High-gain preams/high sensitivity power amps

PaulFolbrecht · « **on:** 17 Jun 2006, 02:54 pm »

In considering 845 SETs and the First Watt F3 (15W) for my Gallo Ref 3s, one consideration is that I can squeeze a bit more power out of the system with a high-gain pre. My current Prima Luna 3 is only 11.5db; was considering a MiniMax pre at 20dB.

But what I'm wondering is if this poses a problem with a high-sens amp - one that can be driven to full power by, only, say, 600mV.

Does this mean I'll only have the VC open a crack before driving the amp to full power? And that the high-gain pre is essentially wasted?

I'm not understanding some of the basics here (maybe) cause I know that, for example, the MiniMax power amp is high-sensitivity and meant to mated with their pre. They made the pre so high gain in part, actually, because the power amp is 8W/ch.

Thanks.

PaulFolbrecht · « **Reply #1 on:** 18 Jun 2006, 06:56 pm »

Anybody willing to clarify this for me? :-} Is my thinking correct - I don't want a high-gain pre with a power amp with high (600mV for full power) sensitivity?

My source outputs the standard 2V as well.

JoshK · « **Reply #2 on:** 18 Jun 2006, 07:18 pm »

If your amp is indeed 600mV for full power, then you don't need any gain at all, in fact you will always be shunting away voltage with a 2V source. I would just double check the 600mV sensitivity figure.

PaulFolbrecht · « **Reply #3 on:** 18 Jun 2006, 08:30 pm »

That's what I thought, but this is really confusing to me, because almost ALL digital sources put out 2V or close to it these days. Why does ANYBODY make high-gain linestages?

Davey · « **Reply #4 on:** 18 Jun 2006, 09:55 pm »

Quote from: PaulFolbrecht

Why does ANYBODY make high-gain linestages?

THAT is an excellent question.

6db of gain should be more than adequate for most users who use line level sources only. The usage of highish gains in the line amp sections of preamps dates from the era when LP's were the primary source and the typical phono section gain wasn't quite enough.

A super loud volume as soon as you touch the volume control might impress your friends with all the "power" your system has,

but it's terrible for useability. That's usually a horrible part of the volume control for left/right tracking and you can never seem to get the volume "just right."

Also, your premise that "I can squeeze a bit more power out of the system with a high-gain pre" is incorrect. The voltage gain of the preamp has nothing to do with the power capability of your system......(assuming your preamp has the capability to drive the power amp to its rated output.)

In your proposed system it sounds like you don't need a preamp at all.

Cheers,

Davey.

PaulFolbrecht · « **Reply #5 on:** 18 Jun 2006, 11:01 pm »

I'm not entirely sure about that. Though a CDP may be capable of 2V, most of the time the signal is far below that level, no? However, I think you're right in this particular example that with a sensitivity of 600mV a high-gain pre is moot, and counterproductive even.

At the very least, active pres almost always seem to improve dynamics, which must be related to gain of some sort.

Davey · « **Reply #6 on:** 18 Jun 2006, 11:14 pm »

Most CDP's will output around 2 volts with full-scale recorded information, but the average recording level on CD's can vary quite a bit. Thus, you may or may not need a few db gain in the line amp section of a preamp to get good useability of the volume control range.
In your case I would try the new amplifier sans preamp to begin with and use a simple potentiometer for a volume control and see how it works.

For info....A 12db reduction on 2 volts will yield 500mV. Just short of your amps sensitivity for rated power.

If active preamps are "improving dynamics" (that's a subjective evaluation I take it) then they are adding distortion.

Cheers,

Davey.

JLM · « **Reply #7 on:** 19 Jun 2006, 12:13 am »

Full 2 volt output from your CDP into a typical sensitivity amp WILL BE VERY LOUD! (Full volume, if not wildly distorting.)

Frank Van Alstine recently listed the attributes of a good pre-amp nearby in these circles.

The primary purposes for a pre-amp with line level inputs (like CDPs) is volume control and impedance matching. Additional features like switching between multiple sources, tone controls, and gain can also be beneficial. My modded Squeeze Box for instance only has an output of 1 volt, so 3 dB of gain would double the signal strength and put it up to the 2 volt standard. Other features are quite secondary.