# Apheared's CMoy variant #42: HD600



## Apheared

(God only knows what the actual count is)

 It's 2am, this is gonna ramble a bit.

 A few people have stuck hansen's pcb in the ET version of the HML-9VB PacTec case, to fit 2 9Vs in there. That's a killer idea, but the hansen board still takes up as much "floor space" and limits what caps, jacks, and pot you can use.

 I decided to make an HD600 portable amp. Not that I really like HD600s or plan on walking around with them, but hey it's a project. 
	

	
	
		
		

		
			





 To be different, instead of laying the board flat, I made it a vertical board... look at all the room. And since there's no "bottom" to the board, I can stuff both sides.

 One chip I really like the sound of on HD600s is Analog's AD823. It's a beautifully designed chip, although 15mA isn't much drive for our needs. It's a true single supply opamp (although I didn't use it that way) and can swing like the dickens because of it.

 I was going to buffer the output with a low power discrete stage... 2N3904/06s or BC549/559s, or BC317/337s... but ppl graciously sent me some 100mA buffers from Elantec to try, the 2001s (baby brother to the 2008s I love)

 The best thing about all this: battery! The 823 is 6.5mA quiescent for both channels, the 2001s are 1.3mA each quiescent, and a TLE2426 isn't even worth mentioning. Even with a 1mA CRD per channel, the total is under 12mA! Compared to just one dual OPA132/4 and a resistor voltage divider... sweet.

 Driving HD600s I doubt you can get the drain to 15mA. You can try. 
	

	
	
		
		

		
		
	


	




 An added bonus of the 100mA buffers is it will drive lower ohm phones, although say goodbye to your 9Vs pretty fast... an average rockin volume on Grados is 50mA.

 I wanted a gain around 12 and the parallel of the feedback to be 300. 332 and 4k7 ohm worked close, 308 ohm parallel and gain x14. Add a 301 ohm +input resistor and the offset for both channels is under 0.8mV - It's not bipolar input and this is really overkill, but why not?

 The 2426 doesn't really need the 470uF Cerafines, it's output is under 1/100th of an ohm to like 1k, and 20k is still like 0.5 ohm. For just driving HD600s, you can completely omit the reserve caps. I'm serious, try it. You can't hear the difference (but you can measure it, more on this below) The 470s/1s are for "cheater current" driving lower ohm loads. There is a 22uF stablizer cap in front of the 2426, again just because.

 Since this is for HD600s that I will probably not use portable that much, I added a power jack for an external 24V filtered wallwart. Both the batteries and AC in go thru 4001s in a diode OR gate config. (only the higher voltage will get passed). To add more safety to the thing, the AC jack is switched and the battery snap ground goes here. When the plug is inserted it lifts the battery ground, so diode gate or not - nothing is flowing to/from batteries.

 The silliest part - a _huge_ Noble AP series potentiometer is in there! heh. Took over half the faceplate space. Someone recently posted pics of a cmoy he built for $20... well, this one ain't. The pot was that, alone.

 One thing re: addiction... I have gotten a little obsessed with this, as most of you know. 
	

	
	
		
		

		
		
	


	




 So here I am with a scope trying to find the perfect output resistance to stop the tiny ring/overshoot. But scopes are dangerous. What looks like an insanely large overshoot on 10mV/div isn't audible. And with resistors on the opamp outputs, it adds distortion and shifts the phase. By MINISCULE amounts, but there ya go. I could visually see the tone generator's pulses looking different... from overshoot and a little ring, to mostly flat, to softened corners... depending on the resistance used. In this case with HD600s as load, the closest to perfection was 66 ohms. 61.9 went in, and that's what it's stayin at. But truthfully, _I can't hear a difference._ But I can measure it. Damn measurement tools. 
	

	
	
		
		

		
		
	


	




 All in all, it sounds great! It's a cooler chip, and on Grados the treble might be too agressive... but I didn't make it for Grados.

 edit: duh, photos... ok so it's 2am did I say that?


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## nick danger

I noticed that you are using a 24V wall wart. The one that I am using is 9V. Is 24V better than 9V? and is there any mod that I need to make to use it with the CMoy/Hansen?


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## skippy

24v should be better, especially with cans like the hd600. just make sure your caps can handle the voltage.


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## Apheared

Not just HD600s, everything... the chip's specs are usually much much better if you power them from more. 24V isn't what it is, it's actually 31V. (because of the incredibly low load) DON'T get a 30V thinking you'll run +/-15V, it'll end up being 40V or more. (and most opamps don't like more than 36V ever)


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## nick danger

All my caps are 50wv except for for the power caps, they are rated at 25V. Should I be safe with them or should I go up to 50V? I don't care about blowing the caps or the ICs, it's the cans I'd be concerned about.


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## thomas

One very simple way that i use to switch between external power supply and batteries is to use a DPDT switch- batteries go to one pole, external goes to the other pole, circuit is connected to the centre....

 When its wired like this, only one source will be connected to the circuit at a time... 


 btw, where are some good sources to get audiophile quality parts like your caps and the pots? thx


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## Tides

Apheared,

 Another nice amp 
	

	
	
		
		

		
		
	


	




 Now my question,

 Do you build these portable amps for sale ? 
 Because I am interest in a portable amp but dont know much about the DIY projects and parts ( I do have the tools since I mod game systems) and I dont feel like buying the TA at current TA price tag ( since I have xcanv2 already)

 I am here on Long Island, and can prob drive to the City and pay you a visit ,or you can just mail it to me priority ( if you decide to sell a portable amp)

 let me know
tidesofkali@hotmail.com
 or PM me.

 Tides


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## ppl

Apaheared: Glad you found a use for the EL-2001's. The Quessent Current on these are speced at 1.3 ma but most are about 0.6 MA. Moreover these are not Discontinued like the EL-2008. Insight has the EL-2001's in stock at around $4.00 Ea. last time i checked. The Typical output Current of these are 160 ma into a short. 

 Regarding the 60 ohm resistor you mentioned I gather from your post this resistor is Between the Opamps output and the Buffers Input? I hope that this large of a resistor is not upon the output of the Buffer. The Peaking you menttioned can be taimed by selecting an optimum value of resistor between the Opamp and Buffer. That's what i do. The HD-600's Higgh output impedance along with the Large cable capacitence would Dictate the use of an RC snubber on the Buffer's output.(see data sheet).

 The EL-2001 with the AD-823 should almost be a match made in Hevan. I made a Pocket amp with a pair of 2001's and AD-744's. operating on (2) 9 volts. sounds fine. I do agree with you about Driving Grado's with this Buffer. This is because of the limited output Current. Now i know some people will object but i have found that Grado's and Most Sony's and Most Surley the MDR-V700 @ 24 ohms Need at least 3/4 of an Amp of available output Current to sound right to me.

 Are you using a CRD for that 1 amp opamp Bias? The AD-823 dose not like low impedance loads at all it will load down at loads at 5K or less, so this OPA MUST BE BUFFERED. Did you use Multiloop? 

 Any way enough of this for now Great job.


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## Apheared

ppl, yea I mean opamp output resistor ie between out and buffer input. Nothing on the output of the buffer. the 2001s are a great pairing partner to this chip, more HD600 enjoyable than the 744 config... Multiloop, no. Get this... I was tryin to fit in the extra 4 resistors in the initial layout and couldn't, so decided not to... then in building it, I changed the positions and had plenty of room for them, but didn't. Heh.

 Tides, sometimes. I have built on spec and have sold my frankensteins because they keep piling up (I have this problem, you see) 
	

	
	
		
		

		
		
	


	




 But if you think a TA is too pricey I can't help you. There's alot of hours in one. That amp you're looking at right here costs more than a TA just in parts... you though, it's REALLY not that hard. Even if you have nothing you can build a cmoy, including all the tools, for about $80. If you need motivation head over to the CMoy Pocket Amplifier page @ HeadWize... you _can_ do it! DIY is not about saving money, trust me and the other mad scientists here... we're broke but entertained.

 thomas, I get parts from all over the world and spend waaay too much money on stuff tracking down discontinued and ancient crap... but try Percy, Parts Connection, Angela, Antique, etc. if you want North American guys that'll sell in low quantity.

 nick, you're pretty safe. While the power reserve caps will only see half the supply voltage each, usually you try to have them over the total rails... so in case something goes wrong you don't pop them too. but 25V for +/-15V is ok.


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## ppl

YA ICAN POST AGAIN: Sa it aint so Apaheared I bowared a Clone of my origenel amp that used one EA BUF-634 and a OPA2132. His thinking the same low supply voltage resulting in maximum output "Kids". anyway i replaced the opa2132 with the AD-823 Then compaired it with the AD746 the Dual AD-744 and YA the 823 for sure. Arent this new crop of NEW OPAMPS alot Better and Cheeper than Old so called state of the art just a few years ago. Well i gave the Amps owner the AD-823 installed since he also thought is rocks .


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## jude

Quote:


 _Originally posted by ppl _
*YA ICAN POST AGAIN: * 
 

ppl,

 That was _you_ who wrote me an e-mail about that? I wrote you back. I tried finding the associated profile by crossreferencing the e-mail address you included in the e-mail body (you didn't list your username so this was my only way), but it appears you missed a "c" in that e-mail address which why I wasn't able to find out which user was having problems.

 Anyway, I didn't make any changes to your profile because I didn't know it was you. I'm not sure what problems you were having, but if you want to describe them to me via PM, that'd be cool.

 -- Jude --


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## ppl

Ya i compaired the Dual AD-744 to the Dual AD823 in my pocket amp using the EL-2001CN and a resounding YES the 823 sounds alot better this latest generation of opamps sure outperform their counterparts of yester-year lake the Single AD-825 just blow ayay the older OPA-627 and other prior reference oopamps.


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## Tomo

Hello,

 I screwed up and forgotten to back up multiloop discussions we had. I never thought HeadWize would go down for a while and never thought twice about it. 

 Anyone kindly post the schematics again?

 Thank you,

 Tomo

 P.S. I am looking into Elantecs too.


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## Possum

What do you use to mount the LED so it looks bare and neat, just sticking out of the case? I was trying to do that in a few projects, but ended up having to get some kind of panel-mount LED holder.


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## Apheared

Ah. they're lenses. The bomb. Not tellin you what ones, because it's my thing. 
	

	
	
		
		

		
		
	


	




 They're easy enough to find on your own though.






 edit: whoops... url, img, same diff...


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## skippy

you can hot glue the LED's in. it looks nice if you do it neatly.


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## Possum

Oh, stupid me! I tried to hot glue the LED of my first cmoy/Hansen from the front (too lazy to open the case up again) and of course it looked kind of messy in the end 
	

	
	
		
		

		
			




 Lenses eh?


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## nick danger

Thanks for the wal-wart suggestion. I found a 24V 1.2 Amp power supply and it works very well. Found it at a ham-fest for three bucks. Completed my first project - hooray! I really like the amp with crossfeed. The cmoy does seem to be more solid sounding and with more detailed treble than my trusty old yamaha integrated amp. But the cmoy is not as open sounding as the Yamaha even with the crosfeed off. Hard to evaluate since I haven't turned on the Yamaha for a week. Hmmm....does this tell the whole story?


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## mlloyd1

Hi:

 I've seen a number of posts mentioning a preference for the AD823 over the AD744. I am curious to know if any of you have tried using the AD744 by bypassing its output stage and directly driving a buffer, say an AD811 video speed CFA. I use this as a line stage as well as a headphone amp for my Beyer DT990 and I like it a lot!

 The AD744 is unique in that the output signal that goes to the class B output stage is available at the compensation pin (5)! This allows you to bypass any nonlinearities provided by the decidely undepowered output stage. This concept appeared in some AD literature authored by Walt Jung some years back.

 I have also seen a line stage using the AD823 with the AD815 as a buffer. Haven't built it yet, but its on the list.


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## ppl

The very First Portable Headphone amp i made used the AD-744 in the Method you Discribed. The Comp pin driving the Buffer. I have posted this several times. The Difference between using the AD-744's normal output and using the Comp as an output is like Night and day. Search my early posts for more info. As far as using CFB type of Opamps as Buffers? Well Everyone dose this But this and those DSL drivers whitch are also nothing more than High Current CFB type OPA's also are not what i like to use for an output stage since thay have to use Neg. feed back and thus can be unstable with Certin loads> SO once again I LIKE OPEN LOOP BUFFERS....... I LIKE OPEN LOOP BUFFERS>>>> ect....ect ect..


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## Possum

Apheared, is the shaft of the Noble pot short by design, or did you hacksaw it to a shorter length? The shafts on my alps pots end up making my knobs stick out ~1/2" too far from the panel.


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## eric343

Now someone has to design a PCB for the amp... Then I'll build it. (my experiences with my Cmoy were bad enough... had to do a total rebuild)


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## Possum

If you made a cmoy on your own board, making this amp is almost as easy - just a few changes in part number/values and the addition of VERY few parts.


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## thomas

i think the whole appeal of DIY is being able to customize everything to your exact tastes, and getting to play around with different designs... And its almost impossible to make large modifications to a circuit based on a PCB. So i think you should really try and work with blank boards, it'll give you much more flexibility...

 Do a total rebuild. Do it 10 times... eventually, you'll get good at it... eventually, you'll turn into apheared!


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## source direct

Maybe I'm too green in the DIY area, (that may not sound right but you know what I mean, anyway) but from my reading I cannot tell what the difference is between the cmoy that uses the OPA134 and apheard's "cmoy slayer" the 47 (? I think ?), other than the op-amps that each amp uses. Would anyone care to break it down for me?

 Earlier today I was able to assembe the cmoy, except I used this other opamp that I had laying around instead of the OPA134, I used the National Semiconductor LM6182IN. I haven't gotten a chance to see if it works yet because I couldn't find the right input and output jacks at the local radioshack, so I'll find em tomorrow. What kind of modifications would I need to do inorder for what I currectly have assembled to be considered an amplifier of Apheard's design? By the way I still have it assembled in my breadboard.

 Any guidance would be greatly apprecieated, thanks.


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## thomas

source direct-

 The basic cmoy and the 47 amp both use the same opamps, the OPA134. In the basic CMOY, there is a single opamp per channel which gives both voltage and current gain.

 But for low impedence headphones, a single opamp will not be able to supply enough current, hence the apheared 47 mod. In that design, he paralleled two opamps to double the current output, allowing you do drive low impedence (Grado) headphones better.

 In this design (the HD-600 amp), he has changed the opamp to the AD823. To get enough current, he added a second amp stage, using a unity gain buffer (EL2001). Now, the opamp is used only for voltage gain, the buffer only for current gain. 

 For more about how these designs work, look at C. MOY's Designing opmp hased headphone amps article at headwize


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## eric343

Quote:


 _Originally posted by thomas _
*Do it 10 times... eventually, you'll get good at it... eventually, you'll turn into apheared! * 
 

Ummm, this a good thing? 
	

	
	
		
		

		
		
	


	







 I prefer my teeth white thank you


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## source direct

thomas, thank you, that was exactly what I needed.






 On another note, regarding the switches in my cmoy:

 on the back of the switch I have, there are about six posts, three stacked on the left and three stacked on the right. The switch is supposed to go inbetween R1 and C1, and if that's not descriptive enough, then I'll try another way. The switch goes between the very first resistor from the input, and the capacitor, which is in series with the first resistor ( I think ...).

 Now that we know about the switch, my question remains, and that is how am I supposed to hook up the switch? There are six posts on the back of the switch, which do I attach to what?

 Sorry if this is remedial/lame. Thanks.


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## Apheared

eric, well, you don't have to have nicotine/coffee stained choppers, but its definately a side-effect... you do have to put yer butt into a chair and a soldering iron into your hand and a collection of books up your nose... for hours a day, everyday (or at least every week). I've got 1000 hours in this, easy. And a few thousand dollars over the last year or so. You'll drink and smoke... heh.

 Thomas is correct... do it, over and over and over and over and over... I mean I've made stuff I'd never show online... some things cool (some things lethal/illegal) 
	

	
	
		
		

		
		
	


	




, somethings that didn't work the first 22 times but worked perfectly the 23rd. It's all about exposure.

 Thomas started HW around "the beginning" last year... he's "watched" me go thru all the BS like some of the others. From total newbie to being quite Apheared. I still don't get 1/1000th of what there is to comprehend, but hey... it's fun.

 There will not be a PCB for this, heheah.. anyone that wants one can etch it themselves. Same reason there's no schematic... if you can't figure it out from the EXTREMELY WORDY initial description, you probably don't want to build it... just stick to opamp swapping on hansen boards.

 I'm gonna lock this thread, it's all over the freakin place and gettin long.... any conversations in-progress please create new threads.


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