[FallenAngel]

Active ground.

 

[johnwmclean]

Quote:

Originally Posted by Koyaan I. Sqatsi /img/forum/go_quote.gif 3x Beta22 and 1x Sigma22 for active? What's the third Beta22 for? se

Mate, I think the most of the DIY members here know how you feel about the ground board. Can we move on.

 

[amb]

Koyaan, you can pick nits at what I said all day long, but the effect is what it is. My point was that the current is doubled, therefore there should be more power supply capacity to handle it. The doubling of current is due to doubling of voltage (by virtue of the amps' outputs being 180 degrees out of phase), but to each amp, it doesn't "know" that, it's still swinging the "non-doubled" voltage but is being asked to deliver twice the current, and the only way to characterize that (and satisfy Ohm's Law), is that each amp is driving a an impedance that is half of the real impedance.

V / (2 * I) = 0.5 * R

 

[Steve Eddy]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Active ground.

Uh oh. Emily Litella moment.

Wasn't thinking the Sigma22 was the power supply.

Er, nevermind.

se

 

[Steve Eddy]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Koyaan, you can pick nits at what I said all day long, but the effect is what it is. My point was that the current is doubled, therefore there should be more power supply capacity to handle it.

Understood.

Quote:

The doubling of current is due to doubling of voltage (by virtue of the amps' outputs being 180 degrees out of phase), but to each amp, it doesn't "know" that, it's still swinging the "non-doubled" voltage but is being asked to deliver twice the current, and the only way to characterize that (and satisfy Ohm's Law), is that each amp is driving a an impedance that is half of the real impedance. V / (2 * I) = 0.5 * R

Ok. Though I don't know why it needs to be characterized in such a convoluted fashion as opposed to the simpler and more reality based characterization that the current doubles because the voltage has doubled.

*shrug*

se

 

[nkk]

So, I now have a really stupid question that I am pretty sure I know the answer to:

If I have to boards, with 2 channels each, I would just run one board as R+ and R- and another as L+ and L-, right? There are no additions to the boards for balanced, no?

Also, which would reduce problems, one board for L and one for R, or one for - and another for +?

-Nkk

 

[johnwmclean]

Much better to ask the question, 2 channels for each board. One board for L+ and L-, the other board for R+ and R-.

 

[nattonrice]

Yeah, remember that the M3 has 2 channels on a single board (3 if you include the actively driven ground).

 

[Beefy]

Quote:

Originally Posted by nkk /img/forum/go_quote.gif So, I now have a really stupid question that I am pretty sure I know the answer to:

If you scroll down under the 'M3 as a speaker amplifier' section on AMB's website, it shows exactly how to hook everything up for balanced operation.

 

[nattonrice]

LOL I just realized I already said that and more in the 3rd post~

 

[Jaypee]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif On the M3 front, a single Sigma11 should be plenty, make sure you have good heatsinks and air flow

So.. the only thing that's limiting one σ11 from powering two M³ bridged boards for speaker use is heat production? In theory, if I build one σ11 with a high current power transformer (say 2x15V 180VA), wouldn't the current supply be plenty to power both M³'s, if I'll put in massive heatsinks?

 

[amb]

How massive would that heatsink be? Are you talking about offboard heatsinks? The decrease in thermal resistance as you go from 1.5" onboard heatsink to 2" to 2.5", etc isn't as large as you might think.

But more importantly, the total thermal resistance is determined not only by the heatsinks. The TO-220 MOSFET package is a limitation, as is the heatsink isolation pad. As you go to ever larger heatsinks, you'll find that the total dissipation capability to be limited not by heatsink size, but the MOSFETs themselves. The "Board & heatsinks" section of the σ11 website tells you how to calculate the MOSFET junction temperature. Do the math and you'll see.

Reducing the current in half by using two power supplies will be a big win.

 

[Beefy]

Quote:

Originally Posted by Jaypee /img/forum/go_quote.gif So.. the only thing that's limiting one σ11 from powering two M³ bridged boards for speaker use is heat production? In theory, if I build one σ11 with a high current power transformer (say 2x15V 180VA), wouldn't the current supply be plenty to power both M³'s, if I'll put in massive heatsinks?

Junction temperature is the key here. If you dissipate too much heat by running too much current, you will fry the MOSFETs no matter what heatsinks you put on there. There is a formula on AMB's website. Some quick mental maths, and I certainly wouldn't want to try and push more than 7V drop, 1A (7W) through 1.5" sinks. If you are talking about 2A or more for a balanced build driving an 8 ohm load, things are going to get extremely toasty.

Honestly, I can't see why you would want to do this half-arsed. Either do it properly within the limitations of this design, or build a proper speaker amp.

[EDIT] Gah, and this time AMB beat me!

 

[Jaypee]

Thanks, AMB, for clearing that out. I'll probably use two σ11's with 2x15V 40VA transformers and set the PSU's to 36VDC each. hopefully this will do the job.

 

[nkk]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif If you scroll down under the 'M3 as a speaker amplifier' section on AMB's website, it shows exactly how to hook everything up for balanced operation.

I know. I am just being painfully clear on any question that pops into my mind, as if I build this during the summer, I will have about $0 left over.

There is no room for error.

Thanks again for all the help,
Nkk