Can we improve this low distortion sine oscillator ? - Page 2 - diyAudio
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Old 27th March 2009, 08:09 PM   #11
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Hello

I did find the AN43, and pick-up the best oscillator, I include the schematic.

Can I replace all those LT opamps by one OPA2134 quad opamp ?

Thank

Bye

Gaetan
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Old 27th March 2009, 09:44 PM   #12
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Hello

About the OPA2134, I was mean double opamp not quad opamp.

Bye

Gaetan
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Old 28th March 2009, 12:48 PM   #13
d3imlay is offline d3imlay  United States
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Quote:
Originally posted by infinia
Geez can't you up date that 70 yr old HP design. Use a LED instead of a non green incandescent perhaps
Upon closer inspection you find that the lamp is not intended to produce light.

Here is the link for AN43. Skip to page 29. Appendix C discusses the early days of HP. Appendix describes distortion measurements. By all means, see the last page.

AN43
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Old 28th March 2009, 01:24 PM   #14
infinia is offline infinia  United States
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Quote:
Originally posted by d3imlay

Upon closer inspection you find that the lamp is not intended to produce light.

That was a joke (smiley face winking).
But you'd realized that I knew that, by reading my second post, yes.
The first circuit posted was the start of Silicon Valley industry in 1939 almost 80 yrs ago.
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Old 28th March 2009, 02:41 PM   #15
jcx is offline jcx  United States
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with extra op amps you can rearrange the Wein Bridge use only inverting gain stages which have lower distortion from eliminating common mode V at the input - which is generally worse with fet input amps

see already mentioned LT AN-43 pg32 fig 47 for common mode supression and better gain control

there's also Eagar"s "super op amp" oscillator using composite opamp gain stages - claims ppb distortion

http://www.linear.com/pc/downloadDoc...60,P1029,D4156
(pg 67)
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Old 28th March 2009, 03:15 PM   #16
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Quote:
Originally posted by jcx
with extra op amps you can rearrange the Wein Bridge use only inverting gain stages which have lower distortion from eliminating common mode V at the input - which is generally worse with fet input amps

see already mentioned LT AN-43 pg32 fig 47 for common mode supression and better gain control

there's also Eagar"s "super op amp" oscillator using composite opamp gain stages - claims ppb distortion

http://www.linear.com/pc/downloadDoc...60,P1029,D4156
(pg 67)
I always wanted to play with that circuit. It has a distortion trim doesn't it, which seems a little funny in a way? Jim Williams sent me his collection of papers on Wein bridge oscillators after I mentioned in passing that one without distortion actually can't oscillate. There is a wonderful tech note from HP (1960's) on this.

EDIT - I should correct that to "as the distortion goes to zero the amplitude settling time goes to infinity"
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Old 28th March 2009, 04:20 PM   #17
GK is offline GK  Australia
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Quote:
Originally posted by scott wurcer


I always wanted to play with that circuit.

Me too. Way back when I was a first year apprentice my boss let me souvenir this from the parts drawer as part of my education expenses.
Itís a never-soldered RA53 glass encapsulated thermistor that is now unobtanium but was once the defacto standard bouncing feedback stabilisation component in budget commercially manufactured test bench audio oscillators.

I originally worked out a discrete fully-symmetrical opamp circuit to make a Wein bridge oscillator with it, but then moved onto other things and never got around to it. Iíve been meaning to etch a board for the design for nostalgia for a while already.

Also, I think I can pretty much guarantee that for the circuit presented in this threads opening post at 1kHz the distortion introduced by the light bulbs thermal time constant would be on the negligible side.
Iíve got published oscillator curves for the RA53 and THD doesnít begin to pull out of the noise until <100Hz or so (if my memory serves me correctly).

The thermistor blob of the RA53 is absolutely tiny and the thermal time constant is far from great. This is one of the reasons it was the preferred device for oscillator stabilisation Ė the boing-boing would settle quickly after readjusting the frequency.

Cheers,
Glen
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Old 28th March 2009, 06:29 PM   #18
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Quote:
Originally posted by G.Kleinschmidt



Me too. Way back when I was a first year apprentice my boss let me souvenir this from the parts drawer as part of my education expenses.
Itís a never-soldered RA53 glass encapsulated thermistor that is now unobtanium but was once the defacto standard bouncing feedback stabilisation component in budget commercially manufactured test bench audio oscillators.

I used a Tellabs precision PTAT resistor (the one they made for compensating log amps) to make a .1ppm oscillator once.
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Old 28th March 2009, 06:55 PM   #19
syn08 is offline syn08  Canada
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Quote:
Originally posted by scott wurcer
I used a Tellabs precision PTAT resistor (the one they made for compensating log amps) to make a .1ppm oscillator once.
Ok, ok, but how does it sound?
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Old 28th March 2009, 07:02 PM   #20
Dr_EM is offline Dr_EM  United Kingdom
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Any opinion on this circuit:

http://home.att.net/~theremin1/Circu...scillator.html

I built it as a 500hz sine source (yeah, 1khz would have made more sense!) from bits I had around and it sounds and looks (on a scope) very pure. I used polystyrene capacitors. Used for testing max power output from an amp and checking for any obvious distortion or ringing.
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