[brj]

The total voltage gain that develops between source and speakers is often split, to some degree, between the power amp and pre-amp, with the bulk of it obviously coming from the power amp.  Can any measurable or audible difference result from the manner in which the total generated voltage gain is split between these two components?

I'm asking because the use of a passive (0 gain) pre-amp seems to be a chancy thing in some systems, with complaints involving system noise floor, clipping or insufficient maximum volume being the typcial symptoms.  For systems where a passive pre-amp doesn't seem to work, does the problem really reduce to the fact that the power amp alone doesn't generate a sufficient voltage gain for the speakers at their given sensitivity?

Can the problem also be related to the current side of the equation, which is primarily a function of the power amp?

I've seen both power amps and pre-amps with adjustable gain settings, and I'm trying to get a feel for what trade off you might experience depending on how you choose to divide your total voltage gain.

Thanks for any pointers!

(This question may turn out to be less technical than I expect, and if that is the case, please feel free to move it!)

[_scotty_]

brj, anecdotally speaking I am using a preamp that has no gain but is an active buffer circuit. This facilitates impedance matching between the source and the poweramp.  The source has a internal buffer following its op-amp output stage to take the burdon of driving the 3ft. IC and the 10k load the preamp presents off the op-amp thereby avoiding thermal debiasing distortion in the output stage of the op-amp.  The power amplfier has been set for 26db of gain. The amp will output 110watts into 8ohms and 200watts into 4ohms.The loudspeakers are 95dB efficient. The room measures 25x18x7.75 (feet) and is well damped.  One might view the system as having roughly 31dBof gain if the loudspeaker efficiency is factored into the equation.
  To look at this another way I would be the about same place as system with 6dB gain in the preamp and 26dB in the power amp with an 89db efficient
speaker system.  I would however, run out of power sooner with the less efficient speaker system.  I have no noise floor issues or problems of insufficient maximum volume.  I also have no problems steming from impedance mismatches which inevitably result when a passive preamp is is used.  Scotty

[brj]

Thanks for the reply, Scotty!

brj, anecdotally speaking I am using a preamp that has no gain but is an active buffer circuit.  This facilitates impedance matching between the source and the poweramp.

Oops!  I overlooked the use of active components for the sake of impedance matching ... I was inherantly assuming that an active pre-amp implied some limited amount of gain.

The source has a internal buffer following its op-amp output stage to take the burdon of driving the 3ft. IC and the 10k load the preamp presents off the op-amp thereby avoiding thermal debiasing distortion in the output stage of the op-amp.

I was with you right up until the "thermal debiasing distortion"!  I'll have to read on on that type of distortion and its effects.

While I appreciate the load imposed by the pre-amp itself, can a 3 ft IC really impose much of a burden?

The power amplfier has been set for 26db of gain. The amp will output 110watts into 8ohms and 200watts into 4ohms.The loudspeakers are 95dB efficient. The room measures 25x18x7.75 (feet) and is well damped. One might view the system as having roughly 31dBof gain if the loudspeaker efficiency is factored into the equation.

In my mental manipulations, I was assuming a given speaker sensitivity (with the understanding that greater sensitivity requires less system provided gain) and a varying split of voltage gain between the pre-amp and power amp.  Are you assuming a reference speaker sensitivity of 90dB to generate the extra 5dB of gain on top of the 26 dB provided by the power amp?  If so, what is the reasoning behind this reference condition?

To look at this another way I would be the about same place as system with 6dB gain in the preamp and 26dB in the power amp with an 89db efficient speaker system. I would however, run out of power sooner with the less efficient speaker system.

Speaker effeciency aside, does that fact that you are now using the pre-amp to provide some of the gain in any way alter the sound of the system?  I don't know why this would be, but I'm assuming that the trade-offs are different somewhere.

I have no noise floor issues or problems of insufficient maximum volume. I also have no problems steming from impedance mismatches which inevitably result when a passive preamp is is used.

That was the other problem with passive pre-amps that I wasn't addressing in this post.  It sounds like that might actually be the bigger issue.

Thanks again for the comments!

[WEEZ]

Interesting topic-

I'm certainly no technical whiz-bang   , so I might add to the questions raised here  

It seems that there used to be a 'standard' 26db power amp gain and 20db pre-amp gain that prevailed (in my youth ). But I am probably wrong....

Seems to me that with most speakers today and sources producing 2v outputs- that 32db of total gain is enough for most rooms/and listening levels. Maybe a little more with a vinyl source.

Am I way off base here

WEEZ

[_scotty_]

Thermal debiasing distortion in an op-amp is the result of heat generated by the output stage traversing the die and causing the components in the front end to drift away from their manufactured tolerances.  This causes the feedback loop to be non-linear and results in the bias drift of the circuit.
Op-amps do not drive external loads well because of this. An op-amp operated under these conditions sounds like crap. The easiest cure for this problem is to put a non-negative feedback buffer in the negative feedback loop of the op-amp and let it drive the load.
  On paper where the gain takes place in the system shouldn't really affect how the system sounds. In practice every place in the system where gain occurs has the potential for introducing a non-linearity into the system.

Are you assuming a reference speaker sensitivity of 90dB to generate the extra 5dB of gain on top of the 26 dB provided by the power amp?

    No.
 
WEEZ, I think it depends on the sensitivity of the amplifier.  Many amplifiers will deliver their full rated power with 1volt of input.
This would put the preamp in the roll of an attenuator only in most cases
with no gain being required. My phono preamp has 32dB of gain and around .5volt out.  I have adequate volume on most records without
turning the volume control on my buffer all the way clockwise. Another
6dB of gain in the system would be welcome for 3 records in my collection.
The soundtrack to Tron requires just about all of the gain available to
reach a satisfying playback volume.
Scotty