Great River MP-2 , info, schematics & discussions

[Dan Kennedy]

Actually, there's a little code.

0- MPS-8_0_99

5- MPS-8_5_99

3- 2N440_3_

1- 2N440_1_

It's a lot less messy than all those long strings.

 

[Bluzzi]

I was wondering what those were. Thanks.

Its no problem in the parts layout pdf though so I'll do it for future use.

In any case the PCB is marked with Q1, Q2 etc.

jim

 

[Bluzzi]

First PCB (and I mean 1st as I've only done P2P up to now). My respect to those that solder these tiny little things!

Now to begin second MP-2 board stuffing.

Where's everyone at with this project?

jim

 

[josh]

FYI,

If you are planning on putting your MP-2 into a 1U case then you are going to want to mount your (4) 470mF Caps off board laying down or some other way. On board they are too tall, and I learned this too late now I have to de-solder them and move them over.

Other than that, my boards are stuffed and I brought both the case for this and my Supergreen into work today to get the back panels machined for XLR's and IEC sockets.

 

[Bluzzi]

Congrats on finishing both!

I have a bunch of 3RU case I bought a long time ago so I put everything in there!

I am leaving room for at least 2 more preamps though.

jim

 

[okgb]

Mine fit into a 1ru case no problem ,
check the original bom , to see if it is the same .

I have small stand offs if you need , regards Greg

 

[Ptownkid]

yeah, the caps should fit with no problem, unless you're using big ass stand-offs

 

[josh]

I have them resting on a piece of cardboard right now and they are just flush with the underside of the case.
I'm measuring 1 1/4 to the top of the caps from the bottom of the pcb and the inside of my par metal case is 1 3/8.
With them touching that only leaves 1/8" clear on the bottom. Unless I'm missing something, 1/16" up and 1/16" down isn't enough room.

edit:
I just had a thought! I could put holes in the top of the case so the barrels of the caps can "breathe" and it will look like a classic carbeurator or something :wink: :green:

 

[Ptownkid]

oh, i didn't know those par-metal cases were so tiny inside...a standard 1U case is 1-3/4".

 

[ulysses]

A lot of off-the-shelf rackmount chassis have in the neighborhood of 1.25" inside. Remember, 1.75" is the height of the faceplate but the chassis has to be less than that or they wouldn't actually fit. On top of that you need some extra clearance to accommodate adjacent gear made by numbskulls who don't know the diff between a flathead screw and a panhead screw so you might want the chassis to be about 1.5" tall. The thickness of the lid and the bottom panel will cut into that, so you're lucky to have 1.375" when you're done. That's just barely enough for a 1/4" standoff, 1/16" PCB, and 25mm-tall capacitors and other components.

Now remember that the tops of radial lead caps often are bare metal that often has voltage on it. You don't want it mashed up against the lid, and you sure as hell don't want it poking through a hole in the lid. (sorry josh)

 

[josh]

I was kidding about that, but it might look cool right?

I'm going to make a clip out of UHMW and mount them flatways in pairs of 2 off to the side of the board. No big deal really. :thumb:

 

[Gustav]

I have an oppertunity to have some stuff tooled during the vacation. Is there a final gerber ready for this? I could make some and have them avaliabe.

grinderslevAhotmail.com

Gustav

 

[Ptownkid]

It needs to be reworked as the fet is no longer available.

 

[ToroRojo]

Question regarding the PSU: J1 - What does this connect to? Do you need a second transformer for phantom power?

 

[okgb]

one pin from the preamp feeds signal to whatever is driving the l.e.d. or meter [ or nothing ] of your choice . i think that is what you are talking
about on the back power supply connector .
whatever power supply you choose needs an 50v or so dc to the
preamp board which has regulation for the phantom [ a few volts about 48 is fine cause the regulator will pull it down ]


regards Greg

 

[ToroRojo]

I understand the preamp pcb side of it. I was talking about J1 on the PSU schematic. It shows the transformer connections for the main supply rails, but it has a jumper not connected to anything for the 48v connection. The main transformers has its secondaries wired in a bipolar fashion, so you can't use the same transformer to get the 48v, correct?

 

[okgb]

Yes later versions had a trace cut and jumped the line wired to the 48v side to use the same transformer .
no schematic for that but shouldn't be tough to figure , one cut , one jump

regards Greg

 

[madriaanse]

Quick Q regarding R46:

Dan says: "R46 is determined by putting a FET in the circuit, then adjusting for minimum output offset."

So if I'm following correctly the "FET in the circuit" is 2SK-389, and you find the value of R46 by soldering a 2k pot into R46's place and adjusting for minimum output/DC offset (less than .5mv after warmup).

yes?

M.

PS. I'm one resistor away from getting my first audio card built, and yes... it's R46.

 

[okgb]

that sounds right

 

[madriaanse]

Well damn... So I got my first channel all built, hook it up per: http://www.nrgrecording.de/temporary/MP2%20Wiring1.pdf

and I get (drum roll....) SMOKE!! Oh the excitement. It appears MP2%20Wiring1.pdf has J8 laid out backwards. In other words, "hole 2" on that drawing gets +30V and "hole 4" gets -30V.

It appears the smoke was coming from somewhere around Q12 and Q13. Anybody got any suggestions on what parts I might have fried doing the reverse voltage shuffle?

Thanks!!

M.