[skyskraper]

ok so micro cmoy for my ipod and a cmoy to add to my dj'ing setup are well and truely under construction. im just waiting on the op amps, led's (i want some wanky pink and purple ones

), and ic sockets, before i case them up.

i was thinking about adding a couple of cmoy's in one case to my studio setup for HP monitoring. presently my stand in mixer (behringer, not too bad actually for the price) only has one HP out, i want to be able to work with a collaborator monitoring in headphones, and a-b recordings with two sets of cans myself on the fly. so a pair of hp amps in one box would be the way to go. id want to build them with a balance control on top of volume control, and would power them from a regulated 9v wall wart (im guessing 500ma should be enough ?).

so i was thinking alps pots for volume and balance (gotta have balance for the moment until the fluid from behind my right ear completely dissipates, and it's just a handy feature to have). wall wart to keep internal noise to a minimum. so im tasked with choosing an opamp, resistors, capacitors.

my goal is for maximum transparency and minimum colouration of the sound. the headphones i will be using (ultrasone dj1's and technics rpdj1210's) and the source (behringcrap mixer) will be providing more then enough colour to the signal. i chose to do it cmoy style because i am confident my soldering is up to task on a cmoy (not sure about my skills for a pimeta yet although a pencil tip for my iron may help)and the fact that i can just walk in to dse (like radioshack in .au) and buy the boards there without having to worry about getting them shipped from tangent (no web transactions on my CC atm due to my dad being a bit of a dick, my account is under the family umbrella and i havent had a chance to fix it up myself yet) if i did go pimeta)

i have some opamp samples enroute (sitting at ups's depo in ontario ca waiting to get on a flight to .au

). im sure in what's coming there will be something suitable. so before i just go randomly plugging them in to the ic socket i was hoping to get some feedback off you diy heads on which would provide me with the flattest response and the minimum colouration of the signal.

my options are: OPA2107AP, OPA2111KP, OPA2132PA, OPA2227PA, OPA404KP, OPA4131PA, OPA627AP.

now i know that ive listed some quad op amps, i ordered them to drop in to my urei 1620 replica card to see if it will make a difference (to sidetrack, the 1620 uses tl084's but the mixer has the best sound out of any dj mixer ever built, lets see if burr brown can make it sound even better). i thought seeing as i will be building two into a single case essentially creating one unit, that i could possibly utilise the quad op amps to drive them.

which would you guys reccomend i try out? the 627 is at the top of my list so far. but i want clean flat sound so maybe its not the best choice? would i be better off looking for other op amps that may be good for what i want on top of the list i have made?

on to capacitors. i only really have the generic range and whatever farnell and rs stock available to me. will the fancier audio caps give me a cleaner sound then generic caps, or do they colour the signal a bit? yes i admit im still a newbie at this so i am not sure the difference that audio caps will make to a signal, ie: more "musical" or "cleaner" etc...

with resistors im assuming that the better quality ones will make a difference to my sound and have tighter tolerances then the generic metal film counterparts. am i correct in saying this? if i am correct how big a difference is this likely to make?

i for the connectors i plan on using neutrik locking jacks (so i can have an excuse to use them

). the interconnects (mixer to amp) will be made from canare l2t2s for the fact i can buy it at the store down the road, with either neutrik jacks or generic gold ones (been quite happy with these to date, not sure i can justify the cost of the neutriks atm) both 1/4", sleeved in techflex for add "cool".

is there anything else you guys would suggest i do/use? im using 60/40 solder atm and i suspect that it will make little difference to my sound using 63/37. perhaps i should buffer the cmoys? or just go straight to pimeta/ppa?

id appreciate any input you can give

 

[skyskraper]

bueller?

edit: how about using a quad op amp with 6 buf634's? three driving each output? thats if im understanding using buffers correctly.....

 

[Sycraft]

Errr, well, if you aren't a solder/electrical whiz, something like the Pimeta or PPA probably are better than a modified Cmoy. The reason the Cmoy is recommended as a first is because it is very, veyr cheap with default components and very simple. If you are going to trick the thing out, better to go with a better design. Remember: Tangent sells boards for Pimetas and PPAs. Lot harder to screw up when you are just sticking things to a board than when you are doing it all yourself.

If you are really ocncerned about the best sound, but a PPA from one of the people that sell them. Best to have a professional do it as they won't sell you a messed up one.

As for opamps, of those listed, bing all Burr-brown the OP627 is by far teh best. It specs head and shoulders above the rest and peopel claim it sounds the best. For that matter, it specs to the point that it should not change the charateristic of the sound in the audible range at all. We are talking an opamp that will pass signals in excess of 1mhz.

But at any rate, the Cmoy isn't really a very good design. It was made to be simple and small, not high quality. The better amps have much upgraded power stages, opamps on the ground channel, buffers to drive the headphones and so on. Design really does have a lot of effect on how an amp performs.

If you really want the best in terms of DIY at this point, take a PPA, put on good Burr Brown or Analog Devices opamps, use Vishay-Dale resistors, load it up with capacatence, bias it into class A, drop on some diamond buffers and stick a stepped linear attenuator on the volume control.

 

[bpribadi]

Try AD8065 (single) / AD8066 (dual).

http://www.sgheadphones.net/index.php?showtopic=2628

 

[Earwax]

If your soldering is up to putting together a cmoy, you can do a pimeta. it's easier to solder on a nicely made PCB than on perf board. The extra "challenge" of the pimeta is in parts selection and troubleshooting (if anything goes wrong).

Is this for a portable or a wall-powered amp?

 

[skyskraper]

cheers for the input. i mean my soldering is not dog horrible. but its hardly precision just yet. i thought cmoy would be the go due to the fact that i know i will have no problems getting them to work (touchwood) and the board for it is available for a couple of bucks at a store down the road. would hate to order a pimeta or ppa boards and then have myself do something stupid and ruin them and have to buy another set and wait for the silly .au post service to get them to me from overseas and pay for s/H all over again.

i'll look in to the ad chips, been thinking about finding them anyway for future moving on ups. bpribadi i love your review, been reading them every now and then just to check whats up. very informative.

ill power the amps off a wall wart.

i think more then likely ill put this thing together with cmoy's running for the meanwhile and when im ready to move up to ppa/pimetas then i'll order a couple of extras to stick in the case for monitoring. would you guys be able to help me out with the question about audio caps? i ask for general knowledge on top of wonderment when thinking about this particular amp.

thanks for the help guys.

 

[Sycraft]

Well if you have a desoldering braid and a colder sucker, you'd have to do something really bad to screw up the board of a PPA or PIMETA. A component screwup, just desolder and resolder. Or just solder in a bunch of sockets. What you are far, far more likely to screw up is wiring and hence a component.

Also what you are talking about is a fairly complex Cmoy what with multiple buffers per output and such. That's really just like a PIMETA or PPA but minus the bias circutry and good power stage.

As for caps I dunno. Generally speaking the more you spend on a given amount of capacentce, the better the cap. Thing is, if you make a design like a PPA where there aren't any caps in the signal path, it doesn't matter so much. Caps mostly screw up the signal, they don't mess with the power a whole lot. There are plenty of peole that will tell you, and back it up with measurements, that Panasonic FCs are as good as the best.

I personally went with Cerafines on my PPA since I got a good deal on them and I figured why not? Past those are Black Gates which are real expensive.

For the smaller plastic caps, I'm not sure it makes so much difference, they are all fiarly good, spec wise. Again, matters more if you are talking in the signal path, but if you use a design that's just on the power I think that they are there is mostly what matters.

Also the Cmoy is fairly sensitive to powersupply noise, as these thigns go, since it's got little to shield it. The PPA, on the other hand, seems to be fairly immune. A cheap wall wart is probably not the way to go with it.

Really, you may just want to think about buying an amp. I mean if you are talking about tricking out a Cmoy with AD627s and 6x buffers per channel, you are talking about some serious money in components. Better probably to get a better design and if you don't want to build it, to have someone do it for you.

Design probably matters near as much as components in an amp,a nd certianly limits what you can get out of components. The Cmoy was made to be cheap and simple. You can assemble one for under $10 if you try, and as configured it's real easy to understand the circut. Well the thing is, even if you trick it out, it's still a pretty simplistic circut and there are just limits to what you can do with it.

 

[skyskraper]

sycraft: thank you for a very informative post!

im starting to get what you guys mean about skipping the cmoy and just moving on to the pimeta and or ppa. i was just looking over the schematics again and it just does make sense to move on to something a bit more flexible and probably better suited to what i need. i would go and buy an amp but taking up diy electronics has turned out to be a great way for me to relax. and i just love toying around with things

i like the challenge of learning something new (in baby steps of course) and the satisfaction of creating something is pretty cool too.

time to get some money into my paypal account for some pcb's and off to find some parts

one last question, i think the pimeta is definitely the next step for me until im confident i can populate a PPA without solder bridging. for my application, im assuming you guys would definitley reccomend biasing in to class a of the pimeta's???

 

[Earwax]

Quote:

Originally Posted by skyskraper sycraft: thank you for a very informative post! im starting to get what you guys mean about skipping the cmoy and just moving on to the pimeta and or ppa. i was just looking over the schematics again and it just does make sense to move on to something a bit more flexible and probably better suited to what i need. i would go and buy an amp but taking up diy electronics has turned out to be a great way for me to relax. and i just love toying around with things i like the challenge of learning something new (in baby steps of course) and the satisfaction of creating something is pretty cool too. time to get some money into my paypal account for some pcb's and off to find some parts one last question, i think the pimeta is definitely the next step for me until im confident i can populate a PPA without solder bridging. for my application, im assuming you guys would definitley reccomend biasing in to class a of the pimeta's???

A simple cmoy is still a very good starting point for polishing up your skills, it's just that doing all the upgrades you're planning on gets you into the territory where a pimeta makes more sense. I say, do a simple cmoy first, save all the enhancements for your next project.

 

[bpribadi]

If you are going to use perf board, here is my layout. It is similar to PPA circuit diagram 1.0, but using dual Op-Amp as in Pimeta. The different with Pimeta is just the class A biasing, which I use the Jfet cascode of PPA class A biasing.

Save your time doing the layout if you are going to use perf board:

The orange cap near the Op-Amps are tantalums, and the 100nF are the normal platic cap (polyester of polypropylene).

 

[skyskraper]

earwax: yah i thought starting with a cmoy would be the go for my skill development. after today i now have two cmoy's and three micro cmoy's ready and waiting for their ic sockets and op amps to arrive. all seems to be going fine so far. i have a tl082 lieing around that im going to use to test them before i drop in the 2227's and 2134's, and case them up

ill wait to see how i feel about the finished products then decide what direction i want to go for the studio set up methinks.

bpribadi: thanks a million for that! i will give it a shot. is it just straight up perf board u use for that or is it grouped pads? im assuming the first

 

[bpribadi]

Yeap, the first.

 

[robzy]

If you end up going for the CMoy bare in mind that the board DSE sell actually lacks the holes going down the centre for ground. An easy solution to this is to just use a fast turning drill with a sharp (small!) peice and drilling a few holes yourself... but make sure you go slowly as to not remove the metal tracks. It also helps to have some wood under it to stop too much pressure being put on the tracks.

Good luck with it, whatever you make i can garuntee it will be rewarding, as i have recently found out.

 

[skyskraper]

theyve got another one that does have the drilled holes down the middle too

check it here . its exactly the same as the one advocated by tangent

you can even split it down the middle to get two boards