Re: passive preamp
Passive preamp is an oxymoron it is a passive attenuator. I would build an opamp preamp instead.
passive stepped attenuators are more likely to increase the noise floor in your system than they are to have any audible reduction in distortion.
An opamp preamp will have distortion less than .001% and can be considerably less if you are willing to fork over $4 for the a high end chip. Still well below even the most punch drunk audiophile's ability to hear distortion. Plus they can swing sufficient voltage to insure you drive your amp to its full potential and get all the dynamic range it can deliver.
Passive preamps being better is a myth with zero merit. It is right up there with singing tibetan bowls.
Saying all this there is nothing wrong with it as long as your source player has really low output impedance and sufficient voltage swing to accomodate any amplifier you hook up to it. Problem is most folks don't have a clue what the voltage swing on their source player is or the output impedance. And most manufacturers don't seem willing to tell you. A preamp will insure you don't have to worry.
There are several very good Opamps that have very high input impedance and very low output impedance, both are things you want to have when driving your amp.
If you insist on building a passive attenuator (by the way it is not a passive preamp becuase it can't amplify only attenuate), non-inductive metal film resistors. They have the least effect on the input signal an induce less noise.
Paul Stewart <musicman32150@...>
- Paul Stewart <musicman32150@...>
02/26/2011 01:32 PMTo
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Today's subject is passive preamp designs. I have a couple of boxes of Dale 1% resistors. Not sure what is best or how many steps in the attinuator. Also, to reduce the noise while adjusting the volume.
Time to work on the pool.