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Is this underamping or just sound signature?

post #1 of 7
11/18/09 at 4:39am
Thread Starter 
So, I ran the line out of my CDP through a JDS CMoyBB and also a Compass. The HP were Sennheiser PX100.

The bass was much less tight with the CMoy, though the quantity was pretty much the same. This (the first part at least) is what I would have expected due to less powerful amplification.

However, the CMoy sounded brighter, if less refined, overall. For example, higher-pitched percussion sounded snappier, less softened.

I wonder whether in reality this is a thinness and harshness due to under-amplification. It's certainly not as smooth or easy to listen to over longer periods, and the PX100 do have a warm signature, don't they? This would mean that the CMoy can't really drive the PX100 even at low volumes.

So, can under-amping have this brightening effect?

The Compass was set to neutral/normal, the CMoy opamp is OPA2227P.

TIA.
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post #2 of 7
11/18/09 at 11:28am
It's impossible to say for sure but the PX100s are not 'hard to drive' headphones and yes they do have a dark/bass emphasized sound signature (warm usually refers to mids afaik.) For that reason if forced to guess I'd say it's sound signature of the amps, not 'underamping' in terms of power.
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post #3 of 7
11/18/09 at 11:50am
OP2227 does tend to sound a bit bright in cmoy, compared to the popular choice of OPA2134. I think it is not really underamping, but rather the natural result of cmoy being not as good as Compass and the opamp choice.
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post #4 of 7
11/19/09 at 4:30am
Thread Starter 
Yes, I'd have thought the PX100 should be easy to drive, therefore the CMoy shouldn't struggle so much. However, it's all about current with the low impedance 'phones so I'm not sure, may have to try to do some calculations.

ClieOS, can you elaborate on what you mean by the CMoy not underamping yet not being as good? Do you mean its signature is off, rather than its driving ability (in this case)?
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post #5 of 7
11/19/09 at 1:37pm
actually PX100 does gain a fair bit of bass and bass control with more power; but it is more likely the opamp choice
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post #6 of 7
11/19/09 at 3:35pm
Quote:
Originally Posted by anoobis View Post
ClieOS, can you elaborate on what you mean by the CMoy not underamping yet not being as good? Do you mean its signature is off, rather than its driving ability (in this case)?
I think there are two issues here: 1) whether PX100 is underamping by cmoy and 2) whether cmoy has as good a performance as Compass or not.

First, being only 32 ohm and having a 114dB SPL sensitivity make PX100 a fairly easy to drive headphone, so we can assume cmoy should be more than enough for the job. Then, I think we can safely conclude that Compass is a much better amp than a cmoy. Taking a car analogy: while two car are both capable of 100mph, it doesn't mean a family sedan will have the same performance as a rally car on bumpy road at the same speed. The better hardware gives the rally car better control, and same can be applied to Compass vs. cmoy.
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post #7 of 7
11/29/09 at 7:28am
Thread Starter 
Or, to extend the car analogy, just because two cars are capable of outputting the same power, doesn't mean the one with more total power won't perform better. It's about the ability to respond to changes too, and what's in reserve to be called on.

I managed to listen to another amp and I think the difference between the CMoy and Compass is largely down to sound signature, just didn't expect it to be that significant.
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