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  #21  
Old 10-23-2017, 05:37 PM
tima tima is online now
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Originally Posted by PHC1 View Post
...

As for our example of Reference 6 and C47 and say MC501 monoblocks. The MC501's voltage gain is not high. It needs over 2 volts to reach maximum output. The Reference 6 starts to clip at 2.7V balanced. Ok, perhaps not terrible but it is too close imho.

The C-47 has 100/200 ohms SE and balanced output impedance. The Reference 6 output impedance in balanced reaches 1378 ohms at 20khz. That's quite a difference. Reference 6 should be paired with an amp with at least 100k ohm input impedance (which the MC501 for example has but other amps may not be)

...
Interesting analysis. How did you take these measurements of the Ref 6? From reading test reports, such as Atkinson's in Stereophile, I see manufacturer specs and independent measurements can differ, though typically not by so much.
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  #22  
Old 10-23-2017, 06:53 PM
PHC1 PHC1 is offline
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Interesting analysis. How did you take these measurements of the Ref 6? From reading test reports, such as Atkinson's in Stereophile, I see manufacturer specs and independent measurements can differ, though typically not by so much.
Stereophile and results should not vary much, this is not rocket science. I do have a degree in electronics although I switched careers early in life but I do know that bench test equipment for the most part is very accurate. If results vary, suspect the unit, tolerances and Q/C of such gear. As if that never happened when the unit in for review did not crap out!
Not saying ARC is bad by any means.
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  #23  
Old 10-24-2017, 12:30 AM
tima tima is online now
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Originally Posted by PHC1 View Post
Stereophile and results should not vary much, this is not rocket science. I do have a degree in electronics although I switched careers early in life but I do know that bench test equipment for the most part is very accurate. If results vary, suspect the unit, tolerances and Q/C of such gear. As if that never happened when the unit in for review did not crap out!
Not saying ARC is bad by any means.
No worries, I didn't take your commentary to say anything negative about the ARC Ref 6 or any unit mentioned here. I was just curious where the measurements you cited came from: "The Reference 6 starts to clip at 2.7V balanced." ... "The Reference 6 output impedance in balanced reaches 1378 ohms at 20khz."
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Old 10-24-2017, 07:55 AM
robd2 robd2 is offline
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Good info guys. What is the logic behind matching pre amp output impedance to an amps input impedance? Is it as long as one is higher than the other you are ok?
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  #25  
Old 10-24-2017, 08:10 AM
PHC1 PHC1 is offline
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Good info guys. What is the logic behind matching pre amp output impedance to an amps input impedance? Is it as long as one is higher than the other you are ok?
In theory you would want as low of output impedance in the preamp as possible and as high in the amplifier input impedance as possible. In simplified terms: The amplifier sees the voltage coming out of the preamplifer and creates a larger version of the signal to feed to the speakers. The higher the ratio of output to input impedance, the more voltage can be delivered the amplifier (the amplifier is not interested in current from the preamplifer so don't confuse this with how amplifier/speakers interact.) In practice due to other issues to consider and without getting too technical we say at least a 1:10 to 1:20 ratio is considered good.
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