[Nazo]

I'm not sure if this is the best place to ask this (a moderator could feel free to move it to a different subforum if another might be better) but this seemed like the best spot since it's ultimately more about headphone amps and probably applies most to those who have used the likes of the CMoy (I'm not sure what else anyone would have used an AD8620 in anyway.) So right now I'm using a Fiio D3 connected to a CMoy with an AD8620 OPAMP and it just couldn't possibly suit me better -- I absolutely love it. I've seen someone describe it as making a CMoy sound like a $100 amp, but for me it sounds even better than the iBasso D3 I got a long time ago for a different headphone. Perhaps it's not the best of the best for some, but for me it is. Still, it is a little inconvenient having the Fiio D3 connected to a soundcard then connected to a separate amp, dealing with the amp (especially as far as portability goes -- I'm powering it via 6xAAs since a 9V seemed to drain too quickly, so the case I have it in had to be a little larger and more inconvenient to carry around,) and etc. I've read that the AD8656 is supposed to be completely compatible with the Fiio D3 and that it works very well with it and even sounds great. Certainly it could be a lot more convenient if the one device could basically just do everything. Still, I wonder if it would be a "downgrade" for me to go from the AD8620 I'm using now to that one? It occurs to me that, given the model number, it might actually be somewhat similar to the AD8620 (maybe even in the same series or something?) If it basically sounds the same or even a little bit better, it would be a great way to go.

I still haven't decided for certain if I'll do this in the first place (I haven't really done much actual soldering of chips in the first place, plus I'll have to rig up a volume control somehow -- though I have an idea or two on that -- since most things don't actually let you adjust the volume of the digital outputs and the D3 itself lacks any sort of volume control, so the whole thing is definitely inconvenient) but obviously there's no point in even going to the troubles to try it if it's not really going to be any better. (As a pre-amp the TILMV358 seems to be fine, so while the AD8656 might technically still even be an upgrade for this purpose, it wouldn't be worth it for me at all if I wasn't going to be able to use it directly as a headphone amp.)

By any chance would anyone have any idea how the two really compare? I don't know if anyone would have had much opportunity to compare the two side-by-side, but perhaps someone might have enough of an idea of how each sounds to be able to more indirectly compare? It absolutely has to be really close to be worth all of the trouble for me. In fact, one person's "better" might actually be worse for me.

BTW, IF I am going to do this, I need a good source to actually get the AD8656. I got the AD8620 easily enough (already in an adapter even) from eBay, but the AD8656 looks to be tougher to track down. It seems that Mouser at least doesn't have it which is where I'd normally think to look for things like chips. It would be nice if I could get it from somewhere that wouldn't charge an arm and a leg for shipping, but regardless I'll need to find somewhere to actually get it. Does anyone know of a good source for OPAMPs like this?

 

[kiteki]

I'd suggest emailing iBasso and asking if they'll make a D-Zero DAC/Amp for you with the AD8620 instead of the AD8656 then you have your solution right there.
 
Link to this thread in the email, I'll buy one too if they do it.

 

[Nazo]

That... Wasn't really the question. At all. I can't afford a D-Zero right now even if it is cheap for a quality amp and, more importantly, a D-Zero doesn't do what I wanted anyway. (I'm not really sure how you could mistake them for being interchangeable, but the Fiio D3 isn't a USB DAC for a computer, but a SPDIF DAC for, well, everything that supports a stereo PCM output via optical or coaxial connections. I'm even using it with music games on my PS2.)

 

[mrarroyo]

I have used the AD8656 on various amps that used to be sold by Xin. I felt it was a better sounding than the 8620 in some of the configurations, however I cannot find my notes to give any detailed information. BTW, I recall the 8656 was limited to 5V so be careful how you use it.

 

[ClieOS]

I can say that the AD8656 in D-zero doesn't impress me much, and dropping an AD8620 onto it isn't going to solve the problem since D-zero only supplies 4V to the opamp (last I measured) and AD8620 needs minimum 5V to operate. As far as my opinion goes, AD8620 sounds better to me but that depends on the implementation as well.
 
To the OP, if you are using AD8620 in a typical cmoy, then 6xAA (or a single 9V) means the opamp is underpowered as 9V/2 = 4.5V. You might want to use  2x9V batteries in serial with a combined of 18V instead. Get some 500mAh NiHM 9V rechargeable and they will last much longer.

 

[kiteki]

and AD8620 needs minimum 5V to operate.

 
It will operate at much lower than 5V, the evaluation of how it sounds is another story.
 
 

I'm even using it with music games on my PS2.

 
Which ones?  I have an optical -> coax converter for my PS2 music games.
 
I think you're a bit confused, there is no such thing as stereo PCM via optical.
 
Can you just tell us in a single sentence which IC you want to desolder in which device, and replace with which IC?

 

[Nazo]

It is my nature to be thorough in my posts. I can't give you a one sentence response that incorporates every detail.

I think you're a bit confused, there is no such thing as stereo PCM via optical.

I must beg to differ. I listen to it every day. Optical just means digital -- it's ultimately the same thing as coaxial. http://en.wikipedia.org/wiki/SPDIF

To the OP, if you are using AD8620 in a typical cmoy, then 6xAA (or a single 9V) means the opamp is underpowered as 9V/2 = 4.5V. You might want to use  2x9V batteries in serial with a combined of 18V instead. Get some 500mAh NiHM 9V rechargeable and they will last much longer.

I don't know, with these headphones it has always seemed to be fine with relatively low voltages. I forget the exact number, but I think it didn't start clipping or anything until around 7.5V or so (the cheap rechargeable 9Vs I was using would drain so quickly that I forget where they were when I had to keep changing them out. I'll find out whenever these AAs get there, but they seem to be around 8.1V or so right now and it still sounds just fine.) Bear in mind that all of my headphones and IEMs are of a pretty low impedance, relying more on current than voltage (and not even much of that as each are fairly efficient.) 18V just isn't really realistic, but then if it really needed more, it really wouldn't need that much more. (I'd have to do 8xAAAs or something -- anything else just wouldn't really fit in anything decent.) One caveat of the AD8620 is that it seems to use more current than many other OPAMPs such as the all too popular OPA2132/2134 or 2227 (each of which lasted a LOT longer with those rechargeable 9V batteries.) Better rechargeables 9V batteries would be more convenient to deal with and all, but they'd still just drain too fast I think. Still, for the differences I'm hearing, it's absolutely worth it. (Heck, even if it actually could sound better still with more power, it sounds so amazing right now that it is worth it as-is compared to others like the OPA2132.) Bear in mind also that even the best rechargeables tend to be considerably worse than their rated performance and 9Vs are among the worst about claiming to be one thing and actually being another. Most of my AAAs are rated for 1000mAh and surely do at least half that, but I'm not sure I'd trust any 9Vs claiming to be 500mA to be even half that (it seems around 320 or so is the maximum you normally can get in real performance for 9Vs.)

BTW, I recall the 8656 was limited to 5V so be careful how you use it.

The Fiio D3 would provide 5V of power to it. Its power source is USB with filtering (though I might have to use an battery instead -- I have several lithium-ion chargers designed to power USB devices anyway, so that's not really an issue.) Anyway, I didn't come up with the AD8656 on my own, but instead it was after reading reviews in which it was mentioned that it had been done, so it's known to work with the Fiio D3 just fine.


One thing to bear in mind is that they don't have to be exactly the same or anything, and I'm even ok with it being a slight downgrade if it's not by much. I just don't want to lose the things I love best about the AD8620. I'm definitely not an audiophile and I can't really accurately describe the sound of an OPAMP (and I'm as likely to say it wrong as anything else,) but I guess if I had to put it into words I'd say that, for starters, the AD8620 seems to have more clarity and detail than any of the others I've ever used (not just in the CMoy) and while it seems to have clear highs, they aren't really shrill or anything. It seemed like the mids were just about right, and the bass was extremely accurate even down to some very low frequencies that I guess were more troublesome for others (I could hear individual notes with this where many would run together a lot more.) How accurate of a description that really is, I couldn't say, but maybe it helps? That detail is probably the most important thing I'm looking for but my ears are kind of sensitive towards certain higher frequencies and many setups in the past have bothered me, so I don't want anything that gets

 

[kiteki]

In my experience the AD8620 is quite neutral and impressive sounding, however it sounds quite 'empty' after a while.  You have alternatives like AD797.

 

[ClieOS]

Quote:

 
It will operate at much lower than 5V, the evaluation of how it sounds is another story.
 

Sure, you can underpower opamp and be happy with it, or you can use it properly and be more happy.
 
Quote:

I don't know, with these headphones it has always seemed to be fine with relatively low voltages. I forget the exact number, but I think it didn't start clipping or anything until around 7.5V or so (the cheap rechargeable 9Vs I was using would drain so quickly that I forget where they were when I had to keep changing them out. I'll find out whenever these AAs get there, but they seem to be around 8.1V or so right now and it still sounds just fine.) Bear in mind that all of my headphones and IEMs are of a pretty low impedance, relying more on current than voltage (and not even much of that as each are fairly efficient.) 18V just isn't really realistic, but then if it really needed more, it really wouldn't need that much more. (I'd have to do 8xAAAs or something -- anything else just wouldn't really fit in anything decent.) One caveat of the AD8620 is that it seems to use more current than many other OPAMPs such as the all too popular OPA2132/2134 or 2227 (each of which lasted a LOT longer with those rechargeable 9V batteries.) Better rechargeables 9V batteries would be more convenient to deal with and all, but they'd still just drain too fast I think. Still, for the differences I'm hearing, it's absolutely worth it. (Heck, even if it actually could sound better still with more power, it sounds so amazing right now that it is worth it as-is compared to others like the OPA2132.) Bear in mind also that even the best rechargeables tend to be considerably worse than their rated performance and 9Vs are among the worst about claiming to be one thing and actually being another. Most of my AAAs are rated for 1000mAh and surely do at least half that, but I'm not sure I'd trust any 9Vs claiming to be 500mA to be even half that (it seems around 320 or so is the maximum you normally can get in real performance for 9Vs.)
 

Your average 9V is actually 8.4V, around 170mAh at best. But a good 9V from China can get to true 9V and 500mAh because they use a newer kind of battery construction which you won't find on the West. You might think China stuff must be faking its spec and you will only be half right. Yes, there are plenty of China battery with bad spec but there are also really good one as well. In fact, China has the largest and most active battery industry in the world right now and the even battery powered supercar like Fisker Karma is using battery manufactured by Chinese. I have tried some of these Chinese 500mAh 9V and they are indeed much better than any of those Energizer or iPower variants you typically find on the West. Just eBay them up and look for the one that is made by 'HOBA'
 
AD8620 indeed is more battery intensive than most popular opamp choices. Then again, you can't ask for performance without paying a price.
 
Quote:

In my experience the AD8620 is quite neutral and impressive sounding, however it sounds quite 'empty' after a while.  You have alternatives like AD797.

Yeah, AD797, like AD8620, need +/-5V and up and actually more tricky to implement because it is considered to be very cranky (*could performs badly when the circuit isn't optimum), not to mention it is mono channel.It is not exactly an good option for cmoy.
 
To the OP - go to the DIY forum and search for cmoy opamp. There are plenty of similar threads over the year and a very good number of workable opamp which people have tried in a cmoy setup. Better than asking blindly and hope for the best.

 

[kiteki]

Well AD797 is mono however you just buy the AU kind with 2x on a converter.  I've only heard AD8620 at +-15V I think.
 
Not sure exactly what Nazo is trying to achieve but this article should answer some questions - http://hifiduino.wordpress.com/2011/06/23/inside-fiio-d3/

 

[justin w.]

the AD8656 shouldnt be used with over 5.5V
 
the AD8620 has a minimum voltage of 5V, but is not designed to run at voltages that low.  it's not a rail to rail output type op-amp and you'd have almost no voltage swing left at 5V
 
great example of why amps that allow op-amp rolling are a terrible idea

 

[Nazo]

Except it still works beautifully and far better than the ones people normally use. Without the rolling, the CMoy would be built around something more like the OPA2132 and no one would have any choices.

To the OP - go to the DIY forum and search for cmoy opamp. There are plenty of similar threads over the year and a very good number of workable opamp which people have tried in a cmoy setup. Better than asking blindly and hope for the best.

Just to be clear, I'm not asking about using an AD8656 in a CMoy, I'm asking if it might be similar enough in sound to the AD8620 to use alone in the Fiio D3 without an AD8620 CMoy after the D3 and still get a similar enough sound to enjoy it (while in turn being worth the trouble it would actually be to track down an AD8656 in the first place and then to actually switch with the existing OPAMP on the D3's board. If it wasn't so much trouble to track down and install I'd just do that right off without even asking since it still has to be better than the TI OPAMP.)

Also, I thought that's basically where I WAS asking... If Head-Fi is "asking blindly" then I'm not really sure what's left...

 

[ClieOS]

Okay, using AD8656 in D3 to skip an amp stage has one problem, no volume control since D3 only output line-signal. You'll either have to find a way to digitally control the volume from the source (which generally result in poorer SQ) or use a potentiometer between D3 and your headphone to cut down volume (which isn't ideal either). Also, AD8656 is there as a buffer for the DAC and not for driving headphone directly, so it might not perform well for what you ask it to do.
 
I wonder, you already use D3 which isn't portable at all, why are you want to skip the amp anyway? Just get a wall adapter for the cmoy when you are using it with the D3, then change to battery when portable. It won't drain the battery that way and look easier then trying to somehow hack a DAC to do an amp's job.

 

[Nazo]

Okay, using AD8656 in D3 to skip an amp stage has one problem, no volume control since D3 only output line-signal. You'll either have to find a way to digitally control the volume from the source (which generally result in poorer SQ) or use a potentiometer between D3 and your headphone to cut down volume (which isn't ideal either).

The plan right now is a potentiometer if I do this. It's kind of a pain, but better than nothing.

Also, AD8656 is there as a buffer for the DAC and not for driving headphone directly, so it might not perform well for what you ask it to do.

Supposedly that particular one works fine as a headphone amp here though. Certainly the original OPAMP is meant only to be a buffer and shouldn't be used for headphones, but then that's part of the whole point of changing it.

I wonder, you already use D3 which isn't portable at all

Uhm, if it's not portable I don't know what is really. It's a LOT smaller than a CMoy in an Altoids tin. It is powered via any standard USB source which can include various "battery backup" devices as well as a computer or a USB port on a TV or console among other things. I even found a little USB soundcard for my netbook that has a SPDIF output on the 3.5mm jack which isn't much larger than a 9V battery. Still, the two together are smaller than a CMoy in an Altoids tin... If you mean the cords, the analog output isn't really worse than a CMoy other than using RCA instead of 3.5mm (though if I do start modifying one I'll probably put in a 3.5mm connector to use -- I'm actually kind of thinking of just removing the RCA jacks entirely and using one hole for the 3.5mm jack and the other for the potentiometer, but I'm not sure if I could find one that would fit even with as much room as there actually inside the case.) The optical cable I'm using is pretty thin (I suppose more susceptible to crimping, but it stays in a little DVD player case with the laptop with plenty of room to spare for a lot of other cables and things as well) and ultimately about the same to deal with as a thin 3.5mm patch cord. Really, the ONLY thing that it adds compared to a portable amp is an external power cable, but I already have a very small mini-USB cable I use with it, so that is hardly any issue.

Of course, the idea is to eliminate having to use an external amplifier (assuming it worked of course) in addition to it which would make it a lot more portable. Still, even with it as-is, it's no less portable than an external soundcard such as my Alien DAC (which I've had to put in an Altoids tin since I just don't really have anything the right size for it.)

why are you want to skip the amp anyway?

Audio from the device (pc, console, tv, whatever) going to D3 powered via USB connecting via RCA to an amp. One less device = less inconvenience. It would also result in something much smaller (remember, 6xAAs powering this CMoy, so the case had to be relatively large to accommodate their thickness) that would even be more convenient to power (I can use USB from the source unless it has too much noise, but even if it does it would be fine for some applications where portability is more important and otherwise it's still easier to power such a thing via a thin little battery pack built around a lithium-ion than a bunch of AAs crammed into a holder... Not to mention that even my worst "emergency charger" type thing claims to some 2000mAh, so is better than rechargeable 9Vs and AAAs and possibly even many AAs...)

Basically, if it works, it would just be a LOT nicer. I'd rather just deal with the amp in its big box if I'm going to lose a lot of quality or something, but if it actually worked well and sounded good to my ears, it could actually be very nice and convenient.

 

[ClieOS]

By non-portable, I mean you actually need to use D3 with an USB power supply of some sort since D3 doesn't have any internal power supply (battery). Seems to me that you are going the long way to solve a simple problem, which the effort might out-weight the result. Anyway, good luck to your experiment.