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Re: Who can provide an opinion on advantage vs. disadvantage of using a separate pre amp with kit 1 amp?

Posted by bill mac (A) on August 13, 2005 at 09:02:38

In Reply to: Who can provide an opinion on advantage vs. disadvantage of using a separate pre amp with kit 1 amp? posted by seattlelar on July 26, 2005 at 16:57:57:

There are a couple of obvious advantages in using a preamp - ie mode switching, tape looping, headphone output etc - but in your case these disappear.

The first stage stage of the kit 1 is in affect a preamplifier, the second stage needs something like 5v for full output. But as you correctly point out the volume control is between the first and second stage and this means that you could possibly overload the first stage.

Now the CD red book standard is 2v RMS for CD players although I have seen a number of CD reviews over the years that find players with output as high as 3v RMS.

Now 2v RMS is just shy of 3v peak which is what we need to work with here. I modelled the 1st 2 stages of a kit 1 in PSpice and find that the first stage is biased at 4.75. For a 3v (peak) I get 0.65% distortion (2nd Order) and could see no higher orders. Now this is simulation so it don't mean it ain't there. For a 100mV input (peak) then this drops to something like 0.02% - again remember this is theoretical taken from the tube curves.

I think these figures show that running 2v RMS into a kit1 is probably OK at 3v RMS btw, I got 0.86%, so if your CD player is a bit higher then it may be overloading.

There are two things you could do:
Attenuate the CD input, or
Buy a record deck - this would sound much better ;-)

Seriously though, if I was running a CD player directly in I would do the following:
a)Upgrade the voulme pot, and
b)Attenuate the input.

Bill Mac

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