Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1560 on: December 15, 2018, 04:36:57 PM »
This is crazy. Retested and now 30v test point is now .015V and Cr9 is .56 V

You got all 3 L Brackets tight and secure?  They are part of the grounding.

What is your DC on either of this 1/2W 1k ohm Rs?

Mike
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mixguy

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1561 on: December 16, 2018, 01:26:48 PM »
Brackets are tight. Voltage at the resistors is  .32v

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1562 on: December 16, 2018, 01:29:46 PM »
Brackets are tight. Voltage at the resistors is  .32v

30 VDC rail is still good?

Try testing CR9 in circuit with the diode tester function on your DMM.

POWER OFF.

Mike
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mixguy

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1563 on: December 16, 2018, 01:40:41 PM »
Reading is 1.12 reversed it is over scale.

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1564 on: December 16, 2018, 01:45:02 PM »
Reading is 1.12 reversed it is over scale.

What is your AC V at the each of the orange wires at the power tx secondary.  Power On, use caution.
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mixguy

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1565 on: December 16, 2018, 02:02:45 PM »
No voltage

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1566 on: December 16, 2018, 02:08:26 PM »
No voltage

No AC on either lead w/ power on?

But you have 30V DC at that test point?  Wacky.

Maybe try referencing them against the yellow lead.
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mixguy

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1567 on: December 16, 2018, 02:12:23 PM »
No the 30v rail is .015V and Cr9 is .56 V

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1568 on: December 16, 2018, 02:15:06 PM »
No the 30v rail is .015V and Cr9 is .56 V

Do you have 120 VAC across your L and N terminals on your IEC inlet?  Be careful, and you might have to pull the terminals back a little to measure.
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mixguy

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1569 on: December 16, 2018, 02:24:58 PM »
Thanks Mike. The fuse was not properly seated. Now all voltages are correct. Unbelievable how it's the simplest things that trips you up sometimes. Thanks again.


Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1570 on: December 16, 2018, 02:26:17 PM »
Thanks Mike. The fuse was not properly seated. Now all voltages are correct. Unbelievable how it's the simplest things that trips you up sometimes. Thanks again.

Glad you found it! I'm taking the rest of the day off ;)

Mike
Hairball Audio, LLC
DIY Parts and Kits
https://hairballaudio.com

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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1571 on: December 22, 2018, 01:20:51 PM »
Definitely something in your GR Meter Driver Amp section.  You've been through that a few times?

Mike

Just wanted to give an update that all is well. I did the calibration over several times, and it turns out that I wasn't picky enough with the null adjust. Hopefully this helps someone...then there will be some sort of redemption for my sheepish posture.

mixguy

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1572 on: December 23, 2018, 12:59:41 PM »
Mike I just wanted to say thanks again for the help . I have a UA 1176 and I like the sound of this build better.

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1573 on: January 13, 2019, 12:35:30 PM »
Nice job guys!
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cmac

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1574 on: January 24, 2019, 01:53:14 PM »
Hello,

I have a bult Rev A Rack unit, properly calibrated and was running some tracks through. To me it sounds like a very high pitched DC noise of sorts when turning up the output. Also, the low end was completely out of the passed signal, like a high pass filter.
- Checked proper grounding of rack, its fine
- Power Supply section A ok.
- Q bias voltage checked out perfectly
When checking the Amplification stage, the AC readings were quite less than published on the troubleshooting guide
       - TP1  -  0.071
       - TP15 - 2.896
       - TP17 - 0.356
       - BRWN T - 5.54
       - Output  -   5.53

Since I did check the Qbias volts before doing the Amplification Stage check, I didn't know if referencing the Unbiased numbers listed in the Amplification stage check was correct?
It should also be noted I did a number on the PCB when soldering Q6. The middle pad fell off, I measured the continuity as listed in your previous reply, and it checked out.

"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."

If the low readings in the amplification stage could be related I am willing to try the 22AWG gauge if it seems necessary? As always, thanks for the help!



Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1575 on: January 25, 2019, 02:42:23 PM »
Hello,

I have a bult Rev A Rack unit, properly calibrated and was running some tracks through. To me it sounds like a very high pitched DC noise of sorts when turning up the output. Also, the low end was completely out of the passed signal, like a high pass filter.
- Checked proper grounding of rack, its fine
- Power Supply section A ok.
- Q bias voltage checked out perfectly
When checking the Amplification stage, the AC readings were quite less than published on the troubleshooting guide
       - TP1  -  0.071
       - TP15 - 2.896
       - TP17 - 0.356
       - BRWN T - 5.54
       - Output  -   5.53

Since I did check the Qbias volts before doing the Amplification Stage check, I didn't know if referencing the Unbiased numbers listed in the Amplification stage check was correct?
It should also be noted I did a number on the PCB when soldering Q6. The middle pad fell off, I measured the continuity as listed in your previous reply, and it checked out.

"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."

If the low readings in the amplification stage could be related I am willing to try the 22AWG gauge if it seems necessary? As always, thanks for the help!

Ya could be a lot of things.  I would check continuity through the 2 amp stages and hard wire anything damaged.

Also run that same test above with like a 200Hz signal and 10KHz signal and see where they start to differ.

Mike
Hairball Audio, LLC
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https://hairballaudio.com

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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1576 on: February 21, 2019, 12:40:22 AM »
Hi guys,
I'm having an issue on a Rev. D build. I was able to do everything, from Q Bias setting to Null Adjust and - 10 vu meter reduction. Problem is that when I patch the compressor, with or without compression active, the sound is completely without bass. Sound is only on mid frequencies. Where could I start troubleshooting?

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1577 on: February 21, 2019, 02:00:55 PM »
Hi guys,
I'm having an issue on a Rev. D build. I was able to do everything, from Q Bias setting to Null Adjust and - 10 vu meter reduction. Problem is that when I patch the compressor, with or without compression active, the sound is completely without bass. Sound is only on mid frequencies. Where could I start troubleshooting?

I would triple check all of your capacitors values, particularly the small blue ones in the amp sections.

Report back.

Mike
Hairball Audio, LLC
DIY Parts and Kits
https://hairballaudio.com

Top secret stuff and upcoming releases:
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Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1578 on: February 22, 2019, 05:27:31 AM »
I would triple check all of your capacitors values, particularly the small blue ones in the amp sections.

Report back.

Mike
You mean the small blue ceramic caps?

Hairball Audio

Re: [BUILD] New FET/RACK Official Help Thread - Please read first post!
« Reply #1579 on: February 22, 2019, 11:21:37 AM »
You mean the small blue ceramic caps?

Yes sir.

In general, check all of the components in the line and signal amp boxes.  A mis-placed cap and/or resistor can make a high pass filter.

Mike
Hairball Audio, LLC
DIY Parts and Kits
https://hairballaudio.com

Top secret stuff and upcoming releases:
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