Well, I finished up my first 1176 using Gustav's boards with the "Hitchhiker" cut and the perimeter ground buss wire mods. It's quiet and passes signal, but I'm not sure it's working correctly. I've been trying to calibrate it and wonder if I'm doing something wrong as I can't seem to get the GR Meter Tracking Adjustment to happen.
Here's what I've done so far:
Q-Bias Adjustment
I used the following instructions (don't know who wrote it, but I think it was Dean):
The proper adjustment of this trimmer is made like this:
Input a weak signal, around -10dB or something and measure the AC output level without gain reduction. I did this using a 250Hz signal at .3 volts.
Set the attack and release controls fully clockwise, the ration to 1:4, and the output level to max. Turn the input level so you get something readable, like 100mV on your voltmeter on your output. I did this exactly as written.
Now adjust the Q-Bias trimmer until you have a 1dB drop in output level. That's it. I adjusted the trimmer until the output voltage stabilized at 89mV. Is this right? Also, is the Q-Bias adjustment kind of finicky? When I start with it fully CCW, I have to turn it fully CW and then after a bit the level starts to drop. I then move it back towards the middle of its range and can dial in the correct final drop then. What do you think?
GR Meter Tracking Adjustment
Set ratio to 1:20, set meter to bypass. Input a 1kHz, 50mV signal. Set input level to ~12 o'clock. Set output level so you get 50mV at the ouput also (now you have unity gain). Now set the meter switch to "GR." Slowly turn up the level of your input signal (at the signal source, not with the input level control) while you monitor both input and output levels with a voltmeter.
Now here's where it gets weird for me:
When you reach a point where the output level is half the input level, you have a 6dB of gain reduction in the unit. How many volts are we talking about here? My output voltage doesn't really start lagging until I get a pretty hot signal in the input. Where should the input and output voltages be when they reach this 2:1 ratio? BTW, I'm using the stock wiring setup on the output tranny.
Power Supply Voltages:
Primary: 118 VAC
PCB: 30.5 VDC and -9.8 VDC
Here are the voltages I measured for each transistor:
E B C
Q2--.51--1.03--1.83
Q3--1.20--1.83--11.85
Q4--11.36--11.96--30.5
Q5--4.41--4.87--28.7
Q6--29.3--28.7--14.47
Q7--30--29.3--14.47
Q8--13.84--14.47--30.5
Q9--13.80--13.19--0.0
Q12--2.38--2.88--9.75
Q13--9.17--9.76--30.5
Q14--1.62--2.17--10.69
Q15--10.15--10.69--30.5
Any help would be greatly appreciated.
Cheers,
:guinness: :sam: :guinness: :sam:
Don
