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M³ Project Announcement - Page 16

post #226 of 565
10/26/04 at 5:33pm
I just finished reading this entire thread and want to compliment team M*³ on their achievement so far and to cheer them on in their quest for yet another DIY fix for us with good credit! Veni Vidi Visa!

(I don't know half of what's been discussed, but I do enjoy the "clash of the titans" as much as anyone else.)
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post #227 of 565
10/27/04 at 1:57pm
I can't help at all from a technical aspect, but if you folks at M3 need to borrow any headphones for testing, perhaps I can be of some assistance.
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post #228 of 565
10/27/04 at 3:54pm
Quote:
Originally Posted by gradofan
I can't help at all from a technical aspect, but if you folks at M3 need to borrow any headphones for testing, perhaps I can be of some assistance.
That's very generous of you. Your sig says that you have a HD600, which I already have. Your handle says that you might have some Grados? We'd love to have one on hand for low-impendance testing. But, you're in OH, and Team M³ is located in "Silicon Valley" CA, so we're not exactly neighbors.

Fortunately, though, there are several other head-fi'ers nearby who also have a good collection of differerent cans (including Grados and similar) who we've been able to get help from; not only for the use of their headphones but also their ears.
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post #229 of 565
10/27/04 at 4:44pm
would this design (in 2 channel conf.) work good as preamp? ..if it is the case, could you add some kind of jumper or switch and a "fake gound" to avoid the 3rd channel and use it as preamp?? ... it shouldnt add many extra component but it would add an extra funcionality some people may apreciate.....

about the pot....you could add pins (ala ppa diamond) and connect a daughterboard with all the different pots holes independen of size, this way it can be placed where is needed and it should not take much room..althou it would requiere a taller enclosure and the manufacture of the extra board...just an idea

keep up the good job !!!, it is truly entertaining to see a real world engineering project step by step...


m.
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post #230 of 565
10/27/04 at 5:06pm
Thread Starter 
Any 3 channel amp such as the M³ or PPA can be used as a preamp as long as input ground, not output ground, is used for the preamp outputs. There is no need to alter the circuit in any way. Just remember that output ground is for the headphone jack only.
Quote:
it is truly entertaining to see a real world engineering project step by step...
This is definitely not the real world.
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post #231 of 565
10/29/04 at 1:39pm
Current updates?
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post #232 of 565
10/29/04 at 3:09pm
Thread Starter 
We want to compare FET current source .vs. capacitance multiplier on the opamp power rails before we commit to one or the other. I will post a new layout once we have done this testing. There is no need to ask for updates, we will let you know when we have news for you.
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post #233 of 565
10/29/04 at 3:17pm
Quote:
Originally Posted by morsel
This is definitely not the real world.
Which world is it?
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post #234 of 565
11/2/04 at 1:53pm
Thread Starter 
Our initial comparison of cap multiplier .vs. FET current source .vs. no rail isolation was inconclusive. We were unable to duplicate the results of 2004/10/19, which suggests the improvements were due to the other circuit modifications. We will perform more specific tests and post a new layout as time permits.
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post #235 of 565
11/3/04 at 12:34am
Quote:
Originally Posted by morsel
We were unable to duplicate the results of 2004/10/19
Actually we were able to reproduce the RMAA results of 10/19 almost exactly (with the exception that the crosstalk curve being slightly worse this time, by about 1dB, but this could easily be variations in test setup layout, etc.).

The part that we were not able to conclusively determine was whether the capacitance multiplier was better than simple JFET isolation, or for that matter, no rail isolation. This was not tested with RMAA but was done with a scope and function generator. The residual noise observed on the supply rails drowns out what we were looking for. Come to think of it, I may have had the scope set up with the wrong horizontal time scale, so we were not looking at the right thing.

Quote:
We will perform more specific tests and post a new layout as time permits.
Yes, we will do more testing soon.
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post #236 of 565
11/11/04 at 6:32pm
I don't mean to be a pain, but do you have any idea when you will be complete? How does it compare soundwise & pricewise to the PPA?

I can't be the only person wondering
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post #237 of 565
11/11/04 at 11:40pm
superjohnny,

Morsel is hard at work on the PCB layout and will post a first draft of a complete board for comment soon. We will be building an engineering prototype based on that board layout and verify its design and performance. Assuming that all is well, then we will finalize the M³ v1.0 circuit and layout, and proceed to order the first batch of PCBs. Since we're not working to a specific schedule it is difficult to predict when this will all happen, but rest assured we're pushing along as quickly as we could.

As for cost, both the PPA and the M³ could vary greatly depending on the parts selection (the opamps and capacitors/resistors you use, the pot or stepped attenuator, jacks, power supply, the enclosure and whether you add customizations and options). I'd expect a PPA to be on par with the M³ if you were to build barebones versions of each. The PPA's output buffers are more expensive than the M³'s MOSFETs, but the M³ will have a bigger PCB and enclosure.
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post #238 of 565
11/12/04 at 4:22am
Thread Starter 
Morsel has been playing video games, seeing friends, and doing other lifely things this week, but will try to get back to the layout soon.

There is no ETA on boards. (see post 1 of this thread)

Comparisons between M³ and PPA will have to wait until we have a working pcb prototype.
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post #239 of 565
11/21/04 at 2:05pm
Thread Starter 


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post #240 of 565
11/21/04 at 2:06pm
Thread Starter 
board dimensions are currently 6 × 7 inches
limited ground plane to input area
guard traces for input traces (not sure if this really improves
separation, will be tested in a future PPA v2 prototype)
added series diode for reverse polarity protection
added LED and RLED
added bass boost pot
committed to a single capacitance multiplier for the opamp power rails
removed 10 Ohm series resistors from opamp rails
modified C6 from 1uF to .1uF
modified capacitance multiplier to use NJFETs for both rails
(2N5484 or 2N5457)
choice of TLE locations
choice of 12.5mm or 18mm rail caps

We would like to lower the default gain from 11 to 5, but gain and bass
boost are intimately intertwined, so we are going to defer on that until
some of the concurrent issues are ironed out. Note the thin red lines
connecting the right channel bass boost circuit to the bass boost pot,
which are possible trace routings. Alternatively, the JbbR jumper could
be hand wired to SbbR, eliminating the need for traces from the right
channel passing through the left channel, an issue that may bother some
purists, and may have a small effect on channel separation. The JbbR
under the pot would have to run under the pcb, whereas the other JbbR
could be wired either way.

We need to get a clear idea of the range of bass boost capacitors people
are likely to use for both high and low gain configurations, so we can
better gauge the requirements for Cbb lead spacing. Lower gain and lower
feedback resistors mean larger bass boost caps. Also, I am not convinced
we need 3 pairs of electrolytic caps on the opamp power rails. Dropping
down to one shared pair and moving it to the empty area below the right
channel would save a lot of space, allowing for more graceful routing of
the bass boost functions and reduction of board surface area.

C6 is now a slimmer .1uF film cap, which will provide clearance between
the cap and the opamp, important if using BrownDog adapters. 1uF caps
can still be used, but it will be a tight squeeze on one edge.

There is no rear "no fly zone" because this board is not intended to sit
flush with the rear panel. A 6 × 7" board needs a 6.25 × 8" case. There
are no cases we know of that are close to those dimensions, so custom or
oversized cases are the logical choices. If there are any compelling
case choices that would require a change in layout, please let us know
asap so we can take them into consideration.

There is a tantalizing empty area at the front panel where board mount
headphone jacks might be located, however we did some research on this.
Every make and model of board mount headphone jack requires a different
pinout, many of them require slots, not holes, and the double sided
power distribution bus would have to be replaced by a complex matrix of
parallel traces and vias to allow the outputs and power rails to cross.
We decided that panel mounting and hand wiring the jack(s) is best.
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