2. amps-preamps
  3. 163599-140647

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

Showing 3 responses by georgehifi

georgehifi's avatar
georgehifi
10,312 posts
 


You need to throw some gain away, obvious is to dump the preamp/s. And use a 10kohm passive pre so anything can drive it. (save for some silly high output impedance sources) (usually tube).

Forget inline attenuators, too much of a gamble, you never know if you have an impedance match or not, (unless you know how to measure them) because from what I was told they don’t state what series/shunt resistances they have used inside them

Cheers George
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.
georgehifi's avatar
georgehifi
10,312 posts
 
Your Joule from what I found only has 11db of gain. The AR is still only 12.5db, your problem is the speakers, but if your attached to them then.
You have 108db efficient speakers and an amp that has 100kohm input impedance and 29db gain, "which is perfect recipe for a 20kohm passive preamp", your line source/s should be fine into a 20k passive preamp.
And if you use phono, use a phono stage with gain of 50-60db that has low output impedance say <300ohms.

Cheers George
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