Low-distortion Audio-range Oscillator - Page 64 - 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 9th October 2012, 09:28 PM   #631
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by coluke View Post
Could't agree more
The original 239A employed an HA-2625, which is unfortunately classified either as obsolete or retired by Intersil - it was a bipolar uncompensated opamp featuring high speed (100 MHz GBW, > 60 dB OLG @ 100 kHz, SR 35 V/usec), high input impedance (300 Mohm), low noise current density (0.16 pA/sqrt(Hz)): these are not-so-common specs even in modern opamps, unless you are going to choose expensive beasts like the OPA637 - all in all, OPA2134 is a good starting point...

L.
I have 10 of these in the plastic DIP package if anyone is interested.
__________________
David.
  Reply With Quote
Old 9th October 2012, 10:37 PM   #632
coluke is offline coluke  Italy
diyAudio Member
 
Join Date: Mar 2009
Quote:
Originally Posted by davada View Post
I have 10 of these in the plastic DIP package if anyone is interested.
HA-2625? Lucky man! I would be interested in a couple of them

This is the 239A clone working at 20 Vpp out into 10 kohm - measured THD is almost only the THD of the EMU 0204 itself. A plot of the FET operating Vds (~88 mVpp) is attached too.

Ciao,

L.
Attached Images
File Type: png 239A clone.PNG (59.9 KB, 256 views)
File Type: png 239A clone - Vds.PNG (59.0 KB, 251 views)

Last edited by coluke; 9th October 2012 at 10:42 PM.
  Reply With Quote
Old 9th October 2012, 11:19 PM   #633
richiem is offline richiem  United States
diyAudio Member
 
richiem's Avatar
 
Join Date: Sep 2010
Location: Grapeview, WA
My 339A/239A clone uses an LT1468 for the main amp -- works quite well, considering it has a 10:1 cap ratio instead of HP's 100:1 ratio. I call this version the IG-339B -- it's built into a Heath IG-18 chassis and uses the Heath tuning resistor switches. The Heath mylar caps however have been changed to polypropylenes.

The fundamental is 1kHz at 6.3VRMS, level-adjusted by a 10k pot to 1VRMS and fed into my Active Twin-T filter to reduce the fundamental by 60dB without attenuating harmonics at all. The ADC is an E-MU 0204.
Attached Images
File Type: jpg IG-339B-line-shield.jpg (110.7 KB, 255 views)
__________________
...................
Dick Moore
  Reply With Quote
Old 10th October 2012, 12:23 AM   #634
diyAudio Member
 
dirkwright's Avatar
 
Join Date: May 2011
Location: Virginia
Well, I'm certainly willing to get a PCB together and order it. I use Pad2Pad. Surface mount or through hole devices?
  Reply With Quote
Old 10th October 2012, 01:57 AM   #635
diyAudio Member
 
dirkwright's Avatar
 
Join Date: May 2011
Location: Virginia
Quote:
Originally Posted by dirkwright View Post
Well, I'm certainly willing to get a PCB together and order it. I use Pad2Pad. Surface mount or through hole devices?
Reed relays ok for switching? 5V? I'm having some trouble figuring out the switching arrangement for the frequency setting resistors and capacitors. Anyone have a plan?
  Reply With Quote
Old 10th October 2012, 02:13 AM   #636
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by dirkwright View Post
Reed relays ok for switching? 5V? I'm having some trouble figuring out the switching arrangement for the frequency setting resistors and capacitors. Anyone have a plan?

Everything you need is on Dick's web page.

http://www.moorepage.net/RC.html
__________________
David.
  Reply With Quote
Old 10th October 2012, 02:39 AM   #637
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by coluke View Post
HA-2625? Lucky man! I would be interested in a couple of them

This is the 239A clone working at 20 Vpp out into 10 kohm - measured THD is almost only the THD of the EMU 0204 itself. A plot of the FET operating Vds (~88 mVpp) is attached too.

Ciao,

L.
Just PM with an address.
__________________
David.
  Reply With Quote
Old 10th October 2012, 05:14 AM   #638
richiem is offline richiem  United States
diyAudio Member
 
richiem's Avatar
 
Join Date: Sep 2010
Location: Grapeview, WA
Default Clarification on web page address

IG-18 #4, the IG-339B
__________________
...................
Dick Moore
  Reply With Quote
Old 10th October 2012, 09:59 AM   #639
diyAudio Member
 
Join Date: Jun 2005
Location: Zürich
Quote:
Any experts on SG505's here on this truly exiting thread?

Both my colleage and I recently purchased one of these and we already tried a few things to improve the residual harmonics but to no avail. I don't exactly find the SG505 easy to understand in all details (AGC section, notably) but I don't claim to be an expert. Both units are still fully within spec (as verified on the AP2722), so it's really about tuning the "last bit out of them".

So, anybody have a hint to known SG505 tricks (except for getting the hum down which is managable)? Not that I would expect the Tek guys didn't try tweak the hell out of it at their time, but after so many years there might be a chance that someone found ways to improve it with moderate effort.
Bruce Hofer did (as usual) an excellent job here. There are a lot of subtleties going on (and I'm sur I'm missing one or the other), and it is unlikely that we'll find an easy fix which will significantly improve performance. Just to highlight a few details:

* It looks like residual ripple of the peak level detector is cancelled through C1502 and C1603;
* The NE5534s implement various tricks--feed forward compensation (C1514, C1622), two-pole compensation (C1405, C1406, R1405), forced class A operation (R1621) and even a simple composite opamp (Q1620, see US-patent 4296381);
* The for higher frequency ranges unused integrator caps in the second integrator (C1312, C1320, C1322) are precharged to a specific voltage through R1421/R1422. I presume this speeds up settling after a range switch, because the capacitors are already in the correct phase relation to those in the first integrator (which a precharged to 0 V);
* The power supply of the peak detector is heavily low-pass filtered (R1611, C1600). This localises the current loop of the distorted currents, and avoids coupling to the main signal path.

One thing you could try is to make the drain feedback of Q1501 adjustable. Unsolder the ends of R1510/R1513 which connect to the gate of Q1501; take a (quality multi-turn) 1k trim pot; connect its wiper to the gate of Q1501 and the resistance element ends to R1510 and R1513 respectively. By adjusting the trimmer you might be able to reduce the 2nd harmonic for certain frequencies. But make sure it doesn't get worse for others!

Something else might be the addition of a 68r resistor between pin 5 and 6 of U1401 (as done for U1520). This forces the output stage of the NE5534 into class A operation, with possibly some distortion improvement.
  Reply With Quote
Old 10th October 2012, 01:38 PM   #640
diyAudio Member
 
dirkwright's Avatar
 
Join Date: May 2011
Location: Virginia
Quote:
Originally Posted by davada View Post
Everything you need is on Dick's web page.

About RC oscillators
OK, then I just do this for me and this isn't going to become something for everyone. We're back to punting ideas around, like always.

His page is great for theory, thanks.
  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 11:46 AM
ultra-low distortion audio oscillator geekysuavo Analog Line Level 16 26th March 2013 04:04 PM
Low distortion oscillator? rjm Equipment & Tools 30 4th May 2011 11:45 PM
Can we improve this low distortion sine oscillator ? gaetan8888 Solid State 22 29th March 2009 01:30 PM
Simple, low distortion 1kHz oscillator jackinnj Solid State 4 6th October 2003 04:58 AM


New To Site? Need Help?

All times are GMT. The time now is 05:39 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