# the cmoy slayer - the AD823



## Apheared

ppl gets the credit for this, but since he's insane and many people can't understand his writings... 
	

	
	
		
		

		
			





 As many of you know, I've tried alot of opamps. Probably 40. Many of them sound good, some sound dreadful, but some have exceptional traits... there's a certain something to the sound of many of them; the LM6171s, SSM275s, OPA228s, 627s, 825s, etc. That's why I sent them to some of you guys, cause I know you're lazy ducks and won't even try it if you get the chip for free. 
	

	
	
		
		

		
		
	


	




 Well, no free samples this time... but here's my current ultimate opamp:

 The Analog AD823. I LOVE THIS CHIP. More than 132s, 627s, AD825/6, 6171s, more than any high-end chip I have currently!

 You _cannot_ use it in a cmoy/hansen pcb... it must be buffered by something to drive headphones... a discrete config, a nice opamp like 6171, or a buffer: 6121, buf634, or my personal favorite buffer for this chip, the Elantec EL200x series. An EL2001 provides moderate drive current. This buffer sounds good anyway, but it's a great match to the 823. Both the 634 and the 6121 (and even 6171 really) will work to buffer it's output and keep the sound the same for the most part. If you want to experiment with buffers - do it on breadboard... none of these chips have the same pinouts. Grr.

 I built an 823/2001 amp to drive HD600s (in a nearby thread)... well, this has become my main amp for ANY headphone. Head to head it whoops ass and takes names with everything else I've built in the last year. Maybe my skill has increased, maybe it's just that good. I assume it's the chip. 
	

	
	
		
		

		
		
	


	




 132/4s are still good chips. smooth, soft-ish, almost tube-like in the treble warmth. This chip is not that. Bright and sharp, maybe too much so for some people/headphones. 6171 is a great chip, but it sounds sterile next to this, while accurate they don't have the same "liveliness" effect. I don't know if that makes it more or less accurate, but it certainly makes it more enjoyable to me.

 This isn't comparing by swapping chips in a single amp; this is comparing the 12-some-odd amps I have sitting here with the same source; all built to specifically bring out the best of what's there, using great parts and detail to build.

 This is my favorite amp, plainly. The only thing that equals it is my 823/2008 massive beast (ppl's beast rev3) I goet here by accident - I fried an AD825 that was in my 2008 beast, and started substituting... 823 stopped me in my tracks.

 YMMV of course, but if you've liked my chip suggestions on other chips over the last year; trust me when I say you'll LOVE this one.


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## Possum

Great! Another amp to build! 
	

	
	
		
		

		
		
	


	



 I JUST finished a plain cmoy in Altoid tin with 2 9V, just because I felt left out and had the extra parts.


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## Apheared

Do it. You'll enjoy it. You can get some from alot of places, but Newark has em for under $7 ea... if you wanna try the Elantec buffers, Insight is the only place I know that you can get em. (and I think they have a $50 minimum)


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## Serow

What would you chose as the best dual opamp for the 47 amp? I am planning to use the 2228, with the 2314 as an option in case I want lower gain.


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## Apheared

2228 will work great. Don't use these 823s!


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## Possum

btw, how does your numbering system work? You have the "47" low impedence (e.g. Grado) mod. Is this different from saying #47, like #42 for the HD600's amp?


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## Apheared

47 was because all the resistor values ended up being 47 470 and then .47 caps... just a previlant number...

 this is the 42, as in the answer to life, the universe, everything... HHGTTG. I guess I coulda called it Slartibartfast...

 there's no reasoning to it. 
	

	
	
		
		

		
		
	


	




 Serow, you're randomizing all over the place. Make a new thread and ask your parallel and AD questions together so it'll be easier for others to refer to later...


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## thomas

hmmm, trying to decided Active or digikey for my next part order (ie BB stuff or AD stuff), i guess this decides it... AD823 is also available in DIP, much easier to work with than 825....

 i'll also try the elantic buffers from insight....

 Damnit, DIY is draining all my money!


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## ppl

Apheared: what Differences did you notice Between the AD-823 and The AD-825 using the EL-2008 Buffer?


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## Apheared

Hmm... see, I never tested them swapping... I blew the 825 and then went thru a couple others and when I hit the 823 I stopped. That sibilance issue that the 825 had went away with the 823. It's low thru mid is more forward than the 825... or maybe it's just the config it's in. Again, this is from memory... and my memory sucks. The 823/2008 is what I carry everywhere, ya know? 
	

	
	
		
		

		
		
	


	




 But since I fried my 825 with that CRD failure, I haven't re-tested it in your amp... I had that treble issue with it, and an 823 in there is making me damn happy with the sound.

 My next test is to see how I like a single BUF634 paired with the 823, side by side with this 2001 version... I think I know the outcome already but I will test for completeness (and then you and me will split a huge order for Elantecs 
	

	
	
		
		

		
		
	


	




)


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## sneared

You might want to consider other sources for your EL2008 or EL2001 chips. Insight says they have more orders than they can fill.


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## Apheared

Screw em, it's their BUSINESS to fill orders. Aww, I'm so upset that you have so much business. 
	

	
	
		
		

		
		
	


	




 Besides, I'm used to waiting months to get crap... tis the way of things in this nutty hobby.


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## ppl

Apaheared: I have noticed that also with the 825 the Midrange is recessed compared to almost every other OPA i have tried. I think this may be the reason for the Exsessive sibelence with this Opamp that is not as noticeable with other opamps. The BUF-634 is also recessed in the midrange about as mutch as the 825 so an AD-825/BUF-634 combo should be only for phones with a real fowared midrange IE Grados. Another Issue i have with the BUF-634 vs the ELantecs is somewhat Bloated bass on the BUF-634. I think Both the EL-2008 and EL-2001 sound better than the BUF-634 but with certin Cans and or sources and Opamp choice it's sonic signature can be exploited. BTW the OPA-627/OPA637 are a good sonic match to the BUF-634. But an 825 and BUF-634 No not for most uses, Only recomended if you mids are allready way too foward.


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## mlloyd1

Just curious :

 Anybody tried National's LM6321 or any of the video CFAs (e.g. AD811) or any of the XDL drivers (e.g. AD815) as buffers?


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## ppl

It is sad that today as it was 20 years ago that Buffers are Few and far between But at least nowdays thay cost less than $30.00. The Wonderfull EL-2008 and EL-2009 that have been around for over 10 years is now going away also. No wonder folks are Quick to Look at CFB Type opamps. In Theroy All Current feedback type Opamps are unity gain stable so one would Look Very Good for Buffer use with the Exception of the fact that thay are Still OPamps with voltage gain. So regardless of what elce you do Your output stage is going to use 100% feedback and this Closed loop type of Buffer when combined with the main voltage gain stage and another Feedback loop or two can result in A Radio transmitter rather than a Headphone amp. I Like Open loop buffers because Thay do not use Feedback. now I am not one of those that Dislike feedback In fact i think Feedback is good as long as it is properly Applied. Asking a system to operate well into the MHz. range While driving a Reactive load and also being enclosed within yet another feedback loop is somewhat scary.

 The Alternative is to use just a High Curent CFB as Both the gain stage and output. This is again not an ideal solution because of the thermal problems i have gone into before at the headwize site. In Addition The input Bias currents of CFB opamps require a Buffer on the input, or high DC offsets will result as well as killing your vol. pot. What to Do Find the fastest open loop buffer you can get use your fav. Voltage feedback type opamp with low input bias currents. Then apply your fav feedback method Yes there is life outside of multiloop. Get the cleanest low impedance low noise power-supply you can and Build. Getting back to buffers this leaves just about only a handfull of Buffers the BUF-634, The EL-2001, EL-2002, LM-6321, LT-1010, LH-0033 just to name the most available. Analog devices makes a BUF-03 But it's all NPN output stage turns me right off. Linear tec's LT-1010 also uses All npn output stage, but when combined with the LT-1122 sounds rather good.

 I intend to investigate the DSL driver at some future long away date since these are just high current CFB type opamps I am not very motivated because of all the afore mentioned problems. But when i get a topology that sounds good i may impliment sutch a design.


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## zapel

ppl, I don't think the BUF03 is available any more. They have the BUF04, is this exactly the same as the BUF03? Can you elaborate a little more on the npn output.


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## Tomo

Hello,

 This thing has much higher slewrate than its predecessor. Analog Devices say that it is pin compartible with its predecessor. However, I think in certain applications this may not be straight alternative. The specs indicates BUF04 uses complementary pairs. Looks pretty good from your standards. 

 So all in all, BUF03 and BUF04 are different in constructions.

 Tomo

 P.S. I am in doubt to go completely VFB, CFB sounds pretty good to me at low gains ... 1~3. ... I guess I am more into BUFFER amp than standard type solid state designs.


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## jiggler

Apheared,

 Do I understand your earlier post that you would not recommend using 823s for both op amps in the A47? Would you use a 2132 for a buffer? Thanks.


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## morsel

Apheared has been gone over a year. The CHA47 has been antiquated by various more recent amps. The 823 does not output enough current to use as a buffer. I would not use any opamp as a buffer. I would use an open loop buffer as a buffer.


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## jiggler

Morsel,

 I understood from several other threads that the A47 was very good for driving Grados. On one thread, i think Tangent suggested that for a battery driven A47 the 823 might make a good opamp. What am I missing here?


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## morsel

I'm guessing you are reading ancient threads. I don't think many people build the CHA47 anymore as there are better options available. Since last summer the META42 and Gilmore Class A Dynamic amps have been very popular.

http://tangentsoft.net/audio/meta42/
http://headwize2.powerpill.org/proje...lmore3_prj.htm
http://headamp.com/dynamic.shtml


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## jiggler

Yea, I've seen these amps and would love to build both a Meta42 and a Gilmore at some point after I have gained more building experience and wisdom. But I am still interested in building a portable A47 for my Grados so my question remains unanswered. Would an 823 work in the first stage and then I could use something like a 2132 in the second stage? Or should I use the same opamp (2132s or 2134s, for example) for both stages?


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## da_burl

Jiggler:

 If you are building this for the experience, the OPA2134 will be just fine! Its cheap and sounds reasonably good, and gets plenty loud enough with my 2 different Grado's. I don't think you would really gain much by using an AD843 paired with a 2134, the output stage would override the sonic benefits and add its own signature to whatever the AD843 produced.

 There is nothing wrong with the CHA47, for its time, it was quite impressive. There are still lots of people that list it in their inventory and signatures on the headphones forum!

 I recently revived mine, and was really enjoying it prior to completing the multiloop buffered amp (well, its not really complete). There is about a light year's difference (maybe a more technical term would be "several orders of magnitude  )between the two though!
 Go ahead and try a CHA47, its really simple to build, and you might just end up keeping it around for a 2nd or 3rd amp! I know I need at least 3 for the living room, bedroom and office!
 I started out with a basic CMOY, then the two stage "Hansen" with crossfeed, then a CHA47, then went through the Szekeres stage, but couldn't stand the heat. Its kind of addictive after a while.


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## brschmid

I know this is an old thread, but i just built a CMOY with a AD823 and it is unbuffered(i think, i am not quite sure what that means) and it sounds really, really good.


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## zoboomofo

Quote:


 it sounds really, really good. 
 

... and that's all that really matters en'it? There's a lot of exciting action going on in the headwize.com diy forum. You might be interested in the new ideas for the cmoy amp there.

 btw, I just made a 3rd 47 amp - this time in an enclosure - a small precision job to sharpen me up for the Altoid multiloop amp (like tangent's latest sensation but less tidy). This latest Apheared amp sounds better than the other 2 I've got. The power caps really make a hell of a lot of difference. My overall favorite is a 220 uF Elna RSH cap. Big sound from a small component. Happy soldering!


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## sacriste

I'm really happy you brought this thread back to life. I have a OPA2134 CMOY with crossfeed circuit in a medium size enclosure. To be honest, the sound is clean and loud but too bright for me, some call it UMLT boost. It is really hard for me to get a new amp now (read my location) so I'll be very interested in try something that could change the sound. I'm not very experienced in DIY but if you give me some instructions I could do it or find help. And leaving shame apart because we are a community, if any of you feel in the mood to donate or trade for native things the opamps to me, I'll be glad too. At the moment, dollars are restricted in my country but I still have a mail service from/to US. Sorry for being so open.


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## puppyslugg

sacriste:

 I never found the opa2134 to be bright. So it's my guess changing the electrolytic to a larger value(uf), low esr type may help. Along with possibly using the tle2624(?) rail splitter in place of the resistor divider. Change the opamp to the ad8610/20 or ad843. How it's power also has a bearing on how it sounds. If you are using batteries, use NiMh ones. If you are using a wallwart, make sure it's a non-switching, (linear) regulated one, like some from Elpac.


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## sacriste

Quote:


 _Originally posted by puppyslugg _
*sacriste:

 I never found the opa2134 to be bright. So it's my guess changing the electrolytic to a larger value(uf), low esr type may help. Along with possibly using the tle2624(?) rail splitter in place of the resistor divider. Change the opamp to the ad8610/20 or ad843. How it's power also has a bearing on how it sounds. If you are using batteries, use NiMh ones. If you are using a wallwart, make sure it's a non-switching, (linear) regulated one, like some from Elpac. * 
 

Thanks for your advice. This is a little chinese for me, but I really want to understand:

 1. What value do yo recommend for the new electrolytic?
 2. What's a tle2624 rail splitter exactly? Is it hard to change to that?
 3. The 2134 is not bright for you, but you recommend to change it, why?
 4. I'm using the wallwart that comes with the Sennheiser stupid surround thing, at least sounds better than the cheap universal converter I have (?)


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## puppyslugg

Quote:


 1. What value do yo recommend for the new electrolytic? 
 

It's dependant on how much room you have in the case. Use something the range of 330uf-470uf@16v, bypassed with a polypropylene film cap(0.01-01uf). I would use the Pana. FC's as a mininum.
  Quote:


 2. What's a tle2624 rail splitter exactly? Is it hard to change to that? 
 

It's not that difficult. 

http://headwize2.powerpill.org/ubb/s...rail;splitter;
  Quote:


 3. The 2134 is not bright for you, but you recommend to change it, why? 
 

IMO, the ad8610/20, ad843, and others, sound better.
  Quote:


 4. I'm using the wallwart that comes with the Sennheiser stupid surround thing, at least sounds better than the cheap universal converter I have (?) 
 

I think you may find it sounds better with batteries(NiMh). But if you have to use a wallwart, at the very least, use a LINEAR regulated one from Radio Shack.


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## sacriste

Quote:


 _Originally posted by puppyslugg _
*It's dependant on how much room you have in the case. Use something the range of ETC, ETC, ETC* 
 

Thanks, puppyslugg, you're a master! I'll try everything...


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## tangent

If your amp with an OPA132 is sounding bright, you're probably misdiagnosing the problem. The chip should not sound bright at all, which points to other problems. Perhaps it is letting the brightness of your source or music or headphones show themselves, whereas before they were buried in the mud of your poor amplifiers. Try going back to the previous amplifier: does the brightness go away?

 Alternately, your amp may be oscillating a bit on peaks. Fixing that without a brand new layout can be tricky, but changing the power supply can help here.

 Bottom line, I wouldn't change to an Analog Devices op-amp before you chased this brightness problem down. If the chip is oscillating, the faster AD chips that have been recommended are even more likely to have problems. And if there's a truly bright component in your system, the AD chips have better high-end extension as a rule, which will just accentuate the problem.

  Quote:


 use a LINEAR regulated one from Radio Shack. 
 

Radio Shack doesn't _have_ linear regulated power supplies, and it wouldn't matter to sacriste if they did since a) he's already said he can't buy US parts; and b) Venezuela may use a different power system from the US. (I'm not sure about Venezuela. Its biggest neighbors -- Colombia and Brazil -- have mixed systems, which in places are compatible with the US power system.) Anyway, my point is that he's probably better off buying a power supply locally.


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## aych

this is the same chip that is in the C&C XO headphone amp! www.headb.com


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