Quick Question about Resistors

audiocr381ve

I have a DAC and I'm trying to swap out some resistors. The resistors that are installed are 340ohm and a 1/2 Watt and I wanted to replace them with 390ohm resistors. I accidentally bought 1/4 watt resistors and don't want to make a drive back to rat shack. Is their a work around?

kawizx9r

I'd stick with the same exact type resistor (as in same values).

What is the reason for changing resistors?

If you want an upgrade, radio shack certainly won't have one. If you want an upgrade, go with Duelund, Mills, Holco or another good name brand.

audiocr381ve

kawizx9r wrote: »

I'd stick with the same exact type resistor (as in same values).

What is the reason for changing resistors?

If you want an upgrade, radio shack certainly won't have one. If you want an upgrade, go with Duelund, Mills, Holco or another good name brand.

I went from a 390 ohm to a 340 ohm and their was an apparent loss of dynamics. I want to go back to the 390 ohm resistors and I'm using Radio Shack resistors just for the hell of it.

So their is no work around huh? I have a bag full of assorted resistors at all sorts of values that are unfortunately 1/4 watt! :mad:

Face

Were the original 390ohm resistors originally from Radio Shack?

FTGV

audiocr381ve wrote: »

I have a DAC and I'm trying to swap out some resistors. The resistors that are installed are 340ohm and a 1/2 Watt and I wanted to replace them with 390ohm resistors. I accidentally bought 1/4 watt resistors and don't want to make a drive back to rat shack. Is their a work around?

Where in the circuit of the DAC are they located and why did they need replacing?.

TECHNOKID

I accidentally bought 1/4 watt resistors and don't want to make a drive back to rat shack. Is their a work around?

As previously stated, you have to stick with the original value. Now that you are back to 390 this is fine as your gear is not at risk (wattage is now lower) however, the wattage drop is quite drastic and depending how heavily that part of the circuit works, the resistor will more likely not las too long as the circuit may try to push more current through it than its actual rating efficency.

mrbigbluelight

Is there a work around ?
There's always a work around, but .....

kawizx9r wrote: »

I'd stick with the same exact type resistor (as in same values).
If you want an upgrade, radio shack certainly won't have one. If you want an upgrade, go with Duelund, Mills, Holco or another good name brand.

Excellent advice.


One work around could be:

If you have Five, 340 ohm RatShack 1/4 watt resistors.

Put 3 in series, 2 in series, and put those two legs in parallel.

You'll wind up with 408 ohms, total circuit resistance, which is 4.61% over your nominal 390 ohms original. Okay, so far, so good.

The 3 resistor leg would get 39.5% of total circuit amperage.
The 2 resistor leg would get 60.5% of total circuit amperage.

Each resistor is nominal 1/4 watt; the 2 resistor leg will draw the most current, and will be the limiting factor.

Didn't have my HP 15C, so using MS Paint :redface: and MS Calculator :redface:, you get something like this:

EACH resistor in the limiting 2 resistor leg would dissipate 247 milliwatts, slightly under the 1/4 limit.
Total circuit disipation, both legs, would be about 750 watts.

BUT think of it this way: you have a friend over, want to show him your handiwork, pop the lid, he/she looks at it and says, "Hey, nice can of worms !!".

Follow kawizx9r's advice. Please.

DISCLAIMER: Numbers are kind-of-in-the-ballpark but ... Hey ! I was using MS Paint and MS Calculator, okay ! :eek:

FTGV

All well and good but it depends on where in the circuit it is being used and again why is it being replaced?Did it fail?.

mrbigbluelight

That should have read, "750 mwatt", not "750 watts".
We're building a DAC circuit here, not a toaster. :redface:

In any event, buy the correct SINGLE quality resistor, go from there.