[BUILD] 1176LN Rev D DIY
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Echo North
Well-known member
babaorum said:
Your circuit seems fine.
Set it to the most negative setting (-3V) then go through the qbias section rotating back to 0V. If that doesn't work (checking the output with a DMM) you may have a bad FET.
Mike
Echo North
Well-known member
babaorum said:
Don't worry about the VU meter right now. Let's tackle one issue at a time. Use this procedure:
Here is how we set it at Hairball. Set the controls as follows.
Input = “24″ mid rotation
Output = “24″ mid rotation
Attack = full CCW (switched to off position)
Release = full CW
Compression ratio = 20:1
Meter mode = “GR”
Q-bias adjustment = full CCW
Shorting pin in “normal position” connecting the two pins closest to Q13
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.
Echo North
Well-known member
Hmmmm. I would start by checking your DC voltages as described here:
http://mnats.net/files/1176REVD_VOLTS.pdf
These voltages are for a fully calibrated unit so some in the meter section might be a little off, but compare and see what you find then report back.
Mike
http://mnats.net/files/1176REVD_VOLTS.pdf
These voltages are for a fully calibrated unit so some in the meter section might be a little off, but compare and see what you find then report back.
Mike
JingleDjango
Well-known member
Mike, or anyone:
I am following along here and testing my VDC against the PDF linked. Am I right in thinking that the common lead of my meter should be on the power CT, and the red probe will wander to the points indicated by the schematic?
I am following along here and testing my VDC against the PDF linked. Am I right in thinking that the common lead of my meter should be on the power CT, and the red probe will wander to the points indicated by the schematic?
Echo North
Well-known member
JingleDjango said:
Yes
JingleDjango
Well-known member
Thank you. Moving from top left to top right, everything is normal until I hit Q5.
I'm getting 27.2VDC at the collector, 22VDC at the emitter, 14.2VDC at the base.
(I let the unit warm up for 30 min, meter switch set to GR, no input)
I'm getting 27.2VDC at the collector, 22VDC at the emitter, 14.2VDC at the base.
(I let the unit warm up for 30 min, meter switch set to GR, no input)
Echo North
Well-known member
JingleDjango said:
R29, R30 and C11 are the right values? CR1 is the right orientation?
Is the comp acting weird?
Mike
JingleDjango
Well-known member
CR1 is in right.
C11 is a little blue ceramic cap. I'm having a really hard time reading the value on it.
R29 is correct (I THINK!) Beige 4-band Violet>Red>Green>Gold
R30 I'm not so sure how to identify. When I was stuffing the board I tested each resistor with my meter before placing them and did not rely on the colour codes because frankly they confuse me. The code on this one is: Violet>Green>Blue>Orange>Brown
C11 is a little blue ceramic cap. I'm having a really hard time reading the value on it.
R29 is correct (I THINK!) Beige 4-band Violet>Red>Green>Gold
R30 I'm not so sure how to identify. When I was stuffing the board I tested each resistor with my meter before placing them and did not rely on the colour codes because frankly they confuse me. The code on this one is: Violet>Green>Blue>Orange>Brown
Echo North
Well-known member
You have to learn to read the codes. Measuring with a meter is hit or miss above 10K depending on the meter.
For R29 your saying you have a 7.2M which we don't even send. I think you have a 1.2M which is right (brown, red, green, gold)
R30 should be 150K which is brown, green, black, orange, brown.
What is the issue with your comp?
For R29 your saying you have a 7.2M which we don't even send. I think you have a 1.2M which is right (brown, red, green, gold)
R30 should be 150K which is brown, green, black, orange, brown.
What is the issue with your comp?
JingleDjango said:
Echo North
Well-known member
http://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-resistor-color-code-4-band
JingleDjango
Well-known member
Thanks. I'm reading up on the colour codes now. It's night-time and I'm using a reading lamp to light my workspace. I guess I've been interpreting the brown bands as violet. These resistors are the correct value.
As best as I can make out, C11 is the correct 10pF (it reads "100")
The issue with the compressor is detailed above:
Thanks again for your guidance.
As best as I can make out, C11 is the correct 10pF (it reads "100")
The issue with the compressor is detailed above:
JingleDjango said:
Thanks again for your guidance.
Echo North
Well-known member
JingleDjango said:
Ya I'm not sure what you have going on there. I need to take some time off, but you could look back through the threads where I walk people through tracing the signal level through the gain stages. Or keep looking at the section around the funny transistor.
Mike
JingleDjango
Well-known member
Will do. Cheers.
Echo North
Well-known member
If you have a spare, switch out that transistor. It maybe blown.
Mike
Mike
JingleDjango
Well-known member
I might be able to find some around town. I'm gonna go hunting.
JingleDjango
Well-known member
I got some new transistors (2n3707) from a shop in town. I swapped a new one into place but the values are exactly the same. Looks like the transistor wasn't the issue but I'm happy I could rule it out.
