All things G1176 - the new "repost" thread.

[gswan]

i finish my mnats + psu few days agoo, i get -10.78v and no more then +20v, i have a 30VA toroidal transformer 0,5 A is maybe to less for the board? Also the VU meter is not working only in GR mode i can see it moving.
Checking the unit with my ears and with a oscilloscope is anyway doing what it should.

30VA should be plenty for it. You need to check around the PSU and make sure that you have the correct DC values around the regulator. What is the primary voltage of your transformer?

 

[Spaturno]

230V, i check all component of psu several times all diode are in the right direction all caps also.

 

[gswan]

And the secondary voltage?
How about the DC voltage into the regulator?

 

[Spaturno]

secondary is 2 x 30V (one unused), DC voltage into regulator i have to check, which should be the optimal value?
I'll check this value tomorrow, here is late now. Thanks anyway for the answer.

 

[audiophreak]

Hi All,
      Just wanted to post back that the problem I was having with a hum seemingly controlled by the output pot -

Passes signal, but I'm getting a hum.
The hum is controlled by the output pot.
As I turn the output up, it gets quiet until about half way, then gets really loud.

I have both XLR's grounded to chasis, and using Mogami shielded cable.

Quite a common problem it seems.
1. Check the grounding of your front panel. I have seen ungrounded front panels cause this. Even though the rest of the chassis is grounded, unless the front panel is wired to gound it may have some resistance between it and ground. A quick check with a piece of wire.
2. Check the location of your mains transformer and its associated leads. Move them around and see if it changes amplitude. Find the quietest spot. If the contruction is really packed in you may need to add a metal shield in front of the transformer.

I've seen a few of these come up in the searches , but no one posts back with what worked ...

so this is what is happening in my dual unit , checked all of this - problem persists ,  I have the short leads from Input pin 1 to XLR jack screw with star nut and paint scrapped off , IEC Earth to Chassis Bolt, using an mnats +/- supply to both Rev.J boards .

  This is the WEIRD part ... using my cheep alligator test lead , I clamped on to Chassis Ground bolt and connected the other end to the 0v output from the PSU - Hum goes away - ran a permanent wire with soldered eye from bolt to 0v - Hum is still there !!  .. pull wire out of connector on PSU PCB and clip alligator test lead to it . start toughing things , and when 0v touched again - HUM GOES AWAY !!!!  it seems I have a MAGIC test lead -  any one got any Ideas on whats happening here ???

  Thanks for any and all help / suggestions ,
                                                                    Chip

The only grounding I ever do is to connect the PSU 0V to chassis ground. That's a single point only, anything else could cause a loop if you are not careful. Maybe you need to remove all other connections to chassis ground first and then connect the 0V PSU point to chassis ground.

  Thank You gswan  .... start from square one and work out    ( forest through trees )

  it turns out the problem seems to have been the PT I used , it was an Antek AS-0524 - 50VA - not sure if I got a bum PT or its just too big or what , but I put the 30VA one from HairBall in and with the input at full up I get a slight hisss in the last 5-10% of travel of the output pot travel ... so I'm Good with That - 0v from PSU to star ground point only with mains Earth Ground - I didnt do anything else but pull my hair out a little 

    so its all quiet and working beautifully 

  Thank You All

 

[Harpo]

secondary is 2 x 30V (one unused)...

You need both secondary windings connected in series, this series connection being your needed center tap for 0V reference voltage.

 

[Spaturno]

secondary is 2 x 30V (one unused)...

You need both secondary windings connected in series, this series connection being your needed center tap for 0V reference voltage.

i have secundary 1 (white and yellow) ans secundary 2 (red and black) and if i understand right i have to plug to psu wich has AC-0-AC
white to AC yellow and red to 0 and black to the other AC?

 

[Harpo]

secondary is 2 x 30V (one unused)...

You need both secondary windings connected in series, this series connection being your needed center tap for 0V reference voltage.

i have secundary 1 (white and yellow) ans secundary 2 (red and black) and if i understand right i have to plug to psu wich has AC-0-AC
white to AC yellow and red to 0 and black to the other AC?

Maybe yes. Transformer colour coding is not standarized, so have a look at your transformers datasheet or attached label.
Why do you use a 2x30V secondary transformer when schematic and pcb silkscreen calls for a 48VAC center tapped or 2x24VAC secondary? 30VAC*SQRT(2)-0.6V diode drop giving 42V raw DC, maybe 46V raw DC in a 10% high mains scenario. All excess voltage differential to +30VDC and -10VDC will be transfered to heat or smoke. At least the 1st. 1000uF/35V cap (C26) in the -10V section might not be that amused.

 

[Spaturno]

I have mnats board with external psu so i dont use the C26, the 2 capacitor on my psu are 1000µF/63V so i think that connect the 2 secondary in series should work. At the moment i get 22AC out from secondary.

i use 2x30V because in the shop where i buy my part was the most similar to the one described for the 1176 and i know other people in this forum that use the same trafo as mine, and is working properly.

 

[Spaturno]

Now i have 46V at the output, and with trimpot 5k like is explained here : http://mnats.net/psu.html
At first it melt R4 so i replace it and then came smoke out of the VR2

somebody here has the mnats PSU?

Otherwise i go back, just using one secondary output at least the unit was working.

 

[gyraf]

somebody here has the mnats PSU?

and

This thread is mainly for the G1176 board - the mnats boards are probably covered elsewhere in detail.

 

[swal]

I hope you guys can help, I am at my wits end. Ive got mnats j using the hairball kit with ic input. Its passing audio, but as soon a s I turn output over 1/4 its starts feedbacking and squealing. I double checked all the trans orientations (espicially since I am using 2n5457) and all is good. So, I measured my trans and I got the following measurements comp off at 20:
B C E
2 0.229 0.771 1
3 1.268 14.16 0.23
4 14.24 29.04 19.04
5 4.73         27.34 4.25
6 27.95 13.95 27.95
7 27.92 13.95 28.56
8 13.94 29.05 13.36
9 13.22 0         12.64
12 4.36         14.86 3.79
13 14.83 29.13 14.2
14 3.369 16.19 2.772
15 16.5         29         15

So, my problem is with Q2 -Q4, I checked the resistors coming from the power rail and all is good. I am not able to bias it because after 1/4 turn of output the needle quickly pins. What could possible be causing this?

 

[gswan]

Double-check your measurements and transistor types/polarity. There are several things amiss with these measurements.
Q9 E should be 0.6V above B voltage; Q14-C should be the same as Q15-B (they are tied) and your measurements show something different. There's also a difference between Q5-C and Q6-B. As for Q2/3/4, Q2-C and Q3-B should be the same, and Q2-E should be 0.6V lower than Q2-B.

Check for solder splashes and shorts, incorrect resistors, transistor polarities. Repeat the measurements referring to data sheets for your devices, since you may have some in backwards. Perform a simple Hfe test to confirm their pinout if unsure.

There is absolutely no point in connecting audio signals to a unit which is uncalibrated and untested.

 

[swal]

Thank you for the guidance gswan. I went through all caps, resistors and trans. Everything is in order. I also cleaned off all flux and the underside of the boards look good. I also re-sordered almost every connection.
This is what my measurements came up as:

B C E
2 0.772 1.264 0.233
3 1.264 14.42 1.12
4 14.42 29.16 19.21
5 4.75         27.43 4.28
6 27.43 14         28
7 28         14         28.64
8 14         29.16 13.38
9 12.69 0         13.38
12 4.35         14.82 3.79
13 14.82 29.16 14.2
14 3.371 15.63 2.772
15 15.63 29.16 16.22

So it looks like my voltages are off in Q2-Q4. Would this be causing oscillation and noise whenever I turn myoutput over 1/4?

Thanks for the help in advance.

 

[Echo North]

Did you use the t-pad/3837 input?  If so how did you implement it?  Did you add a load resistor?

Mike

 

[swal]

No, I used the electronically balanced input and wired as mnats guide for using Input Wiring Option A (electronically balanced input). One other thing I have noticed is when I keep Q Bias trimmer fully CW it doesn't go into oscillation, as soon as I turner the Q bias down 1/5 of a turner it goes into oscillation, if my ouput is at 1/4 or higher (36).

 

[warpie]

hey people, is this 4db loss (from 5k to 20k) normal?
To me it seems a considerable amount of gain loss.
I use electronically balanced input and an OEP for the output.
Any suggestions? 

 

[warpie]

Hi again,

after playing around with the termination resistor (R84) I managed to get a more even response (I used a 2k7 resistor).

Now I have another question... 

When calibrating the unit, do I have to measure 0.775V rms (0dbu) between pin 2 and 3 in my input or 1.22V (+4dbu)?
I realise that for the  Q bias adjustment it doesn't really matter but what about the GR adjustment?
I'm using my soundcard to produce the signal so it is balanced.

Thanks
w.

 

[shot]

Hi!

I saw new build manual on Gustav's website. It's nice. Very informative!

But I have rev 7 board, so my question is how much different is this newer board (V/K ed.) from my rev 7 board?

I'm about to start working on it, so I'm wondering is it better to just go and order V/K, or it's a small difference and I should stick with rev7?

thanks


Luka

 

[gyraf]

Please ignore - wrong thread!!

There is VERY small difference to the new version:

- extra R/C filter in psu
- extra +12V point for light and relays
- option for a simple sidechain filter insert (by a single switchable capacitor)

..all other is kept as always.

Jakob E.