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

[Echo North]

Make sure your voltage selector switch is set right.

115 - Americas
230 - EU

 

[ganymedestudios]

I did have it set incorrectly. Weird, I could've swore I followed those instructions early on in the process thoroughly. The cathode is now reaching 29.75 V, however the Diode is sitting around 0V though. Thank you for all the help, I appreciate it.

 

[Echo North]

I did have it set incorrectly. Weird, I could've swore I followed those instructions early on in the process thoroughly. The cathode is now reaching 29.75 V, however the Diode is sitting around 0V though. Thank you for all the help, I appreciate it.

So your negative voltage still isn't sitting right?

Confirm all the diodes and 2 1K resistors are soldered correctly and the diodes are pointing in the correct directions.

Mike

 

[ganymedestudios]

I made sure the 1K resistors are correctly soldered and the diodes and now the voltage for the -10V diode is spiking from +6V to +0.5V.

 

[Echo North]

I made sure the 1K resistors are correctly soldered and the diodes and now the voltage for the -10V diode is spiking from +6V to +0.5V.

Ohhhhhh your whole board is stuffed.  i though you just had the power supply in.

That changes things.  You may have an error in your build dragging down the neg supply or a damaged component. So you were getting -6V DC now you're getting +6V DC to +0.5 V DC?

Mike

 

[ganymedestudios]

Yeah, sorry I thought I mentioned that in the first post. That's why I brought up the broken trace that I had fixed, thinking that might be the cause of it. Sorry for the confusion but now the -10V diode seems to be sitting right on 0 or -0.1 or so.

 

[Echo North]

Yeah, sorry I thought I mentioned that in the first post. That's why I brought up the broken trace that I had fixed, thinking that might be the cause of it. Sorry for the confusion but now the -10V diode seems to be sitting right on 0 or -0.1 or so.

That trace is a concern, there are a few traces between those two components. However, I don't think any of them sit on the neg rail so I don't think it would be the cause.

It's really hard to say. I'd have to look at.

You could check around R35, R60, and the Qbias for shorts or bad values. Check anything that sits near the negative rail. These neg rail issues ones are tough.  I assume you built and tested the supply first and it tested fine, at this point you need to double check all of your component values, placement, soldering etc.

You could always try replacing CR9 as a hail mary. That would probably be where I'd start if you sent it in.

Mike

 

[ganymedestudios]

Actually I did not check the power supply before populating the rest of the board so I suppose thats something I messed up.  I'll keep messing with it a little bit and if I can't figure it out, I'll probably just end up sending it in and learning my lesson for the next time I do this build.

 

[Echo North]

Actually I did not check the power supply before populating the rest of the board so I suppose thats something I messed up.  I'll keep messing with it a little bit and if I can't figure it out, I'll probably just end up sending it in and learning my lesson for the next time I do this build.

Ya it's critical to test the supply first.

 

[bazmcc]

Hi all,

Just completed the build but having a couple of issues when beginning to cal the unit. I have an experienced tech friend who has looked at it but I have a couple of questions;

- When measuring VAC/dBU across the input XLR, my friend's Audio Precision sig gen / meter measures a drop of approx 7dBU as soon as I plug into the 1176, even when not powered up. Seems to be something like a dead short but beep testing across points suggests everything is good and there are no shorts. Any advice?

- Should the input transformer measure 50 ohms between XLR input points 2 & 3?

Thanks all!

 

[Echo North]

Hi all,

Just completed the build but having a couple of issues when beginning to cal the unit. I have an experienced tech friend who has looked at it but I have a couple of questions;

- When measuring VAC/dBU across the input XLR, my friend's Audio Precision sig gen / meter measures a drop of approx 7dBU as soon as I plug into the 1176, even when not powered up. Seems to be something like a dead short but beep testing across points suggests everything is good and there are no shorts. Any advice?

- Should the input transformer measure 50 ohms between XLR input points 2 & 3?

Thanks all!

When you don't have the AP plugged into anything it's unloaded. As soon as you plug it into the FET/RACK (powered or not) it now has a load.  Loading the signal generator will lower its output.  It's really a factor of the output impedance of the AP vs the input impedance of the FET/RACK that determines the signal drop.

If you want to lower this effect, lower the output impedance of the AP as much as you can (50Ω). You will not completely get rid of it though. You can still see a drop of 1 to 2dBu.

When you measure the resistance between 2 and 3 you're measuring the DC resistance which is different than AC impedance (which is higher). 50Ω of DC R on the primary sounds about right.

Mike

 

[mrbobbailey]

I'm on the build of my 2nd RevA FET Rack and just finished building the power supply.  The first unit went well, though I've not calibrated it yet.  On this build I'm getting:

- IEC Inlet = 0.2 ohms as expected
- cathode of CR8 = +30V DC as expected
-  CR9 = -41.65V DC where I should have -10V

I double checked the C9 solder and it seemed fine.  I then tested the two 1K resistors (R81, R82).  I'm not getting a reading from R82.  Do I need to de-solder or anything to get a proper read?  R81 came back fine.  I think R82 is faulty.  Would that cause the faulty diode reading at C9?

 

[Echo North]

I'm on the build of my 2nd RevA FET Rack and just finished building the power supply.  The first unit went well, though I've not calibrated it yet.  On this build I'm getting:

- IEC Inlet = 0.2 ohms as expected
- cathode of CR8 = +30V DC as expected
-  CR9 = -41.65V DC where I should have -10V

I double checked the C9 solder and it seemed fine.  I then tested the two 1K resistors (R81, R82).  I'm not getting a reading from R82.  Do I need to de-solder or anything to get a proper read?  R81 came back fine.  I think R82 is faulty.  Would that cause the faulty diode reading at C9?

Best option would be to lift one leg on R82 off the PCB then test the Ω across the 2 legs.  You should get the 1K reading.

 

[mrbobbailey]

I'm on the build of my 2nd RevA FET Rack and just finished building the power supply.  The first unit went well, though I've not calibrated it yet.  On this build I'm getting:

- IEC Inlet = 0.2 ohms as expected
- cathode of CR8 = +30V DC as expected
-  CR9 = -41.65V DC where I should have -10V

I double checked the C9 solder and it seemed fine.  I then tested the two 1K resistors (R81, R82).  I'm not getting a reading from R82.  Do I need to de-solder or anything to get a proper read?  R81 came back fine.  I think R82 is faulty.  Would that cause the faulty diode reading at C9?

Best option would be to lift one leg on R82 off the PCB then test the Ω across the 2 legs.  You should get the 1K reading.

Thank you.  I did that and got 1K as expected.  I did get a bit of a pop when removing my DMM probe.  That leads me to a new question.  How do I discharge the board when taking it out to continue work on it?  I hope that hasn't damaged anything.

And back to the original question: What else should I test regarding the -41.65V DC reading on CR9?

 

[Echo North]

Thank you.  I did that and got 1K as expected.  I did get a bit of a pop when removing my DMM probe.  That leads me to a new question.  How do I discharge the board when taking it out to continue work on it?  I hope that hasn't damaged anything.

And back to the original question: What else should I test regarding the -41.65V DC reading on CR9?

You can connect the across the terminals of the power supply caps with some insulated wire in series with a higher W resistor. Like 10K/5W. You can think about the charge across the power caps and relation to ohms law to make sure you have a reasonable W resistor that will work.

There are some other methods (insulated screwdriver) but I'll let you google that and decide for yourself if you think that's safe.

Seems like you're measuring closer to what the unregulated/dropped voltage would be directly off the secondary on the neg rail. You're using the chassis as your ground reference? You have all 3 L-Brackets securing the PCB to the enclosure (some of these have an grounding function)?

What is your DC voltage on all 4 of the 1K resistor pads?

Mike

 

[mrbobbailey]

You can connect the across the terminals of the power supply caps with some insulated wire in series with a higher W resistor. Like 10K/5W. You can think about the charge across the power caps and relation to ohms law to make sure you have a reasonable W resistor that will work.

There are some other methods (insulated screwdriver) but I'll let you google that and decide for yourself if you think that's safe.

Seems like you're measuring closer to what the unregulated/dropped voltage would be directly off the secondary on the neg rail. You're using the chassis as your ground reference? You have all 3 L-Brackets securing the PCB to the enclosure (some of these have an grounding function)?

What is your DC voltage on all 4 of the 1K resistor pads?

Mike

Thanks for the quick reply, Mike!  Brilliant!  I don't know why, but I only secured 2 of the l-brackets.  I'll be that is it.  Thank you.

 

[Echo North]

Thanks for the quick reply, Mike!  Brilliant!  I don't know why, but I only secured 2 of the l-brackets.  I'll be that is it.  Thank you.

Nice!

 

[mrbobbailey]

Seems like you're measuring closer to what the unregulated/dropped voltage would be directly off the secondary on the neg rail. You're using the chassis as your ground reference? You have all 3 L-Brackets securing the PCB to the enclosure (some of these have an grounding function)?

What is your DC voltage on all 4 of the 1K resistor pads?

Mike

Unfortunately that was not it.  Still measuring -45V range

4 Pads
R81 = -45.17 & -45.13
R82 = -45.36 & -45.19

 

[Echo North]

Unfortunately that was not it.  Still measuring -45V range

4 Pads
R81 = -45.17 & -45.13
R82 = -45.36 & -45.19

You're not dropping any voltage across your resistors which would mean you're not drawing current on your negative rail.  I would suspect the zener diode (CR9).  Confirm it's soldered well, the pads look good, and it's oriented correctly. If all that looks good you may want to replace it. Email me for a new one.

Mike

 

[Manswikenmo]

Hi!
I just finished my two FET/RACK rev A kits. One is working perfectly and sounds amazing, but the other one is behaving really strange.. I have checked so that all the resistors, transistors, caps etc is at the right place in the right way and compared with the compressor that is working, there is no visual difference between the two.

The problems are as follows:
- The unit passes adio and the sound quality is good, no distortion or strange frequency response, but the signal is quite low.

- There is no compression happening what so ever.

- Also the meter is acting strange. In +8 and +4 mode it works fine, but in GR mode the meter stays at -20 even with "R71" full CW. When switching from "normal operation" to "calibration operation" the meter reaches -3 with R71 full CW.

- I haven't been able to do any of the three calibration steps.
Step 1: When I am adjusting the Q-bias (R59) nothing happens.
Step 2: With R75 full CCW and R71 full CCW I measure 0,922V across TP10/TP11. With R71 full CW and R75 full CCW I measure 1,379V.
Step 3: Since the meter stays at -20 in "normal operation" its not possible to do this step. And as written before, there is no compression going on.

I measured the voltages at the transistors and compared to your document, around Q12 and Q13 it looks REALLY strange but at the other places it seems quite ok. The PDF is attached, my measurements is in green.

Anyone have an idea of what could be the problem? Since everything is soldered the same way in the one not working as in the one that works my guess is that some component is broken, but witch one??

Any help is really appreciated!

Kindly
/Måns