Using a line preamp to drive headphone

[AndrewT]

AKG's 600-ohm cans have low sensitivity and require high level driving capacity to sound right. You may want to make sure your preamp is capable of at least 10Vp-p output into 600-ohm loads. ............

low sensitivity?
Are you sure.
10Vpp is equivalent to 3.536Vac.
Into 600ohms that is only 20.8mW That's +13dB ref 1mW

 

[sgrossklass]

Classic 600 ohm AKGs are rated at only 88 dB/mW (which at 600 ohms does make for fairly low sensitivity by headphone standards), so 20 mW would give you 101 dB SPL. Seems like a reasonable rec.

 

[ginetto61]

I haven't been following The Wire threads closely, but there may be offers for assembled PCBs that have all SMD parts mounted.

Hi and thanks a lot. The interest has come up again then.
I like indeed the idea of a separate buffer that i can move and try with different line preamp. With the line preamp giving the flavour to sound and the buffer doing the tough job.
I will read more carefully the links.
Thanks a lot again, gino

 

[ginetto61]

Its not so much about lacking the 'juice' to drive the cans, rather they're introducing too much noise from the power supply.
Output stage PSRR is a commonly overlooked issue when opamps are being used (as in the O2) as designers assume the PSRR they'll get in practice is the one shown in the DS. But yes I think its the reason for 'sterile, flat' sound - noise does not get placed into the acoustic space by our cognitive processes so 'hangs around' the transducers so to speak. With speakers this translates into reduced depth

Hi and thanks a lot for the very valuable advice.
I think that a good depth is indeed a very telling effect of very good equipment. It implies low noise, low distortion and high linearity.
For me it is one of the most important goal with speakers.
It is quite strange to see that even units from celebrated Companies skip on some details that are not secundary but they impact overall performance a lot. I believe in good mods of existing units a lot.
Some small changes can elevate already good designs remarkably.
Thanks a lot again, gino

 

[nattawa]

low sensitivity?
Are you sure.
10Vpp is equivalent to 3.536Vac.
Into 600ohms that is only 20.8mW That's +13dB ref 1mW

Yes, I'm sure, Andrew.

AKG 600-ohm phones generally have SPL spec of 88db at 1 mW, translated to 90db/V in voltage sensitivity when output (voltage) capacity of the driving device is in concern. That is a vastly lower sensitivity compared with AKG's medium and lower impedance phones such as K240S, 55-ohm spec-ed at 104db/V, or K812 36-ohm at 110db/V.

 

[AndrewT]

88dB/mW is indeed low.
About 10dB to 15dB lower than many headphones.