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

[greggwhite]

Hello,
  I finished building the Rev F and am having problems.  First, should there be a three pin header and shunt for the Rev F? There wasn't one in the box or a spot marked for it on the PCB but the assembly instructions seem to indicate indicate it should have it. I think I assembled the kit otherwise just fine but now going to calibrate it I have zero output AC voltage on the meter.  I'm assuming I'm missing the header?  Thanks for your help.

 

[Echo North]

Hello,
  I finished building the Rev F and am having problems.  First, should there be a three pin header and shunt for the Rev F? There wasn't one in the box or a spot marked for it on the PCB but the assembly instructions seem to indicate indicate it should have it. I think I assembled the kit otherwise just fine but now going to calibrate it I have zero output AC voltage on the meter.  I'm assuming I'm missing the header?  Thanks for your help.

No there is no header in the F, you're fine.

You'll need to start running through this doc and find where the signal dies.  Run through all of the steps but I would suspect somewhere in #2 your signal will die.  You can use the Rev D values for these tests.

https://www.hairballaudio.com/blog/resources/post/fetrack-troubleshooting-guide

Post what you find and that will help narrow down the issue.

Mike

 

[greggwhite]

Thanks, I went through the guide and the Q-bias is fine but when I measure T1 I’m getting .072 VAC.  Is there a good way to narrow down if it’s Q1, the T-Pad, input transformer or something else?  The solder joints look fine on each. I appreciate the help!

 

[Echo North]

Thanks, I went through the guide and the Q-bias is fine but when I measure T1 I’m getting .072 VAC.  Is there a good way to narrow down if it’s Q1, the T-Pad, input transformer or something else?  The solder joints look fine on each. I appreciate the help!

That’s in the ballpark.  Keep going to TP15 and so on.

 

[greggwhite]

At TP15 I’m getting .01 to .03 VAC, that must be the problem area. .00 at TP17.

 

[Echo North]

At TP15 I’m getting .01 to .03 VAC, that must be the problem area. .00 at TP17.

So your problem is in the box labeled "Signal Preamp".

Reflow those solder joints, and check that all the components are correct.  Make sure you didn't get the 100Ω trimmer in that section mixed up with the 2K or 100K trimmer in the other section.

Mike

 

[greggwhite]

Ok, I went through and re-flowed everything, all the components seem correct and the trimmer is marked “101” which should be right. Still the exact same read at TP15. The area marked for C1 has two possible locations for the 1uF film cap, I have it in the slots nearer the front of the unit, could that be an issue?

 

[Echo North]

Ok, I went through and re-flowed everything, all the components seem correct and the trimmer is marked “101” which should be right. Still the exact same read at TP15. The area marked for C1 has two possible locations for the 1uF film cap, I have it in the slots nearer the front of the unit, could that be an issue?

You want that in the middle and yes that will kill your signal.

 

[greggwhite]

Got it! I do believe problem solved! I re-soldered C1 C9 and C10 and calibrated successfully. It was a silly mistake to think they had to be centered on one side of the traces, but I think what threw me and might trip up other folks is on the Revision F components list that I checked off as I went, the diodes are listed as being C1 C2 etc as opposed to the “CR” designation they get on the PCB. I thought that maybe I had to solder diodes in those places at some point as I went through the build and it led me to place the film caps on one side. Anyway, thanks so much for the help! I’ll run some audio through it and get back if I have any issues.

 

[greggwhite]

And yeah no luck. The meter is pinned all the way to the left with no input, when I do put audio through it 4:1 cuts out tons of bass, the other ratios sound fine.  The output knob also cuts out as you turn it, not in a scratchy pot sort of way, just sounds like something is deeply wrong. Frustrating. Should I be looking at the ratio card? 

 

[Echo North]

And yeah no luck. The meter is pinned all the way to the left with no input, when I do put audio through it 4:1 cuts out tons of bass, the other ratios sound fine.  The output knob also cuts out as you turn it, not in a scratchy pot sort of way, just sounds like something is deeply wrong. Frustrating. Should I be looking at the ratio card?

Nothing is deeply wrong, don't stress. I've repaired many of these, it always comes down to a bad joint or two (or 10) or a misplaced component. How confident are you in your soldering? Do you feel like it's clean and good?

I would start by reflowing weird looking joints and triple checking all your values and placements. Report back and we can start troubleshooting.  I would definitely check the ratio PCB, particularly the soldering and values of R22 and R42. Swapping say a 470Ω for a 470KΩ kind of stuff is common.

Also if you're interested:
https://www.hairballaudio.com/build-support-services

Mike

 

[greggwhite]

Thanks Mike, I am really pretty confident in my soldering, I built the Rev A kit back in 2014 with no problems and have handwired patchbays etc. All the joints should be ok and I worry about damaging components by re-heating them.

There’s nothing obvious that I can see. I think my best bet is to send it back to you guys to fix unfortunately.

 

[Echo North]

Thanks Mike, I am really pretty confident in my soldering, I built the Rev A kit back in 2014 with no problems and have handwired patchbays etc. All the joints should be ok and I worry about damaging components by re-heating them.

There’s nothing obvious that I can see. I think my best bet is to send it back to you guys to fix unfortunately.

Totally up to you. We'll get it up and running.

I won't be able to post troubleshooting stuff till late today/tomorrow am and it's kind of hard to think of what to test since you have that weird output pot thing happening.  You're still not passing signal?

Mike

 

[greggwhite]

It actually passes signal just fine besides the odd high pass at 4:1.  It only cuts out as I turn the output pot in either direction. I went ahead and packed it up and sent an email, I think having you give it the once over is worth the peace of mind for me.

 

[Diamondj421]

So I know that the FET/500's has a 2:1 ratio option but is it possible to mod a FET/RACK Rev D so that the ratios would be 2:1, 4:1, 8:1 and 20:1 like on the UA Anniversary Edition?

 

[Diamondj421]

Actually, after changing the wording of my search I found this schematic with the alternate resistor values. Would this be effective?

 

[ron_swanson]

I built a rev A unit a few months ago and all seems well, but over time the meter seems to have a hard time settling in.

When first fired up, in GR mode, no audio present, and cold, the needle shows 4-6dB of reduction - sometimes more - no matter which ratio is chosen.  During a good warming up period (30 minutes or so) the needle will slowly creep closer to 0dB, but often will never reach 0dB.  Changing ratios will sometimes return the needle to 0dB or close to that. 

I've tried recalibrating a number of times which seems to work for a time, but the drift will return over a few days or a week or so.

The unit seems to work fine otherwise ( I guess? ) , but I'd like to somehow fix this so the meter is more consistent.  I also built a Hairball rev F which doesn't do this.

Anyone have any suggestion of where to look for something like this? 

Thanks in advance,
Greg

 

[Echo North]

I built a rev A unit a few months ago and all seems well, but over time the meter seems to have a hard time settling in.

When first fired up, in GR mode, no audio present, and cold, the needle shows 4-6dB of reduction - sometimes more - no matter which ratio is chosen.  During a good warming up period (30 minutes or so) the needle will slowly creep closer to 0dB, but often will never reach 0dB.  Changing ratios will sometimes return the needle to 0dB or close to that. 

I've tried recalibrating a number of times which seems to work for a time, but the drift will return over a few days or a week or so.

The unit seems to work fine otherwise ( I guess? ) , but I'd like to somehow fix this so the meter is more consistent.  I also built a Hairball rev F which doesn't do this.

Anyone have any suggestion of where to look for something like this? 

Thanks in advance,
Greg

Is the board clean of flux?

Could also be an issue in your meter section obviously. Did it work normal at first? (minimal drift).

 

[Echo North]

Actually, after changing the wording of my search I found this schematic with the alternate resistor values. Would this be effective?

Ya that looks right to me.

If you look at the FET/500 Rev D schematic, which has a 2:1, you can see the math involved.

http://mnats.net/files/FET-D500.pdf

 

[Diamondj421]

Ya that looks right to me.

If you look at the FET/500 Rev D schematic, which has a 2:1, you can see the math involved.

http://mnats.net/files/FET-D500.pdf

Ok awesome. Is it possible to switch the off position on the attack knob to a slow attack time? I only ask because I find myself using the AE version of the plugin most between the 3 available through UAD.  Thanks as always!!!