M³ Project Announcement - Page 21

Tophu: .8mm = 31mil. We can enlarge the auxillary bass boost cap holes, but there is no way we can make room for a .5×1.5" cap. 600mil lead spacing is as good as it gets. There are plenty of reasonable choices that are much smaller. Methinks your monsters will have to float.

Skyskraper: There are many good case manufacturers all over the world. Use a case from your country, no need to order overseas.

VC: My principal concern is that without the input traces across the board, people will do a terrible job of wiring which will result in inferior amps. Shield grounded coaxial cables for left and right channels are mandatory for this kind of run, yet the temptation to use ordinary wire is great and that is what lots of people will do, then complain about hum and noise, especially if they use an internal power supply. I know you will do a beautiful job, but what about the unwashed masses with no attention to detail? PCB input traces allow for the use of ordinary wire to the input jacks. Going from 6×7" to 5×7" saves 15% of the board cost.

The input pads don't fit behind the volume pot because of the way the pot traces need to route. As a result there is nothing to be gained by moving the mounting hole between the pots. I don't see why C5+ should be moved, they are plenty far from the opamps, align with their power traces, and are consistently placed relative to the other C5 and C6 caps.

Many headphone jacks are narrow enough for 2 to fit side by side with the bass boost pot in a 5.5" wide case. If really fat bodied jacks are chosen, use a 6" case. I would rather not force a congested panel layout by putting the pots too close together. I haven't done detailed measurements on this since there are so many permutations of jack model and additional panel components such as LED, power switch, etc. but I'm guessing this should not be an issue. Just go with a case wide enough to accommodate your chosen components. The current placement allows for good feng shui and ergonomics in the smallest possible case width.

STEPS, Elpac WM080, or a homemade simple regulated supply will work.

We haven't made the first pcb prototype yet and you are asking if it will be ready for Christmas? Smoking tinsel again, I see.

Use either a bass boost pot or Sbb and Rbb, no need for both. As you surmised, turning the pot all the way down = no bass boost.

There are no pads for optional crossfeed because it tends to compromise the amp circuit and thus is frowned upon by most purists, however you have reminded me that we forgot to include mounting holes for Tangent's crossfeed daughterboard which can be wired to the amp inputs.

2" case height means using short heat sinks, which in turn means your MOSFETs will run hotter. A Hammond 1455 case has no ventilation slots, not a good idea even with the full size heat sinks, but I'm sure someone will try it and report back once boards are available. Another option would be to drill some ventilation holes into the 1455 case.

Our recommended idle current is 80mA per channel. We have tested with the breadboard prototype. We are suggesting 2 headphone jacks be wired in parallel. If headphones of different impedance and/or efficiency are used simultaneously, the volume level will not match.

M³ v018
5×7" board dimensions
1.5" pot shaft spacing
retained cross board input traces
rerouted right channel more directly from pot to opamp
deleted guard traces (found useless in recent PPA v2 prototype tests)
enlarged bass boost cap end holes (1mm/40mil ød, 600mil spacing)

No. The traces are plenty wide at 50mils, and the pads are through hole plated.

All IO pads are 75/40mils, that is a 1mm hole, plenty wide for #20 AWG hookup wire. Most people use #22 or #24 AWG hookup wire. No one has complained about the 100mil distance between pads yet. 100mil spacing allows Molex connectors to be used.

No specific date is set. I just synched the layout to the schematic last night, but amb needs to verify the synch, and we have to be sure there are no more changes to implement. The process may seem slow, but remember we have lives outside of Team M³. Days or weeks sometimes pass without progress because other things compete for our attentions. Once the (2) pcb prototypes are ordered it will take some time to receive them, build them, test them, and invite our golden eared friends over for more listening tests. We will let you know when we have news.