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From the beginning: M^3 w/ Sigma11 build log (and questions)

post #1 of 15
Thread Starter 

Alright, my bank account is drained, and I have started my first major DIY project (aside from stereo restorations):

 

I'm building an AMB M^3 with a sigma11 PSU. I'll keep this thread updated as a build log/blog of the project, and also to hopefully ask any of the questions I may end up having.

 

9/16: Parts ordered. Parts ordered from AMB and Mouser, still need to order the transformer, headphone jack, and case hardware.

 

 

 

 

Now for my first set of questions: is 5x gain going to be good for the HE-400?

 

Any suggestions for an affordable, attractive case for the M^3? If not, I'll build my own (steel bottom panel, aluminum front & back, wooden sides and tops)

 

If the S11 and the M^3 boards are in the same case, does earth/ac ground go to the case, and the other grounds stay insulated from the case? What is the proper, safe way to ground the case?

What is a good part number for the terminal blocks? I haven't been able to find plain, screw type terminal blocks anywhere


Edited by Maverickmonk - 9/16/12 at 4:36pm
post #2 of 15
Thread Starter 

Reserved

post #3 of 15
Quote:
If the S11 and the M^3 boards are in the same case, does earth/ac ground go to the case, and the other grounds stay insulated from the case? What is the proper, safe way to ground the case?

 

From the Wiring & ground section of the M3 site.....

 

http://www.amb.org/audio/mmm/gnd3.png

 

 

 

Quote:

What is a good part number for the terminal blocks?

Which terminal blocks are you referring to?

 

The terminal blocks for the Sigma 11 are Mouser part numbers 651-1729128 and 651-1729144

Try something like Mouser # 538-38280-0104 (for a barrier terminal block) to connect the primary windings of the transformer to the IEC & switch.

post #4 of 15
Thread Starter 

I honestly have no clue how I missed that redface.gif

 

And those are the terminal blocks I was looking for, thanks!

post #5 of 15
Thread Starter 

Any opinion on this hammond transformer? http://www.partsconnexion.com/product12700.html Is it worth it over the $20 cheaper ebay transformer?

Is there any significant drawback to locating the bass boost pot off of the board? I mean, I know the wires will increase the capacitance of the circuit by a small amount, but is it really that big of a deal? I ask because the 2 potentiometer spots are right next to each other, meaning I would need rediculously small knobs for it to be usable.

*edited cus I answered my own question, but MisterX answered it before I could* I feel like I'm asking a lot of dumb little questions, but I'm trying to make sure this thing goes right the first time, and is absolutely tops for what the design can be.

 

 

 

Both boards are mostly populated. Pics tomorrow on the progress


Edited by Maverickmonk - 9/22/12 at 11:56pm
post #6 of 15
Quote:

Any opinion on this hammond transformer? http://www.partsconnexion.com/product12700.html

$58.06 is rather expensive and I'm not seeing any advantage over a $20 Triad Magnetics transformer from Mouser (# 553-VPT24-1040).

 

 

Quote:
Is it worth it over the $20 cheaper ebay transformer?

Which eBay transformer?

 I just took a quick look and there are quite few transformers in that price range on eBay so....

 

 

Quote:

Is there any significant drawback to locating the bass boost pot off of the board?

The Bass Boost pot is in the feedback loop, keep the wires short and away from sources of noise (such as the transformer and primary wires) and you should be OK.

 

 

 

Quote:
Also, I notice the front of the alps potentiometer is metal (not an especially astute observation, duh), but I must wonder, do I have to somehow isolate that from the case if the case is tied to earth-ground?

Since this is the DIY subforum...

 Measure the resistance between the "metal front" and any of the pins and you should have your answer. ;)

post #7 of 15
Thread Starter 

I edited the post since I answered my own question, but you were too quick ;)

You also just saved me a fair bit with that transformer, which is great because my original budget has, as I should have expected, already been exceeded. My parts hunting skills clearly need some work redface.gif Thanks!

 

As promised, here's pics thus-far of the build: Both boards partially stuffed and sitting ontop of their yet unmachined case. Isn't that line of Nichicon Fine-Gold's purdy?
 

 


Edited by Maverickmonk - 9/22/12 at 11:47pm
post #8 of 15
Thread Starter 

Bump for a dumb question 3.0: If I'm doing my logic correctly, the preamp out just goes from the output pads to the preamp output? Do i need a switch to run so that only the headphones or the preamp outputs are connected at any point in time? Again, logic says no, but I'm not so big on trusting my gut with these things.

post #9 of 15

The left and right pre-amp output + signal is taken from the left and right outputs on the M3 circuit board.

The pre-amp output ground is taken from the input, not the ground output on the amplifier circuit board.

 

Adding a switch prevents whatever is connected to the pre-amp outputs from running in parallel with the phones and vise-versa.

( http://www.neutrik.us/NMJ6HC-S is a very easy way to add a switching function)

post #10 of 15
Quote:
Originally Posted by Maverickmonk View Post

Bump for a dumb question 3.0: If I'm doing my logic correctly, the preamp out just goes from the output pads to the preamp output? Do i need a switch to run so that only the headphones or the preamp outputs are connected at any point in time? Again, logic says no, but I'm not so big on trusting my gut with these things.

 

Need or want? 

 

No, you don't need one. Yes, you do want one. 

post #11 of 15
Thread Starter 

Oh, I honestly would not have guessed. Does that mean it is bad to use a single input source (line level) to drive 2 separate amps in parallel (via an RCA Y connector? Or is that case in some way different?

 

 I would think that in either case, Kirkoff's laws would apply, they would each see equal voltage, and the amperage would self balance? Or with the low output impedance of the headphone amp, would the fluctuation in current draw cause distortion?

 

Also, that headphone jack looks like a brilliant solution. I already have my locking Neutrik jack mounted on the panel though, and the hole is bigger (and uglier). I may have to make a beveled "plate" for the center of the amp to hold the jack. Sounds like a beautiful excuse to learn to use the schools small scale CNC writer/etcher/cutter. Might even cut a fancy "M^3" into it.

 

On that note: What's a cheap way to get black labels for inputs and such on the back panel (and maybe basic power/volume indicators on the front panel? is there a way to silkscreen at home or some such? I'd rather not leave it all unlabled.

post #12 of 15
There is nothing wrong with driving two amps from a single source, as long as the two amps' paralleled input impedance isn't a difficult load for the source. Most of the time this is not an issue because amps typically have an input impedance of 10K ohms or more.
post #13 of 15
Thread Starter 

Plugged the Sigma11 in today and... I got the magic blue smoke.

 

I plugged it in, the voltage across the readout got funny for a moment (it climbed really high, ~52volts), i turned it off quickly, checked everything, and turned it on again. This time it all looked good, 24.1v even. Then there was a little pop, and my one power supply capacitor bulged out at the top, and saw a little smoke rise up from it. Polarity on all the parts looks right to me, and there aren't any shorts that I can see on my solder joints.  R10 is 10K, R16 is 1k, the LED has a forward voltage of 2.1V. the heatsinks are isolated. The transformer is putting out a solid 24VAC. Does anything look particularly off here? Where should I start the trouble shooting?

700

 

700


Edited by Maverickmonk - 11/30/12 at 7:51pm
post #14 of 15

Appears your C5 caps are installed backward.

post #15 of 15
Thread Starter 

...mother of god. You're right. How did i switch around the biggest capacitors on the board? and how did I miss that the 3 times I double checked them? *facepalm*

 

Well, that mystery is solved. Are there any other parts that is likely to have damaged that I should order along with it?  And also, is there a "prefered" capacitor series to the PW series for this application? I might as well turn my failure into an upgrade.

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