Can't get signal to pass. Calibration was good

[crossleyacoustics]

Hello All,

We purchased and assembled few Seventh Circle kits for one of our clients and they are looking to install tomorrow, so hopefully we can figure this out!

We built two N72's exactly the same way, side by side. It appears that we have version 3.3 of everything except for the instructions.

Symptoms

Both boards exhibit the exact same symptoms, so I'm guessing it must be something related to the version update.

The symptoms are that signal won't pass. If we feed a high level signal through the preamps and crank the gain and trim way up we hear what appears to be very faint signal bleed but that's it.

What we tried

-We did the calibrations from the instructions and everything went well. The voltages and resistances matched what was prescribed.
-We installed L3-L6
-We tested continuity between Blue and Violet of the output transformer to Conn2 and both passed.
-Measured voltages at all of the transistors (both boards were similar). Here is one:

Q1: C 3.9 | B 2.5 | E 1.96
Q2: C 13.25| B 3.95 | E3.3
Q3: C 2.19 | B 13.23 | E 12.63
Q4: C 6.14 | B .849 | E.311
Q5: C 22.2 | B 6.11 | E 5.57
Q6: C 22.2 | B 5.69 | E 5.08

Here are some photos of the build of one board:

https://www.flickr.com/photos/128988300@N07/

Any thoughts on next troubleshooting steps?

Thanks for your help!

Matt

[Randyman...]

Just a shot in the dark:

What XLR output pins are you measuring/listening across? Likely obvious, but being transformer balanced, you need to test output across XLR Pins 2 and 3 (and not from 2 to 1 or 3 to 1).

If you use pin 1 and 2 (or 1 and 3) you won't complete the circuit at the output transformer, and you only hear a faint signal as described (this also happens when incorrectly interfacing these preamps into an unbalanced input using SCA Pins 1+2 - and that topic seems to pop up frequently).

Probably not that simple of a fix, but worth a mention

[crossleyacoustics]

Thanks for your shot in the dark!

We were actually sending a balanced signal into the preamp and listening directly out of a balanced monitor that worked perfectly with the A12's we built. I used a test tone on a cable tester and also tried two microphones; all of which didn't work.

To clarify, the signal isn't really a faint signal. it's essentially no signal until I pump a line level signal into the preamp and crank the gain and trim all the way up, at which point the slightest bit of bleed is heard due to the high gain.

Thanks!