>I'm gonna hit the surplus stores and hunt down some 12V fuses. I'm thinking that something at 1.5-2 times the rated fan current (probably 250mA tops) in series with the fan before hooking it up should do the trick. The goal is to have the fuse blow on short before the P/S +5V line gets drawn too high.
I don't think a fuse will work well. Fuses tend to act extremely slowly compared to the time that it will take to destroy the electronics. In general you have to protect electronics with more electronics. Use fuses to prevent fires.
My solution to running a fan at lower voltage would be to run it off the 12V supply with an appropriate series resistor. Calculate the value from the power rating of the fan. There's no need to get the 5V supply involved.
You might find that the fan has trouble starting up on the lower voltage supply, but runs fine once it gets moving. In this case, a big capacitor in parallel with the resistor will supply the full voltage to the fan for a short time after the power is applied.
Unless you put diodes in line from the sound card to the Y
Diodes won't work here, because the audio is an AC signal. An appropriately sized resistor has the desired effect without causing the massive distortion that a diode would.
but I think you're better off buying a cheap (<$200) 4 or 8 channel audio mixer.
An active mixer would do the job, but you have to wonder if it's good value when compared with the cost of a few resistors (<$0.20).
As someone else has mentioned, it may be possible to daisy-chain a number of sound cards by connecting the line-out of each into the line-in of the next. No resistors required. Balancing the relative levels of the signals will be a little more difficult, and the degradation of the signal through many cards might be noticable, but it's definitely a possibility.
Combining signals using 'Y' adaptors or cables isn't a very good idea because you'll have many sound cards trying to drive the line to different levels simultaneously. This can cause volume and frequency response problems, and may place undue stress on the output stages of the soundcards. Use 'Y' adaptors to split one signal into many, not to combine many into one.
The simplest way to combine signals is with a 'passive' mixer, which is nothing more than a resistor in each signal line. Have a look at
this page for instructions on how to build one yourself. I keep a few combiner cables around, where I have built 4K7 resistors inside the plugs.
I've never tried to use a mixer like this to drive headphones directly. It's designed to drive an input with a high impedance, while headphones have a relatively low impedance, so I don't think it would work very well. However, for a system with N soundcards, you could use the passive mixer to combine N-1 outputs at line level, and send that into the line input of the last soundcard. Mix the line input with the other signals from that card, and output to your headphones in the normal way. You'd also get a master volume control this way.
Some people have suggested an 'active' mixer, such as those from Radio Shack, Soundcraft, etc. I can't see that they offer any significant advantage for this application, unless you want the extra flexibility in signal routing, metering, reduction in crosstalk, or if you just like the idea of having lots of knobs to play with.
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Steve.
I don't think a fuse will work well. Fuses tend to act extremely slowly compared to the time that it will take to destroy the electronics. In general you have to protect electronics with more electronics. Use fuses to prevent fires.
My solution to running a fan at lower voltage would be to run it off the 12V supply with an appropriate series resistor. Calculate the value from the power rating of the fan. There's no need to get the 5V supply involved.
You might find that the fan has trouble starting up on the lower voltage supply, but runs fine once it gets moving. In this case, a big capacitor in parallel with the resistor will supply the full voltage to the fan for a short time after the power is applied.
Steve
Unless you put diodes in line from the sound card to the Y
Diodes won't work here, because the audio is an AC signal. An appropriately sized resistor has the desired effect without causing the massive distortion that a diode would.
but I think you're better off buying a cheap (<$200) 4 or 8 channel audio mixer.
An active mixer would do the job, but you have to wonder if it's good value when compared with the cost of a few resistors (<$0.20).
As someone else has mentioned, it may be possible to daisy-chain a number of sound cards by connecting the line-out of each into the line-in of the next. No resistors required. Balancing the relative levels of the signals will be a little more difficult, and the degradation of the signal through many cards might be noticable, but it's definitely a possibility.
Steve.
Combining signals using 'Y' adaptors or cables isn't a very good idea because you'll have many sound cards trying to drive the line to different levels simultaneously. This can cause volume and frequency response problems, and may place undue stress on the output stages of the soundcards. Use 'Y' adaptors to split one signal into many, not to combine many into one.
The simplest way to combine signals is with a 'passive' mixer, which is nothing more than a resistor in each signal line. Have a look at this page for instructions on how to build one yourself. I keep a few combiner cables around, where I have built 4K7 resistors inside the plugs.
I've never tried to use a mixer like this to drive headphones directly. It's designed to drive an input with a high impedance, while headphones have a relatively low impedance, so I don't think it would work very well. However, for a system with N soundcards, you could use the passive mixer to combine N-1 outputs at line level, and send that into the line input of the last soundcard. Mix the line input with the other signals from that card, and output to your headphones in the normal way. You'd also get a master volume control this way.
Some people have suggested an 'active' mixer, such as those from Radio Shack, Soundcraft, etc. I can't see that they offer any significant advantage for this application, unless you want the extra flexibility in signal routing, metering, reduction in crosstalk, or if you just like the idea of having lots of knobs to play with.
Steve.