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

[StudioJakubka]

Don't worry about the other stuff. Those other points may not even have DC or are relevant. It just confuses the fact finding process.

What is your DC on either side of R60?

R60 -1.014, -1.015

 

[Echo North]

R60 -1.014, -1.015

that should be -1ish and -1.5ish on either side of R60.  You should be seeing around -1 to -1.7ish at pad 18 with rotation of the bias.

Are you sure R60 and R83 are the correct value of resistor? Triple check. If they are reflow those and the trimmer joints.

Mike

 

[ebenchristensen]

Well, an update, to what I thought was going to be my last post here.

The unit continues to blow fuses, to the level that I went to a 400mA slow blow so that I could even test anything, or attempt a calibration. After trying to calibrate even the q-bias (which I was getting a reading on the xor out only while turning the output dial) the unit bricked. Now I am getting voltages half of what they should be, regardless of the situation.

Refloated the soldering, checked all connections, etc. etc. At this point I am about to erase it in concrete and throw it in the river.

Any ideas?

 

[Echo North]

Well, an update, to what I thought was going to be my last post here.

The unit continues to blow fuses, to the level that I went to a 400mA slow blow so that I could even test anything, or attempt a calibration. After trying to calibrate even the q-bias (which I was getting a reading on the xor out only while turning the output dial) the unit bricked. Now I am getting voltages half of what they should be, regardless of the situation.

Refloated the soldering, checked all connections, etc. etc. At this point I am about to erase it in concrete and throw it in the river.

Any ideas?

Where are you located? You should use a 200mA slo blo for 240 regions and a 400mA for 120 regions.  Never increase the fuse,  if they are blowing at the correct level, something is wrong.

Did you build and test the power supply before stuffing the rest of the PCB as shown in the guide? Did it test fine then?

Don't toss it in the river,  we offer flat rate build repair.

Mike

 

[ebenchristensen]

...Saved from the river.


Everything on the power side tests out fine (as stated before). I am at the recommended fuse level and following the calibration steps. I am sending 0.775 in, and I am registering nothing on the output test points. In fact, the only voltage showing are when the output dial is turned. Are there sectional test points? Something that could be glaringly obvious?

 

[Spaceyjb]

I have judti finished REV A. And this time I am getting into troubles. It seems that none of the q-bias and tracking trims are working. With Null trim I was able to set voltage in between TP 10/11 to 0,002V. Unit compresses but I am not able to adjust VU tracking. I have checked all the leads which seems fine.
I have measured following voltages acros the board:

PSU: 30.63/-9.78
TP 7, 19 =-9.53V
TP 15, 17, 22=0V
TP 18, 21=-9.78

At the R60 ( -9.7/-9.72)
At the R35 (25.79/30.52)

It is beyond my experience to see where I should look at.

Thanks a lot

Jan

 

[Potato Cakes]

Mike!

The new kits are awesome! I was able to build two Rev A's in about the same time it used to take me to build one! And the new chassis is very sexy, very professional looking. I got both of them built up and calibrated without any issue.

The only I have to figure out is the active stereo link. Disconnected both units seen to performing as they should. With the active link engaged, they are about 4-5 dB off on the metering, and this tracks when either compressor's input controls are adjusted (yes, I have checked to make sure one is send and the either is receive). I also confirmed this discrepancy by metering the XLR outputs. I had calibrated both units twice just make sure I didn't make a mistake there, so I guess I just have to see if there is swapped component on the active link card, unless there is something else I don't know about or if there is a super secret procedure I am not aware for setting both compressors for stereo linking.

Again, awesome work. I look forward to doing more of these.

Thanks!

Paul


Thanks!

Paul

 

[mnats]

Are there sectional test points? Something that could be glaringly obvious?

Have you read the FAQ linked from the first post? Blowing fuses suggests excessive current draw. It may be able to be traced by finding which points show the greatest deviation from the typical voltages at various test points on the schematic that matches your revision.

 

[ebenchristensen]

I had overlooked this! My apologies.

 

[Echo North]

...Saved from the river.


Everything on the power side tests out fine (as stated before). I am at the recommended fuse level and following the calibration steps. I am sending 0.775 in, and I am registering nothing on the output test points. In fact, the only voltage showing are when the output dial is turned. Are there sectional test points? Something that could be glaringly obvious?

You're signal is most likely not making it through the two pre and line amp stages. 

Set the input and output at 12 o'clock. GR turned off. 20:1. Release full CW. Feed a 0.775VAC 1K signal at the input. Qbias full CW. Which ever end of the qbias gives you the largest signal at TP 15.

What is your VAC (using chassis as common) at TP:

-TP 1
-TP 15
-TP 17
-OUT +

AC for each.

Mike

 

[Echo North]

Mike!

The new kits are awesome! I was able to build two Rev A's in about the same time it used to take me to build one! And the new chassis is very sexy, very professional looking. I got both of them built up and calibrated without any issue.

The only I have to figure out is the active stereo link. Disconnected both units seen to performing as they should. With the active link engaged, they are about 4-5 dB off on the metering, and this tracks when either compressor's input controls are adjusted (yes, I have checked to make sure one is send and the either is receive). I also confirmed this discrepancy by metering the XLR outputs. I had calibrated both units twice just make sure I didn't make a mistake there, so I guess I just have to see if there is swapped component on the active link card, unless there is something else I don't know about or if there is a super secret procedure I am not aware for setting both compressors for stereo linking.

Again, awesome work. I look forward to doing more of these.

Thanks!

Paul


Thanks!

Paul

Thanks! MNATS and I worked hard on it.

Read the last section of the active link build guide.  About adjusting the in/out/attack for proper tracking.

Mike

 

[Echo North]

I have judti finished REV A. And this time I am getting into troubles. It seems that none of the q-bias and tracking trims are working. With Null trim I was able to set voltage in between TP 10/11 to 0,002V. Unit compresses but I am not able to adjust VU tracking. I have checked all the leads which seems fine.
I have measured following voltages acros the board:

PSU: 30.63/-9.78
TP 7, 19 =-9.53V
TP 15, 17, 22=0V
TP 18, 21=-9.78

At the R60 ( -9.7/-9.72)
At the R35 (25.79/30.52)

It is beyond my experience to see where I should look at.

Thanks a lot

Jan

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

 

[Potato Cakes]

Thanks! MNATS and I worked hard on it.

Read the last section of the active link build guide.  About adjusting the in/out/attack for proper tracking.

Mike

Reading? Who has time for that?

I thought it somewhere easy to find. I have been suffering from an epic bout of laziness since I got home from the road.

Thanks!

Paul

 

[Potato Cakes]

Thanks! MNATS and I worked hard on it.

Read the last section of the active link build guide.  About adjusting the in/out/attack for proper tracking.

Mike

One last question. Maybe...

Is the 4-5dB difference that I am seeing on the output as described in the last part of the Active Link guide within the range one would typically see? Also, there is a slight difference between where the input knobs need to be set for there to be similar (not linked) gain reduction when using a 1kHz tone. I take that is probably due to the tolerance range of the potentiometers.

One thing I would probably recommend and I will do myself next time is use multi turn trimmers for bias and null adjustments, as the single turns make it hard if you really want to be precise (less than 1 mV). I know it's not necessary to be that accurate, but if you're slightly OCD like me, you'll want to have the finer level of control when making adjustments. And if you plan on traveling with them as I do, I think the adjustments will stay in place better when the unit is moved around in a road case.

Thanks!

Paul

 

[Echo North]

One last question. Maybe...

Is the 4-5dB difference that I am seeing on the output as described in the last part of the Active Link guide within the range one would typically see? Also, there is a slight difference between where the input knobs need to be set for there to be similar (not linked) gain reduction when using a 1kHz tone. I take that is probably due to the tolerance range of the potentiometers.

One thing I would probably recommend and I will do myself next time is use multi turn trimmers for bias and null adjustments, as the single turns make it hard if you really want to be precise (less than 1 mV). I know it's not necessary to be that accurate, but if you're slightly OCD like me, you'll want to have the finer level of control when making adjustments. And if you plan on traveling with them as I do, I think the adjustments will stay in place better when the unit is moved around in a road case.

Thanks!

Paul

Right, all the pots are 20% tolerance parts, which is pretty significant.  You could confirm the units are working correctly by testing the max output. Send like a -30dbu signal (0.025 VAC) and with GR off set the in/out to max.  You should see like 40-45db of gain.

There are definitely pros and cons to the multi-turns. Single turns are a lot easier for newer builders to grasp.  But yes harder to dial in perfect.

Thanks!

Mike

 

[Potato Cakes]

Thanks for confirming that for me.

I'm definitely getting tons of gain, much more than I could use. Cranked all the way open with a 1 kHz tone, I can really make the output transformers sing.

Thanks again for yours and MNAT's awesome work. Looking forward to your next projects.

Thanks!

Paul

 

[Echo North]

Thanks for confirming that for me.

I'm definitely getting tons of gain, much more than I could use. Cranked all the way open with a 1 kHz tone, I can really make the output transformers sing.

Thanks again for yours and MNAT's awesome work. Looking forward to your next projects.

Thanks!

Paul

One thing about the trimmers and moving the units.  You can always put a dab of locktite where the trimmer meets the trimmer body to hold it.

 

[[email protected]]

Hi -

My first FET Rack build.  Quick question I noticed instead of two 200pF Blue Caps, I have 220pF caps instead. Are those okay to use in place for C3 and C6 on the REV D?  Or do I need to fill out a missing order form?

Thanks

Elisa

 

[Echo North]

Hi -

My first FET Rack build.  Quick question I noticed instead of two 200pF Blue Caps, I have 220pF caps instead. Are those okay to use in place for C3 and C6 on the REV D?  Or do I need to fill out a missing order form?

Thanks

Elisa

Hi Elisa,

That was a deviation we made at Hairball.

200pF used to be a more standard value. They have become harder and harder to fine and when you do they are expensive and in low stock. We moved to the more standard 220pF.

As MNATs has stated the original used a mica 220pF there is you want to hunt a couple down. Honestly I don't think it would make any difference.

Mike

 

[Potato Cakes]

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