[stew1234]

The led does look bright but I really like the white light with the silver case.

 

[fishski13]

Jaypee,
outstanding chassis work!

 

[amb]

That has to be the most "powerful" looking σ11 yet! Nice job.

 

[johnwmclean]

Way to go, that things a bloody tank.

 

[stew1234]

With an m3 setup as the last option here The M³ Stereo Headphone Amplifier I wanted to clarify a few things. If both boards were set up with a gain of 5 each in balanced mode the gain would be 10 but if one were to use SE headphones run by one board it would still be 5 correct?

Second when wiring the volume pot to run BAL and SE headphones is your only option to wire it before the board inputs? If you wired it to the pads where the alps usually goes only 2/3 channels would be attenuated when running a SE headphone from one board correct? Thanks for the help.

 

[amb]

Quote:

Originally Posted by stew1234 /img/forum/go_quote.gif With an m3 setup as the last option here The M³ Stereo Headphone Amplifier I wanted to clarify a few things. If both boards were set up with a gain of 5 each in balanced mode the gain would be 10 but if one were to use SE headphones run by one board it would still be 5 correct?

Yes. Also, in balanced mode, the gain would be doubled only if your source output voltage is also doubled in that mode.

Quote:

Second when wiring the volume pot to run BAL and SE headphones is your only option to wire it before the board inputs?

Whether you wire it before or after the board inputs doesn't matter. It's the same electrically (the board input pads go straight to the pot pads). See the schematic and PCB layout. That being so, you might as well use the board traces to carry the signal from the rear jacks to the pot, rather than running long wires.

Quote:

If you wired it to the pads where the alps usually goes only 2/3 channels would be attenuated when running a SE headphone from one board correct?

The volume pot does not act on the ground channel, if that's what you're asking.

 

[stew1234]

So if my source put out 4VRMS in balanced mode and 4VRMS in single ended mode the gain of the m3 amp when run in balanced mode using both boards or single ended mode using one would be 5 in both cases? Sorry if that's unclear but when people talk about the gain doubling in balanced mode that's a result of the source's voltage and nothing to do with the amp acting on the input signals? Thanks for the help.

 

[amb]

Quote:

Originally Posted by stew1234 /img/forum/go_quote.gif So if my source put out 4VRMS in balanced mode and 4VRMS in single ended mode the gain of the m3 amp when run in balanced mode using both boards or single ended mode using one would be 5 in both cases? Sorry if that's unclear but when people talk about the gain doubling in balanced mode that's a result of the source's voltage and nothing to do with the amp acting on the input signals? Thanks for the help.

That is correct. However most sources that have both balanced and unbalanced outputs don't output the same voltage at 0dBFS, but the "doubling" of gain in the amp is also a bit misleading because the gain increase isn't in the amp itself, but in the source.

 

[stew1234]

Ok thank you for clearing that up. Very helpful.

I have two more questions I've been trying to find answers to. If my balanced M3 only used 1 Sigma 11 how much larger would the transformer need to be to compensate. I wont be driving speakers but would like to make sure I have plenty of juice to run the psu with some of the higher voltage opamps in balanced mode.

Lastly if I were to stick the sigma 11 and 2 m3 boards in a case and put the transformer in its own little case for shielding as long as the wire runs from the transformer to the sigma 11 are reasonable (under 3-4 feet) would that matter at all? Thanks again.

 

[amb]

Quote:

Originally Posted by stew1234 /img/forum/go_quote.gif I have two more questions I've been trying to find answers to. If my balanced M3 only used 1 Sigma 11 how much larger would the transformer need to be to compensate. I wont be driving speakers but would like to make sure I have plenty of juice to run the psu with some of the higher voltage opamps in balanced mode.

The recommendation for one fully-populated M³ board is 15VA to 25VA, so for two boards plan on doubling it.

Quote:

Lastly if I were to stick the sigma 11 and 2 m3 boards in a case and put the transformer in its own little case for shielding as long as the wire runs from the transformer to the sigma 11 are reasonable (under 3-4 feet) would that matter at all? Thanks again.

That would work just fine.

 

[Beefy]

Quote:

Originally Posted by stew1234 /img/forum/go_quote.gif Lastly if I were to stick the sigma 11 and 2 m3 boards in a case and put the transformer in its own little case for shielding as long as the wire runs from the transformer to the sigma 11 are reasonable (under 3-4 feet) would that matter at all? Thanks again.

If you are going to do that, perhaps consider a 24VAC wallwart. You should be able to find something in the 40-50VA range, because they are a common item for powering security equipment. Saves you the second round of casework, IEC inlet, etc. and the AC voltage is perfect for the S11/M3 combo.

 

[Jaypee]

Regarding the original topic

: A quick review of my now finished amp.

As explained earlier on this thread, my goal was to build a longlasting, maintainable, modifiable, high-quality stereo amp to act as an amplifier to my multimedia PC. This PC is used for listening music, making music, watching movies and (some) gaming. The main reason I chose to go with the balanced M³ + 2xσ11 design was it’s fairly low build cost and the simplicity of the design. Since I didn’t need too much output power with my PC-setup I was quite convinced the M³ would provide me the high-quality watts I needed. There was a lot of speculation, wether the M³ would be able to stay cool. Well, now I can verify that they can. After several hours of serious listening, I measured the temp of the 2,5” heatsinks, and got 42˚C (that’s about 107˚F), and the PSU sinks keep their temperature below room temp

.

The volume levels I’m getting from my fairly unefficent speakers is more than enough for my medium sized room. The amp is nearly silent when music is off, at least my ear can’t tell wether the amp is on or off if I put my ear against the speaker (the trafos make a REALLY subtle sound. You can hear it if you put your ear against the PSU). I’m using OPA604AP opamps, which, for me, work extremely well. You can definitely separate all the different sounds that are put to the record, just the right amount of bass and although the treble isn’t chiming clear I think it’s also just right. Overall, the sound is quite well balanced.

Movie sounds really come alive with this amp. Yesterday, I watched a very cool (a not yet released

) movie, and I was blown away how incredibly good it sounded! WAAY better than my previous amp!

All in all, I’m more than pleased with this amps performace.

I would like to thank AMB, Beefy and all others @ head-fi.org for helping me out with this project. And a HUGE thanks goes to my friend TJV who has helped me a lot with the casework.

PICS:

 

[PScal]

That amp looks great. Congrats on the successful build!

 

[Beefy]

Top work! Looking at it now, I'm really glad I wasn't able to talk you out of it...... lesser DIY'ers would have failed, but you've done a great job

 

[amb]

Industrial strength!