[BUILD] 1176LN Rev D DIY

[babaorum]

yes all negative values

 

[Echo North]

yes all negative values

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

 

[babaorum]

ok thanks I'll try it.

 

[babaorum]

First problem when I want to do Qbias adjustement. Vu meter doesn't move when I switch bet<ween GR and GR off (lowest in left)

 

[Echo North]

First problem when I want to do Qbias adjustement. Vu meter doesn't move when I switch bet<ween GR and GR off (lowest in left)

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.

 

[babaorum]

Ok but That is my problem in fact. Input = 5 => I can just to put the output level at 0.579V (AC) at maximum level ...
I think I have a gain pb. (0dB signal on Input XLR -> 0.780Vac)

 

[Echo North]

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

 

[JingleDjango]

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?

 

[Echo North]

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?

Yes

 

[JingleDjango]

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)

 

[Echo North]

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)

R29, R30 and C11 are the right values?  CR1 is the right orientation?

Is the comp acting weird?

Mike

 

[JingleDjango]

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

 

[Echo North]

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?

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

 

[Echo North]

http://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-resistor-color-code-4-band

 

[JingleDjango]

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:

Okay, here's the scoop.
>I'm running the test tone (1kHz) out from Ableton Live through a line out from my Focusrite Saffire Pro 40 at  ~0.775VAC (closer to 0.78VAC).
>into the input of my compressor unit
>feeding the output back into the interface. I believe that using a TRS plug like I have into the XLR/1/4" jack will bypass the mic preamp.

I get an audible signal back, which I'm taking as a sign of progress, though this whole endeavour is starting to try my patience! Can't wait to get it working. . .

The signal is very quiet. 0.18-0.20VAC. Despite being this low, the signal also sounds distorted.

I'm keeping the input dial set to 24.
If I turn the output down to 48, the distortion is no longer audible but the signal is so low I have to really drive the gain on the input and turn up my monitors to hear it.
Between 30-24, the signal is distorted but audible, increasing in volume as I turn the dial.
There is an abrupt step up in volume (and distortion) when the dial hits 18.

I don't know if this is relevant, but if I hit the off switch while the tone is going, there is an abrupt jump up in volume before the machine runs out of juice and it fades to silent.

Does this help anyone interpret my signal at all?

Thanks again for your guidance.

 

[Echo North]

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:

Okay, here's the scoop.
>I'm running the test tone (1kHz) out from Ableton Live through a line out from my Focusrite Saffire Pro 40 at  ~0.775VAC (closer to 0.78VAC).
>into the input of my compressor unit
>feeding the output back into the interface. I believe that using a TRS plug like I have into the XLR/1/4" jack will bypass the mic preamp.

I get an audible signal back, which I'm taking as a sign of progress, though this whole endeavour is starting to try my patience! Can't wait to get it working. . .

The signal is very quiet. 0.18-0.20VAC. Despite being this low, the signal also sounds distorted.

I'm keeping the input dial set to 24.
If I turn the output down to 48, the distortion is no longer audible but the signal is so low I have to really drive the gain on the input and turn up my monitors to hear it.
Between 30-24, the signal is distorted but audible, increasing in volume as I turn the dial.
There is an abrupt step up in volume (and distortion) when the dial hits 18.

I don't know if this is relevant, but if I hit the off switch while the tone is going, there is an abrupt jump up in volume before the machine runs out of juice and it fades to silent.

Does this help anyone interpret my signal at all?

Thanks again for your guidance.

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]

Will do. Cheers.

 

[Echo North]

If you have a spare, switch out that transistor. It maybe blown.

Mike

 

[JingleDjango]

I might be able to find some around town. I'm gonna go hunting.

 

[JingleDjango]

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.