M³ Project Announcement

i dont want to steer this thread off topic. but i was wondering have many people bought parmetal cases who arent from the usa? i have yet to contact them, but is shipping/pricing/payment reasonable?

Well, they're big Orange Drop ones, about .5x1.5 inches. They also have .8mm leads.

Chris

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.

Sure, floating is no problem. Larger holes is all I was after. I suspect I won't be the only one, as I've seen at least two other PPAs with similar monster bass boost caps.

Power supply

Is STEP still a preferred solution, at 28v, or is this yet to be determined?

Are any components fairly well locked down, just in case friends & family want last minute Christmas gift ideas?

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.

Something has to keep the elves merry... and to keep them from getting in on the porta Corda group buy...

Good things come to those who wait. But, at Christmas, it seems to be use-it-or-lose-it...

It took a while to read this huge thread, but it was well worth it.
I'm really exited about this project, and I hope to find more people locally that are interested.
It looks like you got most things set, but I am a bit unclear about some things. It looks like the bass boost pot is sized for another alps pot, and it seems to be the Sbb switch in the schematics, right?
Will there not be any need for a switch? Just turning the bass boost down will have allmost the same effect?
I can't find any hole planned for mounting wires to an optional crossfeed. Was they forgotten or intentionally left out?
Would it be usefull to have prepared holes for stealing power to something (like to an active crossfeed) ? Ofcourse it can be taken from the power supply directly, but that means less clean wireing.

I put my wote on the smaller board (v016) since it gives more case options.

Whats the chance that you can make the final product including mounting under the board to fit inside a case with internal height 48.63mm (1.915") ?

I figured that ordering the case from over seas won't be a good idea, so
I'm thinking specifically about a Hammond 1455 series case.
Full measurements available here:
http://www.hammondmfg.com/pdf/1455T2201A.pdf

I guess height is mostly a heat issue to keep heatsinks low, so it might matter a lot if we need to dump 1 or 2 watts on the hottest heatsink. I understand that this depends on how much idle current is needed to still stay in class A with 32ohm phones. Has this been tested?

Having 2 headphone jacks has been mentioned. I hope we are not talking about driving 2*32ohm in parallell without tweaking the original setup.
Can you just wire up 2 jacks in parallell without getting any other problems?

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)

Overall I do like the new changes. Cleaner as always good, especially the more direct routing of the right channel.

It guess the intention is to use the inputs are the rear as they was on the v018 (just as they where on the v015, but not on v016).
If the front hole for inputs on that track is unused, won't the tracks be very narrow? Could this affect sound?
If this could be a problem the tracks could be made a bit wider around the front inputs?
Is the input hole too close together (and perhaps to small holes) to mount thick input wires from the RCA jacks? Since the holes will be so close to the jacks this might not be a big thing, but some people might want to mount in a big box, and then really good cables might be nice.

Any plans on when the first prototype PCB will be ordered?

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.

i appreciate the effort you are putting in to this hugely i can understand the time issue completely and the fact that you are putting so much effort in is just so cool for all us diy'ers. i cant wait to build this amp, it looks gold. but my anxiety to get building may not be able to hold out until its ready for a pcb order, hehehehe.

thank you so much guys

I'm just wondering, if you only used the pot for the bass boost, wouldn't bad things happen if the wiper on the pot lifts?