[Andrea]

Nope...I'm still not feeling confident enough that the AD9631 would be the proper choice for the 0HA-REP.

I have a few LMH6654 on order, 'cause these and the AD8397 will be my contenters for the "current buffer of the day" prize

For the voltage gain, it's AD823 or AD8620.

 

[NelsonVandal]

I'm still awaiting AD746 (they promised it to be delivered today). Did you ever try to use it with the battery, Andrea? I fear it will distort. I think I'm going to order some AD8058 as well (it should go nicely in the Xtra amp with 7,4V LiIon, i think, if I ever get it). I just want a smoother sound than AD8620. Any more suggestions?

You never tried BUF634, did you? Is it possible to use it in Xenos?

 

[Andrea]

The AD746 is what you want, I think. I don't know how soon it'll distort when the battery is low, certainly it won't distort at 9V.

It's doubtful if the AD8058 would go well in the Xtra. It depends on if it has the balanced input impedances or not. I'd rather go with an LM4562, if I wanted to try a bipolar op-amp in it.

You can tweak the Xenos to use buffers (not the easiest of tweaks though), but I don't think it's worth it. Buffers have a lower output voltage swing @ 12V than op-amps like the LMH6654 and its peers. Besides, there's a possibility that they would sound less transparent(?)

 

[Andrea]

Eventuallyyyy... TI has shipped my THS4031 samples.


It looks like I'll be doing LM4562 + THS4031.

 

[NelsonVandal]

The AD746 is now in. I'm going to let it burn-in. My immediate reaction is it's soundwise more like the LM-chips (with a pinch of Burr-Brown). Not the same punch or well-defined soundstage as AD8620. A little "slower" and muddier. The treble is much nicer without harshness or sibilant voices. The mids are more emphasized, but I think it maybe is Xenos that boosts mids, not the chip itself. I think it's better suited for my Philips than my Sennheissers, but as I said I'm going to let it burn-in for i while now. I'll report how it sound later.

I'm going to order AD823 and AD8058. The AD746 seems to be good but not a perfect match.

 

[Andrea]

Quote:

Originally Posted by NelsonVandal /img/forum/go_quote.gif I'm going to order AD823 and AD8058. The AD746 seems to be good but not a perfect match.

I would agree with your conclusion.

The AD823 has the tight punch, and a lifelike mid-treble. (Have I said) I really like it.

 

[Andrea]

I've now the AD823 + LMH6654 in my (2nd last, out of 3) 0HA-REP. By tonight I should be able to give some impressions (at least with the HD485).

 

[Andrea]

Gave it a brief listen.

It seems that I got just the sound that I like: solid, refined and subtle. I couldn't point out any significant flaw, instead all was quite musical with a touch of fun in the bass punch. The treble was...subtle, fine and crisp without any harshness at all. Sweet, well rounded, refined vocals; beautiful guitars and trumpets etc. All intended: with the HD485 and playing Calexico, Feast of Wire.

This amp will stay as it is.

 

[NelsonVandal]

I've listened some to the AD746/LMH6654. The 746 is much harder to describe than the other op-amps I've tried. It doesn't seem to add much colouration, rather subtract. It's very smooth without harshness and sibilance. It's spacious with both great width and depth, but not unnatural like the LM-chips. For instance voices and drums are where you expect them to be. Different recordings really sound different. I can't say that it sounds so or so in the highs mids or lows, the tonal balance is probably very accurate, and as I said it doesn't seem to add much. It draws you in to listening to music and not Hi-Fi. It doesn't impress, but kind of grows on you. This would be the perfect op-amp if it wasn't for the lack of energy. It's a bit too soft and lazy, a bit dull. Maybe this should be my definite op-amp for Xenos, but after what I've read about AD823, I can't resist give it a try. I'm going to live with this until my Xtra X1 arrives, so I'll have a good amp to compare it to.

One odd thing is a channel mismatch. Left is about 3 % weaker than right. Lucky I have a balance control in my iRiver. This is why I thougt the soundstage was a bit weird and LM-like. The noise level is quite audible with my 32 ohm cans, much more than AD8620.

 

[Andrea]

Do you mean that there's a channel mismatch only with the AD746? I hope so - otherwise the volume pot of your amp might have some imbalance (that none of my 2 amps so far have).

I definitely agree with your general views on the AD746. For me, notwithstanding the positives, it ultimately was a little too dull. The AD823 seems to be my sweet spot in the "FET input" AD offering...although the AD8620 is mostly fine, too...

 

[NelsonVandal]

Yes the mismatch is only with AD746. AD8620 was absolutely flawless with a pin-point accurate balance and soundstage, which I think was one of it's strongest points. I hope that I haven't messed something up in the amp. I've resoldered the op-amp, but with the same mismatch. I'll find out when I get the AD823.

 

[Andrea]

Sorry to hear that - hope there's nothing wrong with the amp, and that the AD823 can fix it.




Back to my AD823 + LMH6654 amp... Marveilleux! This is doubtlessly a better amp than my Go-Vibe v4 with AD8058 and Panasonic FM's. More solid, full and dynamic; more lifelike/musical; as a result it also feels more refined. It sounds more like a "big amp".

Btw, yesterday night I could make out (still with the HD485 that have a slightly overdone treble as compared to neutral, btw) that mild treble liveliness that's typical of the AD823, and that I don't mind - at all!

 

[NelsonVandal]

Now I can't wait until I get my AD823 (and my Xtra). From what I've heard from you, 823/6654 will be the final op-amps for Xenos.

 

[NelsonVandal]

But... can you really keep your fingers from it? Class-A biasing? Tamper with feedback loops? Gain?

I wish I did know more electronics. I know what kind of sound I like (and music). Do you know any easy-to-understand-amp-tweaking books or sites? Do you have the schematics for Xenos?

 

[Andrea]

The schematic of the amp I do have...printed in my mind

You can make it out easily enough from the pcb traces.

The feedback loops are already optimised. The only thing I could fancy modifying about them is the gain of the controlling op-amp (if needed, not my case).

The class-A thing I find is overrated. The only other useful tweak I see would be changing the two 220uF/10V reservoir caps with two Panasonic FM's of equal value (220uF/10V or 16V). Not sure if the difference is entirely worth it, anyway. (me, in this amp here, I finally settled with two 100uF/25V Elna's, mostly for their size - and secondly, 'cause I removed that 1.1 ohm resistor on the output of the virtual ground driver for the lowest impedance)


With just the AD823/LMH6654 in place of the standard chips (forgetting of the other mods that my amp here has, which don't necessarily make up for a perceivable improvement), I think this is a great amp that competes with amps 2x the price (that would be $244

). I'll compare it with the XTRA when it comes.