[gadfly]

Hello,

Anyone have any experience using a headset
with the Ava CF pre?  If so what headset and
your opinion as to sound quality? 

thanks,

gad-

[edn4x4]

Yes-
Drives my T1's with authority.
Very dynamic - SQ is great.  I haven't used it in a while, but I wish I had the cf prior to the other dedicated headphones amps I have.
Most of the time I am listening to my big rig in the room that has the cf that is the only reason I haven't used it much.  I always thought Frank should come out with a dedicated headphone amp as well...

[dB Cooper]

He should IMO, but has shot the idea down several times. I think this is a mistake as the headphone market is the one segment of 'high end' audio that is booming. He already has a suitable enclosure, the one the standalone phono pre and HumDinger come in. I have read that the output impedance at the headphone jack in the current AVA preamps is 47 ohms, workable for high impedance cans like your 600 ohm T1's (DF=~12) but maybe not so much for increasingly prevalent mid-to-low impedance 'phones for reasons explained better than I can here and here. If the info I saw (in a thread on the RB preamp) is inaccurate, I apologize in advance.

[edn4x4]

... He already has a suitable enclosure, the one the standalone phono pre and HumDinger come in. ..

This would be cool for a small setup, I was thinking more in the lines of using the Ultravalve Vacuum Tube Amplifier.

[I.Greyhound Fan]

edn4x4, give me an email.

Larry

[dB Cooper]

Regardless, AVA seems to have little interest in the headphone space beyond the provisions in their preamps. If you are using low impedance headphones- which are more and more common- a 47 ohm output impedance (if that is correct) can cause audible problems described in the articles I linked. Here's another linked article about headphone amp design guidelines that explains why, in #1 on the list. I'm not an electrical engineer, but the authors of both those articles are, and they make their case using objective data.

No disparagement to AVA, a company that makes remarkable, rock-solid products that punch way above their weight dollar-for-dollar. They just seem much more speaker-focused. That's fine; there are plenty of good choices in the dedicated headphone space.

[gadfly]

What <$500 headphone might sound decent
with the CF pre.  Sennheiser 600 or 650
or.........., dac is a Yggdrasil currently used
with speakers, but I'm gettin headphone
curious.

[dB Cooper]

Look at the 600 ohm versions of the Beyer DT880 or 990 would be my suggestion, based on the reported 47 ohm output impedance (that was the RB and the CF might be different) and the venerable rule of thumb that source impedance should be no more than 1/8 load impedance for best performance. Dale might know some good candidates also but there aren't as many high impedance options as there once were.

[G Georgopoulos]

since this is line preamp may have trouble driving the headphones adequatly
let's assume 2v output from preamp
headphone impendance 600 ohms
((2/600)=3.3mA x 2) =6.6mW
6.6mW sounds very low to me
next take headphone sensitivity at 1mW this will give you an idea of the dB level
(dBcooper is right about source impedance should be less than 1/8 load impedance)
to me it doesnt cut,unless the preamp can provide more o/p volts

cheers   

[avahifi]

All Audio by Van Alstine amplifier have outstanding headphone performance.  They also drive low input impedance headphones just fine.

I use Grado SR-225 phones here myself (30 ohm input impedance) and these sound lovely with our preamplifiers.  I also have older phones with 600 ohm input impedance and they never sounded so good either.

In our vacuum tube preamplifiers the headphone drivers are simply current buffers to provide a high current and low output impedance to any headphones.

The active current amplifier for each channel is an LME49600 which has a 2000V/µS slew rate and all of 0.00003 percent THD.

So with AVA tube preamps, what you are actually listening to is the line tube section with only that ultra distortion buffer afterwards.  No gain stages or transistors used at all.

Regards,

Frank Van Alstine

[dB Cooper]

In our vacuum tube preamplifiers the headphone drivers are simply current buffers to provide a high current and low output impedance to any headphones.

Thanks Frank. What is the output impedance the headphones see? In the first article I linked to (nwavguy) he suggests (and gives engineering reasons for) a maximum output impedance of two ohms (assuming a headphone load of 16 ohms and a desired damping factor of at least eight). Most high quality headphones will be higher than 16 ohms but the average has probably crept lower since the ascendance of portable lifestyle appliances.

[G Georgopoulos]

Thanks Frank. What is the output impedance the headphones see?

dbcooper very nice question 
since this is tube buffers
the current of the tube => x8 the headphone current
VRk/Ik=Zout