2. amps-preamps
  3. 1255561496

Amplifier input tech question

In my current system the volume control can only be turned
up to the 9 o'clock position or so, until the music is too
loud. The components are as follows;

cd- Rotel RCD-990 (transport only)
PS Audio DLIII with Cullen stage 4 mods

pre- Parasound JC 2

amp- Aragon 8008st

spks- KEF reference model 3

I am just starting to do my research for upgrading the
amplifier. And, would like to make certain that I select
an amp or amps that are less sensitive than the Aragon.
I have read about the minimum 10 times impedance difference
between pre-out and amp-in. But there must be more to it,
as the JC 2 output imp is stated as < 60 ohms and the
Aragon is listed as 22k ohms. My guess is that there is also a relationship between the preamp output voltage
and the amout of voltage the amp needs for full output.
Is there a formula I can use for finding a good match?
ska_man

Showing 1 response by davehrab

davehrab's avatar
davehrab
380 posts
 
>>"My guess is that there is also a relationship between the preamp output voltage"<<

That's the relationship you want to look at not impedance

The Aragon 8008 amp has an input sensitivity of 1.68 volts according to the factory spec

That means a signal of 1.68 volts will drive the amp to it's full rated output of 200watts

Your Parasound JC2 pre can put out as much as 8 volts which is 4 times more than you need to drive the Aragon

It seems that the Parasound's output voltage is directly related to it's input sensitivity

From the Parasound site it states that a 200MV input signal will output 1 volt at the JC2's output ... so if your source (Dac) is putting out 400MV it would probably be just about right to drive the pre so the pre would output about 2 volts and not drive your amp into overload

But your PS Audio dac probably puts out 2 volts to the JC2 pre and causes the JC2 to output the full 8 volts

This 8 volt output from the JC2 is way to much for the 1.68 volt input sensitivity of your Aragon ... so you have to turn the volume control on the Pre down, so as not to dive the amp into overload

This is probably why you can't turn the volume control on the Pre up pass 9 oclock

Simply put the 2 volt output of your dac is driving the JC2 pre amp to full gain and outputs 8 volts to your amp which is way to much ... so you turn the volume control down to 9 oclock so as not to over drive the amp

Volume controls are attenuators and can only turn volume down by adding resistance ... the more you turn the volume down the more resistance you add to the circuit

The more resistance added the less transparant the signal will be

So ideally you would like to have your volume control turned all the way to 1 oclock where there is little to no attenuation or resistors in the circuit to reduce transparency

Here are two links which may explain it better than I did

http://www.rothwellaudioproducts.co.uk/html/attenuators.html
http://www.rothwellaudioproducts.co.uk/html/how_attenuators_work.html

HTH Dave
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