Great River MP-2 , info, schematics & discussions

[okgb]

Double / triple check the input xfmr wiring , there is no switch
for impedance , just wire them 1:5
the ground is only for shielding , you can try to break
the ground to the input xfmr  , the xfmr unbalences on the
board

Are the relays in the correct way ?

 

[3nity]

Greg i know there is no impedance switch...i hardwired the transformer for 1:5 ratio.
http://cinemag.biz/mic_input/cm-75101APC-schematic.html

Look at the pins...so i should wire only 6 & 7 as shielding/ground...and 5 is hot and what about 8?

 

[Spendor]

Just wondering what sort of power transformer would be adequate. i have a 20-0-20 15VA - would this be OK? Or if someone could provide info on the range that would be OK that would be great.
Cheers - I'm looking forward to this!

 

[ward]

from the  first post in this thread:

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

 

[okgb]

i would think you could get away with the voltage but the VA looks low
and why not get all the headroom you can make the most of the circuit

 

[jpuhhuh]

Well it looks like it is my turn for the redundant questions forced on by limited understanding.
I am just about done with this little beasty. Before I blow anything up I would appreciate some clairity.

A. Am I correct that J8 (power) is wired as follows?:
1-Led Driver  It looks like I have pin 1 & 5 mixed up.
2-Neg 30v
3-  0v
4-Pos 30v
5-48v
I have it this way with no smoke. No heat either, and the Led Driver is not in place as I am using a JLM power station and transformer for now.

Next up is regarding setting R48:
With a 2k pot in place, the power is turned on and I measure "dc offset" at pins 3 & 4 on audio output to the tune of less than .5mV on my meter.
B1. Do I need to have anything selected such as gain in order for this to work?
B2. Or signal coming in?

C. In regards to grounding to the PC boards. Am I understanding correctly that a wire from the ground buss wire (also attached to pin 1 at XLR) is to be run to pin 1 at the output of the pc board?

D1. Finally (Oh is it ever the last one...) when using a transformer and wanting to parallel to a 1/4" output as an option, how are things wired to remain in polarity?
D2. Pin 4 to tip and 3 to shield? or opposite?

Thanks for your time in advance.
JP

 

[Spendor]

Thanks for that - I can't find a 22-0-22 transformer here, but I can get a 20V 30VA so that should suffice.
Is it OK to use BC547 or BC549 as substitutes for the BC107 - different package but still OK?
Also is R47 20R or 10R as they are different on BOM and schematic? 1W Carbon film OK for this one?
Thanks again
Cheers

 

[hotbaby]

as i had the same question with the trannys you can use a 22-24v power transformer.
this one on digikey "Product Number": TE62075

One man here did the power supply with a JLM Powerstation where you can adjust the
power to get the needed votages but you can build it with a few elkos yourself...

With the 10 1w  i have the same problem. im unsure cause there was no resistor in the mp2 kit to fit this last hole.
the bom says 10 and on all pictures i can see that they used 20 like the other ones... but i had no 20 in the kit too.
so i must buy it. i will take 20 cause all pics i saw used it instead of 10... dont know why but cant be wrong doing the same

hope i could help

aaron

 

[hotbaby]

anybody knows sourcing the blue 20nf 1w con´s?

 

[Ptownkid]

Use the 20R 1 watt resistors

 

[hotbaby]

Thanks Ptown but i had just 5 in my kit and need 6. So i´m gonna buy this one to get it done. Can you tell me what kind of resistor it is that i can order it? All the other rest is complete and done.. thanks.
Thank you. Aaron

 

[Ptownkid]

you only need 5, but the part number is in the BOM

 

[hotbaby]

You mean i can let it stay blank?

 

[Ptownkid]

If you look at the schematic, you'll see that you don't need it. The output connector has 4 pins instead of three, just ignore the one that the 10R should be connected to.

 

[hotbaby]

ah yes you are right,i understand. Its just for a second different output. ok. thanks.

 

[Ptownkid]

my pleasure, enjoy.

 

[jpuhhuh]

So I managed to blow up Q13 on one of my channels. I was set to measure offset with a 5k pot in R48, pin 4 to ground, 1&2 to my meter at the output. No OP transformer in circuit, no signal, just turned on. As soon as I gave it power "snap" and half the transistor blows off. Cool, but I don't want to do it again. So what the heck caused that? Power is right, (I am using a JLM) and I can find no shorts on the board, I've been careful about component placement...
I figured I'd drop the ground on output pin 4 and try again on my other board. This time no explosions, but I am getting an OL on the meter. I am feeling no "heat" on any components as some have described. Am I doing this procedure right?
So before I blow anything else up I am off to buy some more transistors and hoping someone can guide me better than I am doing myself.
And answer at least one of my own questions from my former post, I noted that I had pin 1 and 5 mixed up on the power input.
As always thanks.
JP

 

[Dan Kennedy]

I had to knock one of these old beast's off this week for a buddy, thought you might
get a kick out of one built from "scroungin's"

 

[Cpartipilo]

WoW!

Cool, that's what i would call a Brand New Old Stock    ;D

 

[hainter]

finally got my boards all put together.  I fired it up with the 2k pots in place of R46, everything seemed fine, checked and double checked the power wiring before i turned it on.  I haven't hooked up the XLR in, or the output transformer and i was doing the calculate R46 and checking the DC offset at the output (with nothing hooked up)  my only question is, with the trimpots in place, i was measuring about -3mv DC at the output on both channels before i adjusted any trimpots, is this normal?  before i put the trimpots in i measured them at about 2.4K for one and 2.6K for the other.  Just wanted to make sure i didn't do something wrong.

rock on and thanks for this wonderful project