CHANGSTAR: Audiophile Headphone Reviews and Early 90s Style BBS
Lobby => DIY => Topic started by: OJneg on July 12, 2013, 05:07:31 AM
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This will be the AMB thread, dedicated to all things AMB.
http://www.amb.org/audio/
Feel free to post pictures of your own projects (past and present), reviews, impressions, discussion, troubleshooting, whatever. If you have any AMB gear and want to vent about how much you love it or hate it, both sides are welcome.
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Be populating the board tis week(even if I have gotten most of the parts a few weeks back). Pics be up this week or next. Just ordered the casing(went with Par-Metal in the end). Opamps inside be 4627 and 4898 for the other.
I have a Mini 3 and I think its fantastic except for its limited drive capability, clips into low sensitivity phones and too much noise for sensitive IEMs. Its very nice though. The first thing I noticed was how nice the bass sounded, pretty fast too.
As I said in shoutbox, PM me if you want a Mouser BOM for the M3(if you bought the rest of parts from AMB) and Sigma 11.
Also on sb is that my stuff from parts connex(wire, dmm, knobs, switches) have not arrived, its been 4 weeks via small packet, should I be worried? I should have stuck with priority, I was so stupid.
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I built a Sigma 22 to power my Dynalo. It gives 15 good volts and plenty of current. I find it to be a good readily available kit for many applications.
Recently I heard the Beta 22 and it seemed pretty capable. Maybe a tad too bright for my tastes. I've also heard Spritzers uberM3 and it was nice with the RS1.
Here's my Dynalo with the top off-
(https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-snc6/704340_477076195678520_2051719076_o.jpg)
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I have a Mini 3 and I think its fantastic except for its limited drive capability, clips into low sensitivity phones and too much noise for sensitive IEMs. Its very nice though. The first thing I noticed was how nice the bass sounded, pretty fast too.
Try this:
remove U4, connect pin6 of U4 with a piece of wire directly to pin1 of U3 and increase both C5s to 2200uF(16V).
Alas this will be too big for the enclosure perhaps, but will increase power output in low impedance headphones, will do nothing for headphone impedances above 120 Ohm though.
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I've got a half built 3-channel b22, and the parts for an M3 sitting in my workshop. They've been sitting there for years... just can't seem to find the time/motivation to finish them off. My original plan was to hack them somewhat to make an active balanced ground configuration like in Jan Meier's amps. If I were feeling particularly adventurous/stupid, I'd use the M3 to generate the signals and feed those into the b22 boards.
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Here's some pictures from my latest build, the CKKIII.
http://www.amb.org/audio/ck2/ (http://www.amb.org/audio/ck2/)
Why'd I pick this one? In short, because I didn't want to spend $500+ on all the parts necessary to build a B22. I also like the idea of a regulated power supply, discrete JFET inputs, and no global feedback design. Having something that could fit in a fairly small chassis with it's own power transformer was also a must for me. Made the whole order a few months back and it's been sitting around for a while before I could finish the chassis. I ordered the majority of the parts from Digikey (PM me if you want my own BOM) and that came out to $140 (with shipping and tax). PCBs, pot, and a handful of transistors from AMB was another ~$50. Neutrik and RCA jacks from PartsExpress put the total cost a bit over $200.
(Zoom out)
This is a nice looking chassis. Hammond makes 'em well.
(http://i.imgur.com/lzJmpJB.jpg)
(http://i.imgur.com/gturhII.jpg)
Papa's drill press, but this is my first time trying to cut metal
(http://i.imgur.com/HgXTImw.jpg)
Made these little cutouts with the Front Panel Express software. They turned out to be very helpful.
(http://i.imgur.com/OrQaHno.jpg)
As you can see, I botched the IEC cutout pretty bad. All the cuts were done with the drill press, but that one had to be done with a Rotozip and a special bit. Something about my table/clamps wasn't stable, so I lost control and blew it. It's not as bad as it looks, but it's still noticeable even with the module installed. Also notice how the backplate cuts aren't nearly as clean. I have no idea what happened there.
(http://i.imgur.com/d71Ahg8.jpg)
V regs on their heatsinks
(http://i.imgur.com/iWUoAmX.jpg)
Hats off to AMB for having such a high quality PCB. A real joy to work on.
(http://i.imgur.com/K6Oi9d6.jpg)
Heatsinks on the output pairs. Ti says they're optional, but I can't imagine running this amp without them.
(http://i.imgur.com/cXW6LPz.jpg)
Again, this is a good looking amp.
(http://i.imgur.com/n92sHLJ.jpg)
Here's the front plate. The shaft sticks out a bit, but if I had a larger knob it probably wouldn't be a biggie. I frickin' love the locking Neutrik connector though. Super solid and makes going back to other connectors painful.
(http://i.imgur.com/AuVFPXe.jpg)
I'm guessing this chassis was meant for running wires down the side panels. It works really well. Also, is my mains wiring considered dangerous? It was the only way to get it to the switch. I should find a way to heatshrink it or something I guess.
(http://i.imgur.com/1CCCwJd.jpg)
The rest of my wiring is pretty good I think. Not as bad as some vintage amps. 18 AWG, solid core copper used all around.
(http://i.imgur.com/EzxPqb7.jpg)
That's an HD600 and an A900. I chose the 4x gain configuration. With the CD player's output, I sit around 10ish on the knob. With my laptop, it's around 12ish. I'm measuring around 300mV RMS for fairly loud listening levels on the HD600, which is in line with Tyll's number. I used pink noise and some Tool to gauge it. If you really want to rock out, they can take about 500mV+, which corresponds to about 1-2 oclock. I imagine these require a fair bit more voltage swing for peaks if you listen to dynamic classical music, but my RMS meter can't measure that obviously. Overall, I don't think I'm running out of gain any time soon.
(http://i.imgur.com/fGzMxQv.jpg)
(http://i.imgur.com/AwaXADY.jpg)
Random notes:
- Output stage is biased at around 30mA as Ti recommends. I can leave my finger on the heatsink for about 5 seconds before I want to pull away. There doesn't seem to be much heat radiating though, and I'm thinking I could push it a lot higher (60mA is the max according to Ti) even with the top panel installed. But on second thought, I don't have any headphones that draw over 30mA, so I don't think this baby is leaving Class A any time soon. Still might tweek in the future too see how much of a difference it makes
- As you can see, I have a second pair of RCAs that are driven directly from the output. I tested this briefly and it drove my Zamp well enough. Maybe a gainless buffer power amp is in the near-future for me?
- I wired the xformer secondaries wrong at first. I only noticed because it started heating up big time. I think if I hadn't shelled out for the fancy pants, heavy duty diodes I would have blown the them
- I measure 18VAC on secondaries. It does drop a little when loaded
- I can't find the clear rubber feet that came with the chassis. Anyone know where I can find some?
- I might be willing to take on some other aesthetic mods. An acrylic top plate would be cool, like on Ti's own build. More than anything else though, I'd like to get the front plate laser engraved with CKK
In terms of sound...well it sounds great to me. It's a clear step up from my Cmoy or laptop output. ZuneHD seems to have poor extension in both directions in comparison. HD600 and the A900 are both very listenable on this amp. A900 has very noticeably improved bass control; I'm guessing it's the lower output impedance. But the A900's grain in the treble is much more apparent now, although the HD600 is still very smooth up top. Not veiled though ;) I'm not experienced with high-end stuff so take everything with a grain of salt.
I'm sure most you guys out there have heard this amp before. But if anyone in Orange County wants to check it out, just let me know. Overall, I'm happy with this one and I'll be keep listening for a while. :)p7
(ultrabike: OJ I made some mods to your post - pic/text sizing only. Hope you don't mind. Fantastic work BTW!)
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Edit: Phew!
Cool pics, man!
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Good pics and nice build OJ!
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Nice gear guys :D !
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I've bult a CK2-3 as well, but didn't like the sound at all. :( compared to the M^3 it's a bit harsh I think?
your build looks great though! should consider an M^3 ;)
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Really..well I'm not finding it harsh at all. Then again, both my 'phones are on the warmish side FWIW.
M3 looks swell, but no more headphone amps for now. Next project needs to be a speaker amp, but B24 is out of my league right now. Still parsing through the Pass designs to see which would suit me best. F2 (current source) looks like a good option I'm thinking. I could also run headphones off it I'm guessing.
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OJneg,
excellent job. what output devices did you use?
if i may suggest, for cutting dreaded D-holes, i would use a rodsaw mounted on a hacksaw: http://www.mcmaster.com/#handsaw-blades/=nljrxr (http://www.mcmaster.com/#handsaw-blades/=nljrxr). you can get these at any big box home improvement store. just cut a pilot hole, thread the rodsaw through and attach to the hacksaw. cutting straight lines and making small adjustments is super easy since rod cuts all the way around its circumference. i use a CAD program to draw out the cut out dimensions like you did. Scotch tape over the print out, take a decent metal straight edge/ruler and metal scribe to mark the outline. a bastard file is your friend to get the IEC inlet to fit perfectly. after fitting the IEC, it always a tight fit for me since my D-hole is always a little smaller and needs filing, just drill out the chassis screw holes. no need to measure these out.
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Thanks for the heads up fish.
Used the BD139 and BD140, standard stuff.
I actually tried using a rod saw at one point, but the blade was too dull. I had pilot holes drilled at each of the four corners, and I figured as long as I kept it square with an external guide I would be fine as I moved down. It worked for the most part I guess facepalm I think if the damn thing had a speed control I would have been fine. But it only goes at high RPM and that becomes hard to control.
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the BD139/140 should make for a perfect pairing with the Senns. the MJE243/253 sound better with HPs like the K701.
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anybody building a M3 should forgo the decade old opamps in the Part List and go with something more modern. the ADA4627-1BRZ, ADA4898, and OPA1611 are easy recommendations - ancillary gears and ears apply. keeping L/R opamps the same and switching up the G channel will change the sonics as well. i would recommend the SOIC-8 adapters from Leckerton or Brown Dog. up the O11 V-out to get close to the max rating of the opamp you want to roll. 30-31V gives you a lot of opamps to choose from. socket R10 and D5 in the O11 to make sure your V-out is under the max rating of the opamp.
socket the gain resistors. the stock 11x gain is too much for sensitive HPs, but has less NFB.
the Par-Metal 20-series 12x12x3 is a decent chassis for the price. i personally dislike the black anodize, but like the natural anodize and black painted chassis. the 3" tall chassis gives you extra room for taller heat sinks and plenty of ventilation. the stock 1.5" heat sinks are good for 150mA of quiescent current bias. i would recommend at least 100-110mA of bias. if going above 150mA, you may want to consider a TX with more VA like 25VA or more and taller heat sinks. if going with a single chassis build like the 12x12x3, a custom wound shielded/encapsulated TX from SumR is cheap insurance for another $40 or so. Richard is a total pleasure to deal with A+++ customer service.
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@fishski13 :About your bias current recommendations, when do you measure it - At startup, 20 minutes later or after couple of hours of playing music ?
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In my opinion, even good opamps don't save the Mini 3, it has some weird stuff happening with timbre and noise, as if there's some mess up in the topology.
The M3 on the other hand is excellent regardless the opamp choice.
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I've bult a CK2-3 as well, but didn't like the sound at all. :( compared to the M^3 it's a bit harsh I think?
your build looks great though! should consider an M^3 ;)
the BD139/140 tend to be brighter and thinner sounding than the MJE243/253.
@fishski13 :About your bias current recommendations, when do you measure it - At startup, 20 minutes later or after couple of hours of playing music ?
with the lid on after 30 min or so from start up. when removing the lid to make adjustments, i wait around 15min or so. with the MOSFET negative tempco, you may get some reduced bias over a period of hours, but just a little. i would still make the effort to measure after a few hours though. it just kind of depends on the ventilation.
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for the B22, i would would recommend trying higher quiescent current bias. you may want to give yourself some more TX power headroom and go with a slightly larger VA than recommended.
the stock quiescent current is 120-160mA. i upped it to 225mA and felt it sounded a bit too "tooby" and diffuse with uncontrolled, sloppy bass and softened note attack - but i really liked the midrange emphasis that both good and bad tube amps are known for. i personally prefer 190-200mA. you may not. those that feel the B22 to be too reserved and analytical sounding i think would find it to be much less so with more midrange presence and a more forward soundstage with a slightly higher bias. YMMV.
for a single chassis B22, like my own, i would strongly recommend a shielded/encapsulate TX from SumR and a ground-loop breaker. my own B22 has been through various rebuilds, board configurations, and mods over the past 5 years, but is now in a 16x12x3" black painted alodine Par-Metal Series-20 enclosure. 2 boards, single O22, 100VA encapsulated/shielded SumR TX, stock 1.5" heat sinks, and Goldpoint SA. ample ventilation with stock heat sinks for a higher quiescent current bias. even with a gain of 5x, it's very quiet with the 102dB/mW sensitive AT AD2000 and dead silent through the full sweep of the SA with my other HPs.
high impedance signal runs, RCA inputs to pot and pot to board inputs, should be shielded - twisted pair with shield with shield tied to input ground on the boards. after dicking around with numerous wanky wire over the years, i've settled on Belden. this shielded wire is a dream to work with and what Ti Kan recommends: http://www.mouser.com/Search/ProductDetail.aspx?R=8451_010100virtualkey56610000virtualkey566-8451-100 (http://www.mouser.com/Search/ProductDetail.aspx?R=8451_010100virtualkey56610000virtualkey566-8451-100) . for power runs inside chassis and signal output wire i stick with 20awg like this: https://edeskv2.belden.com/products/index.cfm?event=printPrev&pnum=8523&ut=English (https://edeskv2.belden.com/products/index.cfm?event=printPrev&pnum=8523&ut=English). also available from Mouser. for a 2 chassis build with an umbilical, do what TK recommends and go with a larger gauge wire for the umbilical. even with an aluminum RFI-rejecting chassis, i've found it still pays to shield the high impedance signal runs.
the B22 doesn't like to have it's outputs shorted. the TRS plug/jack will short a channel to ground very briefly when inserting and removing the plug. it's best to treat it like an 18W speaker amplifier. the O22/B22 has no current limiting circuit. i've never had an issue, but you read that there have been some rare failures because the outputs are shorted. i think this is largely due to people having the music cranked and/or using power hungry phones and not following the following the following practices. it's basically a non-factor if you: turn down the volume all the way and pause the source before insertion/removal, or add a mute switch on the outputs. the former is good practice no matter what amp you're using. no output device whether it be MOSFET, BJT, or opamp likes to drive a dead short to ground. also, an open-frame TRS jack allows you to adjust the pressure of the contacts by slightly bending them to tweak the force of insertion/removal to avoid slow/clumsy action that can cause a longer dead-short.
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Just the S11 from yesterday, I have been really busy lately and 2 boards was all I could finish before heading back to my day job. Hope to finish up soon..... Also, I had to learn how to use the new dmm as I had returned one of the yellow Flukes I had to my school.
(https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-prn2/v/1084172_10201359127435771_1273844650_o.jpg?oh=3f8e7dca0a16d17da6c6b6a2ae6ce746&oe=51F7CE02&__gda__=1375283824_ba948799186573c1bafce52697e91bcb)
(https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-prn1/v/1068879_10201328700075106_436415297_n.jpg?oh=0434a18d4f57a2ba814a69e93384b6bd&oe=51F80582&__gda__=1375291178_502c0149de5533f77ec234f3817dcdde)
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I have one of those old Flukes myself.
Except things I take from lab are usually forgotten to be returned :&
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firev1,
i would double check the placement of the 220pF ceramic caps. AFAICT, they appear to be in the wrong pads. take a look at the PCB tracings under the pads and double check the drawing on AMBs website.
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OJneg, totally know what you mean, too bad the yellow Fluke was a 'priority' item for them lol.
Thanks for the heads up fishski, will double check on them tonight. Luckily I'm not done with the 2nd board.
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Here's my gamma2. sigma11 will be feeding it the juices. I'll try to finish the chassis tomorrow.
(http://i.imgur.com/SYLqpse.jpg)
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Looks like the gamma3 is moving along.
http://www.amb.org/forum/gamma3-high-resolution-dac-development-t2656-220.html?sid=d0edba081896dc55e67d281c1a74b754#p25053