Help with passive preamp

Hi Usblues,

Can you provide more information about your system, including your source components, cables, and speakers? Specifically how well a passive will fit in your system depends on a number of factors, including (1) the output voltage and output impedance of you source components, (2) the capacitance of your ICs, and (3) the efficiency of your speakers (as well as, of course, the sensitivity and input impedance of your amps).

I see the McIntosh has an input impedance of 20kOhms, which should be "OK" for using with a passive, depending on your source component. Ideally, you would want your source component to have an output impedance of 200 ohms or less. Also, you would want to use low capacitance cables, and keep them as short as possible. (If you have high capacitance cables, you can expect some high frequency roll off).

In terms of whether your system has enough gain, it would depend on your source component output voltage and speakers' efficiency; however, I think the MC7270 has a selectable input sensitivity of 0.75V or 2.5 V, and puts out 270 w/ch - using the 0.75V setting, I think you should have no problem with any volume issues, although the 2.5v setting may be workable as well.

give axiom,s pass.pre a try ,the sound is incredible. Good hearing to you

Use the .75v sensitivity, gain all the way up, and you'll have no problem using a passive. I used that configuration for a few years with various sources and speakers.

Maddoggy, do you mean Luminous Audio Axiom?

Good advice so far, but I think you just need to try it and hear for yourself. If the McIntosh stats stated previously are correct, use the high sensitivity setting (.75V) on the amp. The 20k ohm input impedance concerns me, especially since you are using a resistor-based passive. Typically the output impedance of a passive preamp will vary depending on where the volume level is set. So at certain setting it could be high enough to have a negative effect on the sound.

In my experience you would want greater than 2V output and less than 200 ohms output impedance from your source; use short interconnects, preferably 1m or less; and an amp with high sensitivity, 1v or better along with a minimum of 50k input impedance.

FWIW, TVC and AVC designs are generally more forgiving of impedance mismatches. So try out the Canary and let us know.

You can also consider an audio buffer to lower the output impedance from your passive to power amp. There is a few options out there but the Burson one seems to be well regarded.

http://www.bursonaudio.com/burson_buffer_160.htm