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Headphone amplifier - 6H30

78.91.103.24
Posted on February 4, 2014 at 13:22:19
gormj
Audiophile

Posts: 5
Location: Trondheim
Joined: April 17, 2011
 I am the satisifed owner of a Rakk-dac and tube preamplifier. Now I want to build a headphone amplifier and I liked the simplicity of the schematics on your web-page (the one and only schematic for a headphone amplifier) using a 6H30 and the LL1630.

The headphones are not bought yet, but i expect that it will be a Hifiman HE-500 ( Efficiency: 89 dB/mW Impedance: 38 Ohm) Audeze LCD2 (Impedance: 60 Ohms, purely resistive Efficiency: 90 dB/1 mW) or LCD LCD-X (Impedance: 22 ohms, purely resistive Efficiency: 96 dB/1 mW).

Is the amplifier in the schemnatic suitable for such low impedance headphones?

I am a newbie with tubes and output transfomers, but good fellows on a Norwegian forum have suggested that maybe 6C45 and LL1664 eller 1663 migh be a better choice.

I would very much appreciate your view on this, or if you could suggest another suitable schematics, preferrably a simple SET one.

Best regards
Gorm

 

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RE: Headphone amplifier - 6H30, posted on February 4, 2014 at 14:40:36
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 The circuit with the 6N30P would be good for higher impedance headphones like the Sennheiser HD580/600/650, but not the ones you are considering. Bass damping will suffer under 100 ohms.

The potential problem with the solution recommended by your Norwegian forum colleagues is that of overall gain. Given a mu of 45 for the 6C45P, an LL1663 (24:1) will result in a gain of only about 5 or 6dB. However, if you use the preamplifier in the signal chain after the DAC, the gain not likely to be a problem. The LL1664 will result in somewhat higher gain, but wouldn't be quite as nice a load for the 6C45P with 10 ohm headphones.

There aren't many tubes that can be used in the fashion you describe and I can't recall one that would be better, although caution needs to be exercised with the 6C45P to avoid incipient oscillation. Liberal use of stopper resistors and ferrite beads and good layout will keep the RF stuff under control.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: Headphone amplifier - 6H30, posted on February 5, 2014 at 13:47:07
gormj
Audiophile

Posts: 5
Location: Trondheim
Joined: April 17, 2011
 Thanks for a helpful answer. I will look further in the direction of 6C45. Hopefully you will give further comments when I have a final schematics.

By the way. My KandK RAKK DAC with your active tube preamplifier will continue to make great sound in my living room and will not be used together with a headphone amplifier. The headphones are intended for the mountain cottage. So yes, gain is an issue.

 

RE: Headphone amplifier - 6H30, posted on February 5, 2014 at 17:15:37
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 I will gladly provide whatever input I can.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

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