Great River MP-2 , info, schematics & discussions

[okgb]

Most of what you need should be in this first post
schematics & tech doc's here
http://www.groupdiy.com/index.php?topic=48791.0

Here is some info from Dan and would like to not bother him
with too many questions , most are answered in thread

F.E.T. resister value need to be determined in circuit , see instructiuons
below , not sure if there is much else tricky ,

Adding some info here so it is easier to find

power xfmr requirements = An off the shelf 30va 22 + 22 transformer will power this up fine
you don't need to build the supply in the schematic , although it is nice with o/l l.e.d. drivers

Good supply design with comparitors for overload [ they work nice ]
though they are they only part that is surface mount size [ on psu pcb ]
Simple " raw dc " psu design cam be used  with 22-0-22 30va psu Xfmr

Suggested input Xfmrs
Cinemag CMMI-5C 150:3750
Lundahl 1538 XL 1+1:5
Jensen JT-13K7 1:5

Outputs Cinemag  CMOQ-1H
      Or  Jensen    JT-11-BM

Any 24 pos. shorting switch  may be used for the gain control , although not recommended  a 2k2 reverse log pot may be used to get the pre working until you find a switch

Finding the value for R46 [ with fet ]

R46 is determined by putting a FET in the circuit, then adjusting
for minimum output offset. This value drifts some with temperature, so
I try to adjust for <.5mv when the circuit is warmed up.

You are selecting r46 for minimum output offset voltage at output
[ before output transformer of course  , if you installed one ]

just power the board up, it already has the feedback resistor, and put
a 2K or so pot in for R46, adjust for minimum, let things warm up some
more and readjust. After 15 minutes or so take the pot out of the
circuit, measure and replace with a fixed resistor of the closest 1%
value and then retest for warmed up minimum offset.

It takes a little while, but it's something you can walk away from in
between tweaks.

Further refinement [ and quote ] from Dan on slecting the resister

When adjusting for R46, I first power the boards up, and see that the
offset is less than about 15mV, and frankly I forget which polarity.

This proves that the FETs are a reasonable match.

Then insert the trimpot in for R46, adjust for zero offset, which you can't
do because just breathing on the board will move it a little, but you can
get it trimmed into less than 1mV pretty easily.

Remove and measure the trimpots, then replace with the closest 1%
resistor you can get.

It's not super critical, the offset won't get any worse, and anything under
5 or 10mV's of offset isn't going to cause any problems.


Grounding scheme
As recommended by Dan 
Run a heavy bus wire along the back of the i/o connectors - in Canada & U.S. the copper house wire fits perfectly into the XLR connector
Have the Chasis & PSU grounds meet at this point
Run the Preamp board ground [ including the psu ] to this point
Run the Input Xfmr screen & ground as well as any shielded i/o wire to this point , preferably between their respective i/o connectors .
Do not connect any of these grounds [ i/o & Xfmrs ] to the input side of the board

regards Greg

 

[Samuel Groner]

If you are asking for a host I'm happy to provide this. For a group order Fabio would be the more adequate person.

Samuel

 

[okgb]

Asking for who would most likely make best use of them , it would be bit of work still to make them [ more than i can handle ]

I 'm just concerned if i put the whole thing out there , Dan would get
hasseled with too many questions , so if we can find a point person
[ that is , if there is enough interest for boards ] i 'll send them on .

I can relay some info into the thread if it gets going ,

thanks , regards Greg

 

[mkoz]

If they are legally released, I can host them as a mirror too. I have over 300GB free space out there somewhere.

Mach

 

[thenovice]

I'd like to see these as well.
but i'd doubt they be officially released. :roll:

 

[thenovice]

damn i didnt know Great Rivers was based out of MN.

 

[okgb]

The info will likely spread quick anyway , but my thinking is if
a couple of the people here start on it then a dialogue can begin
without too much confusion [ i don't need anymore myself ]

i'm trying to avoid having people bug Dan with questions that he's
too busy to answer .
............update ..............Dan says it's o.k.

O.k. post your email and i'll send a few out to get them up ,
Sammy ?????? what's your email ?

I've sent a couple out allready , so someone post a link into this thread ?



standb y ! regards Greg

 

[matta]

Okay Guys,

Lets play ball!

My suggestion is that we ask Gustav if he wouldn't mine fabbing the PCB's since he does an EXCELLENT job of the various other projects. I will alert him and direct him to this thread and see if he will be willing to be the PCB Point Man.

Next suggestion is that since Greg is already the point man on the project and has built a few units for himself that we correspond through/in this thread and he can answer questions, or at least provide additional information for us to work from RE assembly, testing etc.

I think the key thing is to under NO circumstance bother poor old Dan Kennedy with questions via E-mail, PM etc as he has enough to take care of, hopefully he will pop in if he has the time.

To get us started here is the thread in the 'Drawing Board' that Dan commented on a year ago: http://www.groupdiy.com/index.php?topic=6573

Without further a due here are the files as presented to me by Greg:

Audio Card Schematic – 30Kb
Gain Switch Schematic – 30Kb
PSU Schematic – 15Kb

Audio Card Parts Overlay – 14Kb

Digikey BOM (with part no's)

It is great to have a new project here again

I'm off to eat some dinner, will post back with more suggestions in a while.

Cheers

Matt


EDIT: Okay guys, since Gustav will be fabbing the boards I'm pulling off the Gerbers as I'm not so sure they should be 'lying' around as someone may start fabbing them and they end up on Ebay.

Boards will be availble in about 2 months.

 

[flaheu]

Matta,

Audio Card Schematic – 30Kb
Gain Switch Schematic – 30Kb

I think there is a mistake, these two links point to the same file, the psu schematic.

Cheers and great info :thumb: :thumb: :thumb:

 

[flaheu]

Oops my mistake, forget what i said

 

[Neeno]

Well done my friend ! :thumb:
And thank you Dan ! :grin:

[quote author="matta"]Okay Guys,

Lets play ball!

My suggestion is that we ask Gustav if he wouldn't mine fabbing the PCB's since he does an EXCELLENT job of the various other projects. I will alert him and direct him to this thread and see if he will be willing to be the PCB Point Man.

Next suggestion is that since Greg is already the point man on the project and has built a few units for himself that we correspond through/in this thread and he can answer questions, or at least provide additional information for us to work from RE assembly, testing etc.

I think the key thing is to under NO circumstance bother poor old Dan Kennedy with questions via E-mail, PM etc as he has enough to take care of, hopefully he will pop in if he has the time.

To get us started here is the thread in the 'Drawing Board' that Dan commented on a year ago: http://www.groupdiy.com/index.php?topic=6573

Without further a due here are the files as presented to me by Greg:

Great River MP-2 Gerbers – 275Kb (Contains the files below as well)

Audio Card Schematic – 30Kb
Gain Switch Schematic – 30Kb
PSU Schematic – 15Kb

Audio Card Parts Overlay 1 – 14Kb
Audio Card Parts Overlay 2 – 14Kb

It is great to have a new project here again

I'm off to eat some dinner, will post back with more suggestions in a while.

Cheers

Matt[/quote]

 

[matta]

Thanks, Paul alerted me to this a few minutes ago via PM and I have corrected it, prob just before you posted :green:

Cheers

Matt

 

[okgb]

O.k. standby for Digikey Bom , perhaps if there is enough interest
my Canadian cousin , PtownKid will look at kits ?

I second & third the not bother Dan , once there are a few quesitons
i'll contact him [ see first post for fet resister value ] but when he's busy it can take weeks , guys got a business to run ya know

If helpful here are a few pix sorry no macros on my camera

 

[bernbrue]

Hi,
initially I had no idea what the discussion was about. After reading a short description of the preamp, it seems that a very interesting DIY project is coming upon us. Thanks to all, who contributed to this project with their knowledge and enthusiasm. For better understanding (for newbies like me):

http://mercenaryaudio.com/greatrivelmp.html

regards
bernd

 

[Gustav]

If were 100% its cool with Dan, Ill make these. Give me a little time to get it rolling.

Also, is there just "one board" in the gerber file? I dont have viewer at home, but it looks like there are schematics for different parts of the design in the gerber package, but only one actual board.

sorry for being retarde, no viewer here

Gustav

 

[clintrubber]

[quote author="bernbrue"]Hi,
initially I had no idea what the discussion was about. After reading a short description of the preamp, it seems that a very interesting DIY project is coming upon us. Thanks to all, who contributed to this project with their knowledge and enthusiasm. For better understanding (for newbies like me):

http://mercenaryaudio.com/greatrivelmp.html

regards
bernd[/quote]
The link you gave is for the -NV-version, which is a completely different beast. Without ever having had hands on either the MP-2 and the MP-2NV I'm fairly confident to say that the sound of the -NV will be in a different area than of the circuit of this thread (the MP-2).
The -NV (as coming from Neve as you'll have understood) is about 'colour' (sorry folks) and as I understood it the MP-2 is about as little colour as possible, transparent (sorry again).

Got a question myself: anyone has put his ears to both the MP-2 and say a Green ? I'm curious what the MP-2 has to offer w.r.t. sound/applications where one of the other DIY-preamps here doesn't already go (Green ? SSL 9k ?)
Please understand that I like it a lot of course that a new design becomes available to the DIY-community (much appreciated; thanks DK & also of course thanks to the other people involved making this project possible :thumb: ), but as said I was wondering where the MP-2 stands compared to the other clean preamps.

Bye,

Peter

 

[matta]

[quote author="bernbrue"]Hi,
initially I had no idea what the discussion was about. After reading a short description of the preamp, it seems that a very interesting DIY project is coming upon us. Thanks to all, who contributed to this project with their knowledge and enthusiasm. For better understanding (for newbies like me):

http://mercenaryaudio.com/greatrivelmp.html

regards
bernd[/quote]

Hi Bernd,

Just for your reference and others who may be wondering... this is NOT the MP-2NV that Dan currently manufactures, which is a Neve like design.

What Dan has offered up is the ORGINAL MP-2 Mic Pre, which was a transformer coupled, Class-A, Discrete Mic Pre. I think he designed it back in 1991 and it was manufactured in the mid-late 90's. It has been favorably compared with the Millennia Media design and in the words of Greg.

The MP-2 to me is smooth and solid in the midrange , neither sweet nor dry , can't say anything bad about it ! Frequently when I am using it and not happy with the sound I wonder what I can change and it is never the preamp . As good as the Millennia I think , perhaps a touch less airy but not as thin either.

Here is a review of the ORGINAL MP-2: http://mixonline.com/mag/audio_great_river_electronics/

[quote author="gustav"]If were 100% its cool with Dan, Ill make these. Give me a little time to get it rolling.

Gustav [/quote]

Thanks Man! I knew we could count on you. By virtue of the fact that Greg has sent me these files to host and in light of him saying he wouldn't until he got the okay, I assume we are A for away, but Greg/Dan can confirm this before we do a run of boards.

Also I have just posted the a BOM above from Digikey, it is rather rudimentary with no additional info, unlike some others, but if anyone wants to put it into an excel doc and work out the cost that would be great! You can e-mail it to me @ matt(@)matt-allison(.)com (Remove the brackets), and I'll host it.

Cheers

Matt

 

[Whizard]

Looks good!
It does not matter that I have got a number of other things going - I am in on this one!
Thanks, everyone involved so far!

 

[matta]

[quote author="clintrubber"]

Got a question myself: anyone has put his ears to both the MP-2 and say a Green ? I'm curious what the MP-2 has to offer w.r.t. sound/applications where one of the other DIY-preamps here doesn't already go (Green ? SSL 9k ?)
Please understand that I like it a lot of course that a new design becomes available to the DIY-community (much appreciated; thanks DK & also of course thanks to the other people involved making this project possible :thumb: ), but as said I was wondering where the MP-2 stands compared to the other clean preamps.

Bye,

Peter[/quote]


Hi Peter,

Well the topology of the the MP-2 and Green are quite different. The MP-2 has a transformer couple input, unlike the Green and it a Class A, Discrete design, while the SSL9K and Green are use a differential pair (I think) and balanced/unbalanced using IC's.

I expect it to have a different tone/character from both the Greens and the SSL9K, though I've not done A/B test... heck I've not even heard the MP-2, I'm just up for a new, interesting project!

Cheers

Matt

 

[matta]

Greg,

Gustav pointed out to me that Gerbers are just for the single pre board, is there a PSU board as well, or is the idea just to use a generic PSU unit?

Cheers

Matt