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M³ Project Announcement - Page 2

post #16 of 565
Thread Starter 
Bass boost is part of the circuit. Rbb, Cbb, Sbb are the bass boost resistor, capacitor, and switch. I thought that was obvious.
post #17 of 565
Originally Posted by morsel
Bass boost is part of the circuit. Rbb, Cbb, Sbb are the bass boost resistor, capacitor, and switch. I thought that was obvious.
Thanks morsel for your answers. Sorry, my bad as I barely looked at the schematic.....BTW remember that sometimes what is obvious for you, is not that obvious for others, and there are a lot of members that would like to venture themselves into a first good DIY project, but they are not DIYers in any way.
Even though I will be really interested in trying this out, definitelly, I own a PPA, and I love it, and I was always curious about this Sheldon D. Stokes project, just that nobody seems to care too much about it, and offer it as a DIYFSE option (other that himself, a very expensive labor BTW)......
post #18 of 565
nevertheless you should consider 2sj76 / 2sk213 series. A mosfet designed
for amplification isn't the same as one designed for switching. Rds means much less in an amp than linearity. also I don't recall them costing more than a few bucks and easy to get from mcm or wherever.
post #19 of 565
The spec'd transistors look reasonably linear to me, at least from the datasheet, unless Vgs is very small.

I would be a big fan of a well considered voltage regulation system on the board to give us a greater choice of power sources. If we can take control of the voltage regulation, then we can make it as robust as necessary. Since the circuit board is targeted for such a large size, it seems reasonable to aim for independent regulation for each channel, with, perhaps, some sort of jumper option to use a single regulator.

Maybe a Jung regulator? Is it called that anymore?

post #20 of 565
Very nice work on this long anticipated project!

The LaRocco and Glassman discrete buffers have shown the merit of this approach, having an integrated design - opamp voltage amplifier + discrete buffer - seems like the logical next step.

I think it would be nice if there would be a configuration that could be built in a case smaller than the Par 20 series, especially if there is an outboard PSU. The 1455N series case used in the PPA seems to me an ideal size for a headphone amplifier. I do like the idea of the outboard PSU, and also the idea of more options for board-mounted components.

Whatever you decide, I look forward to building it.
post #21 of 565
sweet. what an exciting news for the diy audio community. you mentioned it's goign to have a better price and performance ratio than the ppa, but any idea what the price range is goign to be? (200-250, 300-350, etc...)

cant wait to hear it/hear impressions of it.
post #22 of 565
Hi all,

I am glad that hardly a half day has passed and this announcement already generated so much interest. This is going to be a very exciting project because it combines the essential qualities of the PPA with that of a very robust class-A MOSFET output stage (I love the term "studly" that morsel used in the announcement ), and makes several significant enhancements over the SDS Labs MOSFET amplifier as well.

I built and tested several iterations of prototypes on breadboards, exploring some different possibilities. As Morsel said, we tried a diamond buffer output stage, except with MOSFET output devices. It worked well enough, but ultimately didn't measure as well as a simpler, directly-driven MOSFET topology. Just for kicks, here is a photo of the diamond buffer-based amp prototype:

As for the choice of MOSFETs, we had to consider several factors. Since this amp is going to operate in class A, we would like to choose high current devices for reliability. The Ciss should not be too high, and yet high current devices always have higher Ciss due to their larger internal junctions. Stable and assured availability is also an important factor in our consideration. Linearlity, performance and suitability for the application, and last but certainly not least, the cost is also considered because we want this amp to deliver a lot for the money.

The Hitachi 2SK213/2SJ76 series were considered. These are nice devices with low Ciss, but IMO just a bit "weak" with a Ids rating of 0.5A. The 2SK1058/2SJ162 are stronger, but the IRF devices we chose are even more robust yet with comparable linearlity, Ciss. Plus they are stocked in quantity at Digikey and Newark Electronics. The 2SK/2SJ devices are scant by comparison (at least in the US) and more expensive. The choice then became clear. The Renesas/Hitachi parts are not pin-compatible with the IRFs, so we had to choose one or the other for our PCB layout.

As for the op amps, both Morsel and I like the AD8610. However builders/users can substitute others like the OPA637/627 just like you could with the PPA.

We would definitely welcome more comments about the other open choices as listed in the announcement. In particular the power supply, casing, heat management, etc.

post #23 of 565
I think it would be nice to have one larger heatsink in the center of the case, dividing it in two halves, one half for the amp itself, the other for the PSU w/ transformer.. I think having everything in one box is a better approach for such project, you're choosed rather big casing where there is enough space to prevent input section being interfered by PSU.. as for the PSU, the output section is a Class A beast and as such I'd choose a capacitance multiplier for it and keep the voltages rather high! for the opamp power I'd simply go with 78xx regulator for each channel with 317 as a preregulator for them all.. or some TL431 + pass transistor job..

I don't think those Hitachi MOSFETs are hard to get either.. the question is if they're sonicaly better or not.. considering one bigger heatsing for all MOSFETs, you can add pads for both types of MOSFETs.. it won't take much space..
post #24 of 565
Thread Starter 
Aos: AMB already addressed the Renesas MOSFET issue, but I will add that the IRF IRFZ24N/IRF9Z34N 18A MOSFETs are about $1 each from Digikey, the Renesas 2SK1058/2SJ162 7A MOSFETs are about $9 each from B&D Enterprises, and the Renesas 2SK213/2SJ76 .5A MOSFETs are about $5 each. Multiply that by 6 for the 7A devices and 12 for the .5A devices and you have $54 to $60 for Renesas MOSFETs .vs. $6 for IRF MOSFETs. MCM Electronics prices are even worse.

2SK1058 Ciss = 600pF
IRFZ24N Ciss = 340pF
2SK213 Ciss = 90pF
2SJ162 Ciss = 900pF
IRF9Z34N Ciss = 620pF
2SJ76 Ciss = 120pF

The 2SK1058/2SJ162 make no sense at all from either the cost or spec perspective. The 2SK213/2SJ76, once doubled up to compensate for their wimpy output, are too costly and space consuming despite the low Ciss. The IRFZ24N/IRF9Z34N are modern, 5th generation HEXFETs that sound good to us.

Drewd: We might be talked into classic IC regulators but there is not room for a Jung regulator per channel, nor is it necessary.

Jamont: Even with an external power supply, the eurocard format used for the PPA is probably too small for the M³, mostly because of the real estate the heat sinks require. We might be able to cram it on a eurocard if we sacrifice the Aavid extrusions, go for small clip-on heat sinks, and forego a more spacious layout, but I suspect this would not be a popular decision.

h3ng: No ETA on boards or assembly cost.
post #25 of 565
Thread Starter 
Glassman: Perhaps your central heat sink idea is something best left to the individual user? Many feel that the power supply does not belong inside the case. Those that want it in the case may do so (at their own risk!)

It may be tough to have the MOSFETs spaced for Aavid extrusions and also have them mate to a central heatsink.
post #26 of 565
Originally Posted by morsel
It may be tough to have the MOSFETs spaced for Aavid extrusions and also have them mate to a central heatsink.
yeah I know.. maybe you can arrange it like Kevin did with dynahi - output devices mounted horizontaly on L shaped extrusions.. that way it's possible to use Aavids as well as one big heatsink.. I'd just like to have the ability to use big heatsink profile at one side of the board.. keep that in mind when laying out the board, I think it's doable

oh and jung regs are most likely overkill here, opamps have very low current requirements as well as very good supply rejection, it's more important to focus on good bypassing close to the supply pins.. I'd go with 100n polypropylenes.. and also I'd like to have SOIC pads available..
post #27 of 565
MMM, Mosfets
Have you ever tried a M² version?
post #28 of 565
Thread Starter 
and also I'd like to have SOIC pads available
Hey Tangent, are you listening to this? We found someone besides Kurt who wants so8 pads. Glassman, where were you when we were working on PPA v1.1?

Peter, yes we have, I confess we have only tested with 2 channels so far. No worries though, we will be testing with 3 channels soon.
post #29 of 565

ask IpsilonSound and you'll realise there's more then two people wanting SOIC pads regarding my location at the time of discussing PPA v1.1, well I might have been busy with designing the buffers
post #30 of 565
what about M4 and balanced operation ?

I agree with Glassman that having all the hot parts lined on the side for a big heatsink would be a big plus in my view.
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