1176 clone problem Hairball Audio FET/RACK Old Version

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juscar

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Joined
Aug 18, 2017
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I'm having a problem with an 1176 clone FET/RACK Old Version

After building it, I'm trying to calibrate it according to this link:
http://www.hairballaudio.com/blog/resources/build-guides/calibration

Starting at the first test - Q Bias, when I apply a 1KHz tone at 0dBu (0.775VAC), I'm supposed to see 2.75VAC at the output but I'm only seeing less than 1VAC. So something is wrong. I've checked the power supply and I am getting 30V from VR1.
Any advice on what to do next?

Here's a schematic.
http://mnats.net/files/1176REVD_VOLTS.pdf
Thanks! J
 
Welcome.

> what to do next?

Get the board out in the light with a magnifier and check every solder joint.

Go through the little red DC Volt numbers on the schematic and verify none are way-wrong.
 
Apply a 1 KHz O dBu signal to the input and confirm with your DMM between pin 2 and 3 of the input XLR.  Now move your DMM to the output XLR and measure AC between pin 2 and 3.  Adjust the output control to read +11dBu (2.75 VAC) on your DMM at the output. Slowly turn the Q-bias adjust (R59) CW until a drop of 1 dB occurs, and your DMM reads +10 dBu (2.44 VAC).  This places your gain reduction FET Q1 slightly into conduction. 

Did you adjust the output control to read 2.75vac?  There wasn't a mention of it so I figured I'd ask....

 

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