AMB.org's M^3 diy headphone amp

[t0wer]

I really love DIY projects, and the documentation is fantastic from AMB

 

All the tech specs, options, and instructions are here.

 

http://www.amb.org/audio/mmm/

 

 

PSU

I've used both a regulated wall wart(24v), and amb's sigma11(27v) for power.

The PSU difference isn't huge. 

 

The wallwart had a slightly louder turn on click/thump and had some SLIGHT hiss when you turn the volume up.

The sigma11 is borderline silent on turn on and dead silent even on max volume(hiss depends only on the DAC)

 

yea, I botched up the led wire.

 

nice 25va transformer, plenty of power for headphones or speakers

 

AMP

Where do I start.

It's a diy amp with as many options as you want to include.

The front end for mine is pretty standard, Power switch, power led, headphone out, bass boost, and volume

 

 

I initially used it with my D4 as a dac so I had a 1/8" line in, and once I upgraded to a full size dac, I added RCA and a input switch.

 

 

 

I really can't complain about the sound quality, it's extremely clean and clear.

The bass boost is very subtle with the default caps and resistors, I wasn't sure what to expect but would have liked a little more effect.

with my hd595 it was almost unnoticeable. It's more noticeable with my he-500 or srh-840's but it's still really subtle.

 

For a while I soldered a 1/4" jack on my speaker leads and was powering my marantz hd770's(4 way speaker, 1" tweeter, 2" tweeter, 4-5" mid, 12" woofer)

Holy smokes, this amp is powerful. Plenty of volume, especially for my small room. Only reason I stopped using it with the speakers, was because I got tired of swapping cables from headphones <> speakers.

 

 

(the thin silver/copper wire on the top/right has all been replaced, I'm just too lazy to update the picture.

 

 

I've used ad8610 for the voltage gain.

They sound great and haven't had any desire to roll other opamps.

 

 

 

 

Final Thoughts

I absolutely love this amp, Plenty of power for everything I can throw at it.

It's more than just buying an amp, it's about the time and work I've put into this.

 

"everyone should create. You should do something, then sit back and say, "I did that."
-Ricky Gervais 

 

 

The only upgrade I would consider after the M^3 is a beta22, and I'd probably make it a speaker amp and not for headphone use.

 

[h264]

http://nwavguy.blogspot.com/2011/05/amb-mini3-diy-headphone-amp.html

 

If you were wondering why I was interested in your thoughts on this amp, the more portable version of this amp happens to be one of NwavGuy's biggest dust-ups with an amp designer.  The designer Ambien banned him from the forum.  Honestly, in this case I found NwavGuy a lot nicer than he usually is, but w/e. NwavGuy wrote another piece afterwards explaining why he wasn't in favor of using a virtual ground design on a portable amp.

 

http://nwavguy.blogspot.com/2011/05/virtual-grounds-3-channel-amps.html

 

It's worth noting both that this is a DESKTOP amp, and is both bigger and more powerful than the mini^3.  Also NwavGuy always held everything to MUCH higher standards.  However, did you ever note any of the issues NwavGuy talked about that would be indicative of a 3-channel amp like this one?

[t0wer]

The channel imbalance sounds like out of spec resistors or a poor potentiometer.

I didn't see if he bought his already build from YMB audio, or built it himself.

whoever built it should have measured and double checked to see if everything was in spec when they built it.

 

The m^3 has opamps for voltage gain and fets for current gain, so I don't think it is as prone to the power issues that the opamp only mini^3 is.

from my speaker use, it sounded great with 200w 8ohm speakers, definitely wouldn't try that with the mini^3

 

 

for the virtual ground.

I thought it was to reduce the cost of the PSU.

it uses a tle2426 for the opamp ground so it almost seems the cost of the amp goes up so it doesn't need a dual rail supply.

now I wonder if that made the whole unit cheaper, or just put the cost in a different area.

 

 

I'd really love an oscilloscope and function generator to test this.

but I have a feeling, I would test my amp, then never use it again, so it hasn't been high on my priority list.

[h264]

The channel imbalance sounds like out of spec resistors or a poor potentiometer.

I didn't see if he bought his already build from YMB audio, or built it himself.

whoever built it should have measured and double checked to see if everything was in spec when they built it.

 

The m^3 has opamps for voltage gain and fets for current gain, so I don't think it is as prone to the power issues that the opamp only mini^3 is.

from my speaker use, it sounded great with 200w 8ohm speakers, definitely wouldn't try that with the mini^3

 

right, the M^3 is a totally different design.  He built the mini^3 himself, and even left out a part he said "had no effect on the circuit".  I've read the article numerous times and don't get everything yet, but I can understand how a 3 channel design might be a downside in a small form factor o

r battery-powered design.  Virtual grounds are used in portal audio only where you absolutely can't have two batteries and usually aren't very powerful since the voltage of that battery is cut in half.

 

However, I believe NwavGuy's main complaint was his choice of op-amp

 

 

I'd really love an oscilloscope and function generator to test this.

but I have a feeling, I would test my amp, then never use it again, so it hasn't been high on my priority list.

 

Having my own DScope is a personal dream...

[fishymamba]

Really want to do something like this, how much did it cost you altogether? 

[t0wer]

Really want to do something like this, how much did it cost you altogether? 

 

 

If I remember right.

The amp w/ wallwart was ~$300

The sigma11 PSU was ~$150

 

if you know someone with a laser cnc or 3d printer that can give you a cheap case

and if you source cheaper parts (toroidial transformers are expensive)

you might be able to knock off  $50 - $100

 

 

if you're looking for a cheaper amp altogether

you could go with a cavalli-kan kumisa III

http://www.amb.org/audio/ck2/

 

I had a hard time deciding which one I wanted to build.

[fishymamba]

Hmm..I think something like this is a bit too advanced for my soldering skills. And quiet a bit more expensive than what I can afford.

I'll probably just get a cheap pre-built headphone amp for now because my headphones are not really that high end. Saving up for the Hifi Man HE-400, or the Sennheiser HD 600 right now! 

[mr moose]

Looks Good, love it when people do it themselves.  Are the schematics for this amp available online or is it a kit?

[t0wer]

everything is in the link on the 3rd line of the review, but you might have to search for what you want on the left menu list.

[mr moose]

WOW, that is a really basic design, you say its sounds good?   If you had to guess at the THD or IMD or any other wave shape anomalies what do think they'd be? Sorry for the weird questions but I am considering a new project and a head phone amp was one of them, then I saw your review.

[t0wer]

I really haven't heard anything weird come out of it except when I had cold solder joints on the opamps (first time with SOIC) and more cold solder joints on the ground connection to the headphone jack.

I also bought a dc jack that wasn't isolated and blew out the tle2426.

 

I did try replacing the top aluminum cover with a plexiglass cover.

I had my wireless router <1ft away and had some obnoxious clicking.

plexi would have looked nice, but a quieter amp is better so I went back to the aluminum cover.

 

All my fault, and once fixed has been a fantastic amp.

 

I say go for it, plenty of options with gain or bass boost, input/output is all up to you.

If I sold mine, it would only be to build another one or a beta22.

[h264]

WOW, that is a really basic design, you say its sounds good?   If you had to guess at the THD or IMD or any other wave shape anomalies what do think they'd be? Sorry for the weird questions but I am considering a new project and a head phone amp was one of them, then I saw your review.

 

Probably quite good.  What would probably suffer on a 3 channel design is you'd get a bit more distortion, crosstalk and:

 

 

I had my wireless router <1ft away and had some obnoxious clicking.

 

without good case grounding and shielding.

 

Another one to consider building is the O2.  Whenever I get around to learning to solder, it'll probably be a project.

[t0wer]

 

without good case grounding and shielding.

 

Another one to consider building is the O2.  Whenever I get around to learning to solder, it'll probably be a project.

Yea, I learned, that day, that shielding is important.

 

if you're new to soldering I agree, the o2 would be another good option,

 

If you're on a severe budget or don't want to risk burning out money/components, jdslabs cmoy is good, but the soldering pads are rather small.

I bought 2 kits and I think the total cost was just over $30 ea.

1 order from jdslabs, 1 order from mouser, and 2 volume knobs from radioshack.

I skipped the dc wall wart and jack to avoid an order from digikey.

 

I'd steer clear of DIY dacs until you build up your soldering skills, as I don't know of any through hole DACs, I've only seen SOIC or smaller.

The ad8610 opamps were my first soic soldering moment and I had plenty of cold solder joints, but have been soldering through hole for years.