You can use whatever combination you want to acheive the value you want. The fewer the better, because the soldered joints can be problematic for sound. You don't have to get exactly 47k, because it is not that critical. 1/4 watt is fine for this. High quality resistors with 1% tolerance will sound better, and also cost more. If you want to get as precise as possible, you'll have to measure each resistor to get it's exact value, and then calculate. But, at 47k, a couple hundred ohms one way or the other is not going to amount to a hill of beans.
resistors in series/parallel questions...
Background:
I'm trying to build some loading plugs for my phono preamp.
The pre unloaded is 100k ohms. My target value is 47k. After speaking ot the designer of the preamp, my understanding is that the correct resistor value to load the pre is calculated as follows:
R2 = 1/((1/Rt)-(1/R1))
Rt = desired load resistance
R1 = 100,000
R2 = resistor for loading plug
To get 47k, I need the new resistor to be a value of 88.7k, 89k, somewhere in there...
OK, now I need to determine what resistors to use in series or parallel to get the desired value. What issues do I need to consider in terms of power handling (designer said 1/4w is sufficient for this purpose)? It seems that it would be easier to get my desired value by going in series (with an 82k and an 6.8k, yielding 88.8k which is nigh perfect), but is there a better way of doing this via parallel resistors of common values or is series the easy way to go. If I go in series is it best to minimize the number of resistors in series by using the highest and lowest values that will give the desired value, or is it better to use similar values or does it matter? Assume I could use two 44.4k resistors. Would this be a better choice vs the 82k and 6.8k I mentioned? It seems like that since resistors are rated in terms of tollerance, that in theory, I should go with a bunch of very small values, since the overall error would be much smaller and possibly cancel each other out for some actual high and low values relative to stated resistance. Obviously the issues with soldering dozens of resistors in series negates this from a practical (and I'm assuming an electrical) standpoint. I think that I would gain power handling relative to each resistors rated power if I go in parallel, so is it correct that in series, I'm goin gto need to use higher wattage resistors?
If you're still reading, I'm sure it's obvious that I'm pretty clueless here, but I want to learn. I posted this only after spending some quality time with Google and learning the basics of parallel v. series calculations. Ohms law is now taped next to my monitor...
Thanks in advance for any primers, pointers, or help you can provide.
tw
I'm trying to build some loading plugs for my phono preamp.
The pre unloaded is 100k ohms. My target value is 47k. After speaking ot the designer of the preamp, my understanding is that the correct resistor value to load the pre is calculated as follows:
R2 = 1/((1/Rt)-(1/R1))
Rt = desired load resistance
R1 = 100,000
R2 = resistor for loading plug
To get 47k, I need the new resistor to be a value of 88.7k, 89k, somewhere in there...
OK, now I need to determine what resistors to use in series or parallel to get the desired value. What issues do I need to consider in terms of power handling (designer said 1/4w is sufficient for this purpose)? It seems that it would be easier to get my desired value by going in series (with an 82k and an 6.8k, yielding 88.8k which is nigh perfect), but is there a better way of doing this via parallel resistors of common values or is series the easy way to go. If I go in series is it best to minimize the number of resistors in series by using the highest and lowest values that will give the desired value, or is it better to use similar values or does it matter? Assume I could use two 44.4k resistors. Would this be a better choice vs the 82k and 6.8k I mentioned? It seems like that since resistors are rated in terms of tollerance, that in theory, I should go with a bunch of very small values, since the overall error would be much smaller and possibly cancel each other out for some actual high and low values relative to stated resistance. Obviously the issues with soldering dozens of resistors in series negates this from a practical (and I'm assuming an electrical) standpoint. I think that I would gain power handling relative to each resistors rated power if I go in parallel, so is it correct that in series, I'm goin gto need to use higher wattage resistors?
If you're still reading, I'm sure it's obvious that I'm pretty clueless here, but I want to learn. I posted this only after spending some quality time with Google and learning the basics of parallel v. series calculations. Ohms law is now taped next to my monitor...
Thanks in advance for any primers, pointers, or help you can provide.
tw