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Gain Matching - need advice

I recently added an Audio Research Ref 6 to my system (it was a dealer demo unit so price was right).  The preamp is paired with Pass Labs XA 60.8 amps (26db gain and 100K ohm input impedance) and Avantgarde speakers (sensitivity of 108 db at nominal 8 ohms).  The problem I am having, that I did not have with my previous Joule Electra LA150, is volume control.  The AR preamp has a 103 position volume control.  At position #7 the volume is almost ear splitting.  Sure I can turn it down but it’s very difficult to dial in a suitable volume.  I am inclined to blame it on the new AR preamp (output impedance of 600 ohms and 12db of gain).  I am stuck into using balanced interconnects which I won’t go into.  My first conclusion was that I have a gain matching problem since the old preamp did not behave this way.  Looking at the difference between the output impedance of the preamp and input impedance of the preamp ... why would there be a gain matching problem (at least as I understand the subject ... which I may not.  Anything that can be done about this, or a new preamp the only solution?
chilli42
georgehifi's avatar
georgehifi
10,312 posts
 
The only problem with in line fixed attenuators, is you don’t know what resistors they have used in series and to ground to get the attenuation.
This can ruin the minimum 1:10 input to output impedance ratio, could end up 1:2 or something, won’t hurt anything but may screw with the sound.
mickeyb
585 posts
 
This is my biggest fear when purchasing a new preamp. If you love those amps, which are special, I’d sell the arc and research a good match for the pass amps. Good luck. 
jjss49's avatar
Ag insider logo xs@2x
jjss49
6,612 posts
 
op

iirc audio research can take the ref line stages and alter the gain profile at user request for situations such as this

contact greg c their service manager
geof3
1,129 posts
 
What jjss49 said. If you are dead set on the Ref 6, let ARC modify it and do it right. They did my LS17SE. Took a bit, but it was done right and wasn’t a hinky “fix”.
clearthinker's avatar
clearthinker
1,582 posts
 
Don't see Miller replying to this one:
'Dimwit, your speakers are way too sensitive, concentrate on getting speakers with less than 87dB efficiency'. :-))

Crazy to ask AR to modify the piece.  They would need to work out what to do and charge you $000s.  And the amp would be unresellable after.

In any case, the big matching problem is not with the Ref 6.
You need to change the power amp or the speakers.
Changing the Ref 6 for a pre-amp that's flat with no gain will only partially solve the problem.  Losing 12dB of gain will mean your volume tops out at position #(7 + 12/0.3), as each step is about 0.3db.  That's #47 which is still less than halfway up to #103.

Having said that, I run a Ref 6 too.  With Krell Reference 200s upgraded to 400w per side and Martin Logan CLX Anniversary specced at 90dB sensitivity but probably a bit less, the volume is certainly very full on at around #40-45 and I get enough differentiation from those 40 steps.

It wasn't so long ago when I upgraded to Ref 6 and vdH The Grail SB.
I calculated the system gain very carefully before diving in.  I recommend others do the same.
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