Greate River MP-2 *finished

[okgb]

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.

IN millivolts      http://www.groupdiy.com/index.php?topic=20333.0

with the schematic inject a signal  and start checking before and after every part in the signal chain
even before and after the input transformer .
maybe the signal is just bleeding through and not really making it

 

[hotbaby]

i put a 2k pot in and measured on the output (PCB Output Pin2) 0,002v with 2k Pot-resistance. if i drive the potentiometer down to 0 ohm i measure 0,232v.
So i need a 0Ohm Resistor ??? I do not understand it this tweaking part  :-\

 

[okgb]

leave the pot in and listen to the circuit that way ,
see if any of that is helping your problem
otherwise continue tracing

 

[hotbaby]

okbg, i want to thank you for helping very much.
I am not at home yet and can´t forward figuring out the problem but before i left i found out
that the polarity switch seems to be broken that the relay cant be fed with 12v...
i was lucky recognizing it when i swiched the knob and the sound on the oscillator was ok for the first time.... when i switched the knob again i could not get this state again and i just bridged the connections manual and i had no problems and could set the amplifaction with the gain knob, how it should be...
I will figure it out tomorrow when im back at home.
Thank you guys, i will tell you if i hit the bull´s eye 

A bad Switch, Lo and behold! :

 

[hotbaby]

i figured out the problem. not the switch was the problem, it was the wrong connected left (mine) pcb. I swaped the +22 and +48v on the left pcb that the 22v juice flow on the left pcb away and the right pcb which i tested with had not anough to work right... that assert that the relays sometimes worked when there was a current peak and sometimes not... also the switches which worked just sometimes.
absolutly my blame. i didnt care about the left pcb and it was power connected all the time...

what i had to do more was really bring the psu to 30vdc just to feed all the relays with 2x12v.
when i had 25vdc i had just 6-8v on the relays which was not anough...

The grounding is fine, i have no problems with it. i simply connected all xlr1 (In and Outs) direct to the chassi with the neutrik chassi connection on the xlrs.
The Input Xfomr is grounded to the PCB and the PCB is grounded just one time to the Star point to avoid ground loops.
i have really no noise there.

-108db (rms) Noise floor.

Now im just waiting for the second xfomr and the machine is done my second diy.
okbg thank you again for your assignment.
aaron

PS: okbg i could adjusting the r46 now and adjust it to 0,000v and replace the testpot with 1,58 K-Ohm.
thanks

 

[okgb]

Good work
sometimes i have to go through problems i have so many times i stop seeing things
but what's important is you stuck to it , so enjoy

what input xfmr did you use ?  and btw the g.r. is quite fine with no
output xfmr [ slightly more pure ] and a bonus with one .

Thanks Dan

 

[3nity]

I dont understand what was the problem congrats!
Greg he is using CM75101APC wired for 1:5 ratio.
Thanks.

 

[hotbaby]

yes i let it without an output tranny and read just good things about it too. for more color i have the original Mp-2 NV 
Dan, i will take new "finish-Pictures" as soon the second xfmr arrives.

Jorge, i try to explain it better. My english is not the best
I simply interchanged the power on pins +22v and +48v on the left (unused) mp-2 and cause they are mp-2s are power-paralleled one engine run wrong and tryed to suck 48v from the 22v cable which was connected to the mp-2 i have tested with... There was not anough current that it could work fine especially the relay switches that had not anough current.

i had no bless. Some days sleeping took the answere for my litle blame :

Aaron

 

[3nity]

I simply interchanged the power on pins +22v and +48v on the left (unused) mp-2

Does that means that you sent +48V into the 22V place?
Havent you fried the fet?? take care.
Glad you sorted that out.

Jorge Aristondo

 

[okgb]

the on board regulators probably didn't like it much ,
but he said there was some funky interaction between boards

 

[hotbaby]

yes exactly 

no i have not fried the fet  ;D
i had luck to have exactly 45v dc and 29vdc from the jlm psu.
i think if id had 60v (for the 48v) like suggested in the gr info thread the fet would be fried.
like okgb said there was some funky interaction... i really would now what exactly happened when i
interchanged the two pins but my brain is over these days all i can say is that really nothing worked as it should
and i had a lot of nightmares as you know puh i´m so happy that it works now without damaging anything...

PS: but i think it was anything that the left connected mp-2 tryed to rective 48 from the 30v and that made troubles with the
other paralleled mp-2 which i tested with... it was a really stupid mistake 

Have a nice week
Aaron

 

[Ptownkid]

Mistakes can be annoying, but they are by far the best way to learn.

 

[Whoops]

what software are u using?

 

[hotbaby]

i have used two softwares. An oscillator for generating a signal and the freeware oscilloscope "WINSCOPE" http://www.mitedu.freeserve.co.uk/Prac/winscope.htm.
One useful shareware i used too is MultisineV1.74 with a signal generator and much more options.