hi,
I have access to a transformer that has parallel 24v outputs - but I need 12v outputs. I think a couple of 20k resistors on a heatsink will do the job dropping the voltage (warning - I'm new to all this so please feel free to call me out if I'm totally off here!)
PF2205-20KF1 Riedon | Resistors | DigiKey
My question is, if I throw a couple of these on a heatsink and use them to drop 24>12, how much heat is this going to produce/will it be too much head inside an enclosure (with minimal ventilation/no active fans ideally).
Primarily, this will drive a DAC and tube stage buffer - so there shouldn't be too much draw (the tube buffer runs on 12vac)...
ACF 12Vac Tube Stereo Buffer
I have access to a transformer that has parallel 24v outputs - but I need 12v outputs. I think a couple of 20k resistors on a heatsink will do the job dropping the voltage (warning - I'm new to all this so please feel free to call me out if I'm totally off here!)
PF2205-20KF1 Riedon | Resistors | DigiKey
My question is, if I throw a couple of these on a heatsink and use them to drop 24>12, how much heat is this going to produce/will it be too much head inside an enclosure (with minimal ventilation/no active fans ideally).
Primarily, this will drive a DAC and tube stage buffer - so there shouldn't be too much draw (the tube buffer runs on 12vac)...
ACF 12Vac Tube Stereo Buffer
I did this on paper, but same formula as found on this site.
Voltage Divider Calculator
Are there variables in here I haven't considered? Again - very very new to this stuff. 🙂 thanks for the help!
Voltage Divider Calculator
Are there variables in here I haven't considered? Again - very very new to this stuff. 🙂 thanks for the help!
That's correct, but this is not the best method.
Let me first comment on your method:
In your case, you don't just have R2, but also the equipment you are powering. So that means there is current running through R1 into your DAC etc, that you should also consider, as it caused voltage drop across R1. You can convert the current your DAC etc wants to a resistor-equivalent, but there is a much better method: find the current your DAC needs. You also know you want to loose 12V across R1.
Then use a simple equation (actually it is called Ohms Law): R = V / I. Example: your DAC needs 100mA (= 0.1A), then R1 has to be 12 / 0.1 = 120 ohms. No need for R2.
But although this works, it is not recommended as the voltage will vary with the momentary current changes with audio level. In fact there is no easy simple solution for this to get it right in all situations. You really should get a new xformer or, as recommended by John, a wall-wart. They can't be that expensive.
Jan
Let me first comment on your method:
In your case, you don't just have R2, but also the equipment you are powering. So that means there is current running through R1 into your DAC etc, that you should also consider, as it caused voltage drop across R1. You can convert the current your DAC etc wants to a resistor-equivalent, but there is a much better method: find the current your DAC needs. You also know you want to loose 12V across R1.
Then use a simple equation (actually it is called Ohms Law): R = V / I. Example: your DAC needs 100mA (= 0.1A), then R1 has to be 12 / 0.1 = 120 ohms. No need for R2.
But although this works, it is not recommended as the voltage will vary with the momentary current changes with audio level. In fact there is no easy simple solution for this to get it right in all situations. You really should get a new xformer or, as recommended by John, a wall-wart. They can't be that expensive.
Jan
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A better solution would be to just buy the right transformer.
You dont need hot resistors or a heatsink for them then.
You dont need hot resistors or a heatsink for them then.