2. amps-preamps
  3. 147091-75522

Confusion on amplifier impedance

Hello to all. My question is, is the imput impedance of an amp the same in RCA and Balaced mode. In setting up the M5-HP crossovers ( Balanced) for my Vandersteen 5a speakers  I have to use the input impedance of my amp. Now what I dont understand is the amplifier, a Musical Fidelity M6PRX, is rated at 50K of input impedance but when I decided to check with a voltmeter it was way off the 100Hz target of the crossover. Requirement is play 1KHz tone at 1VAC and measure, then play a 100Hz tone and measure. The resuts should be .707 VAC of the first reading or as close as you can get.
In order to get a proper reading I had to set the M5-HP for 200KHz. My results were then 1KHz at .990 VAC and 100KHz  .722 VAC. I previously had a set of RCA crossovers on a set of Vandersteen 5 with the same amp and had no sonic problems however I never did the check I did now. I just set it at 50K impedance and that was that. Can the difference between RCA and Balanced be so great ? Not sure how this works. Thanks in advance for any help.
cerberus79

Showing 2 responses by chipl3

chipl3
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chipl3
2 posts
 
I just re-read, a few days ago, the M5-HP sheet that is part of Vandy 2Wq info. It says to try the settings at, above and below the  input impedance for your amplifier.  You might still call Richard and ask why. I guess, not that is satisfying, that the filter is not so precise across different amps and subwoofers, that one might get better sound - to your ears - off an alternate setting. I have run two separate amps, ARC and Ayre, with these crossovers at the amp-indicated sitting. However, I am not "electric' enough to understand circuit math and so forth. I use the input impedance from the amp manual, and read elsewhere (Vandy's Ask Richard page, maybe) to not double for balanced. (The reason I read it this week is, I am not always good at reading the whole manual, and just picked up somewhere that an alt setting might sound preferable.

A call to Vandy, or perhaps some online research, can also give you correct safety guidance on changing M5-HP dipswitches with main amp on-off, or preamp volume up-down.
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