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In Reply to: RE: Passives posted by jrdoe on May 03, 2016 at 18:16:37
"Is there a downside to running the Amp harder relative to using an active pre?"
That doesn't follow.
If you have a input level control on your power amp and you run your source straight into it and adjust the level control to achieve your normal listening level, you will not be running the "Amp harder".
You will be running it the same.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
In my setup, if I max out the volume of the Pre (zero attenuation), the average output volume is 100dB. I can achieve this same dB at about 12:00 - 3:00 setting on my active preamp.
So...the amp is "working harder" to achieve the same volume level with the passive.
Make sense?
No it doesn't.
Your active preamp has gain, your passive preamp does not.
A 12:00 to 3:00 setting of the volume control on your preamp equals unity gain and gives the same signal voltage to the power amp and the same volume out of the speakers as your passive pre turn all the way up.
Either way the power amp is doing the same amount of work. That is made evident by the speakers outputting the same SPL into the room.
There's an easy test you can do.
Get a 60Hz test tone off the internet. Open it in a audio editor like Sound Forge. Normalize it. (That sets all the peaks and valleys of the wave form at a digital zero)
Loop it so it's a few minutes or so in length and then burn a CD of it.
Play it in your CD player and measure the output voltage of the player with a AC voltage meter (any multimeter will work).
Now do the same with the signal going through the passive pre adjusted to max. (the output voltage should be about the same)
Now do the same again with the signal going through the active pre.
Adjust the active pre so that it's output is the same as the passive pre set to max. (according to what you said that setting will be somewhere about 12:00 to 3:00)
With the active pre set to the same signal output voltage as the passive pre, the power amp receives the same amount of signal voltage from the CD player and it therefore is doing the same amount of work.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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.
" 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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