[BUILD] New FET/RACK Official Help Thread - Please read first post!

[Echo North]

Mike,

Just wanted to report that Active Stereo link works very well in my tests with program material. Using just tone is not a great indicator of whether or not it is functioning properly. Both compressors seemed to track the same and it definitely sounded like both sides were being compressed equally.

My one question is, since the new PCBs don't have holes drilled on all four corners, how you would recommend mounting directly to a different chassis for stereo builds? I guess one could rig up some sort of support for the side that does not have mounting holes. That was the one of the first things I thought of when building the units.

Again, the new rack compressor kits are killer!  I'll post some notes a little later that may be helpful for people building these units. Or it may not be helpful.

Thanks!

Paul

That's funny, I had the same issue in testing.  I can't believe I forgot to mention it earlier.  Ya the sine wave just tracks poorly, I suspect it may be a phase issue in the summing amp but who knows.  I pulled my hair out over it for a few days until I used actually program material and got much better results. I like it too.

For stereo builds we're still recommending the older boards for now. However, as you've mentioned, with a little ingenuity you could get these working in a dual build.

Mike

 

[RR25]

Hi Mike and everyone else,

I have just built a Rev A (new version) and everything seemed to be going pretty well until calibration step 3.

The power supply test results were +30.13V DC and -9.18V DC, I was able to get the 1dB drop during Q bias calibration and I was measuring 0.00V DC across TP10 / TP11 for the null adjust step.

Unfortunately when I try to put the unit into compression to complete the meter tracking adjustment I am only able to achieve 0.4dB of gain reduction.
The only thing I can see is that might be an issue is that my voltages for Q2 and Q3 are low. (all other transistor voltages are very close to spec)

Q2.
G - 0.66V DC
S - 2.04V DC
D - 2.09V DC

Q3
G - 1.55V DC
S - 2.10V DC
D - 20.5V DC

Any help would be much appreciated.

Cheers,

 

[ebenchristensen]

1776 rev A v1.12

Conditions:
Sending 0.775VAC into input XLR
W/ GR meter in "off" position
qBias pot in any rotation does not change voltages.
TP1:0.000VAC
TP15:0.007VAC
TP17:0.000
Out+:0.016VAC

 

[Echo North]

1776 rev A v1.12

Conditions:
Sending 0.775VAC into input XLR
W/ GR meter in "off" position
qBias pot in any rotation does not change voltages.
TP1:0.000VAC
TP15:0.007VAC
TP17:0.000
Out+:0.016VAC

What's your VAC at the input transformer pin 1?

 

[Echo North]

Hi Mike and everyone else,

I have just built a Rev A (new version) and everything seemed to be going pretty well until calibration step 3.

The power supply test results were +30.13V DC and -9.18V DC, I was able to get the 1dB drop during Q bias calibration and I was measuring 0.00V DC across TP10 / TP11 for the null adjust step.

Unfortunately when I try to put the unit into compression to complete the meter tracking adjustment I am only able to achieve 0.4dB of gain reduction.
The only thing I can see is that might be an issue is that my voltages for Q2 and Q3 are low. (all other transistor voltages are very close to spec)

Q2.
G - 0.66V DC
S - 2.04V DC
D - 2.09V DC

Q3
G - 1.55V DC
S - 2.10V DC
D - 20.5V DC

Any help would be much appreciated.

Cheers,

Try this:

Input/output: Mid Way
release/attack: full CW
Ratio: 20
Meter: GR

Feed and confirm a 0.775VAC 1K signal measuring between input XLR + and -.

No measure these TPs using chassis as your common.

TP22 - Measure for AC for all ratios and list them.
TP21 - Measure for DC for all ratios and list them.

Mike

 

[ebenchristensen]

same conditions as stated above

input trans pin 1 is 0.006VAC

 

[Echo North]

same conditions as stated above

input trans pin 1 is 0.006VAC

Carefully remove Q1. Do you get VAC at any of those TPs with Q1 removed?

Mike

 

[mnats]

Hi Mike and everyone else,

I have just built a Rev A (new version) and everything seemed to be going pretty well until calibration step 3.

The power supply test results were +30.13V DC and -9.18V DC, I was able to get the 1dB drop during Q bias calibration and I was measuring 0.00V DC across TP10 / TP11 for the null adjust step.

Unfortunately when I try to put the unit into compression to complete the meter tracking adjustment I am only able to achieve 0.4dB of gain reduction.
The only thing I can see is that might be an issue is that my voltages for Q2 and Q3 are low. (all other transistor voltages are very close to spec)

Q2.
G - 0.66V DC
S - 2.04V DC
D - 2.09V DC

Q3
G - 1.55V DC
S - 2.10V DC
D - 20.5V DC

Any help would be much appreciated.

Cheers,

You wrote Rev A but those voltages correlate much closer to voltages on the Rev D. Keep in mind that Q3 on the Rev A is a bipolar transistor and so has a base, emitter and collector. In any case, if those voltages are being accurately measured it suggests that the signal preamp isn't working properly. But you also said that you were able to calibrate for a 1 dB drop.

Do your output levels seem right (very hot)? Are you measuring your input level on the test points provided behind the XLR on the main PCB (this ensures the measurement points are under load)? Are you using pins 2 and 3 as the input, rather than connecting one lead to ground?

If those voltages are accurate it would be worth checking components around those transistors for value, shorts, poor joints etc.

 

[ebenchristensen]

Same conditions as above, removing Q1 completely.

TP-1:  0.000VAC
TP-15: 0.000VAC
TP-17: 0.000VAC
Out+:  0.002(+/-)0.001VAC

 

[Echo North]

Same conditions as above, removing Q1 completely.

TP-1:  0.000VAC
TP-15: 0.000VAC
TP-17: 0.000VAC
Out+:  0.002(+/-)0.001VAC

Your signal is dying like immediately after the input.

So you have 0.775 VAC between input + and -, but nothing between input tx pin 1 or pin 4 and the chassis???

Is your tpad fully soldered?  Check all 9 tpad solder pads carefully.

Mike

 

[ebenchristensen]

For clarification: Fet Rack A v1.12

I'm uncertain what you met by tpad (though I have found that in the older revision builds). Sorry for the hassle, but could you please clarify?

 

[Echo North]

For clarification: Fet Rack A v1.12

I'm uncertain what you met by tpad (though I have found that in the older revision builds). Sorry for the hassle, but could you please clarify?

The 3 deck input pot.

 

[ebenchristensen]

re-floated all the soldering, and followed the testing conditions with .775 in etc etc and still showing zeros.

 

[Echo North]

re-floated all the soldering, and followed the testing conditions with .775 in etc etc and still showing zeros.

Reflow the input XLR.

Then with 0.775 VAC at the input (between 2+3). Measure for AC (chassis as common) for all 9 pins on the T-Pad.


7 8 9
4 5 6
1 2 3
output pot this way->
SHAFT/Front Panel HERE

 

[ebenchristensen]

      7                  8                9 
(0.764)    (0.766)    (0.762)
    4                  5                6
(0.006)    (0.766)    (0.766)
    1                  2                3
(0.768)    (0.766)    (0.769)

            (front of Unit)

 

[Spaceyjb]

Voltages are meaningless unless you specify AC or DC.

First things first.  Get the Qbias calibration working.  All the calibration steps must be completed in order and each one must been done correctly before moving on.

Read my response to ebenchristensen 2 posts above. Same steps for you.

Mike

Thanks Mike,
It was just poor soldering jobs on two pads. I should have looked closer at first time.  You made great job first with kits and here as well.  I read everything and it helped me a bit to understand whats going in there.
Thanks
Jan

 

[Echo North]

      7                  8                9 
(0.764)    (0.766)    (0.762)
    4                  5                6
(0.006)    (0.766)    (0.766)
    1                  2                3
(0.768)    (0.766)    (0.769)

            (front of Unit)

And your input is mid way? Doesn't make any sense.

Can you safely remove your input transformer?

Mike

 

[ebenchristensen]

Conditions:
0.775 VAC measured at (+) & (-) XLR input
Ratio: 20 /Metter "Off"
Input dial half way / Output dial halfway
Attack off (full CCW) / Release full CW

Pad VAC measurements are as follow:

      7                  8                9 
(0.205)    (0.207)    (0.033)
    4                  5                6
(0.001)    (0.207)    (0.188)
    1                  2                3
(0.219)    (0.207)    (0.782)

            (front of Unit) >Output knob


At this point I feel like I'm taking crazy pills, as this isn't one I reported yesterday.

 

[Echo North]

Conditions:
0.775 VAC measured at (+) & (-) XLR input
Ratio: 20 /Metter "Off"
Input dial half way / Output dial halfway
Attack off (full CCW) / Release full CW

Pad VAC measurements are as follow:

      7                  8                9 
(0.205)    (0.207)    (0.033)
    4                  5                6
(0.001)    (0.207)    (0.188)
    1                  2                3
(0.219)    (0.207)    (0.782)

            (front of Unit) >Output knob


At this point I feel like I'm taking crazy pills, as this isn't one I reported yesterday.

What about input tx pin 4?  That's on the ame side as pin 1...at the opposite end of the row.

Mike

 

[ebenchristensen]

Getting

0.032 VAC


Q1 is still removed (per your recommendation ) btw