All things G1176 - the new "repost" thread.

[W DeMarco]

Sup Mako

I assumed(uhoh) That it was grounded through the interconnect with the input xlr...Please tell my ******* Im wrong!

 

[W DeMarco]

Star grounding scheme isolating the various sections of the circuit and bringing them separately to the star point beneath the output transformer for elimination of hum.

From mnats website.. Should I just connect this point to chassis?

 

[gswan]

Try moving the wiring a bit, particularly anything near the transformer. Try moving the transformer as well and see if it changes the amount of buzz.
Do you have a photo of your grounding scheme?

 

[W DeMarco]

Ill try to get the photo up soon...  Tryed moving wiring anywhere possible.  Didnt help.  I'm not sure how I am supposed to ground the main pcb.  I tried grounding from the main ground below the output tranx to the chasis but that seemed to make things worse. 

 

[gswan]

If you need to ground the PCB, do it at the PSU 0V point, as close as possible to the transformer CT.

 

[adrian]

Hello!
i need some help on finishing my 1176 mnat with 5534 Input and oep output,
i've some problem but the unit compress,
my first problem is that in GR mode my vu (sifam al19) stay at -20db but when it's compressing i can see the needle going from -20 to -7 db etc... i tryed inversing my wiring between 29 and 28 but it's not that, i checked and i have -10v at pin 7 of the tl71 and +30 after R49,
then i checked tension before cr11 : i have -8,3vdc and after i have only -0,1vdc,
is that normal?
what else can i check?
should we have a tension between point 28 and 29?

 

[user 37518]

OMG Good find...Almost 1200 bucks without the output Iron.   What a shame.  They also have a dual fet comp as well as a dual pultec style that looks pretty damn familiar.

Yeah, to me doing that kinda thing is like really really lame, then again, i could be wrong and they made their custom design (but its not very likely).

 

[beaversaber]

Not normal. Check the values of the capacitors you have attached to the GR FET drain lead.

which ones are these? would it be safe to just go through and check all the ones in the signal pre amp section?

the problem was hf roll off when the q bias trim was turned CW

thanks!

 

[beaversaber]

anybody?

 

[Echo North]

C1 the 1uf cap.

Checking all of them wouldn't hurt.

Mike

 

[thedude]

I have a question about grounding the g1176. I have a Mnats board and i wired it like it's described on his website, with only pin1 on the input connected to my chassi star ground, where i have the IEC ground connected. I've had some problems whit Hum and noise introduced by my computer. So last week i installed a ground lift switch between the connection from XLR 1 - star ground (the PCB ground still connected to pin1 when switch is lifted), and it really help getting rid of that nasty noise from my computer.

The question is though, will this ground lift make the "CT 0V"  floating? Can it in anyway be harmful to the circuit or any other equipment connected to the unit if this ground point is lifted?

Maybe this is a stupid question, guess i am missing some basic knowledge about grounding and power-transformers. Tried searching but all these discussions about grounding is a little bit confusing.

 

[mac]

Hey Dude,
from my recolection of Mnats wiring guide I am not sure you are meant to bring them together. I grounded my xlr's next to the sockets on the back panel, and took my IEC to a separate chassis ground. My case is 3m steel and like a tank -  i havent ever had hum probs.


Mac

 

[extremewillis]

Hi all!

I'm finished assembling my Mnats Rev J G1176.  I powered it up to calibrate and of course it's not quite working - can I get some advice?  It passes audio but won't calibrate.  Something peculiar happened by chance: Output seemed low and had to be cranked to get audio through, also metering didn't seem right.  As I was moving and measuring, the connection from Pad 7 on main board to the attack/rel pots snapped - I didn't see it right away.

Powered up again and metering was right, GR near zero, output metering correctly, and output volume was normal (didn't have to crank it)

Next, I discovered the broken connection and re-connected it.  powering up again, I noticed output is low and meter stays to the far left in GR mode - like it is compressing many many db

In both cases I cannot calibrate the first step (Qbias)

Suggestions on where to start?  Should I measure all the transistor voltages?

 

[gswan]

You could try reading back through this topic.
You will see that I mention every so often that you should not pass audio through these devices until you have performed the full range of tests and calibration.

Once you have done all this, come back with any problems.

 

[casrec]

Also, you want to start the calibration with QBias trimmer and tracking trimmer full CCW. When you calibrate tracking, adjust R54, then bypass and adjust R55(Zero adjust), then unbypass and adjust R54, then bypass and adjust R55. Keep doing this so when bypassed meter is at zero and when compressing meter is at -6.

 

[mac]

It is one of those things....at the time you think you're doing everything wrong, or your unit is broken....but keep logically working through the procedure step by step.....I did mine about 8 or 9 times until i realised what was happening and how everything was working. I even counted the turns on my multi turn trimmers so I could 'reset" them to centre to start again a few times  : very unscientific I know!!

Definitely measure all the voltages first....

I found this a help at the time http://nimbleswitch.com/diy/1176_revD/index.php?page=calibration sometimes it is good to read the same info written three different ways before it actually sinks in ;D

you'll get em runnin......just remember to walk away and get some fresh air when it does your head in...
mac

 

[extremewillis]

thanks gswan, casrec, and mac.  I am reading more today and will take some measurements. 

 

[extremewillis]

Hi

I have made some measurements and tried to calibrate again - this time trying to calibrate with a DMM instead of the VU meter - that seems like a better idea.  When I input .775V 1kHz sine wave, with both in and out pots at 12 o'clock, output is at .15V, looks like something is wrong right away.  I measured voltages with the schematic.  Point that should be 30V is 29.6V and -10V spot is -9.8V.  That looks OK.  Here are the transistor voltages.  I think they are also OK.  Can someone give me a direction to look?  As I stated earlier, I accidently disconnected pad 7 once before and then the input / output seemed normal.  Can't get it to calibrate though.  Thanks for your help

        C    B      E

Q2  1.75 1.00 .500
Q3  11.8 1.75 1.15
Q4  29.6 11.8 11.2
Q5  27.9 4.80 4.30
Q6  14.1 27.9 28.4
Q7  14.0 28.4 29.1
Q8  29.6 14.1 13.5
Q9  0.00 12.8 13.4
Q12 15.0 4.40 3.90
Q13 29.6 15.0 14.4
Q14 16.5 3.40 2.90
Q15 29.6 16.5 16.0

 

[thedude]

Hey Dude,
from my recolection of Mnats wiring guide I am not sure you are meant to bring them together. I grounded my xlr's next to the sockets on the back panel, and took my IEC to a separate chassis ground. My case is 3m steel and like a tank -  i havent ever had hum probs.

Mac

Thanks for your reply. At first i didn't bring them together, that was when i had the hum problem. The hum though was not very high and it did only occur when my input and output pots where set in either CW or CCW position, not in the middle. The most annoying thing was the the noise that my computer brought to the ground. But the ground lift switch fixed that problem.

My question is still, is it a bad idea to lift the ground at this point (input pin1 to chassi star ground)? Does the CT(PCB-ground) have to be connected to ground? At least it solves my problem and the unit seem to work well anyway, so i hope the answer is NO ;D


Martin

 

[mac]

dude,
i usually start by moving or changing wiring first before changing the grounding scheme. I have solved more hum problems in the past through changing plain wires to twisted pairs or sheilded cable (as necesary).

Hey willis,
Your voltages all look good to me - compare to the two units I just finished recently. What trimmers are you using for Q, and tracking? Make sure you havent got the Q bias trimmer oriented incorrectly (depending upon the type).

Mac