How to "Parallel" Resistors

audiocr381ve

Guys, I apologize in advance for multiple threads, I just wanted to be more direct, and this question is very different. My Valab DAC is the version that has a clipping issue. The manufacturers fix is to lower the value of the resistor. I have a few options but I have absolutely no idea how to parallel resistors. Please read the option I'd prefer which I outlined in the quote.

Quote:
Originally Posted by tubes

Don't know if this what you're looking for.


Originally Posted by TeraDak
For those concering the clipping issue.
We current use a 390R resistor for the i/v conversion and it will output 2.19V at the full range audio data. It is impossible to listen the 0-db audio signal from the DAC , to pre/power amplifier and to speaker without any attenuation. It the source doesn't exceed -3db, there will be no clipping issue. However, if you would like to attenuate the signal in the preamplifier and keep the range as full as possible and without clipping. The i/v resistor in the TDA1543 output should be lowered to 340R ~ 350R to avoid clipping. The clipping issue is just a tradeoff for signal attenuation and it depends on the user listening condition. We will show the picture for analog output with i/v resistor 340R ~ 350R. For signal analysis, it should be 340R~ 350R, but it may not be the best for users in most real listening conditions.

(1) For user using the original 390R resistor, if you care about the clipping issue, you can reduce the resistor to 340R ~ 350R without loss the audio quality. If you don't have 340R ~ 350R resistor at hand ( 340R ~ 350R resistor is difficult to buy), you can parallel a 3.3k or 3.6k on the original 390R resistor. However, a 330R resistor is good aslo. The main difference is the maximum output voltage when a 0db signal is input.

(2) After that, connect the USB line to our DAC and repeat playing a 1kHz 0DB sine wave in PC. The wave could also be downloaded form our share space ( Public - Windows Live )
Use a meter and set it to measure AC voltage segment. Measure the RCA output or our DAC. The AC output is approximate 2.0V initially. Trim the VR nearby TDA1543 to find the maximum AC output. We usually trim the VR with the help of scope. But a meter is also good enough for tuning. If you have a scope, you can trim the VR such that the sine-wave is the most symmetric. The most symmetric output implies the maximum AC output in a meter.

The second step can be skipped it there is no meter or scope at hand. There is only few difference after step (2) adjustment.
/********************** Notice **********************/
The most important should be noticed is the VR trimming should be after the DAC power-on 30 mins. After that, the DAC will be in a stable state for adjustment. In the first 30 min, the TDA1543 was not in a stable stage. Trimming in the unstable state is no use.
/**********************************************/

I do not want to remove both 390R resistors because the traces are on their last breath. Outlined above is an option to "Parallel" a 3.3k resistor (is 3.3k also known as 330k? Because I have a few of those) on to the 390R resistors.

If someone had some type of illustration or could explain it slowly, it would help a lot.

FTGV

3.3k is 3300 ohms,330k would be 330,000. Googles your freind .http://en.wikipedia.org/wiki/File:Parallel_resistors.svg

BlueFox

Think of it as one resistor on top of the other (parallel). Connect the lead of the top resistor to the lead on the same end as the bottom. Connect the other lead on the top resistor to the other end of the bottom resistor. Ta-da. You have two resistors in parallel.

You can do the same with capacitors, but just remember capacitors in parallel add like resistors in series.

Face

http://www.sengpielaudio.com/calculator-paralresist.htm

audiocr381ve

Face wrote: »

http://www.sengpielaudio.com/calculator-paralresist.htm

That's an awesome resource.

Got it! Thanks guys.

Thread closed, good night.

audiocr381ve

Thread back open to ask another silly question.

What would happen if I heated a resistor leg to the point where I couldn't touch the body of said resistor when trying to parallel it? It wouldn't ruin the resistor would it?

Didn't happen to me, I heard about it happening to someone else ;P

Oh, and do resistors need to be burned in?

mhardy6647

Resistors can take quite a bit of heat, but will fail (e.g., burn open)if exposed to too much (thus are they rated for power - 1/4 watt or 1/2 watt or...). Generally they're pretty forgiving of heat during soldering. Odds are you're fine.


Nothing needs to be "burned in" (except speaker surrounds... possibly). {ducks and heads for cover}

Gadabout

If your worried about too much heat, switch to bit cooler heater... say 20 watt instead of a 30. Tin the existing resistor leads first, and you won't be applying much heat to the resistor. If your still really worried about put a small clamp between the existing resistor and where it bends to go into the board. This will act as a partial heat sink and get rid of some of the heat before it gets to the resistor.

All that being said, I have never popped a resistor using a 20w heater and just soldering. You should be fine. If you don't have a lower watt or variable heater then just try and be quick.

Scott