The only clean way to adjust the volume is to use a log pot or do it with DSP. The best log pots are from Penney&Giles. These are used in pro mixing consoles and cost $150 and up. A good sub is the black beauty pots available for Parts Connection http://www.sonicfrontiers.com/tpc/.
yes, you can use a simple potentiometer with a couple caveats.
One end of the pot should is fed the input signal (which has a DC blocking cap connected between the input connection and one fixed end of the pot. The other fixed end of the pot is connected to ground. The wiper is then fed to the input of the amplifier stage. A good value for the pot would be 10K (dual for stereo) and the input cap should have a value of 4uF or higher to keep LF distortion at a minimum.
Good Luck!!
One end of the pot should is fed the input signal (which has a DC blocking cap connected between the input connection and one fixed end of the pot. The other fixed end of the pot is connected to ground. The wiper is then fed to the input of the amplifier stage. A good value for the pot would be 10K (dual for stereo) and the input cap should have a value of 4uF or higher to keep LF distortion at a minimum.
Good Luck!!
There is more to volume than just levels
A lot of people have seen many variations of the circuit suggested by bmcevers. I think that Rod Elliott's website has about the easiest explanation for it's workings.
http://www.sound.westhost.com/project01.htm
JKL: You raise a more complex question than maybe we all think.
I've found that the problem with varying the level in different parts of the signal path is that changes are not linear, in amplitude, phase and frequency response. Case in point: 1-channel mixer into power amp with gain control. The final sound can be described as mixer gain + mixer level + mixer master + amp gain. Even if you match SPL, a lower level in one with a corresponding boost in another, can remove high frequency harmonics (like the kind that cause mic feedback) or even change the equalization, or a number of other "effects."
Simple to me may be just something that changes the overall volume in the complex manner I just described, in which case, the circuit as suggested by BMC will suffice. If you are looking for something that affects the signal in a very linear fashion, the design will be more complex, but the results will be simpler -> IN X GAIN = OUT.
ensen
A lot of people have seen many variations of the circuit suggested by bmcevers. I think that Rod Elliott's website has about the easiest explanation for it's workings.
http://www.sound.westhost.com/project01.htm
JKL: You raise a more complex question than maybe we all think.
I've found that the problem with varying the level in different parts of the signal path is that changes are not linear, in amplitude, phase and frequency response. Case in point: 1-channel mixer into power amp with gain control. The final sound can be described as mixer gain + mixer level + mixer master + amp gain. Even if you match SPL, a lower level in one with a corresponding boost in another, can remove high frequency harmonics (like the kind that cause mic feedback) or even change the equalization, or a number of other "effects."
Simple to me may be just something that changes the overall volume in the complex manner I just described, in which case, the circuit as suggested by BMC will suffice. If you are looking for something that affects the signal in a very linear fashion, the design will be more complex, but the results will be simpler -> IN X GAIN = OUT.
ensenThis type of volume contrtol is very simple in design, but the performance is good and it is reliable. As far as phase shift? As an Electronics Engineer I see no possible way it could introduce any phase shift in the audible spectrum, the HP frequency is about 4Hz (with the Cap value I gave) which is 5 times lower than the lowest audible frequency, very sufficient. If someone in this forum can hear sub-20Hz phase shifting (INAUDIBLE), they're not from this planet.
One more thing, you can make this control into a quasi-log pot by placinig a 15k to 20k resistor from the wiper to ground, to most people it has a "more pleasing" gain law.
One more thing, you can make this control into a quasi-log pot by placinig a 15k to 20k resistor from the wiper to ground, to most people it has a "more pleasing" gain law.
I forgot to add one piece of info on the "quasi log pot" with a 10k or 15k resistor connected to the wiper and ground, the pot value will need to be increased to 100k (as per several sources i.e. Rod Elliott) this will in turn raise the input impedence to to amplifier significantly at most settings and could set off another whole chain of consequences that is beyond the scope of this thread. If you do use the quasi-log concept you might want to buffer the input of the amp with a JFET op-amp (i.e. opa134). This will keep the input of the power amp constant.
In conclusion, if you want to keep it simple use the 10k pot and 4uF blocking cap, it may not have the "nicest" gain law, but it won't dramatically change the input impedence of your amp.
One final thought. I am a scientist, I don't "buy into" the philosophy of EXCESS COST=BETTER PERFORMANCE. There isn't any potentiometer on the planet (for audio use) worth paying $150 dollars for. Your wallet will be a lot lighter and your ears will be straining to hear some non-existant quality that somebody told you about. I prefer to buy many inexpensive (cheap) Xicon carbon pots with 20% tolerance at $1.92 (dual linear) from Mouser. I'll buy ten at a time and test them to find which have the closest tolerances between the two halves. I use the ones with tight tolerance (for 10k usually +/- 300 ohms) for my audio projects, the other ones I save for other projects that don't have sensitive matching requirements.
Good Luck...
In conclusion, if you want to keep it simple use the 10k pot and 4uF blocking cap, it may not have the "nicest" gain law, but it won't dramatically change the input impedence of your amp.
One final thought. I am a scientist, I don't "buy into" the philosophy of EXCESS COST=BETTER PERFORMANCE. There isn't any potentiometer on the planet (for audio use) worth paying $150 dollars for. Your wallet will be a lot lighter and your ears will be straining to hear some non-existant quality that somebody told you about. I prefer to buy many inexpensive (cheap) Xicon carbon pots with 20% tolerance at $1.92 (dual linear) from Mouser. I'll buy ten at a time and test them to find which have the closest tolerances between the two halves. I use the ones with tight tolerance (for 10k usually +/- 300 ohms) for my audio projects, the other ones I save for other projects that don't have sensitive matching requirements.
Good Luck...
Can't he use this?
If you search under "Passive Preamp" you will probably find more...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=2608&perpage=15&pagenumber=1
here's another:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=7680&highlight=passive+volume+control
This should be more than you ever wanted to know about the subject! -but simple
If you search under "Passive Preamp" you will probably find more...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=2608&perpage=15&pagenumber=1
here's another:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=7680&highlight=passive+volume+control
This should be more than you ever wanted to know about the subject! -but simple
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