plots I made of my basically unmodified 339A oscillator output (orig. opaqmps, etc, but I added a trim to the feedback resistor on the JFET to help with 2nd H -- this tirm hasn't been touched in almost two years).

The oscillator was at full output of 6.3VRMS at 1kHz, feeding a 30k wirewound pot to adjust level, then through the Active Twin-T filter to drop the fundamental by 40dB and on to the ADCs -- so the oscillator was running essentially unloaded. I've found that the distortion goes up by about 2-3dB when I use the internal level pot and switched attenuator to set the output to 1VRMS.

One plot is the EMU 0204 ADC and ARTA software, the other is with the QA400 and b0.97 software. The plots look very similar, and show the very low distortion of the HP design -- and both have about the same THD calculated manually, although the SW numbers differ. I offer this as a reference for comparison to any improvements to the oscillator -- hope they help -- note that ARTA calculates the THD+N about 20dB higher than the THD alone.
Attached Images
File Type: jpg 339A-osc-EMU.jpg (121.3 KB, 174 views)
File Type: jpg 339A-osc-QA.jpg (50.8 KB, 142 views)
__________________
...................
Dick Moore
  Reply With Quote
Old 22nd December 2012, 07:17 AM   #1276
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
How did you get the 0204 to work with PC? I use win7 on a PC. Where did you get QA400? I have same trimmer being used. That 339A oscillator really good. -RNMarsh
  Reply With Quote
Old 22nd December 2012, 05:02 PM   #1277
richiem is offline richiem  United States
diyAudio Member
 
richiem's Avatar
 
Join Date: Sep 2010
Location: Grapeview, WA
@Richard -- The EMU drivers work for me in XP SP3; I think there is a driver package that runs in Win7, though Creative may call it a beta. ARTA then runs the EMU from its device setup menu. Like David, I'm beta testing the QA400. The EMU and QA both having rising noise floors (due to noise-shaping used) above 30kHz, so their dynamic range goes away fast. BTW, I have an HP 239 which is very similar, and it is equally good. But if you're going to be driving low-Z loads, then the LT1468 seems to be the real deal.
__________________
...................
Dick Moore
  Reply With Quote
Old 22nd December 2012, 07:27 PM   #1278
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Here is question for John Curl.

John the limit of 339a analyzer measurement seems to be with the noise floor of the analyzer.
You are an expert in this area of low noise circuitry.
Is there any insight you can share with us on how to get the noise down?

Cheers,
__________________
David.
  Reply With Quote
Old 22nd December 2012, 10:18 PM   #1279
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by davada View Post
Here is question for John Curl.

John the limit of 339a analyzer measurement seems to be with the noise floor of the analyzer.
You are an expert in this area of low noise circuitry.
Is there any insight you can share with us on how to get the noise down?

Cheers,
Have you pushed the limit of FFT size and averaging or computed the noise floor in volts/root-Hz to see how much you can get. You should be able to compute the expected value with SPICE. The same issues apply voltage noise, noise gain, current noise, and the impedance of the gain network.
__________________
Silence is so accurate.
  Reply With Quote
Old 22nd December 2012, 10:27 PM   #1280
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by scott wurcer View Post
Have you pushed the limit of FFT size and averaging or computed the noise floor in volts/root-Hz to see how much you can get. You should be able to compute the expected value with SPICE. The same issues apply voltage noise, noise gain, current noise, and the impedance of the gain network.
Yes there is this.

I have a 7a22 which I can use to isolate section noise and calculate the 1/f noise.
Nice amplifier. Heard you miss it.

Cheers,
__________________
David.
  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 06:32 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