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

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ratty_7 said:
Seems like bad solder joints on input pot on Unit B the readings are now....

20 = 381.9
12 = 189.1
  8 = 128.3
  4 =    66.8

 

So can you calibrate now?  Is either unit working?
 
Hi guys.
Just finished my second 1176 rev d rack build and I am glad to say the unit is working well with one small concern.
Compared to my other slightly older first gen build and to my vintage Urei unit, the input gain seems to be quite high. I have completed the calibration and the output seems to be  all good. But i seem to need very little gain to reach the compression threshold compared to the other units.  The input pot is right at the bottom of its travel and the output is high.
Could I have wired the input pot/pad wrong?
Seems to me that there is very little between the input and the q1 so perhaps I am not attenuating the input enough.

I have a very decent set of external meters for calibration and testing so I am certain that I am delivering +4dbm to the input.

As I say the unit otherwise is working perfectly. It is just that running the input down that low does not give me much flexibility of movement.
Normally I would run the input pot at around the 11 o'clock position. However on this unit it seems to want to run around  the 7 o'clock position  to produce the same gain reduction results.

Any insights would be much appreciated

Richard
 
RspenceT said:
Hi guys.
Just finished my second 1176 rev d rack build and I am glad to say the unit is working well with one small concern.
Compared to my other slightly older first gen build and to my vintage Urei unit, the input gain seems to be quite high. I have completed the calibration and the output seems to be  all good. But i seem to need very little gain to reach the compression threshold compared to the other units.  The input pot is right at the bottom of its travel and the output is high.
Could I have wired the input pot/pad wrong?
Seems to me that there is very little between the input and the q1 so perhaps I am not attenuating the input enough.

I have a very decent set of external meters for calibration and testing so I am certain that I am delivering +4dbm to the input.

As I say the unit otherwise is working perfectly. It is just that running the input down that low does not give me much flexibility of movement.
Normally I would run the input pot at around the 11 o'clock position. However on this unit it seems to want to run around  the 7 o'clock position  to produce the same gain reduction results.

Any insights would be much appreciated

Richard

Hi Richard,

One difference between your FET/RACK and a vintage unit...the input pot (t-pad attenuator) on the original units had a very odd taper. It’s not a taper you commonly see in potentiometers today. Your input attenuator has a more common taper, which leads it to be a little “hotter” earlier in the clockwise pot turn. Even compared to out old blue T-pad.

That said 7 o'clock seems low.  I suspect it's a combination of the hot input pot and our meter having a little more over shoot than the originals.  They have $150 meter in them, we decided not to go that route.  We feel like out meter is 90% as good at a fraction of the cost.

The meter should be a little more accurate in the full CW position and should show you less compression. Hard to say what is right because I don't know what your input level is compared to ours.

Mike

Mike
 
Got ahead of myself and started a new thread before reading this thread!!  Sorry, I'll post my issue once again.


Just finished the build, cleaned up the wiring, calibrated, all is fine.  As soon as I attempt to test with a real track, I find that engaging the attack DRAMATICALLY reduces the output.  Also turning the output up past 24 results in a pop and nasty interference, pretty much with no output.  Completely reset the trim pots and tried calibration again, voltages on the money.  Same issue persists.  With the attack off, signal is fine until the same output threshold is reached, then the pop and noise is there once again.  Everything on the PCB looks fine, nothing is melting, no smoke.

Help?
 
I got through 99% of the build this weekend on a pair of Rev. Ds.  Amazing instructions, BTW.  A couple of quick questions:

Question 1 - Build Guide says there will be a pair of 2n3707 transistors that are taped together because they have been matched, to use for Q12 and Q13.  Neither of my kits had a pair taped together, so I avoided putting any 2n3707s in for now - do I need to try and match the transistors myself, or are they all close enough to use any 2?

Question 2 - I put in header pins for the match pair of FETs for Q1 and Q11.  Instructions say to put the FETs in the header pins and solder.  Is this correct?  I should solder the FETs in the headers?  Want to make sure this is not a typo.

Thanks!  Can't wait to finish these puppies!
 
ashtonv19 said:
Got ahead of myself and started a new thread before reading this thread!!  Sorry, I'll post my issue once again.


Just finished the build, cleaned up the wiring, calibrated, all is fine.  As soon as I attempt to test with a real track, I find that engaging the attack DRAMATICALLY reduces the output.  Also turning the output up past 24 results in a pop and nasty interference, pretty much with no output.  Completely reset the trim pots and tried calibration again, voltages on the money.  Same issue persists.  With the attack off, signal is fine until the same output threshold is reached, then the pop and noise is there once again.  Everything on the PCB looks fine, nothing is melting, no smoke.

Help?

Pretty stumped on this one.

If it calibrated normally, and the voltages are normal, it should work fine. However, what you are describing is not at all normal.

Check all the connector headers, especially the 6 pin, for shorts or bad joints. Make sure the pcb has been cleaned of flux.

Mike
 
tkobrick said:
I got through 99% of the build this weekend on a pair of Rev. Ds.  Amazing instructions, BTW.  A couple of quick questions:

Question 1 - Build Guide says there will be a pair of 2n3707 transistors that are taped together because they have been matched, to use for Q12 and Q13.  Neither of my kits had a pair taped together, so I avoided putting any 2n3707s in for now - do I need to try and match the transistors myself, or are they all close enough to use any 2?

Question 2 - I put in header pins for the match pair of FETs for Q1 and Q11.  Instructions say to put the FETs in the header pins and solder.  Is this correct?  I should solder the FETs in the headers?  Want to make sure this is not a typo.

Thanks!  Can't wait to finish these puppies!

Q1: Weird, not sure what happened there. If you have a meter with a HFE function, use that to match them. If not just try a random pair. If you can calibrate the meter, all is good. If not send us an email.

Q2: That is a type-0...do not solder the FETs in the pins.

Mike
 
Hairball Audio said:
Pretty stumped on this one.

If it calibrated normally, and the voltages are normal, it should work fine. However, what you are describing is not at all normal.

Check all the connector headers, especially the 6 pin, for shorts or bad joints. Make sure the pcb has been cleaned of flux.

Mike

The only real struggle I had with a JST was CN10, I could barely get the leads halfway through the PCB.  There was no kink in the outside leads as the build guide suggested.  So perhaps that's the culprit.  All the other headers dropped in nicely.
 
ashtonv19 said:
The only real struggle I had with a JST was CN10, I could barely get the leads halfway through the PCB.  There was no kink in the outside leads as the build guide suggested.  So perhaps that's the culprit.  All the other headers dropped in nicely.

So does the attack and release daughter board fit ok?

Do you get the weird noise with the unit in GR off mode?

Mike
 
Hairball Audio said:
So does the attack and release daughter board fit ok?

Do you get the weird noise with the unit in GR off mode?

Mike

The attack/return board fits fine, nothing is being strained.  CN10 is sitting 1 or 2mm off the PCB. 

Yes, I get the noise in any configuration regardless of meter, ratio, or attack/release, even with no signal present.  I can try to record a sample and send it later.
 
ashtonv19 said:
The attack/return board fits fine, nothing is being strained.  CN10 is sitting 1 or 2mm off the PCB. 

Yes, I get the noise in any configuration regardless of meter, ratio, or attack/release, even with no signal present.  I can try to record a sample and send it later.

I doubt it would help to hear it.

With a 1K/0dB tone at the input, set your unit to:

in and out at 12 o'clock
attack in GR OFF
release FCW
20:1
Meter: GR

What is your AC V at TP1, TP15, TP17 and out + with respect to ground (chassis).

Mike
 
Mike,
    Thank you,  you were right, it was two separate issues.  And I got the meter working, I was a little sloppy with my solder and created a short.  That's fixed.
I thought everything was fine and got it calibrated with no problem, but realized when I twisted the Output knob, while in +4 or +8 meter mode,  the needle bounces.    All with The rumble is still there.

BTW, I have another working unit, to compare readings.
So, I checked the resistance on the R23 output resistor and it shows odd readings
It reads maximum around 38K ohms, but my working unit reads 128K ohms.
Another anomaly is,  the C7 Orange Drop capacitor reads 15VDC on one side and 2VDC on the other
My working unit reads 15VDC and 0VDC .
I was wondering if the Orange Drop is bad or the R23 potentiomenter is bad.

What do you think?  I hope all that makes sense.

Thanks,
Chris

Hairball Audio said:
Sounds like you have 2 issues.

Issue 1: Meter sits left in GR mode, is most likely an issue with your GR AMP section.
Issue 2: Rumble. No idea...are you passing signal?  How did calibration go?

Mike
 
YoDudeRock said:
Mike,
    Thank you,  you were right, it was two separate issues.  And I got the meter working, I was a little sloppy with my solder and created a short.  That's fixed.
I thought everything was fine and got it calibrated with no problem, but realized when I twisted the Output knob, while in +4 or +8 meter mode,  the needle bounces.    All with The rumble is still there.

BTW, I have another working unit, to compare readings.
So, I checked the resistance on the R23 output resistor and it shows odd readings
It reads maximum around 38K ohms, but my working unit reads 128K ohms.
Another anomaly is,  the C7 Orange Drop capacitor reads 15VDC on one side and 2VDC on the other
My working unit reads 15VDC and 0VDC .
I was wondering if the Orange Drop is bad or the R23 potentiomenter is bad.

What do you think?  I hope all that makes sense.

Thanks,
Chris

That rumble is probably DC getting into the pot then. You shouldn't have DC in your pot, C7's job is to block that DC on the side. Though just because you have DC at the pot side of C7 it doesn't necessarily mean the DC is coming through the cap.  It could be come "backwards" from another location.

Do you get the rumble in GR OFF mode? (attack FCW)

Mike
 
Hello all,

So I finished the build and went to power up and it doesn't turn on. After building the power supply I tested it with my DMM following the build guide and the readings were accurate to what they should be. Now as I'm trying to trouble shoot they don't read the same, and I'm not sure why, nor do I really know where to begin, so what do I do? Thanks!
 
Jacob123588 said:
Hello all,

So I finished the build and went to power up and it doesn't turn on. After building the power supply I tested it with my DMM following the build guide and the readings were accurate to what they should be. Now as I'm trying to trouble shoot they don't read the same, and I'm not sure why, nor do I really know where to begin, so what do I do? Thanks!

You said it doesn't turn on but you were able to test the voltages accurately?  That would not be possible.

Confirm your fuse is in and not blown, confirm your voltage select switch is set correctly, confirm your DMM is set to AC V.

Mike
 
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