Great River MP-2 , info, schematics & discussions

[Dan Kennedy]

I gotta be honest, the board looks a little brutalized, why don't you send
it to me, I can fix and test it in a few minutes, save you headaches.

Just send it to me care of Great River

164 Hardman Ave S
South St Paul, MN 55075

 

[Ptownkid]

You're the man Dan! ;D

 

[riggler]

OK Dan I will send it! Thank you.

Man, I am humbled.
PTown, thanks anyway about the spares, no need to send now.

...I hope I didn't kill it...

This place The people on here are just awesome.
And, the place is awesome too.

 

[52ftbuddha]

Ok I have been following this thread and have populated a board that I bought from Ptown (thanks, I will order another once I have this one up and running) The generosity of Dan is downright moving, the offer to rebuild and test riggler's board is the high point of a rather good week. Just amazing.
On another note, where are all the builders sourcing a 1u case that will accomodate the boards. Has anyone done a decent looking front panel?

rob

 

[riggler]

Well maybe I can contribute something for once!

You can do it in the Par-Metal 1U rack case, even the 8" deep case, even using the 4 tall caps in PTown's kit. But it's tight.

What I did is make some nice plastic cutouts for underneath the audio cards, to protect them from a possible short, since I had to use very short standoffs for the audio cards in order to have those caps clear. (Mouser part number 728-FC2098-632-SS). 6/32 screw through bottom of chassis, through standoff, tighten down, then through card, then 6/32 tall standoff on top. Why use a tall standoff on top when you can just use a nut? Because it makes it much easier getting a tool on there for removal and installation!!

So, that was my trick to getting it to fit. For safety, I will be taping over the top of the caps for insulation just in case of contact with the top. Also be sure the toroid mounting bolt can't short against the top case. I cut my mounting bolt down a little and made another plastic shield that goes over the entire toroid.

PSU filter caps are really big. These I obviously laid down and went with short standoffs for the board, with plastic insulation underneath.

 

[vgdb]

Hello,

I am on holliday  ;D so I wanted to finish my 4 channels GR-MP2 preamp (I already built 2 that work very well as long as I don't close my box, if I do a "buzz" appears so I suppose I have to check my ground connection...). But when I tested the last card for determining the R46 value, I measured a 12 volts output that didn't vary when trimming the pot I plugged in the R46 slot.

After "a few" verifications I noticed I unfortunately soldered the Q14 transistor (8099) the wrong way.
My questions :
- Could this have damaged other components on the card ?
- Could this have damaged the 8099 (Q14) transistor ?

To sum up : I managed to remove Q14. Could I simply resolder it the right way on the board without risking to burn something ?

Thanks for helping and greetings from France.

Vincent GdB

 

[lsskmki]

After "a few" verifications I noticed I unfortunately soldered the Q14 transistor (8099) the wrong way.
My questions :
- Could this have damaged other components on the card ?
- Could this have damaged the 8099 (Q14) transistor ?

To sum up : I managed to remove Q14. Could I simply resolder it the right way on the board without risking to burn something ?

When building my first 2-channels of MP-2 I mixed up transistors and put some in wrong places and also wrong way around.  : I was positively suprised after removing them and soldering them in again the way they should be, nothing was damaged.  ;D

If possible, solder a socket in place of that transistor, put Q14 in and see what happens. It will probably work ok...and if it does, just solder Q14 on the socket. Hope all is well with your transistors

 

[vgdb]

Thank you lsskmki for your testimony.

I resoldered the 8099 and the board seems now to have a "standard" behaviour. I could measure a normal level output and evaluate the value for R46.
I am now waiting for the resistor to arrive, it takes some time because I'm on holliday...

Thanks once again for encouragements and for proposing an action plan.

Best regards everybody, thanks to Dan as usual.

Vincent GdB

 

[okgb]

there is Dan & pete on the white market offering panels
i can send you some designs but it's straight forward
4 pres in a case gets tougher but two should be no problem

 

[disorder]

is it possible to run unbalanced output into an XLR connector? or are those simply for balanced out?

I will be using the MP2 to run into a Digi002 so I would assume I would need 1/4" unbalanced outputs on the MP2 to then run into the 1/4" LINE inputs on the Digi002?

 

[okgb]

Before the output trasformer , the board actually has two
output points [ the difference only being a resister i believe ]
to feed bal & unbal
It sounds quite good unbal out and i wouldn't worry about
the xfmr unless you needed the isloation or wanted slight color

you could wire it on a 1/4" jack and use a cable that grounds
the unused pin on the input  [ or sleeve if the line in 1/4" ]

ground it or floating , the two main options

 

[disorder]

thanks, make sense I think. so I still need to use one of the resistors even if it's going straight to a 1/4" TS jack? Or should I wire a jumped in place there? some other final questions before I fire this guy up!

what knobs are you guys using with these Elma switches? The shaft and threads make for a very long length and most knobs won't reach to my faceplate so it doesn't look too good. are there some decent deep knobs or maybe knobs with large skirts that would hide the nut/threads?

I am using a JLM AC/DC power supply and it has two "grounds". One ground is the stand off hole that connects to the rack enclosure. The other is the 0V lead on the board. JLM says to connect the 0V lead to an isolated starground with all other preamp grounds. Now I followed the ground scheme mentioned here and ran a wire buss along the back of the XLR i/o jacks in that little tab with a hole in it that is on the back of the XLRs. This buss is obviously connected to the enclosure because the tab is and I feel it is not "isolated" like JLM suggests. Think I'll experience extra noise because both PSU grounds are connected to chassis?

could someone explain how to wire the DI 1/4" input jack? what kind of switching arrangement is it supposed to be?

THANKS!!

 

[okgb]

All grounds should be ran to a single point at the xlr connectors
it is suggested to use heavy copper wire like that used for houses
[ taking one wire from the the normal insulated 110 3 wire type ]
psu ground to this point not the board and all grounds on the board
to this same point as well

the quarter inch jack is a switching type with 3 terminals hot  , ground
and a third which is connected to the hot when no plug is inserted
so secondary of the input transformer from the board goes to the switch
of the 1/4" jack and the hot of the 1/4" jack goes to the input of the board
that way it makes connection until a 1/4" plug is inserted then that breaks the
connection from the transformer and becomes the input instead

 

[disorder]

got it running, sounds great! thanks for all the help okgb. to finish it off i need one of the elma rotary switch nuts... is there any way to get just one? i believe elma has a 10 piece minimum. also, looking for suggestions on knobs for these switches. they require quite a bit of torque to move them and have a longer shaft so i've been looking for a heavy duty knob that covers most of the shaft but haven't found much.

 

[shabtek]

those sato knobs linked to in the rca knob thread work really nice on them elmas and look pretty good

 

[okgb]

you could always cut the shaft down ,
i use two different knobs on my quad
but they both have two set screws each

 

[scondon]

Hello all,
This is my first non-stompbox diy project, and I'm having a bit of trouble with the racking.  I've had the boards stuffed for many months now but only recently got a case (par-metal) and input and output transformers (cinemag).  

My big problem is that the CMOQ-1H is too wide to be mounted sideways in the par-metal 1u case.  What case have those of you who have used the cinemag transformers used?  I'd prefer not to go to a 2u case.
Thanks for any help you can offer.

edit: Found a solution. These cases have 1.5" internal height and have pre-cut rear panels to boot:
http://www.groupdiy.com/index.php?topic=41963.0

 

[herrmann]

I was just checking the LSK389 pinout, and found that R12 and R13 are actually reversed in the audio card placement pdf ? Can anyone confirm ?

 

[okgb]

Pdf's directly from Great River Production ,
no mention of any problem before, so
I'd double check that .

I used L brackets to mount Jensen's Outputs
to mine , case dependant it would seem

 

[herrmann]

I have reversed them in mine, and all is working fine. I guess this is not critical, because of the TBD parallel resistor.