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Ref 3 Impedence Mismatch HELP please

I've recently discovered I have an impedence mismatch between my Xilica XD 4080 digital crossover and the ARC REF 3. The input impedence on the Xilica is 10K. Which is too low for the REF 3. This causes issues with the sound in the high frequencies and lows. It seems like a Burson Audio XLR Audio Buffer would be the solution but apparently they are not importing them into the country any more.
I was wondering if there is another product or manufacturer that might have a product as a solution or if there is any way to raise the input impedence of the Xilica Crossover by adding caps or resistors as in internal mod.

Any ideas? I know I can always replace the preamp with a solid state unit which I'm contemplating.

As an after thought, wouldn't it be great if the audio manufacturers could at least codify the specs for all audio equipment so that these problems could be prevented? All manufacturs would have to at least hit a target input and output impedence so that all equipment could work together electrically. It seems a no brainer for the industry to develop.
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herman
2,273 posts
 
..

So 600 out to 10K in? Lower than I would like but not a gross mismatch as it is about 1 to 15. Most recommend a minimum of 1 to 10. With your system it seems a shame to add a buffer, why not get a Krell preamp? I doubt you will find a tube line stage with lower Zout.

If you have more than enough gain you could try some step down transformers between the pre and Xover. Dave Slagle at Intact Audio could wind you a custom pair to meet your needs.

If you can DIY or know somebody who can the Zin of the crossover is probably set by a single resistor for each channel which could be changed. You might contact them to see.

As for a standard I doubt that will ever happen.

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atmasphere's avatar
atmasphere
12,014 posts
 
The problem here is that the output impedance of the ARC goes higher as the frequency goes lower. If driving a high impedance this is no problem, but a middle impedance like 10K (less than 2000 ohms being 'low impedance'...) is problematic as the coupling caps at the output of the preamp are rolling off the bass with the reduced load at the output.

There is no good way to fix this- either you somehow find a way for the preamp to drive a higher impedance or change out the preamp.

We got around this problem by direct-coupling the output, so there is no bass roll off. Herman is right, there is far too much variance in high end audio so there is not likely to be much in the way of standards, about all you can expect is that tube amps will likely have an input impedance of 100K or higher, whereas its likely that with most solid state components 10K is more likely.
herman
2,273 posts
 
.

the output impedance of the ARC goes higher as the frequency goes lower.

Good point, any idea how much that would be? I have no idea what size caps they use.

There is no good way to fix this- either

Bigger caps? I realize that most would be reluctant to do surgery on such an expensive pre but if not then why not just up the value?

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almarg's avatar
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almarg
9,670 posts
 
Any idea how much that would be?
http://www.stereophile.com/content/audio-research-reference-3-line-preamplifier-measurements:
The output impedance was also to spec., at 635 ohms balanced and 326 ohms unbalanced in the treble and midrange, but rose to 1437 ohms and 625 ohms, respectively, at 20Hz.
The OP's processor has only balanced inputs. A rise in preamp output impedance from 635 ohms in the mids and treble to 1437 ohms at 20Hz is non-ideal in relation to a 10K load (assuming that spec is accurate), but on the other hand doesn't seem likely to cause more than a very slight bottom octave rolloff.

Not sure why there would be issues with the highs, as the OP reported, unless the interconnect cables are particularly long and do not have low capacitance per unit length. In that situation, perceptible upper treble rolloff could result from the interaction of cable capacitance and preamp output impedance.

Best regards,
-- Al
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