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Advice on DIY Headphone amp for AKG K712s
Advice on DIY Headphone amp for AKG K712s
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Old 12th June 2019, 04:33 PM   #1
deeptransmissions is offline deeptransmissions
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Default Advice on DIY Headphone amp for AKG K712s

As you can imagine these are very hard to drive, and I'm more of a transformer guy than a tube guy. My DIY experience is moderate, replacing and repairing some synths, I built a DIYRE summing mixer, and am about to build a set of CAPI VP28 pres.

My output is coming from my Motu audio interface (Ultralite AVB) and it's just not enough for those cans. My Grado's are better for production than the AKGs at this point and that's kind of a bummer.

Is the DIYRE amp enough for these cans? I'm hoping to keep this under $100 as I'm not looking for nirvana, just somethign that can get these can running as they should so I can hear my synths and productions clearly.

Also, if you make a recommendation, would you mind telling me a little about how you arrived at this? I'd like to understand thigs like impedance and sensitivity a little better (per the specs below).

Thank you in advance, can't tell you how much I appreciate all the help I get from kind internet friends with audio and synth stuff.

AKG K712 PRO Specifications:

Headphone type: Open.
Audio Frequency bandwidth: 10 Hz - 39.8 kHz.
Sensitivity (headphones): 105 dB SPL/V.
Max. Input Power: 200 mW.
Rated Impedance: 62 Ohms.

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Old 12th June 2019, 10:39 PM   #2
Mark Tillotson is offline Mark Tillotson
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What I see in the specs:

1 volt rms in gives 105dB SPL

more than 200mW will damage the phones (though your hearing will be damaged before that, its about 116dB)
At 62 ohms 200mW corresponds to 3.5Vrms, so yes these take fairly high voltage levels to
drive to the limits. R.P = V^2, so V = sqrt(R.P) = sqrt (62 * 0.2).

But full power only needs 56mA rms (P = R.I^2).

Almost any opamp could drive this current, but not without distortion due to the low impedance (from an opamp's point of view - normally 500 to 2000 ohms is the highest clean load for opamps, though some can do a fair bit more)

I'd suggest a headphone amp capable of 3V rms output with adjustable gain upto +15dB or more, that will take 0.5Vrms up to 3Vrms or so. Ought to be enough level I think.

That ultralite AVB box probably has a low quality phones output anyway, using one of the cheap chips for the job, as well as being too low level. A separate headphone amp from the main output signal might be better sounding anyhow.
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Old 13th June 2019, 05:39 AM   #3
PRR is offline PRR  United States
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Originally Posted by deeptransmissions View Post
...Is the DIYRE amp enough ...
Would be nice to provide a link for those of us who can not remember every model of every amp ever made by any company.

It will "play" your phones as shown with 9V battery. If you are not happy now, you should perhaps be thinking a 24V supply. (The board is good to 44V but that is for HIGH-impedance work and just reckless with 62r phones (4 Watts!!) and the only ears you own.)
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