Oscillator: does transistor tempco "cuddle" do anything in this circuit? - Page 1
Forum section: electronics / beginners

author: rthorntn
author_rank: Frequent Contributor
timestamp: July 06, 2025, 12:40:47 am
content: Hi,So I built a noise reap paradox VCO and I just found out the 1K tempco's are supposed to cuddle the BC847BPN's, I didn't do that and I'm trying to figure out if its worth fixing it?https://github.com/odeliy/noise-reap/tree/master/modules/paradoxA friend shared this:https://modwiggler.com/forum/viewtopic.php?t=160910But that seems to be harping on about separate vintage transistor sandwiches and not teensy BC847BPN transistor pairs?Surely in the BC847BPN the transistors would be at the same temperature and the miniaturisation would mean that its putting out a lot less heat, also how much of the tempco is actually contacting the transistors package, 10% maybe, it seems like the tempco is a lot more exposed to the ambient temperature, ambient probably would be a fairly toasty eurorack case surrounded by dozens of modules with very little airflow?Thanks!Richard

author: mtwieg
author_rank: Frequent Contributor
timestamp: July 06, 2025, 01:05:21 pm
content: You forgot to share a schematic (no, I'm not going to clone a random git repo on my personal machine).

author: rthorntn
author_rank: Frequent Contributor
timestamp: July 06, 2025, 11:54:09 pm
content: Thanks!

author: MrAl
author_rank: Super Contributor
timestamp: July 07, 2025, 12:07:41 am
content: Quote from: mtwieg on July 06, 2025, 01:05:21 pmHello,In an instrumentation application, the device to be controlled AND the temperature sensor would be in the same insulated package if possible, or at least in close contact with each other using something like thermal epoxy.If they are far from each other, then the sensor tracks a temperature that may have nothing to do with the device being controlled. That could be a big problem, a little problem, or no problem at all, depending on how accurate the tracking has to be. You would determine that from what the application has to achieve with respect to temperature changes.This includes two or more devices that have to track each other. Each senses the temperature of the other and possibly they even conduct some heat to each other.Again, it depends how well this has to work in the environment it is intended to have to work in.As an example of using an insulated package assuming a relatively mild temperature range, wrap the two devices in Styrofoam, then wrap in aluminum foil, then in another layer of Styrofoam, for starters. The first layer of Styrofoam insulates the two devices from the external environment while the layer of aluminum helps to evenly distribute the heat from outside in through the second layer of Styrofoam across the surface of the first layer of Styrofoam. The aluminum keeps temperature differentials lower so that the two devices stay very close in temperature over distances across their surfaces. Without that, there can be more significant temperature differentials; insulation by itself does not stop heat it just lessens it.Of course the insulated package, although very effective, may not be possible in many cases because the devices themselves may develop too much heat inside the package.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: July 07, 2025, 01:21:58 pm
content: Quote from: rthorntn on July 06, 2025, 12:40:47 amI have never heard of the term 'cuddle' used in regards to any electric(al) device.Please define your definition of 'cuddle' in this situation. Thank you, Richard.

author: Grandchuck
author_rank: Super Contributor
timestamp: July 07, 2025, 01:30:38 pm
content: Side by side and touching?"cuddle" is also new to me.

author: TimFox
author_rank: Super Contributor
timestamp: July 07, 2025, 02:34:35 pm
content: Intimate contact?

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: July 07, 2025, 03:33:51 pm
content: And sharing warmth?Now seriously, what is a 1k Tempco? A thermistor? What is its reference designator in the schematic?Because tempco is a short hand for temperature coefficient, not a component.

author: mtwieg
author_rank: Frequent Contributor
timestamp: July 07, 2025, 10:55:04 pm
content: Yeah I had to do some googling to figure out the slang:"cuddle" means components are thermally coupled to each other"tempco" means a component for temperature compensation/stabilization. I'm guessing "1k Tempco" refers to a thermistor.It's not clear which resistor on the schematic is the "Tempco". I'm guessing it's R19 and R20?The two devices within the same package are likely thermally matched to each other. But thermal matching likely isn't the purpose of the thermistors. Usually this is done to prevent thermal runaway due to self-heating. But based on the component values, it doesn't look like there components will be dissipating significant power, maybe a few milliwatts at most? If that's the case then I don't think you need to worry about "cuddling". The thermistors might be not be needed at all. Hard to say without knowing more details about how the circuit works.

author: coppercone2
author_rank: Super Contributor
timestamp: July 07, 2025, 11:13:12 pm
content: you can use boron or aluminum nitride or other non conductive solder jumpers to thermally couple parts on SMT (link footprints).I wish FENIX flashlights did this instead of drooling thermal secretions to try to help heat sink the transistor, which explodeshttps://www.digikey.com/en/products/detail/vishay-dale-thin-film/THJP1206AST1/11313255https://www.vishay.com/docs/60157/thjp.pdf

author: MrAl
author_rank: Super Contributor
timestamp: July 10, 2025, 09:54:10 am
content: Quote from: BILLPOD on July 07, 2025, 01:21:58 pmHi,It seems to be a cute poetic metaphor that in this context clearly means objects that are thermally coupled.This is why I don't usually like poetic verse used in technical contexts ... if not anything else, it often delays the transfer of the truth in a matter when the receiving person has to stop and think about what the author really meant. Imagine if we did this with everything; we'd all be stuck thinking for hours just trying to understand a simple technical issue that already has a clearly defined way of describing it.