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In Reply to: RE: Passives posted by Tre' on May 04, 2016 at 08:42:17
Now we're getting somewhere...
I was uncertain if my description or yours was the correct one. I had an answer from someone (don't recall which forum) that told me the description that I gave was correct. But yours makes more sense to me.
Except...My A21 has an input sensitivity of 1V. The Dac has an output of 2V. Am I getting a voltage drop of more than 1V in the 4' of cable + preamp? My blue jeans cables are 25AWG, so even at 48", that's only about 0.1ohms of resistance.
Follow Ups:
" Am I getting a voltage drop of more than 1V in the 4' of cable + preamp?"
That question is a little confusing but I'll give it a try.
No and Yes.
No. You are not losing any appreciable voltage through the cable.
Yes. You will be losing voltage through your preamp depending on where you have the volume control adjusted to.
If you are referring to your active preamp and you have the volume control adjusted to less than unity by more than 6db then that's where the loss is.
If you are referring to your passive preamp and you adjust it to more than 6db of attenuation then that's where you are losing more than 1 volt.
Point of fact; a 2 volt signal attenuated by 6db is a 1 volt signal.
Again, with a steady tone to test with you can measure this and then you will know.
You will know things like, how much voltage gain does your active preamp have and at what setting of the volume control equals unity (input voltage = output voltage)
You will also get an idea of how much signal going into you power amp produces how much SPL from your speakers.
BTW Your DAC only outputs 2 volts when the music signal hits digital peak, not all the time.
That's why I said to make a normalized test CD with a single tone. Then you would know exactly how much signal you are working with.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Thanks. I will test it out as you suggested. Sounds like the 2V output is deceptive. The average is obviously much lower.
" Sounds like the 2V output is deceptive. The average is obviously much lower."
Exactly. But you should setup you gain structure so that the 2v peak will never place more than 1v at the input of your power amp.
That way your power amp is never over driven but instead only driven to max power at the peak of the music and never higher.
Most systems have too much gain and, if the operator is not careful, can be easily over driven.
Sometimes I think that what people don't like about passive preamps is they lose the ability to over drive their systems.
They confuse over drive distortion with dynamics. Upper order harmonic distortion can sound "exciting".
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
!
The Mind has No Firewall~ U.S. Army War College.
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