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Help a German!
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sebber



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PostPosted: Wed Dec 27, 2017 5:41 am    Post subject:  Help a German!
Subject description: heatingtemperaturestabilizedoszillatordesignoszillator
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Hello everybody,

I need help finding the correct term for an analogue oscillator whose pitch drift is stabilized by a heating circuit. Would something like "temperature compensated analogue oscillator" be correct? Is there are shorter way to say it? Does a technical term for this rather common device exist?

Sorry for this non-technical question which I have to ask nonetheless in a technology forum Smile

Thanks
Sebastian

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JovianPyx



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PostPosted: Wed Dec 27, 2017 6:02 am    Post subject: Re: Help a German!
Subject description: heatingtemperaturestabilizedoszillatordesignoszillator
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sebber wrote:
Hello everybody,

I need help finding the correct term for an analogue oscillator whose pitch drift is stabilized by a heating circuit. Would something like "temperature compensated analogue oscillator" be correct? Is there are shorter way to say it? Does a technical term for this rather common device exist?

Sorry for this non-technical question which I have to ask nonetheless in a technology forum Smile

Thanks
Sebastian


Search engines are a funny thing, you may have to try several or many different approaches, but the answer should be there.

I know what you're referring to, but I don't think I've heard a specific name for it. There is more than one way to do this.

In early designs, an "oven" was created (a thermally insulated box) around the sensitive parts. The oven was heated well above the ambient temperature of the room so that the oven's temperature could be regulated and remain stable regardless of temperature changes outside the oven.

More modern approaches use a multiple transistor array in which a transistor is used as a heater and another transistor is used as a temperature sensor (for temperature regulator servo feedback). The other transistors on the array are used for exponential conversion of input voltage to output current. In both cases, the idea is to keep the sensitive parts warmer than ambient so that external changes in temperature have no effect on the operation of the expo parts.

HTH

EDIT ADDED:
One thing I should have mentioned is that this method requires waiting for the oven's temperature to stabilize, otherwise the expo CVs generated will wander and cause detuning and other problems. This is one reason why the use of tempco (temperature compensating) resistors are used in more modern designs. This allows the circuit to operate in a wide temperature range. Instead of heating the sensitive parts, they are allowed to remain at whatever temperature is ambient and the tempco resistor "corrects" for the variations caused by the transistor doing the expo conversion. Tempco stabilized designs are ready for performance almost immediately with no warm-up wait required.

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Last edited by JovianPyx on Wed Dec 27, 2017 8:12 am; edited 1 time in total
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Blue Hell
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PostPosted: Wed Dec 27, 2017 6:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Sebastian,

Temperature compensation would be for the expo converter not directly for the oscillator itself.

When you make a voltage controlled analog oscillator you'd usually start with a current controlled analog oscillator. This design will change frequency in a linear way depending on current.

As, for music, it is desirable to have the oscillator respond to voltage in an exponential way (frequency doubling with each amount of voltage added, usually one octave / Volt), an exponential converter will be added.

This exponential converter usually is made with a transistor, where the relation between base voltage and collector current is exponential. This however depends very much on temperature, but the temperature effect can be compensated away.

A little more trickery is involved to make things better, but the above sketches the basic ideas.

So .. I don't know what information you need for what purpose ... but maybe you should look for a temperature compensated exponential converter.

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sebber



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PostPosted: Wed Dec 27, 2017 7:48 am    Post subject: Reply with quote  Mark this post and the followings unread

This is already super informative information, thank you! I'll check out schematics and probably come back when I understood and know more!

Thank you very much both of you.

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Ricko



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PostPosted: Fri Dec 29, 2017 9:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

The term would be "temperature-stabilized VCO".

This is distinguished from "temperature-compensated VCO".

Rick
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sebber



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PostPosted: Wed Jan 03, 2018 12:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Rick, thanks for your input. Could you explain the difference between the two? When is it compensated and when is it stabilized?

I could guess that the oven method is stabilized and checking the temperature with a sensor is compensated, but then, it could be just the other way as well Smile

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Ricko



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PostPosted: Wed Jan 03, 2018 7:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Temperate-stabilization attempts to keep the temperature (of the exponential converter) stable (or at least wobbling around a centre temperature). Usually with a heater. (You might also try a cooler, but probably it is not effective or simple.)

Temperature compensation attempts to read the temperature and adjust values accordingly: thermistors usually. There is no attempt to maintain an ideal temperature, but to cope with changes.

(Of course, you could have a system with both stabilization and compensation each contributing part.)
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sebber



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PostPosted: Sat Jan 06, 2018 9:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks, Ricko, I think I got it now. And thanks BlueHell, finally I know why VCOs are actually CCO, it's something I read a few times and never understood. And JovianPyx, after I understood the other answers I understand now that it's exactly what you said. It took a bit more understanding though.
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