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

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Ya wacky.

With the signal as described in the troubleshooting guide, your signal should be at the base of Q2.  You're saying you have signal at the drain (about 60mVAC) but nothing at the base of Q2?

Either:

-C1 is dead
-R8 is the wrong value or dead
-R9/C2 are dead
-A trace/pad between any of those is dead.

Mike
 
Hairball Audio said:
Looks like an older build.

Have you confirmed continuity in your cassis and to the IEC ground.

Resolved.  After swapping everything on the compressor, the problem was a nick in the signal wire coming out of the attenuation transformer that probably got jostled when adding the new caps and began touching shield foil around it.
The 60hz noise is from the stereo link jack being wired to the shield on the wire, creating a ground loop during the trouble shooting.  The 120hz was from the nick in the wire coming out of the attenuator
 
I just finished two FET/RACK REV F's. The calibration procedure doesn't seem to apply to this version other than the Q-Bias setting and the Distortion Trim setting, but no Meter Tracking Adjustment that makes sense for this rev. For example, the Rev F has an R54 Tracking Adjustment and an R16 Linearity trim which are not addressed in the cal procedure. There are also no jumpers on these boards. Is there another doc somewhere which I missed?

Rob
 
3dB said:
I just finished two FET/RACK REV F's. The calibration procedure doesn't seem to apply to this version other than the Q-Bias setting and the Distortion Trim setting, but no Meter Tracking Adjustment that makes sense for this rev. For example, the Rev F has an R54 Tracking Adjustment and an R16 Linearity trim which are not addressed in the cal procedure. There are also no jumpers on these boards. Is there another doc somewhere which I missed?

Rob

I'll update it today.  Ignore the null adjust it's not needed. Then trim the tracking the same as the Rev A or D.
 
The FET/RACK calibration guide has been update to include the Rev F.  Please post here if there is any confusion and I'll update accordingly.

Mike
 
Hello,

On my REV A Rack build  I inadvertently left off the plastic standoff for Q6.  I had already soldered and trimmed the leads when I realized this mistake. After learning it runs hot I decided to desolder the joints to get the plastic standoff on there. I trimmed the plastic standoff down on one side as there were little ridges, in an attempt to get the leads further down into the holes.. After resoldering, it appears the pad in the middle of Q6 when looking from the bottom of the PCB,  has been removed. The other two seem fine but I sure did a number on the bottom side. I cannot get any further solder on this middle joint, as the pad has been removed.

I have read on the forum it is possible to use a "jumper wire" when a pad comes off.  Is it possible on Q6 with the additional heat? I may need to order another Q6 transistor to get the leads to fully reach out of the bottom, then having to desolder yet again? I have stopped the build at this point, as I don't want to continue adding additional components until I know this is repairable. Looking at the schematic I am a bit confused as to what it would "jump" to, if this is even possible.

In my power supply section of the REV A, I have triple checked all wiring, resistor values, and polarity on everything. I can't seem to figure out why my unit won't read the proper DC voltage. I have a Fluke 117 set to the proper setting, V with one solid line and dashed line above it, to read DC volts. It is properly grounded and reads less than 0.2 resistance. When testing the common probe on the top panel mounting hole, touching CR8 reads 1.549 volts DC. Touching CR9 reads .154 volts DC.. It may be worth noting this value is the same with the "OFF" button selected, as well as the "GR" button.

I have built four Hairball Pre's with no problem! I am a bit embarrassed at all of my issues. Love the products and thanks so much for the help. Really did a number on this one!
 

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cmac said:
Hello,

On my REV A Rack build  I inadvertently left off the plastic standoff for Q6.  I had already soldered and trimmed the leads when I realized this mistake. After learning it runs hot I decided to desolder the joints to get the plastic standoff on there. I trimmed the plastic standoff down on one side as there were little ridges, in an attempt to get the leads further down into the holes.. After resoldering, it appears the pad in the middle of Q6 when looking from the bottom of the PCB,  has been removed. The other two seem fine but I sure did a number on the bottom side. I cannot get any further solder on this middle joint, as the pad has been removed.

I have read on the forum it is possible to use a "jumper wire" when a pad comes off.  Is it possible on Q6 with the additional heat? I may need to order another Q6 transistor to get the leads to fully reach out of the bottom, then having to desolder yet again? I have stopped the build at this point, as I don't want to continue adding additional components until I know this is repairable. Looking at the schematic I am a bit confused as to what it would "jump" to, if this is even possible.

In my power supply section of the REV A, I have triple checked all wiring, resistor values, and polarity on everything. I can't seem to figure out why my unit won't read the proper DC voltage. I have a Fluke 117 set to the proper setting, V with one solid line and dashed line above it, to read DC volts. It is properly grounded and reads less than 0.2 resistance. When testing the common probe on the top panel mounting hole, touching CR8 reads 1.549 volts DC. Touching CR9 reads .154 volts DC.. It may be worth noting this value is the same with the "OFF" button selected, as well as the "GR" button.

I have built four Hairball Pre's with no problem! I am a bit embarrassed at all of my issues. Love the products and thanks so much for the help. Really did a number on this one!

There should be traces coming from the middle pad of Q6 (base). They may be on the top of the PCB. In this case, looking at the schematic there should be continuity from the base of Q6 to the emitter of Q5 and that's it.  Look for continuity there. If there is no continuity you need to connect them with something like a 22AWG solid core wire.

Are you sure your fuse is inserted? Does your fuse looks like it might be blown?

Mike
 
Hairball Audio said:
There should be traces coming from the middle pad of Q6 (base). They may be on the top of the PCB. In this case, looking at the schematic there should be continuity from the base of Q6 to the emitter of Q5 and that's it.  Look for continuity there. If there is no continuity you need to connect them with something like a 22AWG solid core wire.

Are you sure your fuse is inserted? Does your fuse looks like it might be blown?

Mike

Thanks for the quick reply! Thanks for the help. To me the best news there is continuity! What a botched job but hey it appears to be working. Now with the power supply, I swapped out the fuse with the other 400 mw amp provided in the kit, still nothing. I also tried another power cable to just rule that out and nothing. At a loss, I have verified everything three times, going through my build.. Ill go through it all again tomorrow, any other suggestions are appreciated! Thanks again Mike, appreciate it.
 
We'll need  to measure the power supply section from start to finish to see where the issue is.  You'll want to be very careful while doing this, there is a dangerous level of V/I in this section.

To start, with the unit ON (GR Push switch IN). Measure your AC V between the Live and Neutral terminals at the IEC. You may have to pull back the connectors a little.

Mike
 
Hi Mike!

I built 2 units of 500/Rev D. So far so good... It's working properly, but for 2 things.

1st is the VU meter... I can't get to set -10 on the calibration process... The VR2 almost does nothing to the VU behavior...

The other thing is about the stereo link... when I plug the p2 cable in both units, one of the units reacts really weird. GR meter gets pinned to -9 varying a lil bit and it acts very weird, not properly. Any ideas?

Also, I kind of didn't understand how it works... It sums both sidechains? Or it's about the settings I do at one of the units that controls the other one?
Sorry for the newbie question... But it'd help me a lot to clarify this!

I'll come back with pics of the st link issue and maybe upload a video of the calibration thing...

Thanks very much!
 
Moved to FET/500 thread

https://groupdiy.com/index.php?topic=57192.0



guismarquesrj said:
Hi Mike!

I built 2 units of 500/Rev D. So far so good... It's working properly, but for 2 things.

1st is the VU meter... I can't get to set -10 on the calibration process... The VR2 almost does nothing to the VU behavior...

The other thing is about the stereo link... when I plug the p2 cable in both units, one of the units reacts really weird. GR meter gets pinned to -9 varying a lil bit and it acts very weird, not properly. Any ideas?

Also, I kind of didn't understand how it works... It sums both sidechains? Or it's about the settings I do at one of the units that controls the other one?
Sorry for the newbie question... But it'd help me a lot to clarify this!

I'll come back with pics of the st link issue and maybe upload a video of the calibration thing...

Thanks very much!
 
Hairball Audio said:
We'll need  to measure the power supply section from start to finish to see where the issue is.  You'll want to be very careful while doing this, there is a dangerous level of V/I in this section.

To start, with the unit ON (GR Push switch IN). Measure your AC V between the Live and Neutral terminals at the IEC. You may have to pull back the connectors a little.

Mike

Alright, I went through the entire power supply section, following the guide piece by piece. I missed soldering the four pins on the off button! I must have attached the connectors and simply missed soldering these four pins during the build. The devil is in the details, always something to learn in DIY. I have a completed Rev A Rack unit, powers on and looks great.  Just need to calibrate. Thanks for the help Mike!
 
Building Rev A kit and power supply test shows 50 volts at the zener 30 volt check point. Don't see anything obvious that would cause this.  Any ideas?
 
mixguy said:
Building Rev A kit and power supply test shows 50 volts at the zener 30 volt check point. Don't see anything obvious that would cause this.  Any ideas?

Most obvious cause would be the voltage selector switch is set to the wrong setting for your mains.  Double check that.

Also make sure we wired your 7 pin connector correctly. Should be whit/blk/blu/red check it against the picture in the guide.

Report back.

Mike
 
Everything is wired correctly. Just grasping at straws but if the switch is manufactured wrong and 115v and 230V are reversed will it damage my circuit if I switch it to 230V and it is correct and supplies 230V?
 
mixguy said:
Everything is wired correctly. Just grasping at straws but if the switch is manufactured wrong and 115v and 230V are reversed will it damage my circuit if I switch it to 230V and it is correct and supplies 230V?

I’d be fine, but it’s not that.

I’ll be back in a bit (might be tomorrow) and we’ll go through testing the supply.  If you scroll back I think someone have the same issue a while back. We walked through it.

Mike
 
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