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My desk C-Moy - Finally complete!

post #1 of 8
3/13/13 at 11:23pm
Thread Starter 

Hi all, I've posted some images of this amp in the DIY project gallery. I've finally sorted out the niggles I was having with it, and finalised the wiring and whatnot, So I thought it deserved its own thread.

 

It's powered off a 19v switch-mode laptop PSU, and that is dropped down to 10 volts with a linear regulator. The result is near silent operation, at any gain Ive felt the desire to use. Its currently set at 4x, which makes 2/3rds of the volume adjuster usable with my HD465s.

 

I've experimented with a few op amps in here, namely 2132, 2134, 4556, 4560 and 6558. It seems stable with all but the 6558 (which was only tried because I found them in a headphone amp in some commercial gear, I'm not sure what it requires to be stable.

 

The board I used is the Cmoy RA1 from Fred's Amps, running a resistive divider and 0.1uF decoupling on the V+ and V- This was responsible for helping the sound with more tricky amps a great deal. Even though I've played around with different chips, the 2132 has ended up being my choice in the long run since it sounds smoother, cleaner, and over all, seems to distort a lot less than anything else, in every situation I've tried it in. I  don't intend to be using this as my primary amp for long, but I think it'll be a useful tool for hearing the differences between op-amps.

 

Well, I'll offload some pictures now, Any questions, feel free to ask!

 

 

details of the board and inside, notice the caps on the bottom side to fit them easier

some of the amps I tested, plus the linear regulator

This pic, plus a few above, aren't exactly the final piece, eg. volume knob, and a few other details

 

 

Finally, check out what just arrived in the mail today... smily_headphones1.gif

I have most of the semis on the way from element14, I still haven't made up my mind on the main channel op maps though... Has anyone tried opa 2132 or 2134 with the O2? I'm thinking it could be worth a try since I already have one spare and love how they both sound. We shall see.

 

Thanks for reading this far anyway!

 

Peace

 

Chris

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post #2 of 8
3/14/13 at 12:04am

Nice Chris!!  Curious, why are you stepping down to 10V, couldn't you give it the full 19V swing?  I run mine at 18V... sounds better that way with the OPA2107, IMHO.

 

Mine says HI!!  Cmoys are so much fun.  my tube amps sit idle as I type this.

 

18V NiMH

OPA2107

TELE2426 rail splitter

Dubilier low ESR caps

 

My cmoy feeds a pair of output transformers... just sounds better/smoother that way to me.  I am thinking about re-casing it in a larger enclosure with 14 Eneloops and some output transformers.

 


Edited by kramer5150 - 3/14/13 at 12:07am
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post #3 of 8
3/14/13 at 3:25am
Thread Starter 

Thank you!

 

In all honesty, the highest regulator I had sitting in the junk box was a 10v one. I've run it on 18v in with batteries before however, and it didn't really sound any different to me, basically all I noticed was slightly higher max volume. It could be partly in that my cans aren't really pushing the amp, or it could also be to do with the op amp I've chosen driving more happily at this level. I intend to replace it with a 15v part when I get a chance to buy one though, just because I want to be getting the most of the hardware I'm using. I'm also planning to etch a little board for the package to mount on since it's currently soldered p2p with the caps and a lot of tape to keep it insulated ;)

 

I've never actually heard of the 2107 until now, I might give it a try in this since I'm looking for a possible replacement for the standard 4556 that's recommended for the O2.

 

That's the first time I've seen output transformers on a CMoy before, how does it influence the acuity of the sound? you say it smooths it out, is that at the expense of detail? What headphones do you use it with mainly? I do like the case you're using, I reckon the Cmoy is a little amp to begin with, it's nice to keep it in a nice compact enclosure like that, even if it spends its days on a desk

 

I really must get myself a hot glue gun asap, I still want to get the wiring as neat as yours! haha, I love tape, you can probably tell.

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post #4 of 8
3/14/13 at 4:25am
Thread Starter 

Woah, I just read up on the 2107, that's a serious op amp very fast slew and higher bandwidth than most I've used, I'm surprised that you can keep it stable, what cmoy board did you build yours on? I want one! biggrin.gif along with one of those chips to try out. I'm bummed out that I cant get the 6558 stable in my cmoy, huge distortion and the sound fades in and out, I havn't been able to fix it, so i suspect my board isn't designed for cranky op amps. Thinking, about it, I might try the pair of 6558s in the o2 when it's finished , just out of curiosity . //Edit: Derp, i was reading the 4558 datasheet I think, The 6558 is 500-something mhz bandwidth, AND only meant to be driven at 7.5v MAX, those poor chips, lol//


Edited by crispchicken - 3/14/13 at 4:30am
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post #5 of 8
3/14/13 at 10:34am

Its an old Guzzler Gmoy build from ~2005.  If you google search it you should be able to dig up the old HF discussions on it.

 

I like the OP2107 and use it in my DAC as well as old ~2005 GoVibeII.  The DAC feeds it with a ~16V swing.  Although the govibe is only 9V, so its not really optimal.  That amp only really works well with fully charged battery. The speaker transformer with the Gmoy seems to work best with the RS1 and my 16 ohm IEMs and the "hot" ~2V output from my DAC.  It just "spreads" the sound out just a little bit so its not so closed-in sounding.  Like taking deep drawn breaths of air, versus multiple shorter gasps.

 

When you think about it, many OP-amps are made for data send/receive in "number crunching" circuits and stuff like that.  So many are not really made for low-Z impedance loading, and impedance miss-matching can result.  Most of my amps are pretty high gain (considering my DAC has a pretty hot output).  So the transformer also lets me use more of the volume knob rotation... and it definitely sounds better than any of the resistance based impedance adapters I have made over the decade.


Edited by kramer5150 - 3/15/13 at 12:35am
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post #6 of 8
3/14/13 at 11:44am

DUDE! 

This amp goes to 11! 

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post #7 of 8
3/14/13 at 11:58am
Hahaha I didnt notice that
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post #8 of 8
3/14/13 at 10:06pm
Quote:
Originally Posted by crispchicken View Post

Woah, I just read up on the 2107, that's a serious op amp very fast slew and higher bandwidth than most I've used, I'm surprised that you can keep it stable, what cmoy board did you build yours on? I want one! biggrin.gif along with one of those chips to try out. I'm bummed out that I cant get the 6558 stable in my cmoy, huge distortion and the sound fades in and out, I havn't been able to fix it, so i suspect my board isn't designed for cranky op amps. Thinking, about it, I might try the pair of 6558s in the o2 when it's finished , just out of curiosity . //Edit: Derp, i was reading the 4558 datasheet I think, The 6558 is 500-something mhz bandwidth, AND only meant to be driven at 7.5v MAX, those poor chips, lol//

All 3 of my 2107s have been very stable.  The only time it gave me fits was in my DAC.  I was using semi-conductive solder flux to prep the thru-holes and I left enough flux residue on the PCB surface and apparently was getting some i or v bleeding from one lead to the next.  Drove me nuts!  With a jewlers magnifier my through hole job looked PERFECT.  It was just enough cross-conduction to short "something" in the OP amp and throw it into fits of oscillation.  A generous forum member offered to troubleshoot and re-do my work.  Its been bomb proof reliable for the past 4-5 years.

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