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mikeb
Joined: Nov 20, 2006
Posts: 59
Location: The Automotive Capital of Canada
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 Posted: Sun Jan 28, 2007 6:53 pm Post subject:
Best way to do "Thermal Contact" for tempco and IC |
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I'm just wondering if anyone has any good advice for mounting the temperature compensating resistors to be in thermal contact with the IC's.
Should I be using thermal paste, and should I also be using some sort of glue (hot glue?) to keep things from moving around? It seems to me like getting them really well connected is going to be impossible anyways, since the round resistor won't be touching the flat IC much at all.
It all seems very inefficient and would require a lot of time to get the resistor at the same temperature as the internals of the matched transistors in the plastic IC. Which means that the oscillator is going to be drifting for a while when first powered up.. anyone have any tips/tricks to best do this? |
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State Machine
Janitor
Joined: Apr 17, 2006
Posts: 2810
Location: New York
Audio files: 24
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| Posted: Sun Jan 28, 2007 8:40 pm Post subject:
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| Quote: | | I'm just wondering if anyone has any good advice for mounting the temperature compensating resistors to be in thermal contact with the IC' |
Well, I mount the resistor to come in contact with an IC then use a fillet of thermal compound between the resistor and the IC to get the lowest thermal resistance. This way the components will track each other in temperature fairly quickly. Your gear should stabilize within 10 minutes.
I would never use hot glue to attach the components ... 
Bill |
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andrewF
Joined: Dec 29, 2006
Posts: 1176
Location: australia
Audio files: 4
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| Posted: Mon Jan 29, 2007 2:39 am Post subject:
Re: Best way to do "Thermal Contact" for tempco and IC |
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| mikeb wrote: |
It all seems very inefficient and would require a lot of time to get the resistor at the same temperature as the internals of the matched transistors in the plastic IC. |
amen to that, guess thats why the big companies went digital.
the other analogue technique is a 'chip heater' circuit. EFM had such a VCO - but it took even longer to settle. |
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State Machine
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Joined: Apr 17, 2006
Posts: 2810
Location: New York
Audio files: 24
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| Posted: Mon Jan 29, 2007 10:42 am Post subject:
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| Quote: | | amen to that, guess thats why the big companies went digital. |
Yes, phase accumulators used in modern digitally controlled oscillator (DCO) circuits certainly have enough bit "width" that the effect of a drifting crystal oscillators can be rendered negligible.
It would be interesting though to actually measure how much, and over what period of time, a modern analog voltage (current) controlled oscillator, with an exponential converter controlling it's frequency, actually drifts. I emphasize modern since newer components are so much more stable than older devices. Without data or evidence to support claims, can anyone really say its a problem unless they can prove it? 
Just some comments ... Thanks
Bill |
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blue hell
Site Admin
Joined: Apr 03, 2004
Posts: 24432
Location: The Netherlands, Enschede
Audio files: 297
G2 patch files: 320
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| Posted: Mon Jan 29, 2007 11:31 am Post subject:
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| State Machine wrote: | | It would be interesting though to actually measure how much, and over what period of time, a modern analog voltage (current) controlled oscillator, with an exponential converter controlling it's frequency, actually drifts. |
Do you mean for a constant environment temperature ?
[Exp. converters usually rely on the exponential relation between a transistor's Vbe and Ic, which inherently has a temperature dependence. But maybe I misunderstood the "question"]
_________________
Jan
also .. could someone please turn down the thermostat a bit.
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State Machine
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Joined: Apr 17, 2006
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Location: New York
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| Posted: Mon Jan 29, 2007 12:21 pm Post subject:
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| Quote: | | Do you mean for a constant environment temperature ? |
No, one where the experiment could be conducted in a thermal chamber. I am lucky enough to have several computer controlled thermal chambers available to me to qualify designs. I know not everyone does. The experiment would be no good if the temperature were constant.
| Quote: | | [Exp. converters usually rely on the exponential relation between a transistor's Vbe and Ic, which inherently has a temperature dependence. But maybe I misunderstood the "question"] |
Exactly right, but thats what the TEMCO is for, to mitigate this dependence so that we get a nice "reliable" doubling of collector current for every 47 millivolts or so on the base-emitter junction. The question was in the lines of "Gee, how well does the temperature compensation work .. how fast ... etc...?"
Thanks Blue Hell ...
Bill |
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blue hell
Site Admin
Joined: Apr 03, 2004
Posts: 24432
Location: The Netherlands, Enschede
Audio files: 297
G2 patch files: 320
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| Posted: Mon Jan 29, 2007 12:53 pm Post subject:
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| State Machine wrote: | | No, one where the experiment could be conducted in a thermal chamber. I am lucky enough to have several computer controlled thermal chambers available to me to qualify designs. I know not everyone does. The experiment would be no good if the temperature were constant. |
Ok, that makes more sense to me
Yes ! would be an interesting experiment to try such for some configurations.
_________________
Jan
also .. could someone please turn down the thermostat a bit.
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State Machine
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Joined: Apr 17, 2006
Posts: 2810
Location: New York
Audio files: 24
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| Posted: Mon Jan 29, 2007 3:02 pm Post subject:
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| Quote: | Ok, that makes more sense to me
Yes ! would be an interesting experiment to try such for some configurations. |
It would be nice to see Blacet vs. PAIA vs. Waird vs. Your DIY vs. Moog Modular VCO ... etc .... who is the most stable of all and how do they compare in their tracking accuracy across several octaves? Too bad we have barely enough time in a day for more meaningful things right? 
Thanks for your responses.
Bill |
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synthmonger
Joined: Nov 16, 2006
Posts: 578
Location: flada
Audio files: 3
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| Posted: Thu Mar 05, 2009 2:59 pm Post subject:
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| Is there a schematic or website that explains how a heater transistor works? I'm looking around for a design that uses a single NPN or PNP as a heater. Still fishing around in google, no luck yet. |
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Sebo
Joined: Apr 27, 2007
Posts: 564
Location: Argentina
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| Posted: Thu Mar 05, 2009 4:48 pm Post subject:
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Hi:
The Moog Prodigy and Rogue uses a heater, you can check the schematics
to see how it works, also the EFM Rogue VCO Clone have a little explanation
about how it works (if I recall right).
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Sebo
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My Music:
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