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Project: M³ home studio speaker amp (now finished!! pics at page 10)

post #1 of 153
11/18/09 at 2:14pm
Thread Starter 
Hey!

I’m a new M³ builder from Finland. I’ve previously taken on various DIY projects, but usually they were complete kits – “just look at part numbers and solder”. So this is my first project with many options and a huge variety of parts to choose from. The reason I started this thread is to partially act as a progress log, but mainly to get info and help from those with more experience with DIY-audio hardware, so I’d do this right the first time.

Thankfully, AMB.org is VERY helpful with this project, but since this is a variation of the traditional M³-build I might need a few tips here and there.

The purpose of the finished product is to act as a speaker amplifier used with a HD-audio computer soundcard. I use this computer to make and listen to music (all kinds, mostly rock). The room is medium sized (~12m²).

I’m going to build the amp using 2 M³ boards in a balanced configuration. I’m planning on leaving the ground channels completely unpopulated. I’m also not going to add the bass boost option, but to use the bass boost potentiometer as a variable gain control instead. The power for this setup will come from two σ11’s (one per M³ board) and their voltage will be set to 36VDC. The casework for both the amp and the PSU will be completely handmade. I’m on a budget, and won’t be using fancy boutique parts (which is one of the reasons I ended up with the M³ design).

Hopefully I’ll receive my circuit boards from AMB soon, and can start working on this! Feel free to comment on the project, my part selections, or anything else for that matter! To be continued…
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post #2 of 153
11/18/09 at 3:13pm
I hope you pay both careful attention to the heat sinking and air flow that a M³ speaker amp will require. Also, in a room that large, you may have trouble depending on what speakers you are driving and their relative efficiency. It will also be crucial to know the impedance of the speakers.

Bottom line - it would not have been my choice but best of luck.
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post #3 of 153
11/18/09 at 4:38pm
Thread Starter 
Quote:
Originally Posted by n_maher View Post
I hope you pay both careful attention to the heat sinking and air flow that a M³ speaker amp will require.
That can be concidered when designing the casework and buying heatsinks. But yeah, I agree those issues need to be taken seriously.

Quote:
Also, in a room that large, you may have trouble depending on what speakers you are driving and their relative efficiency.
The last amp (cheap philips) I used gave 2*20W out, and I was really happy with volume levels.
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post #4 of 153
11/18/09 at 5:05pm
Keep in mind the M3 board layout really does not allow for offboard heatsinks so that really limits the amount you can heatsink them.

Look forward to seeing your progress. Good Luck
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post #5 of 153
11/18/09 at 5:20pm
Quote:
Originally Posted by Jaypee View Post
The last amp (cheap philips) I used gave 2*20W out, and I was really happy with volume levels.
If used for sustained periods of time that's going to be a hot running amp.
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post #6 of 153
11/18/09 at 5:50pm
Good luck with build, I agree with Nates comments, that's one big room - I hope it works out for you.
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post #7 of 153
11/18/09 at 5:54pm
Quote:
Originally Posted by johnwmclean View Post
Good luck with build, I agree with Nates comments, that's one big room - I hope it works out for you.
It is? In US figures that is only like a 9foot x 12foot room. I would count that has medium to small.
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post #8 of 153
11/18/09 at 7:58pm
Quote:
Originally Posted by m1abrams View Post
It is? In US figures that is only like a 9foot x 12foot room. I would count that has medium to small.
Ok yeah, your right, Blond moment!
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post #9 of 153
11/18/09 at 8:16pm
Thread Starter 
Okay, a few questions already concerning the σ11's. I'm a little confused obut the amount of amperes the amp is going to need. The power transformer I've thought about using for this setup is a 2x15V / 40VA toroid transformer (2x1,33A). AMB.org recommended a 36VDC / 5A PSU for this setup, so does that mean 5A each channel or in total, in other words, am I good to go with the transformer mentioned earlier?

Also, I'm having a hard time finding C5 or C14 for the σ11 from Finland.
The AMB.org recommended components are:

C5= aluminum electrolytic capacitor 63V low-ESR high-reliability 2*1500μF or 1*2700μF
Theres one option from evox rifa (1500μF/200V) which will take about 1/5 of my total build budget
So if I can save some money here, that would be great.. The closest cheap things I could find here were:
Panasonic NHG series 1800μF/100V or 2200μF/63V

C14 metallized polyester film capacitor 3900pF, voltage not defined
The closest thing I could find:
Wima FKS 2 series 3300pF/100V or 4700pF/100V

Does anyone (AMB?) have any info on the required accuracy of capacitances / types of capacitors of C5 and C14, are there any alternative options for these two?
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post #10 of 153
11/18/09 at 9:06pm
5A is total rating.

C5 capacitance is not critical, you don't need something rated higher than 63V (all that would do is increase the size and cost of the capacitor). Choose something that would fit the lead-spacing and diameter footprint of the PCB. The default capacitances are based on maximum capacitance possible (for the size) from the recommended Nichicon and Panasonic lines.

C14 should ideally be 3900pF because that's been optimized to maximize bandwidth while maintaining stability. 50V or higher is good enough. If you have difficulty finding suitable caps, I can supply them.
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post #11 of 153
11/19/09 at 12:48am
Quote:
Originally Posted by Jaypee View Post
The last amp (cheap philips) I used gave 2*20W out, and I was really happy with volume levels.
Just to echo what others have said, I doubt you will reach that level of power without melting something.

Quote:
Originally Posted by Jaypee View Post
Theres one option from evox rifa (1500μF/200V) which will take about 1/5 of my total build budget
Why do I get the impression that this is not going to end well?

Staying optimistic though...... as I said in the other Balanced M3 thread, have you contacted Glass Jar Audio? Jeff used to do M3 kits, and may be able to help you out. Explain that it is for speaker use, that you need the biggest heatsinks available, and explain to him the other modifications recommended for speaker use as detailed on AMB's website.

To save yourself some more money, used a fixed gain. Variable gain with the bass boost pot will be next to useless because it will be very difficult to channel match.

Speaking of which, have you considered what you will use for balanced volume control? If you want to use a single volume knob, a 4-channel pot might take up a big chunk of cash.
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post #12 of 153
11/19/09 at 1:28am
Go GainClone or the ChipAmp or the T-amp route...seriously.
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post #13 of 153
11/19/09 at 6:34am
Thread Starter 
Quote:
Originally Posted by cyberspyder View Post
Go GainClone or the ChipAmp or the T-amp route...seriously.
I've already ordered circuit borads for the M³ project so I'll see this thru.. If it doesn't work for me, then I'm open for other design suggestions.

Quote:
Speaking of which, have you considered what you will use for balanced volume control? If you want to use a single volume knob, a 4-channel pot might take up a big chunk of cash.
I might go with two separate volumeknobs, think that's the budget way to do it.

Quote:
C5 capacitance is not critical, you don't need something rated higher than 63V (all that would do is increase the size and cost of the capacitor).
So is the "low-ESR"-part how important here? If I put one of the Panasonic NHG series 2200μF/63V in there, would it work tho not low-ESR?
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post #14 of 153
11/19/09 at 6:47am
Low-ESR is a desirable characteristic, but the circuit will still work with non-low-ESR caps.

Btw, if your room is about 9x12 ft or similar, then M³ should be able to achieve good listening levels with efficient speakers. I don't recall reading what type of speakers you will be using, but that is a very important factor. In any case, use the tallest heatsinks you can find that would fit on the board, and perhaps augment them with a heat-spreader bar over the top, linking all the heatsinks together and then mounting an additional large heatsink on top of the bar. Obviously, you'll need to make sure you use isolation pads on your MOSFETs to prevent short circuits. The casing should have ample ventilation.

When you're done building the amp, keep an eye on the heatsink temperatures.
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post #15 of 153
11/19/09 at 7:58am
Thread Starter 
My current speakers are low-cost silverstone 220. Impedance=4-8Ω(no more specific info found), sensitivity=88dB. If I'm happy with the build, I might concider upgrading my speakers to match the quality of the amp.
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