matching input impedance

[aragorn723]

Hi,

My system has a Quickie and a large professional amp (175W X 2), but i'm wondering about the matching of the input impedance of the amp and output impedance of the preamp (4k).  The thing is, the specs don't state the input impedance of the amp..  Below is a link to a picture of it:

http://www.iavscanada.com/1003%20Inventorypics/1003-3629/Innovative%20Audio%20Surrey%20BC%20InterM%20R500%20Power%20Amp_b_l.jpg

In the bottom right of the pic under the input section (1/4" and XLR) it says "balanced 0dBm/10k ohms."  Is that the input impedance both for 1/4" and XLR?  The next question is matching-based on the 10x rule, the input impedance should be at least 40k.  There is a ton of bass right now, is there any reason to be concerned about the mis-match?

Dave

 

[Paul Joppa]

As long as the input impedance is resistive, and the preamp output  capacitor is large enough to deliver deep bass, and the preamp can produce enough current to adequately drive the power amp, then there is no limit to the impedance it can drive.

Those are big qualifications though:

If the load device (power amp in this case) has a transformer at the input, then the impedance is not resistive and the question becomes more complicated.

The stock Quickie output capacitor is 2.2uF, which can drive 10K ohms with a -3dB frequency of 7Hz. That's quite satisfactory in most cases.

At the low-battery point (24 volts from the 36-v array) Quickie can - in theory - make around 2.0 volts into a high impedance, and 1.0 volt into a 4K impedance, without either voltage or current clipping. We have not done these measurements, this is just simplified theory. Below 4K both gain and maximum output voltage fall rapidly. And below around 50K there will be an increase in distortion and a change in the distortion character. Whether this is audible, or whether this is unpleasant, is too subjective to predict.  A highly sensitive amp and/or speaker will reduce the signal level demanded from the preamp, greatly reducing the distortion in practice. As you can see, this is the most complex and situation-specific of the three criteria.

Bottom line, for those who are still with me, is ... if it sounds good, it IS good. Everything else is just explanation and rationalization.

 

[aragorn723]

Thanks Paul, I think i followed most of that  8)  Guess it all boils down to how it sounds, if bass is the only concern, it should be good (went from a 10" b&w 150 watt sub before the Quickie to no sub at all, though i'm tempted to try it lol).