Low-distortion Audio-range Oscillator - Page 266 - 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 11th May 2013, 05:18 PM   #2651
diyAudio Member
 
chrispenycate's Avatar
 
Join Date: Aug 2006
Location: Geneva, Switzerland
I don't like their "no settling time"; the trouble with that is that if the gain control element (here an unspecified photoresistor) reacts fast enough, and the LED controlling it is bound to, at ultra low frequencies the gain changes in each half cycle (= distortion). I agree that the 'bounce' in level as you change frequencies with a thermistor one, like the one I've been using for the last forty years (to the point where the batteries it needed became unavailable and I was forced to build it a mains power supply), can be annoying, but not intolerable, but I'd prefer this to not trusting the distortion below a hundred Hz.

Driving the output from a pot assumes the load impedance is resistive. I'd have preferred a buffer stage (particularly since there's a spare op amp in the package unused). Distortion will be generated by mismatch in components, particularly the tracking on the stereo pot; they haven't specified close tolerances, and if the actual frequency is important (which it quite often is) you're going to have to borrow/hire a frequency counter to calibrate it.

Still, depending on your use (I certainly wouldn't choose this for looking for 0.05% distortion in an amp) it'll sound better than a function generator, and will be massively more stable and portable than the beat frequency oscillator that was the first low distortion signal source I used professionally.
  Reply With Quote
Old 11th May 2013, 05:43 PM   #2652
diyAudio Member
 
Join Date: Nov 2008
Location: Oakmont PA
Quote:
Originally Posted by RNMarsh View Post
The Bible on contacts is: Electric Contacts by Ragnar Holm. Published by Springer-verlag.

For what its worth --- My notes on a paper inside the book says these contacts are OK for our use here: 30%/50% Pd/Ag or Au/Rh/Ag = OK and Rh/Ag.

THx-RNMarsh
Yes,

If you ever look up his bio, an interesting career.

Until the US telephone network stopped being a monopoly, virtually all low level relays were made by Western Electric. They were the ones who used the bifurcated crossbar technique. The contacts were made of Western Electric alloy #2. So one's choices for those applications were quite limited. Just to limited things even more AT&T as large as it was only built parts of the switching network. NEC built parts for AT&T. So in return NEC bought parts from AT&T's Western Electric division.

With the end of the monopoly and consumer purchases of those parts significant changes have come. So it is easier to get low level relays. But we are still limited to what the manufacturers' offer. Good thing they all have folks who have read his book!

The other nice bit is the gold flash on contacts. This is very good for low level signals but not for levels above a few volts. So when you use a low level relay for even moderate voltages this blows through the gold flash to the contact material below. That is why the small signal relays are rated for currents as high as a few amps. The issue is that as long as the contact sees low power it is a good low power contact. Once used for a bit more it is no longer good for the lowest signal levels. It is sort of self adjusting to the circuit in which it is used.


ES

Last edited by simon7000; 11th May 2013 at 05:45 PM.
  Reply With Quote
Old 11th May 2013, 05:57 PM   #2653
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by simon7000 View Post
Yes,

If you ever look up his bio, an interesting career.

Until the US telephone network stopped being a monopoly, virtually all low level relays were made by Western Electric. They were the ones who used the bifurcated crossbar technique. The contacts were made of Western Electric alloy #2. So one's choices for those applications were quite limited. Just to limited things even more AT&T as large as it was only built parts of the switching network. NEC built parts for AT&T. So in return NEC bought parts from AT&T's Western Electric division.

With the end of the monopoly and consumer purchases of those parts significant changes have come. So it is easier to get low level relays. But we are still limited to what the manufacturers' offer. Good thing they all have folks who have read his book!

The other nice bit is the gold flash on contacts. This is very good for low level signals but not for levels above a few volts. So when you use a low level relay for even moderate voltages this blows through the gold flash to the contact material below. That is why the small signal relays are rated for currents as high as a few amps. The issue is that as long as the contact sees low power it is a good low power contact. Once used for a bit more it is no longer good for the lowest signal levels. It is sort of self adjusting to the circuit in which it is used.


ES
Is this a power effect or strictly to do with voltage level? Will voltages higher than a few volts with currents in the low mA range have this effect?
__________________
David.
  Reply With Quote
Old 11th May 2013, 06:22 PM   #2654
diyAudio Member
 
Join Date: Jun 2005
Location: Zürich
Quote:
Originally Posted by davada View Post
Is this a power effect or strictly to do with voltage level? Will voltages higher than a few volts with currents in the low mA range have this effect?
See section "contact life": http://relays.te.com/appnotes/app_pdfs/13c3236.pdf

Samuel
  Reply With Quote
Old 11th May 2013, 07:02 PM   #2655
diyAudio Member
 
dirkwright's Avatar
 
Join Date: May 2011
Location: Virginia
Some low signal relays have a slight self wiping action that cleans them.
  Reply With Quote
Old 11th May 2013, 07:59 PM   #2656
diyAudio Member
 
Join Date: Nov 2008
Location: Oakmont PA
Quote:
Originally Posted by Samuel Groner View Post
See section "contact life": http://relays.te.com/appnotes/app_pdfs/13c3236.pdf

Samuel
Nice cite!
  Reply With Quote
Old 11th May 2013, 10:43 PM   #2657
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
Is this a power effect or strictly to do with voltage level? Will voltages higher than a few volts with currents in the low mA range have this effect?
If you stay under 10 volts and low current (typical signal currents of analyzers and oscillators) you will not have an issue with arcing and the like. And a completely sealed relay from atmosphere is needed.

Gold plate/clad (not flashed) over silver or as I indicated is excellent. After that there are other issues in the construction that need attention; Such as the metal of the contact arm and how it is connected to the contact metal... rivet, solder, spot-welded, ferrous metals, coil fields etc) which will add distortion to the signal flowing thru the entire relay contact path.

Thx-RNMarsh

Last edited by RNMarsh; 11th May 2013 at 10:51 PM.
  Reply With Quote
Old 12th May 2013, 05:28 AM   #2658
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
BTW -- Some of the Panasonic/National THD analyzers are using relays made by NEC and by Sanyu Electric Co.


Well, I recieved my service manual for the Panamax VP-7722A. And, after looking over the calibration proceedure and sleeping on it for a couple days, the old subconcience came thru for me---- recall the 2H and 3H differences between analyzers? Well, that is now likely because I used a seperate/external generator... not the internal osc which the analyzer is tuned to. Just a fraction of a percent freq difference will cause the analyzer to be off the peak and read low.

:-)

Thx-RNMarsh

Last edited by RNMarsh; 12th May 2013 at 05:31 AM. Reason: Why the error --
  Reply With Quote
Old 12th May 2013, 06:06 AM   #2659
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Maybe, that wasnt it. using two different source generators, I get different harmonic results between two seperate analyzers Might it be different source Z interacting with analyzer inputs circuits? Gotta check it more.

-RNM

Last edited by RNMarsh; 12th May 2013 at 06:22 AM.
  Reply With Quote
Old 12th May 2013, 06:44 AM   #2660
ghg is offline ghg  Austria
diyAudio Member
 
ghg's Avatar
 
Join Date: Apr 2002
Location: Vienna
How is the quality of the 7722A service manual ?
Did you you get an original one or a pdf via scan ?

BR

Gary

[R.N. Marsh
Well, I recieved my service manual for the Panamax VP-7722A]
__________________
I hate "sounding amps", except these are Marshalls, driven by Eric C. or Jeff B., period.
  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 12:15 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