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M³ Project Announcement - Page 24

post #346 of 565
1/13/05 at 4:39pm
Quote:
Originally Posted by morsel
If the motivation is to cut costs to the bone, a few bucks could be saved by using hand selected resistors. It would require a significant stock of various 1% resistor values, or a separate parts order whose shipping charges would nullify the savings from not using trim pots. It would be easy for us to add the pads, but do we really want to encourage this practice? Let's hear your thoughts on this.
IMHO, you needn't bother with the resistor pads, the trimpot is much easier to work with


/U.
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post #347 of 565
1/13/05 at 7:57pm
Quote:
Originally Posted by amb
This is ok, but the LM317 or LT1085 adjustable regulators have better performance.

amb:

You might want to try LM2937ET-15 & LM2990T-15. Mark Levinson replaced LM337&LM317 with those in their ML380S preamp.
Also a friend of mine building SDS Labs exchanged LM for the above with positive results.

/kasra
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post #348 of 565
1/13/05 at 9:02pm
Quote:
Originally Posted by kasra
You might want to try LM2937ET-15 & LM2990T-15. Mark Levinson replaced LM337&LM317 with those in their ML380S preamp.
The LM2937 is a 500mA negative regulator which would be operating near its limit with this amp. The LM2990 is also a negative regulator with max output of 1A. Its "complement" is the LM2940 positive regulator.

At any rate, this is a bit OT since the M³ pcb doesn't have any voltage regulators. If you want to design your own PSU for the M³, the LM2940 is probably ok, but I would feel a bit more comfortable with the LM317 which is rated at 1.5A or the LT1085 at 3A.
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post #349 of 565
1/14/05 at 10:56am
Thanks for the quick answers. My questions about the bias clearly showed my lack of knowledge in this area, so just disregard that. Btw the trimpots looks very neat on the board you made.

With the answers about the power I should have no problem building a simplified version of the STEPS with localy available parts so I have it ready before I get hold of an M³ board and parts for that one.
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post #350 of 565
1/14/05 at 1:30pm
Thread Starter 
Thanks for your kind words. With AD8610 opamps and 80mA MOSFET bias, the total current draw will be around 250mA, well within 24V wallwart range if you wish to use one. The classic Elpac WM080 is a good choice. A STEPS and OPA627 or OPA132 opamps will allow you to choose a higher operating voltage from 30-36V suitable for the most demanding applications such as driving small speakers or the AKG K1000.
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post #351 of 565
1/17/05 at 7:08pm
An update: The prototype pcb has been assembled and is now working well. We will be doing measurements and conducting listening tests on this rig.

One minor thing that occurred to me as I was building this rig is that the input pads at the rear of the pcb, as viewed from the front (the side with the pots) are oriented as G-R-G-L-G. In other words, the right channel trace is on the left side and the left channel trace is on the right. If the amp will have its RCA input jacks on the rear panel arranged in a side-by-side manner, then the most "direct" wiring will be R L when viewed from the front. From the rear it would be L R, of course. I wonder if this might be counter-intuitive for some people, and note that on many commercial stereo gears with horizontal jack arrangements the left channel jack is assigned to the left side when viewed from the front of the case. It's not a big deal to simply cross the wiring, of course, but just want to ask your opinion about this. If this bothers you then we could simply re-label the left channel as the right and vice-versa (without changing any actual pcb components or traces).

Here is a picture of the test rig.

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post #352 of 565
1/17/05 at 7:53pm
Very cool! I've been following the thread (not reading every post...) and was just wondering what you expect the fully populated board to run? The original thread mentioned that one of the design goals was a better bang for your buck over the PPA. I don't know if this meant that it would be an overall cheaper build, better performance at a similar price, or more $$$ but way better performance.

I'm hoping that the M³ will be my first project of 06!

Keep up the great work.

Nate
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post #353 of 565
1/17/05 at 8:36pm
Quote:
One minor thing that occurred to me as I was building this rig is that the input pads at the rear of the pcb, as viewed from the front (the side with the pots) are oriented as G-R-G-L-G. In other words, the right channel trace is on the left side and the left channel trace is on the right. If the amp will have its RCA input jacks on the rear panel arranged in a side-by-side manner, then the most "direct" wiring will be R L when viewed from the front. From the rear it would be L R, of course. I wonder if this might be counter-intuitive for some people, and note that on many commercial stereo gears with horizontal jack arrangements the left channel jack is assigned to the left side when viewed from the front of the case. It's not a big deal to simply cross the wiring, of course, but just want to ask your opinion about this. If this bothers you then we could simply re-label the left channel as the right and vice-versa (without changing any actual pcb components or traces).
IIRC the PPA has its L/R input pads placed so that the most direct wiring would lead to L-R from the rear (R-L from the front) which seems to be the case here. Personally I've made all my amps that way, but then I don't own any commercial stereo gear at this point, so I can't say what the real standard is.

Honestly I would like it to remain the way it is just because all other "standard" DIY projects are made that way but it probably won't make a big difference to most people either way. As long as it sounds good!
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post #354 of 565
1/17/05 at 9:05pm

Cost comparison...

Quote:
Originally Posted by n_maher
The original thread mentioned that one of the design goals was a better bang for your buck over the PPA. I don't know if this meant that it would be an overall cheaper build, better performance at a similar price, or more $$$ but way better performance.

Nate
Hey Nate,

It did some estimating, and it looks like the entire output stage not including the cascoded current source or the 1 uF cap, which are used in the PPA anyway, will cost right at $10.00 per channel. Compare this to $24.40 per channel when you max out the buffer arrangement with BUF634's and you can start to see the benefits already. Not to mentioned the simplified output stage from an electronic standpoint. I'm not sure about the prices on the different diamond buffer versions. The simpler the better.

Now if we could get away from these IC op-amps altogether and design a completely discrete front end to go with a similar output stage.

I really like what has been done so far, its rather inspiring. Maybe I'll get back on the horse.

Later,

Todd
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post #355 of 565
1/17/05 at 10:38pm
Thread Starter 
I think having the jacks L R as viewed from the rear, which is how you look at them when you hook them up, is the intuitive way to do it. Of course anyone is free to orient their jacks vertically or in reverse order, and color coded input jacks should be the primary method of identification, but my vote is to leave the amp channels in the order L R G rather than change them to R L G.

The initial choice to go L R G was made with deliberation, not chosen at random. The work required to swap channels would be extensive. The swap would mean those people who wire input jacks R L would no longer have to cross input wires 200mils, while those who wire input jacks L R would now have to cross input wires 200mils, and the channel layout would be bass-ackwards from a left right perspective.
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post #356 of 565
1/17/05 at 10:45pm
Thread Starter 
Another solution for those who want R L G order is to wire both headphone jacks and input jacks with left and right channels reversed. You get to have your alternate order and don't have to cross your input leads, but, ohmygod, the labels inside the amp will be wrong!
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post #357 of 565
1/21/05 at 7:07am
Thread Starter 
NeilPeart and Raif joined us for listening tests of the M³ pcb prototype this evening. It sounds great. There were no technical problems. Thanks so much for helping out, you guys. It was a lot of fun.

We are going to wrap up development soon, so now is the time to bring up any last requests, or reiterate old ones we let slip by the wayside.
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post #358 of 565
1/21/05 at 8:25am
My thanks also to NeilPeart, Raif and Morsel for visiting. It was a fun evening listening to the M³ prototype with various headphones and other equipment, as well as having great conversations. While I know that the M³ measured well and sounded good to my ears, it's reassuring to be confirmed by all in this micro-meet.
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post #359 of 565
1/21/05 at 9:14am

Meet

I met with Morsel, AMB and Raif today to conduct some listening tests to aid the development of the M3 (M Cubed) amplifier project. The evening was rife with passionate discussions regarding the merits of happy hardcore, the obligatory Rush vs. Yes debate and the casual reference to Nakamichi addictions. I had a blast discussing audio and life with Morsel and AMB, and Raif is always in the enviable position of being cooler than me. I brought over Ayt999’s Audio-Technica ATH-L3000; Raif brought his DAC1, Audio-Technica ATH-900 and Grado PS-1 Pro, while Morsel and AMB supplied their DT990-600, HD600, PPA and M3 amplifiers. I’d already been introduced to the pleasure of proper tape listening, but this was re-affirmed tonight with renewed vigor. AMB’s homebuilt turntable and DIY speakers are nothing short of amazing. The M3 sounds very similar to the PPA, but if pressed I would say the M3’s bass is just slightly superior in terms of decay and impact. I also prefer the M3’s design to the PPA’s but my limited knowledge of EE obviously renders my opinions in this regard basically valueless. I can’t wait for the next meet!
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post #360 of 565
1/24/05 at 4:03pm
Thread Starter 
M³ v024 changes

restored the second set of output pads
(they are in line down the cap/heat sink canyon)
notched the power rails for the output pads
modified the TO-220 part to fit better
(pads moved 25mils to the front)

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