hi, how are you?
Hi, i want to build a passive mixer with some 10k 1/4 1% resistors. The question is, will it decrease the signal volume and lose sound quality from the sources? Do i have to build a preamp for the passive mixer output? How about a 9v JFET preamp? What is the simplest preamp design for this that would work with 9volts?
Passive Mixer
Preamp
Hi, i want to build a passive mixer with some 10k 1/4 1% resistors. The question is, will it decrease the signal volume and lose sound quality from the sources? Do i have to build a preamp for the passive mixer output? How about a 9v JFET preamp? What is the simplest preamp design for this that would work with 9volts?
Passive Mixer
Preamp
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Yes of course you'll lose some volume. At maximum volume setting the mixer just passes the input directly to the output (depending on the circuit), but anything less than full mixer volume means decreased--never increased--output.
However, you shouldn't lose any sound quality. In theory, and largely in fact, resistors don't affect sound quality.
Having a preamp stage sort of defeats the purpose of a passive mixer in the first place, since a passive mixer's advantage is supposed to be simplicity.
But anyway you quite likely won't need a preamp if your source is a CD player or similar. These can be expected to have an output level of one-half to three-quarters volt or so, which is probably high enough to let you lose some and still drive your amp. Headphone outputs are similar.
The way to find out is simply to plug your source into your amp. If you have volume to spare, then you don't need a preamp.
FYI: Your link to comoloharia.com didn't work for me.
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Yes of course you'll lose some volume. At maximum volume setting the mixer just passes the input directly to the output (depending on the circuit), but anything less than full mixer volume means decreased--never increased--output.
However, you shouldn't lose any sound quality. In theory, and largely in fact, resistors don't affect sound quality.
Having a preamp stage sort of defeats the purpose of a passive mixer in the first place, since a passive mixer's advantage is supposed to be simplicity.
But anyway you quite likely won't need a preamp if your source is a CD player or similar. These can be expected to have an output level of one-half to three-quarters volt or so, which is probably high enough to let you lose some and still drive your amp. Headphone outputs are similar.
The way to find out is simply to plug your source into your amp. If you have volume to spare, then you don't need a preamp.
FYI: Your link to comoloharia.com didn't work for me.
.
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The jFET preamp has a maximum output signal that is limited by the 9V supply.
Expect the maximum output to be < ~9V/3 Vac i.e <3vac
The circuit in common source topology will have a voltage gain somewhere between 2times (+6dB) and 4times (+12dB). Some of the experts here can show you how to calculate the gain.
This will (voltage) overload when the input signal reaches somewhere between 0.75Vac and 1.5Vac.
And being in single ended mode will distort significantly when the output is nearing, or exceeding, ½ the maximum output voltage.
If you want a mixer, the best type is an inverting amplifier with multiple inputs (also known as a adding/summing circuit). An opamp, or your common source jFET, meet this. But set your jFET to a gain of 1 (+0dB) for a no gain mixer.
If you want/need a passive mixer then you will have NO ACTIVE components, NONE.
Expect the maximum output to be < ~9V/3 Vac i.e <3vac
The circuit in common source topology will have a voltage gain somewhere between 2times (+6dB) and 4times (+12dB). Some of the experts here can show you how to calculate the gain.
This will (voltage) overload when the input signal reaches somewhere between 0.75Vac and 1.5Vac.
And being in single ended mode will distort significantly when the output is nearing, or exceeding, ½ the maximum output voltage.
If you want a mixer, the best type is an inverting amplifier with multiple inputs (also known as a adding/summing circuit). An opamp, or your common source jFET, meet this. But set your jFET to a gain of 1 (+0dB) for a no gain mixer.
If you want/need a passive mixer then you will have NO ACTIVE components, NONE.
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I was doing other things and remembered/ran-across this, possibly of interest:
Designing JFET Audio PreAmplifiers
You barely have to read the text, just look at the circuits, the guys at Rane know what they're doing. Note that the MPF102 is no longer made (I'm pretty sure), but substitutes are provided.
Or Google "jfet preamp" (sans quotes), everybody in the world has one, including Tillman's very well known circuit: http://www.till.com/articles/GuitarPreamp/
Oh wait, Tillman's circuit is the one you posted. Well, good choice.
.
I was doing other things and remembered/ran-across this, possibly of interest:
Designing JFET Audio PreAmplifiers
You barely have to read the text, just look at the circuits, the guys at Rane know what they're doing. Note that the MPF102 is no longer made (I'm pretty sure), but substitutes are provided.
Or Google "jfet preamp" (sans quotes), everybody in the world has one, including Tillman's very well known circuit: http://www.till.com/articles/GuitarPreamp/
Oh wait, Tillman's circuit is the one you posted. Well, good choice.
.
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