Xenos OHA-REP with LM4562/LMH6654
Dec 2, 2006 at 10:22 AM Post #17 of 72
Quote:

Originally Posted by NelsonVandal /img/forum/go_quote.gif
The AD8620 is now in my Xenos. Threre's a distintive different sound now. It plays much better with my Senns but slightly worse with my Philips.

With the Senns: The bass and mids are clearer more focused and "truer", a bit drier. Most of the time the vocals are straight in the middle (like they should be). It really brings out the best of the Senns mids, and that's goood! The treble is a bit more coarse, and a little bit sibilant. It's not as spacious as LM4562 (wich is probably over-spacious), but much more open than OPA2134. It surprised me that the noise level is much lower, it's barely audible. All amps I've used so far have brought in front a nasty 3 kHz resonace wich is the major fault in HD650 (due to it's horn construction I think). With AD8620 it seems attenuated. The chip isn't totally neutral. I can hear it's distinctive character listening to different songs/CD's. All in all there's great synergy now between the amp and the 650's. If there was just a little bit less sibilance and shiny treble it would have been perfect.

With my Philips it's not as fun to listen to as with LM4562, or my cheap MP-amp with LM6171. And it's too sibilant as well. Nothing is better exept the noise level. I didn't believe in this synergy-thing before, but now I'm convinced.

Andrea, do you think the fun-factor is from the AD823 or the AD8397 as buffers?

Wich combination do you refer to when you say "Sounds wonderous! Awesomely natural and neutral with my HD650 & for my ears. Meaning that besides a fine balance, timbre is beautiful too. Vocals sound splendidly, smooth, focused, intimate and full of subtleties. The whole soundscape is very spacious and clear. Bass & treble are extremely resolved and controlled."?


Thanks for the impressions.

Out of curiosity, how are you powering the amp? With the 9V battery or with DC power - and if the latter, are you using a 12V *unregulated* power supply. This feature is necessary as the amp has an internal 12V regulator that won't work properly if the DC power supply is already 12V regulated. The supply voltage of the op-amps would thus drop to about 9V, and badly regulated to boot.


That said, I don't hear treble sibilance (btw, I always though that sibiliance was all about vocals?) or excessive shininess in my amp through the same op-amp combination. Keep in mind that my amp has more tweaks though: bypassed regulator/charger (so, me, I'm actually powering the amp with 12V regulated), AD825 rail splitter in place of the original MC33201 (don't know if this makes a real difference), & 3x Panasonic FM reservoir caps (1x 470uF on the 'power supply' board and 2x 330uF on the 'audio' board).
 
Dec 2, 2006 at 10:28 AM Post #18 of 72
In fact, there possibly is a little bit of treble artificialness left - at least so I thought at the beginning. Then I didn't clearly notice it anymore.

The AD823/AD8397, IIRC, had a little silkier treble. But it had a somewhat less smooth, slightly harder midrange in change
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Dec 2, 2006 at 12:17 PM Post #19 of 72
You know what? I've decided that I ditched the AD746 too quickly. Ahh, this impulsiveness.
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Now that my new 0HA-REP has just been shipped, I'm pondering on whether the gain op-amp will be the AD746 or the AD823. Probably the AD746 (the buffers should remain the LMH6654's since so far I'm not aware of contenders for this purpose in this amp). Btw, I don't think I'm gonna change the railsplitter nor bypass the internal regulator anymore - I wanna compare to determine if it makes a difference or not. So I guess I'll need to make myself a unregulated power supply.


The AD746, for the record, sounds smoother/silkier in the mid-treble and less dry in the bass-mids than the AD8620. I guess that's more neutral.
 
Dec 2, 2006 at 1:00 PM Post #20 of 72
I mostly listen with the battery. It's really 10 V. Most of the time using iRiver IHP120, sometimes a Harman/Kardon CD-player. When it's wall-powered I use an unregulated 12 V PSU.

AD746 sounds interesting. Silkier treble/mid and wetter bass is exactly what I miss in the AD8620.
 
Dec 2, 2006 at 1:19 PM Post #21 of 72
I guess you'd be happy with the AD746.


However. How come I didn't think of it earlier. Since the op-amp & buffers each have their own independent feedback loop and, secondly, since all chips are bandwidth limited... Finally, since this amp easily accepts bipolar preamplifier op-amps... One could very well use the AD8058 to drive the LMH6654's, likely without risk of oscillation... Gonna try it right now
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Dec 2, 2006 at 5:02 PM Post #22 of 72
Done. It's playing right now, but I'll only put the headphones on tonight. I have a good feeling about the sound quality. AD8057(8) + LMH6654(5) seems a nice combinations of numbers
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Dec 2, 2006 at 8:46 PM Post #23 of 72
Wonderful! The AD8058 is more natural sounding than the AD8620 though with a not so different balance. Sweeter treble, richer more involving midrange (great!), similar bass (perhaps a touch more of it). Sounds a little more detailed, too. It really seems the perfect partner to the LMH6654...

In short this last mod fixes the (very) small reservations I still had about the sound of the amp. Now it's sheer goodness...
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Luckily I have one more AD8058 for the incoming amp. In change I'll have to order a few more LMH6654's
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Dec 2, 2006 at 10:30 PM Post #24 of 72
How guilty of me - I forgot to mention that I listened to John Mellencamp, Cuttin' Heads. This is one great record and the amp let it sound enchantingly good.
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Dec 3, 2006 at 10:44 AM Post #25 of 72
I just measured 13 mV of DC offset with the AD8058 in. It's fine for the HD650, but I guess less than ideal with a 32 ohm headphone. So I'll leave it out.


I think I'll try to simplify my strategy... I'll profit by the LM4562 samples I'm waiting for and replace the OPA2134 with it. The standard LMH6642's being rail-to-rail are good for this amp and I want to see if the LM4562 will bring their tonality to life. Let's see if that'll suffice to give me satisfaction
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edit- If not... I'll watch out for alternative output drivers. A possibly good choice is the AD9632.
 
Dec 3, 2006 at 3:28 PM Post #26 of 72
Just orderd AD746 from Analog, I hope this will be final. Otherwise I'll maybe have to look for a stationary amp for my Senn's, but I really want a portable. Are there portable amps with discrete components? I'm a bit reluctant to buy a portable for hundreds of dollars like a Xin or Hornet, when I know I'm going to hear the same colorations from the opamps. I don't care about fancy casings. I just want a true and musical sound.
 
Dec 3, 2006 at 7:07 PM Post #27 of 72
Another chip that you could safely use in the Xenos (it's FET input) is the AD8034 (the dual version of the AD8033). I'd like to try it with the LMH6654. With a "3345668", it looks promising
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I still can't decide between doing AD8034 (or AD823) + LMH6654 , or LM4562 + LMH6642 ...
 
Dec 3, 2006 at 9:36 PM Post #28 of 72
Ok... I've made up my mind for the buffer (at least). I looked again through the datasheets and there's no doubt that the LMH6654 is a better chip (like my ears had suggested).

I might also leave the standard OPA2134 in. It should make a pretty good partner to the LMH6654's (never tried this combination!).
 
Dec 4, 2006 at 8:02 AM Post #29 of 72
OK this is what I'll do: LM4562 + two AD9631's.

And so be it
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Dec 5, 2006 at 8:20 AM Post #30 of 72
One more day of pondering has produced this,
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LM4562 + two AD8397


The AD9631 isn't completely worth it, as it consumes almost 20 mA/each, that is, more than a (dual channel) AD8397 ! And with a 12.6V 'absolute max' supply voltage it would be at the edge in the Xenos. And of course the AD8397 is more 'fit' as a headphone driver due to the abundant output current. Moreover, it's rail-to-rail (@ G= +2 as will be in the 0HA-REP).
 
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