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Questyle CMA800 Current Mode amp - Page 8

post #106 of 589

You have hit the nail on the head here. Fully balanced through the Eximus is not as good (for me) as dual mono through the Naim. There was also a massive improvement in sound stage moving from one CMA800R to two in dual mono. The bass especially is incredibly powerful but not overbearing (although part of that is down to the Naim). I would never have thought it was possible to get such good, strong bass extension through HD800's.

 

It is also an excellent upgrade path as well.

 

I will be sticking with what I have for the time being, until the right preamp/DAC/balanced combination comes along to match the Questyle (I have already suggested to them that it is something they need to consider).

post #107 of 589
CMA800:
Max Output Power :180mW (7.5Vrms) @300Ω, standard Stereo Mode
710mW (15Vrms) @300Ω, Mono Mode

This power is ok to drive LCD-2s?
Because the current output goes through the impedance of HP, and generates power so that the max power 710mW through 300 ohms becomes 71mW for 30ohms.

It seems too weak for the power to drive Lcd-2s that demand about 1w.

Could you guys give some explanation?

thanks
post #108 of 589
Quote:
Originally Posted by Joong View Post

CMA800:
Max Output Power :180mW (7.5Vrms) @300Ω, standard Stereo Mode
710mW (15Vrms) @300Ω, Mono Mode

This power is ok to drive LCD-2s?
Because the current output goes through the impedance of HP, and generates power so that the max power 710mW through 300 ohms becomes 71mW for 30ohms.

It seems too weak for the power to drive Lcd-2s that demand about 1w.

Could you guys give some explanation?

thanks

what equation is it that gives a logarithmic relation between impedance and power?

 

 

simply using the normal equation:

 

(7.5^2)/60 = 0.9375 W

 

or

 

(15^2)/60 = 3.75 W

 

It should drive the LCD2 fine

post #109 of 589
Quote:
Originally Posted by Joong View Post

CMA800:
Max Output Power :180mW (7.5Vrms) @300Ω, standard Stereo Mode
710mW (15Vrms) @300Ω, Mono Mode

This power is ok to drive LCD-2s?
Because the current output goes through the impedance of HP, and generates power so that the max power 710mW through 300 ohms becomes 71mW for 30ohms.

It seems too weak for the power to drive Lcd-2s that demand about 1w.

Could you guys give some explanation?

thanks


Read this post of mine:

http://www.head-fi.org/t/692923/review-questyle-cma800-current-mode-amplifier#post_10029600

 

If this amp hasn't got enough power to drive the LCD-2 the next step would be to connect it directly to the speaker posts of a 500w power amp!! I know some people do this for some crazy reason. There are other ways to blow your eardrums to smithereens :)

post #110 of 589
Quote:
Originally Posted by KamijoIsMyHero View Post

what equation is it that gives a logarithmic relation between impedance and power?


simply using the normal equation:

(7.5^2)/60 = 0.9375 W

or

(15^2)/60 = 3.75 W

It should drive the LCD2 fine
If the amp is a voltage source, you are right.
However it is current source, the power is equal to IIR in peak to peak.
Because ideal current source has infinite source impedance.

For this regard, my estimation too rough.

To be exact, the power through the 50 ohms of LCD-2 The p-p power is 0.025^2 x 50=31 mW.
where 0.025 amps = 7.5 V/300 ohm per spec and the current does not vary with load that is HPs.
My assumption is that CMA800 is A current source with at least source impedance of 10 Mega ohms.
thanks.
post #111 of 589
Quote:
Originally Posted by Joong View Post


If the amp is a voltage source, you are right.
However it is current source, the power is equal to IIR in peak to peak.
Because ideal current source has infinite source impedance.

For this regard, my estimation too rough.

To be exact, the power through the 50 ohms of LCD-2 The p-p power is 0.025^2 x 50=31 mW.
where 0.025 amps = 7.5 V/300 ohm per spec and the current does not vary with load that is HPs.
My assumption is that CMA800 is A current source with at least source impedance of 10 Mega ohms.
thanks.

 

meh once I got introduced to Norton's theorem, I never bothered calculating using amperes. To me, its all the same as you can get an equivalent look at how the circuit will work. I don't think it matters too much. Nothing seems to suggest they are using Amperes in their calculations, it's quite the opposite as their specs give VRMS as well as

 

 

Maybe their rep can clarify. It'd be nice.

post #112 of 589
Well, based in the specs given I to a 64 ohm load (700 mW) and a 32 ohm load (1100mW), we can assume the LCD-2 would fall somewhere in the middle. So maybe 900mW or so, give or take a little? Basically close to 1 W. LCD-2 is no HE-6 in my experience.... It likes some juice, but not THAT much. The CMA800 seems to have plenty available.
post #113 of 589
Quote:
Originally Posted by Joong View Post

However it is current source

But it isn't a current source amp, it's a voltage source amp. Project86 confirmed that in his review.
post #114 of 589

Thank you for your clarification.

The all the signal paths prior to the output buffer that may convert the current signal to voltage one in order to get low output impedance.

This case of signal processing is an usual signal processing in Integrated Circuit.

Because current handling is very convenient to handle both the magnitude and the phase. both of which are actually signal.

The headphones are really a motor that is directly driven by current that generates magnetic flux that is proportional to acoustic pressure.

The voltage information is not equal to the acoustic information in this regards.

But the current information is equal to the acoustic information due to motor relation.

This is a reason why I want CMA800 to be an ideal headphone driver that is the most effectively driven and is truly tracing the original record.

 

Why did Questyle deviate from the current passage, and finally ended up with voltage source driver?

 

There is certainly technical barriers?


Edited by Joong - 12/7/13 at 1:00pm
post #115 of 589

Thank you for your kindness, and your effort.

 

Quote:

Originally Posted by KamijoIsMyHero View Post
 

 

meh once I got introduced to Norton's theorem, I never bothered calculating using amperes. To me, its all the same as you can get an equivalent look at how the circuit will work. I don't think it matters too much. Nothing seems to suggest they are using Amperes in their calculations, it's quite the opposite as their specs give VRMS as well as

 

 

Maybe their rep can clarify. It'd be nice.


Edited by Joong - 12/7/13 at 1:55pm
post #116 of 589
Well for one, headphones aren't currently designed to be driven by current sources, so frequency response anomalies will almost always result and two, you lost electrical dampening that way, which I think most dynamic drivers need.
post #117 of 589

I see that there are too much impedance gap between dynamic HP and ortho HP to hit market location with single architecture of current source amp.

Therefore the current mode amp can not easily find the market for large volume sales, which are certainly related to dynamic phones.

post #118 of 589
Be careful not to put too much emphasis on specs alone when considering hifi equipment. I'm very well aware that Audez'e recommends amps that produce 1-4w
but power isn't an issue here. Schiit Lyr doesn't sound nowhere near as good with its 4w into 50 ohms.

I think it goes for any decent headphone that it will benefit from some more headroom or a better damping factor. But LCD-2 is not a power hungry headphone such as some of the HifiMans planar magnetics. LCD-2 plays fine straight out of my iPhone, iPad and Sansa Clip without distortion at dynamic peaks. Of course it isn't highend but it sounds dynamic and distortionless.

The CMA800 has more than enough power to drive the LCD-2 sufficiently, period.
I might as well argue that it's got too much power as it hasn't got an attenuator. thus making the 9 o'clock position the ideal for normal listening level with most kinds of music. However most pots work best electrically at around 12 o'clock, a position that will most likely give me a hearing loss with my LCD-2!
post #119 of 589
Quote:
Originally Posted by SebastianL View Post

I might as well argue that it's got too much power as it hasn't got an attenuator. thus making the 9 o'clock position the ideal for normal listening level with most kinds of music. However most pots work best electrically at around 12 o'clock, a position that will most likely give me a hearing loss with my LCD-2!


That's not too much power, that's too much gain wink.gif
post #120 of 589

Anyone compare this to the Bryston BHA-1?

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