AKG Pro Audio K712PRO headphone amplifier

[Aquilauno]

Hi guys,
This Christmas I received these beautiful AKG K712 pro headphones, due to the 62 ohm impedance connected to my SX900, even if you set the volume to maximum, the volume remains too low to be able to appreciate them at their best. Can anyone suggest me a good (but not too expensive) headphone amp. A friend suggested "Schiit Fulla 2", unavailable in Europe, I don't know if it can be connected to the SX900, I assume through the headphone output... I take the opportunity to send all the members of the Forum my best wishes to happy holidays.
headphone specifications:
Impedance: 62 Ohm
Peak SPL: 105 dB
Frequency Range: 10 - 39,800 Hz
Maximum Power: 200 mW

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[BogdanH]

I have AKG K242HD which has similar specs (2x200mW, 55Ohm, 105dB) and I have no problem with volume when connected to my PSR-SX700. Actually, if I turn volume to full, it is way too loud. For comfortable loud listening, I have volume knob in the middle position.

Bogdan

[Aquilauno]

Hi Bogdan, maybe I need to set up some headphone output?
I tried looking for something on the SX900 but I didn't find anything that worked... To get enough listening I have to bring the knob to max and remember to bring it back to 60% when I unplug the headphones... it's annoying and if I forget to doing so I risks damaging the speakers of the SX900.
Pietro

[mikf]

I had a similar problem with my CVP705 when it was new. Still under warranty, they sent a technician to investigate, but he came to the conclusion that it had to be a design issue and he could not change it. He did tweak the compressor to give more volume, but that has the same issue you mention. Volume is then too loud when you unplug the headphones. But at least I don't have to have volume control to full up.
Mike

[BogdanH]

hi Pietro,
Headphones have no specific settings on keyboard. Just so you have an impression how loud headset should be: I have about the same loudness on headphones as on keyboard speakers.

Have you tried AKG headphones on some other audio device or on PC? Do you have latest firmware (v1.11) installed on keyboard? Have you tried keyboard Factory Reset? Do you have some other headphones which you can try on keyboard?

Bogdan

[Bill]

There's nothing wrong with your keyboard, it's simply the headphones have a slightly higher impedance than that recommended.  If you look on Amazon you can find several headphone amplifiers for less than £20.

Bill

[mikf]

In the case of the CVP the problem was with the headphones than Yamaha supplied with the keyboard. So if there was an impedance mismatch they surely should have known and addressed it.
Mike

[Graham UK]

I use AKG240 mk2 55 Olm on my DGX670 with plenty of volume available.
my DGX volume is not used above 50%.
Adjust your EQ & Compression, plus EQ does contain a gain adjustment.

Most DAC's contain gain controls.

[Aquilauno]

Yes, the problem is the impedance of 62 ohms, I have a pair of old Sennheiser HD 205 headphones with an impedance of 32 Ohms and they feel very loud (unfortunately they are very uncomfortable headphones, even if worn for a short time they give me pain in the ears). That's why I asked for these new Agk as a gift, they are light and very comfortable even after hours of listening. So I'll have to see for a headphone amp... any suggestions?

[BogdanH]

There's nothing wrong with your keyboard, it's simply the headphones have a slightly higher impedance than that recommended.

-that's not the reason in this case.
Pietro's "quiet" AKG has impedance of 62Ohms vs my 55Ohms AKG headphones -the difference is academic: at listening, both headphones should be equally loud. The loudness becomes more apparent at bigger impedance differences, for example, 60Ohm vs 200Ohm headphone.
Right now, nobody knows where the problem is and that's why I suggested to "try this and that".

PS. Just reading your latest post.. Pietro, 62 vs 32 Ohms IS a big difference: it's the half of impedance! But the difference between 62 and 55 is negligible.
I wouldn't buy an headphone amp at this point.

Bogdan

[Aquilauno]

Hi Graham, you mean in the eq master? i will try to adjust the parameters but i think the best solution is a small headphone amp. I assume that the headphone output of the SX900 must go into the input of the amplifier, I just hope it can be powered by the USB keyboard port, just to avoid other plugs and jacks.

[Aquilauno]

Hi Bodgar,
I also thought it wasn't a big difference, perhaps the sensitivity or the frequency range also comes into play... Looking better on the web, if I understand correctly, on these types of headphones, an increase of 10 ohms corresponds to a doubling of the output power needed for the same volume...not sure what i'm saying lol...but if so that explains the difference in volume between the two akg headphones.
Now I'll try to see on the specs of the SX900 if it says anything about the output power of the headphones ... and  I'll have the answer. Then, I will be need the fix...lol
PS: I think that I have understand... the problem is that the audio source of the SX900 headphone socket is low voltage, lower than that necessary to drive the Akg 712pro properly(which have nice big drivers...) therefore the best solution is to use the headphone amplifier... or change headphones LOL.
suggestions for a good amp?

[MarkF_48]

I would not spend a lot on a headphone amp for the SX900. While the SX900 headphone outputs are likely good, they are not going to be 'audiophile' quality and using anything that is expensive that is intended for high end audio may not help improve the audio from the SX900. I do have a headphone amp I bought for an audio interface that has a low headphone output and it would likely be of an adequate quality for the SX900 output. Behringer or similar priced headphone amp would likely work fine.
https://www.amazon.com/Behringer-HA400-Ultra-Compact-4-Channel-Headphone/dp/B000KIPT30

A small mixer connected to the SX900 line outs might be another option that may also allow some hands on adjustment of the EQ to headphones.


I have a pair of Sony MDR7506 studio headphones I occasionally use with my PSR-S900. The 7506's are 63 ohms, similar sensitivity (106dB/mW) to the K712's and get loud enough to be at an uncomfortable volume. You don't want to cause ear damage from loud volumes.

[Aquilauno]

thanks MarkF, you never stop learning... happy holidays

[mikf]

When I had the tech in to look at the problem I still had my PSR3000, and the same headphones worked perfectly on that with tons of volume. The tech thought they must have changed output design in the later keyboards but was scratching his head why they would do that. He said he would feed back the info but seems nothing changed.

Mike

[BogdanH]

...on these types of headphones, an increase of 10 ohms corresponds to a doubling of the output power needed for the same volume...

-no, that is not true.
Because we are using impedance values (=resistance that depends on frequency), we can apply Ohm's law to calculate all necessary values. Without going into details and to keep post short, the fact is:
If at certain conditions (defined by pre-amp inside keyboard) my 55Ohm headset delivers power of 0.2W (200mW), then your 62Ohm headset should deliver power of 0.18W (180mW) at the same conditions. That is, the difference in power (that comes out of headphone) is 20mW or about 10% -which is already quite small. But more important is, loudness doesn't drop linear with power. To even notice the difference in loudness, the difference must be at least 2dB (depending on our hearing capability). However, the difference between 200mW and 180mW is only [10 x log (200/180)=] 0.5dB -which no human can notice.
I know, all this doesn't really help to solve your problem... I just think you shouldn't be too fast with buying headphone amp.

Bogdan

[Aquilauno]

Bogdar great explanation, just a doubt at this point. If the impedance is not such as to justify the low volume then it must be another specification that makes the difference. The headphones are advertised emphasizing the generouse size of the drivers... but I not be an expert... However I will have time to try them and possibly investigate the problem..
and in case buy something cheap but not too much. Thanks you

[Bill]

Hi Aquilauno

Bogdan is correct in his assumption, HOWEVER he is making the comparison between 55 & 62 Ohms. In your case though the difference is (or should be) between 8 ohms and 62.  8 Ohms is what what the expected impedance of "normal" headphones are.

The other point which some people have missed is that tweaking the KB Gain & EQ will effect the overhaul sound of the Keyboard And the headphones, which is what you did not want to do as mentioned about blowing your speakers should you forget to turn down the volume when you are unplugging the headphones.

Bill

A cheap headphone amplifier has its own gain control so you can balance the two. 

[BogdanH]

...8 Ohms is what what the expected impedance of "normal" headphones are.

I have to disagree again. To my knowledge 8 Ohm headphones don't exist -at least I haven't seen some (but I'm always ready to learn something new). Impedance range between 4 and 16 Ohm is used for "normal" speakers to deliver more power (compared to headphones).
There's a reason why headphones have higher impedance than speakers -and that is current: the lower the impedance, the higher the current. Headphone preamp isn't capable to deliver much current (hence "pre" amplifier) and headphones can't handle much current either. Reason is simple: headphone speakers need to be very small and so speaker coil needs to be small as well.. means, very thin copper wire is used for coil -and thin wire can't handle high current (coil would overheat).

The reason I made comparison between 55 & 62 Ohm is, because my (55Ohm) headphone works perfectly on PSR-SX, but Aquilauno's (62 Ohm) don't. I just wanted to point out, that on PSR-SX, there shouldn't be audible difference between these two headphones.

Bogdan

[MarkF_48]

Headphones that are 8 ohms did once exist and I still have two pair of old Pioneer's that are 8 ohms. Back in the 60's it was common in stereo amps/ receivers to have the headphone jack tapped off from the speaker connections which were generally rated at 8 ohms for speakers. I think an ancient pair of Koss headphones I have are also 8 ohms. The 8 ohm headsets gave way to what we have now as headsets commonly rated anywhere from 30 to 600 ohms. Back some 25 years ago I bought a pair of AKG K240's that were 600 ohms. Not much that I had for gear would drive them and I later found that 600 ohms had a special place in certain studio applications.

Ohm's does make a difference, but the difference between 50 ohms and say 65 ohms may not have much of a noticeable difference. There is a spec that manufacturers usually give which is the 'efficiency' of the headset drivers and given as dB/watt (sound level per watts)  but manufacturers sometimes 'fudge' the numbers or have different ways of measuring that the number may have little meaning.



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[Aquilauno]

Thanks for the quick replies.
The "problem" is that I expected them to play loud, instead setting the keyboard volume to maximum the sound is "normal" I mean sufficient for listening but nothing more. The Yamaha headphones, the top range settle on an impedance of 48 Ohm so a minimal difference.
Very Little difference too between these Agk712 and headphones from BogdanH and Graham, who are satisfied with their volume. After testing a pair of Sennheiser HD 205 headphones with 32 ohm impedance, the sound is louder but not by much, so I assume the keyboard specs are the bottleneck (or perhaps, my hearing).
After all, as Markf observed, keyboards have no reason to have high-quality audio in headphones, a "standard" pair of headphones is enough. So it's just my expectation due to "ignorance" in this field that creates my disappointment.
I tried the headphones with an old Yamaha RXV440 amplifier and here the headphones perform well and show their potential despite the amp not having exceptional specifications (it's an "old" 6.1 home theater). I tried them with the multi-effect Zoom G3 for guitar, connected directly to the Zoom nothing special, but connected to the small Fender G10 amplifier, we are in another world, the Agk 712 headphones sound great. This little amplifier has channels: volume , gain, high, mid and low separated. Now I know how I can make the most of these amazing headphones.
The alternative remains a small headphone amplifier or a small mixer that increases the output gain of the headphones of the SX900, to enjoy a satisfying sound without compromising hearing, 
Thanks everyone and happy holidays.

[MarkF_48]

Is your Yamaha RXV440 amplifier anywhere near the SX900 that you could try sending the line outs of the SX900 to that amplifier and give a listen with the AKG712's?

[Bill]

Hi All

We can debate until the cow's come home.

Aquilauno requires 2 things

1.  Sufficient volume from his Existing high quality headphones.
2.  He does not want to blow his speakers if he forgets to lower the volume before disconnecting.

What do you suggest he does which does not involve getting a technician to check his KB circuitry (and charge him an arm & a leg).

My suggestion of a cheap single channel headphone amp and give a try, seems to me to be his best option.  If he does not get the result he want. — he simply sends it back to Amazon free of charge.

So WHAT DO YOU SUGGEST

Bill

[BogdanH]

We can debate until the cow's come home.
...

-true 

From what Aquilauno said in his latest post, now I'm quite sure that there's a problem at headphone output on his keyboard (like mike mentioned). And of course, it's irrelevant what I think might cause that or how I would try to solve the problem. So yes, separate preamp seems to be the only solution for him.... did I mention I hate cables lying around? 

Bogdan

[Aquilauno]

Is your Yamaha RXV440 amplifier anywhere near the SX900 that you could try sending the line outs of the SX900 to that amplifier and give a listen with the AKG712's?

unfortunately not... but I should have a small mixer in the garage... that to work on battery also. Provided that the rust has left something functional... that would be enough for a litmus test.
i did a test i put the sx900 to max volume and unplugged the headphones, the speakers didn't explode...they were holding the max, not too happy my neighbors, but still i will rarely forget to realign the volume lol sure not late at night. My closeness to US friends who are under the storm of the century.
Pietro

[travlin-easy]

I've been using Marantz MPH-2 headphones with my S-950 for years. They're very comfortable, 50 ohms, and never had a problem with volume. I crank my keyboard's master volume up to 12 O'clock and it's enough to blow your ear drums out.

https://www.amazon.com/Marantz-MPH-2-Professional-Studio-Headphones/dp/B01E75MKRY

Gary

[Aquilauno]

I decided to buy a headphone amplifier, the Choice fell fell on this gem: Topping L30II (10 x 13,5 x 3,5 cm.) In reality it is not the best solution from an economic point of view, given that it costs 149.00 euros at this price Gary's idea would have been wiser whit the  headphones more suitable for the SX900, limiting extra cables and cables and saving something.
But this expensive solution allows me to take advantage of the AKG in further areas: TV, HiFi, Tablet ... since the headphones deserve it.
I say this because if others were in the same situation they will know what to decide about their money...
Now the power is felt at just over half the volume of the SX900  (EQ set Flat) at 60% of the Topping, the sound is perfect with a pleasant hint of bass (not intrusive) and an excellent mid/high performance . The result is exalted violins, guitars, brass instruments. The sound output of the styles is almost equal to that of the speakers, now the sound in the headphones is exactly what I wanted to hear in my ears being very careful not to damage my hearing lol. Thank you all and good new year. Pietro

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