Greate River MP-2 *finished

[hotbaby]

Hey,
I am going to finish my gr mp-2 and wired up the first channel for trying and i can not hear any sound.
Fireface out feeds music to the "mp2-Mic Input" and theres no sound on the unbal-Output.
If i jump 2+3 on the highZ imput together i can hear the loud buzzy music or if i use the highZ input instead of the Balanced input...
could there be a problem with the cinemag wiring?...

I tryed the left channel too... no sound with balanced input too.

The DC Voltage of the JLM powersupply is 25v. A little low but should be anough ???
here are pics.


I use a Cinemag input 75101a Tranny.

If i power on the mp-2 the music stays very buzzy for a 2-3 seconds and than the music brakes down.

Hope this can be figured out. i have no idea at moment...
Thanks

 

[okgb]

There is a thread for the MP2 already

but after the input xfmr the signal comes back off the board
to the 1/4" d.i. jack , this is a switching type which breaks the signal to take unbal high imp in
is this jack wired up correctly  ? if not using it two pins on the pcb must be jumpered
[ don't recall but is obvious if you look at the block diagram ]

 

[hotbaby]

of course! Thanks i forgot it! just for trying i let the jack unwired... that was the reason for no sound.
ok now i have sound but is it normal that the music is sounding so broken? Perhaps the low ohm Output on my fireface which doesnt work with the balanced input?

Thanks again!

 

[okgb]

the original thread also has a procedure for selecting
proper value of resister to bias the fet
have you done this ?

 

[hotbaby]

i bought the right "green" pcb from a neighbour from ou and he used a 150K resistor to load the cinemag. i let the 150k stay...
perhaps i missunderstood the fet-resistor with the loading resistor bridged from j2 to j3 (for my cinemag 150k)...  Or do you mean with fet the small inductor between/near the large 450uf caps`?

In the original Thread you explain adjusting the R46 Resistor:

"Finding the value for R46

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.

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 I'll 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. "


I have a 2k2 Pot lying arround. If i adjust it, what do i need to do for measuring "smaller than 0,5mv" getting the right value for a fix resistor?
The pot capacy with an ohmmeter?
The R46 is next to the r47 right? I soldered all parts and can´t see the labeling...  :-\

heres a soundfile of my mp-2 problem.
http://www.megaupload.com/?d=K9HSEAD6

 

[3nity]

Hello!
My sugestion is to work up the grounding scheme bro!!
Thats how i fixed 2 others GR for Jim (bluzzi)
Thanks.

 

[okgb]

yes once it has settled down for lowest reading , remove the pot
measure and replace with that value resister

I believe someone loaded the G.R. files to the general account and one
of them has the parts placement , otherwise  , AFTER you've looked
i could dig it off the other computer and email it

A good point , all the voltages are correct you've triple checked the wiring ?
including grounding ? [ power & signal both need ground , and you have to be a little
careful to avoid loops ]

 

[hotbaby]

i just can find the card layout with the part values but not the number-labeling R46, R47....
If you have thos i d be glad gettin it. send you my emailadress.


Hey 3nity, did you hear the music file i put in? i dont think it is a ground issue. everything with
the impendance or with the resistor like okgb says... but i will check the grounding again too.
all wires seems to be correct now...
damn that i cant see the R-labeling anymore, perhaps anyone has a pic of the unsoldered pcb?
many thanks

 

[3nity]

you're pluggin a Line in into a mic in??
Try a microphone...
BTW: hows the wiring on the output? balanced or not??

 

[hotbaby]

i feed the balanced input with balanced music output of my fireface (xlr)... usually should it work.
ill drive to the studio in the evening for catching a mic...
The output Wiring is unbalanced as i have no Output tranny.
I just took the 2 "pcb output pin" to the "xlr pin3", i also tryed the other output and the pin2 of the xlr with no luck.
The audio cards are grounded and the  xlrs1 are grounded too. The input tranny can be grounded or not with no differences.
but the sound doesnt sound like a grounding mistake to me. Loud passages of the music brake in very distorted and low passages
are very very low (listen to my mp3-File http://www.megaupload.com/?d=K9HSEAD6)...

i didnt tryed to setup this r46 resistor with a potentiometer as i am still not sure where the r46 sitts on my pcb. i soldered all parts and they hide the
labeling... :-\ 

 

[3nity]

look at the pics...http://www.groupdiy.com/index.php?topic=31677.0

 

[hotbaby]

nice, looks like mine pcb did you use a balanced output or are the cinemags input trafos?

 

[3nity]

The Great River MP-2 its whatever someone else says very..sensitive to a bad ground scheme.
Trust me..on those ones you see the pin 1 IN was connected to the  input transformer case..
And if i remember well the ground output was sent to the XLR input pin 1.

My 002 cents.

Jorge Aristondo.

 

[hotbaby]

ok i rewired the ground and put a 2,2k rev log pot to r46.
i feed it with a sine wave 1khz and get such a distortion:

If i rotate the potentiometer from full to 2,2k the noise is lower for 1 second and than it gets full distorted again.
Yes i thought this could be a ground loop but my grounding is correct and i tryed other groundings too...
And if i power off the mp-2 the sine wave gets short time louder and than dulls it down.
audiofile power off: http://www.megaupload.com/?d=8LODQIRX


jorge, perhaps the tranny? did it really work with the cinemag 75101 input tranny for you?
thanks...

 

[okgb]

it should have a 1:5 input xfmr not higher

try sending a -20 signal into the 1/4 input

grounding at the input xlr's via a heavy copper
shielding grounded at one side only [ xlr's ]
the thread should be correct for grounding ideas

Carefull it may be very hard to find replacement fets now

 

[3nity]

Yeah!!! It worked fine with me...i didnt even put it together i bought it from Greg....(@ Capstain Records)
The transformers is wired 1:5?!?!? i dont remember...

You sure you follow the wiring shown on pix? if i rely on pix something is wrong...

Greg: i sold that GR-MP2 to "HotBaby"...

You should bring the JLM statio to +/- 30V

 

[hotbaby]

good morning yes the tranny is jumped to 1:5. But im not shure if the primarys must be jumped together too...
I screwed the jlm to 31vdc... but nothing got better.

if i feed it with -20 db theres no amplifying anymore and the sound is as loud as if i power off the machine.
so the amplification starts above -15 db feeding very distorted, broken and loud. That is sounding like a broken tube if the music has low passages
they disappear and the louder above -15db boost the woofers out...

Jorge, i let all soldered as it was... do you remember if the prim and secondary grounds of the cinemag are the bridged "cinemag-Pins"? or is the transformer-ground just the case of the cinemag?...

Did you hear the audio files? I tryed so much grounding and have no idea what i did wrong.
aaron

 

[okgb]

I think you have to get very basic and start signal tracing
once you are sure the build is correct .
the boards have regulators but there's no need to feed them 31v
say -/+ 25 v
you have an ocilescope ?
feeding the 1/4 in directly will let you know if it's a xfmr problem ,
look in the general mailbox for the g.r. info , i still have to dig mine up
that would be faster , find r 46 and do the caculation , if the fet got
blown you may be in trouble finding another
but is signal getting through ? where does it stop ?

 

[3nity]

Greg i doubt its the FET.
I tried before sendin it and was working like it should.
To me its something missing or left to do.

Anyways i have a FET that its yours if needed...
Thanks.

 

[hotbaby]

I use an Software oscilloscope with my fireface audio card and two patchbay cables with the small TT phone jacks. this works great.

- ok i trimmed the power back to 26v
- The xfmr seems to be ok, i checked it with the osci
- i have found the r46 and put in a pot there but i could not see anything becoming better.
please tell me where should i measure with the volt meter... the FET is the the axial inductor between the long four caps?

thanks