[mrAdrian]

Besides the O2, and all Meier Corda amps, what other amps have low output impedances?

 

[fusionramjet]

Musical Fidelity has two headphone amps.  The budget one is called the V-CAN II ($200) and it has an output impedence of 5 ohms.  Musical Fidelity makes a point of highlighting this.  The higher-end one is called the M1 HPA (something like $800), it lists 1 ohm as the "source impedence", not sure what this means, but I imagine it's also very low output impedence.
I have the V-CAN II along with Musical Fidelity's V-DAC II ($350), which I'm using to drive the LCD-3.  It sounds awesome.  However, I have no reference point because I don't have any other desktop amps.  So, I'm not at all an authority when it comes to amps.

 ​

 

[NA Blur]

Grace Design m903:  Headphone output impedance = 1.2 Ohms
http://www.gracedesign.com/products/m903/m903.htm
 
Headroom's Balanced Ultra Desktop Amp:  Headphone output impedance = .5 - .6 Ohms
http://www.head-fi.org/t/512731/buda-impedance-and-output-spec
 
Benchmark DAC1 Pre: Headphone output impedance = < .11 Ohms
http://www.stereophile.com/content/benchmark-dac1-usb-da-processor-headphone-amplifier-specifications

 

[runeight]

The Liquid Fire has an output impedance of about 0.25R.

 

[Chris J]

Quote:

The higher-end one is called the M1 HPA (something like $800), it lists 1 ohm as the "source impedence", not sure what this means, but I imagine it's also very low output impedence.

 ​

 
Yes, source impedance is another way of saying "output impedance".
 
here's a fairly low output impedance unit:
Matrix M Stage:   5 ohms

 

[mrAdrian]

I know the fiio portable line has a near zeto output impedance too. I hatr starting yo adk for suggestions so early but for around 250 what would be a good amp for grados and denon headphones?

haha zo2+e9+ Arietta into cash into another solid state, any say?

 

[haejuk]

I think you probably won't do much better than your Arietta for the price.  I guess if you wanted better volume control and a worse looking design (and almost the exact same sound) then you could get an O2.  It is really difficult to find amps in this price range with a low enough output impedance for Grados, and especially Denons.

 

[Solude]

Damn near every solid state amp has a low output impedance.  Centrance and the original Burson being the exceptions.  Most transformer based tube amps also have a low output impedance in relation to headphone impedance.  These aren't 4 ohm speakers after all

 

[mrAdrian]

I just found it quite hard to follow the one eighth rule when it comes to the denon

 

[mrAdrian]

Quote:

The Liquid Fire has an output impedance of about 0.25R.

Wow and a tube amp! XD Definitely want to hear one but I don't want to sell any more body organs as of now.
 
Quote:

I think you probably won't do much better than your Arietta for the price.  I guess if you wanted better volume control and a worse looking design (and almost the exact same sound) then you could get an O2.  It is really difficult to find amps in this price range with a low enough output impedance for Grados, and especially Denons.

Have you heard both? I did shortly and I agree with you that they sound about the same. I'm just wondering if I sell it, and sell the E9, and sell the ZO, would I be able to get some improvement. Thanks for the input!
 
Let's get back to the topic, keep listing guys!
 
And another question, how do you measure the output impedance?

 

[mikeaj]

You know, plenty of people report Grados and Denons running just fine on high-Z output sources.  Damping factor is probably not such a big deal for these headphones which have a pretty flat impedance across frequency (pretty much resistive).
 
Quote:

And another question, how do you measure the output impedance?

 
Output a constant tone and take a couple of voltage readings.  Cheap multimeters are under $10.  You just need two different resistors, or for a little coarser estimate, just a couple different headphones with known impedances at the frequency of the test tone you're using.
 
V_L = V_s * Z_L / (Z_s + Z_L)
 
V_L is voltage you measure across the load (resistor or headphones).
V_s is voltage output from the source, unknown.
Z_L is load impedance, which should be known.
Z_s is source output impedance, unknown.
 
So with two different readings using different loads, you have two different (independent) equations and two unknowns.  Solve for Z_s.

 

[mrAdrian]

I'll give that a try with my DV336 after my exams. Interesting note on the Denon and Grado's FR vs impedance graph. Sounds to me the Arietta is a keeper for my solid state amp.
 
Is it particular harder to achieve near zero output impedance for a tube design? How about hybrids?

 

[Chris J]

Damn near every solid state amp has a low output impedance.  Centrance and the original Burson being the exceptions.  Most transformer based tube amps also have a low output impedance in relation to headphone impedance.  These aren't 4 ohm speakers after all

The Beyer A1 has an output impedance of 100 ohms......rather high.

 

[Solude]

That's because Beyer still believes in the IEC 120Ohm spec.  Its on purpose and from a time when cans were 600+ ohms.

 

[haejuk]

Quote:

 
Have you heard both? I did shortly and I agree with you that they sound about the same. I'm just wondering if I sell it, and sell the E9, and sell the ZO, would I be able to get some improvement. Thanks for the input!

 
I own both the O2 and the Arietta right now and used to own the E9.  I think after the Arietta, you would have to spend much more than $250 to get a decent upgrade that will really make you feel like you got an upgrade.  I think Audio-GD makes some decent amps with low output impedance, you might look into that.  I haven't ever heard one, but I have considered buying from them.
 
As for tube amps with low output impedance, they have to be transformer-coupled tube amps.  These can get really expensive because the transformers used in the output stage are pretty hard to find and often hand wound.  I wouldn't be surprised if there were some Tube-hybrid amps with low output impedance, but from my research I found most of them too noisy for the sensitive Denons.  Once again, didn't actually hear any of them myself.  I also happen to own a Little Dot I+ hybrid amp and it performs quite well with my Denons.  It sounds warmer than my SS amps, but other than that I don't really feel it performs as well as O2 and Arietta.  I also saw that the maker of the LDI+ claimed it to have 32 ohm output impedance, so not exactly low.