[guest1632]

Nice point Peak..

There are wide differences in gain of amps and preamps. Some amps have sensitivities from .25 to 5 volts, and preamplifiers have gains from slightly less than unity to 26 db or more.

Then there is also the issue of matching the sonics one likes to the sensitivity one desires. Some like integrateds and preamps with little or no gain, while others like separates with external preamp gainstages.

Mismatch these and one can get either too much or too little overall gain.  :)

Hi Steve, That's one of the reasons I like Curt's aproach. His "Purist" has three settings, 0, 6, or 9.5 DB, and that should take care of most situations.

Ray

[Steve]

Hi Ray,

     Pretty cool idea. I am going to think about that myself. One can always use more flexibility to allow choices that might be normally closed when building a system.

Thanks again.  

[chadh]

This is where I show my total lack of understanding of everything...

If I were looking to buy new amplification, and wanted to save a LOT of time by avoiding inappropriate pre-amp/amp combinations, what should I be looking for?

Obviously, there are synergies that become apparent only upon listening.  But it seems that, to some extent, I should be able to exclude some combinations on the basis of technical specifications.  Should I look at the gain from each unit in dB, add them and then consider the sensitivity of my speakers?  Is this different to looking at the "input sensitivities" in mV?  Is this sort of thing all completely independent of input or output impedence?

I wish I understood this sort of stuff.

Chad

[guest1632]

Hi Ray,

     Pretty cool idea. I am going to think about that myself. One can always use more flexibility to allow choices that might be normally closed when building a system.

Thanks again.  :)

You are most welcome Steve. Glad to be of some help.

Ray

[electricbear]

I like many of you out there use an arc pre. In my case it's a SP6B. I found the gain to be too much so I contacted the guys up at arc and they told me to double up on a pair of resistors in the output stage. Essentially all you do is solder a resistor in parallel with one that is already there. You do this for both channels. This has the effect of halving the resistance which doubles the current flow and in turn halves the output voltage. If you ever change out your amp and need more gain you just cut out the resistors you added and your pre is back to full strength. If you call arc I'm sure they will tell you if this is possable on your particular preamp and possably even offer to do it for you for a small fee.

[peakrchau]

This is where I show my total lack of understanding of everything...should be able to exclude some combinations on the basis of technical specifications.  

Should I look at the gain from each unit in dB, add them and then consider the sensitivity of my speakers?

Is this different to looking at the "input sensitivities" in mV?

Is this sort of thing all completely independent of input or output impedence?

The best place to start is at the speaker end where you clearly are going to need to put out a signal of a certain amplitude (Vout). This can be affected by input signal level (Vin) , the gain(G) and amp  input loading to a limited extent(Rin). These three quantities are capable of defining everything that you need to know.

The amplifier gain is typically fixed to put out a 28.28V (rms)  for a 1V (rms) input. This is about 29 dB of gain.  This assumes an 8 ohm load. For the same voltage level, adding another speaker in parallel of the same type (effevctively a 4 ohm load) will double the current requirement and double the power (P=V*I)...the voltage will stay the same assuming a 1V rms input at 28.28V.  

The higher power amplifiers can take a larger than 1V rms signal and put out more theorectival output power but not for the same input signal. Since they all have pretty much the same voltage gain ( 28.28 ) the input sensitivites of most power amps will be the same.

Conversely, most people will listen at an average level around 1 watt. This sounds about 1/4 as loud and the logarithmic relation between loudness and voltage will result in the input signal only being 0.01V (100x less or -40dB)  and the speaker being driven by 0.28V. Now you know why your parent's 5W car radio/battery from the 70's can play to a pretty decent level. We need a preamp to do this. In this case it attenuates by 100.

In my younger day's when I was a budding audiophile with no money, I had some recordings where I could take the output from my phono-preamp (250mV) and plug it into my amp directly. It was a bit louder than my normal listening level but the lack of a preamp stage made for great listening. The hotter output of modern day CD players (4x lounder) gave a theorectical advantge  of 4 times better signal for a given amount of noise at the preamp inputs.   This could be easily accomodated by turning down the volume know by 12 dB.   It also gave rise to the notion of passive preamps (0dB to negative infinity gain)....with CD sources.

This 12 dB shift resulted in me not being able to plug my CD directly into the power amp as things were generally too loud. Enter the passive preamp which in terms of gain is on average has no gain and only attenuation. The average modern day preamp can be thought of  gain of 4 (12) db stage with a passive preamp tacked onto it.

So the new problem (with passive preamps) is not being able to play loud enough with traditional sources ...but that is another alley better left for another day. Clear as mud ?

 

cheers,
PeAK