On calibrating MNATS 1176 Rev J...

Hi there

I've tried but failed to find a easy to understand calibration procedure, so I'm hoping I'd ask my question on a new thread and will be summarizing the procedure for this particular board.

I've finished stuffing components in the board and made the relevant connections according to the MNATS wiring guide (big thanks to MNATS for doing the board and the wiring guide.)

I've checked all DC BIAS on all transistor and they seem to line up more or less, however I'm struggling when calibrating.

1)  When asked to input a signal @ 0.775mV, I used Pro Tools to generate a 1k sin wave and measured the output voltage from pin 1 and 2 on the XLR.  Is this correct or do I have to half the value because it's a balanced connection?

2) When turning the Q-Bias, the output voltage is changing very slowly, I had to wait up to 30 seconds for the voltage to stabilize, is this correct?  And it seems I could never find the place where it would drop 1db, it'd stop at a very high value (2.75V) and then I keep turning and turning and nothing happens and then I reach a point for it starts to  goes down VERY SLOWLY but will do way past the 1db mark.

Is this correct?!

Is there any obvious problem one can derive from the situation?

Many thanks,

Jyc

jyc said:

I've checked all DC BIAS on all transistor and they seem to line up more or less, however I'm struggling when calibrating.

1)  When asked to input a signal @ 0.775mV, I used Pro Tools to generate a 1k sin wave and measured the output voltage from pin 1 and 2 on the XLR.  Is this correct or do I have to half the value because it's a balanced connection?

Click to expand...

You should really be posting in the "All things G1176 thread".

You should have .775 VAC between pins 2 and 3, retry the calibration with the proper reference level and repost.

Mark

careful with those values guys, it's 0.775VAC. Not mVAC!

http://www.sengpielaudio.com/calculator-db-volt.htm

Kingston said:

careful with those values guys, it's 0.775VAC. Not mVAC!

http://www.sengpielaudio.com/calculator-db-volt.htm

Click to expand...

You're absolutely right!

I thought about this when I got up this morning and came here to correct it.

Mark

I tried again, took me quite a while to find the time. 

I replaced the R81 with Bourns 3296Y, measured the input voltage to be at 0.775VAC (not mVAC), however, this time, it's even more weird.  No matter which way I turn, the output voltage doesn't change .

Any clues?  Last time I've checked DC Bias on all of the Qs they're close enough to the values.

Jyc.

jyc said:

I tried again, took me quite a while to find the time.  

I replaced the R81 with Bourns 3296Y, measured the input voltage to be at 0.775VAC (not mVAC), however, this time, it's even more weird.  No matter which way I turn, the output voltage doesn't change .

Any clues?  Last time I've checked DC Bias on all of the Qs they're close enough to the values.

Jyc.

Click to expand...

Hello, to do the calibration, just shunt (connect) pins 1 and 3, this will connect the reversed signal goes to ground, so measure and inject the signal between pin 2 (hot) and 1+3 (GND)... actually u are unbalancing the signal hard way, hehehehe... so use it to make the calibration.

regard the info in gyraf's page... is quite easy... remember that 1176 attack and release's pot work in reverse, I mean, the fastest position is in CW position, the slowest in CCW... all the settings are explained in Gyraf's page...
take some attention to this:

0dBVU -> +4dBu -> aproximately 1,28VAC
just to you not to be interrogated why you're injecting 0,775VAC (0dBu) and the VU's pointer don't reach the "0" on the VU meter

Hope it helps!

Cheers,

Eddie

Have you followed the calibration video on MNats site?

http://mnats.net/1176_revision_d.html#videos

Mark

Biasrocks said:

Have you followed the calibration video on MNats site?

http://mnats.net/1176_revision_d.html#videos

Mark

Click to expand...

This actually is just for the 1176 Rev D, but why not just take a look??

Cheers,

Eddie

SaMpLeGoD said:

This actually is just for the 1176 Rev D, but why not just take a look??
Eddie

Click to expand...

The QBias adjustment applies equally to all the revisions, not sure about the meter adjustment.

Mark