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

[mnats]

Across R74 with shunt in "normal" position is -0.1dcV or so
Q12 base: -1.95 dcV
Q13 base: -2.06 dcV

R75 FULL CCW
Q12 Base:-1.95 dcV
Q13 Base: 0 dcV

R75 FULL CW
Q12 base: -1.96 dcV
Q13 base: -3.52 dcV

But with the VU meter zeroed and the shunt removed the voltage across R74 is 0.00, right?

With the shunt still removed and the meter at zero with 0.00v across R74 measure both sides of R70 relative to chassis ground. Measure both sides of R68 and R69. Please report your voltages.

 

[junkface]

But with the VU meter zeroed and the shunt removed the voltage across R74 is 0.00, right?

With the shunt still removed and the meter at zero with 0.00v across R74 measure both sides of R70 relative to chassis ground. Measure both sides of R68 and R69. Please report your voltages.

ya the R74 reading is 0.00dcv with the meter zeroed and jumper in "not normal" or removed
keeping shunt in that position, i get the following readings
R70 -4.43dcV / -2.84dcV
R68 -2.53dcV / -2.84dcV
R69 -2.64dcV / -2.84dv

 

[junkface]

Gah, in an unrelated Rev A build, I'm also having a power supply issue. Was getting a hissing sound from that section, and what originally spec'd out (-10V and 30V) went down to basically nothing. Tried replacing the caps ( i figured the hissing might be coming from a bad one, not sure what axials do when they blow/fail) but the same sound came from the new ones as well. They supplied the proper voltages for a second but now again I'm getting next to nothing voltage wise at the test points. Nothing looks or tests burnt but something is obviously awry.
Should I just replace every component in the power supply?  I think I have all the parts, the only one I don't have the specs for is the diode at the 30v test point.

 

[mnats]

Gah, in an unrelated Rev A build, I'm also having a power supply issue. Was getting a hissing sound from that section, and what originally spec'd out (-10V and 30V) went down to basically nothing. Tried replacing the caps ( i figured the hissing might be coming from a bad one, not sure what axials do when they blow/fail) but the same sound came from the new ones as well. They supplied the proper voltages for a second but now again I'm getting next to nothing voltage wise at the test points. Nothing looks or tests burnt but something is obviously awry.
Should I just replace every component in the power supply?  I think I have all the parts, the only one I don't have the specs for is the diode at the 30v test point.

Not enough information to diagnose but replacing every component is like throwing good money after bad. Have you built the power supply first as recommended in the build guide or have you populated the entire board? If fully populated, did you test the supply first? Have you checked the fuse (you don't check it for 'burnt' but for continuity). Show a picture of the power supply.

 

[mnats]

ya the R74 reading is 0.00dcv with the meter zeroed and jumper in "not normal" or removed
keeping shunt in that position, i get the following readings
R70 -4.43dcV / -2.84dcV
R68 -2.53dcV / -2.84dcV
R69 -2.64dcV / -2.84dv

Replace the shunt to the normal position and repeat all voltage measurements.

 

[JingleDjango]

Is the 10MΩ resistor on the ratio pcb optional in both revisions? Neither of my Rev. D kits included one.

(I had a couple lying around from a another project which I used, I'm just curious.)

 

[Potato Cakes]

Is the 10MΩ resistor on the ratio pcb optional in both revisions? Neither of my Rev. D kits included one.

(I had a couple lying around from a another project which I used, I'm just curious.)

From the Rev A build manual:

"Note: The revision A includes an optional 10M resistor on the ratio PCB (R-OPT). This resistor was not in the original revision A, but was added to later revisions to prevent audible pops when switching ratios. "

Thanks!

Paul

 

[ratty_7]

Hi Guys,

I have 2 new Rev A's V1.12
Build was great, however, 
I have a pretty interesting problem here with 3rd Calibration of my 2nd unit ....!!!

With the input at 0.775VAC  @ 1k
All other settings as per 3rd calibration steps

I can only get R44 to about -15db instead of -10db where it is suppose to be. No matter what I do with the R44 and the front panel pot, I cannot get the meter to -10db 

Any ideas
Mike

 

[StudioJakubka]

HI there, Rev A v1.12 problem with Q bias adjustment. No reaction of output AV to R59 adjustment. On T18 I measure -1.75V to -1.01V when moved from CCW to CW, howeberoutput remains still the same. Any idea?

 

[YoDudeRock]

I have built my 7th FET/RACK Rev A "Blue Stripe" (with Stereo Link), but encountered a problem this time.    In GR mode the needle doesn't go to 0 on the VU meter (just sits motionless on the left), but +4 and +8 DO seem to work properly.    Also, there's a low frequency rumble noise when I rotate the Output knob and more so at the top of the range of the knob.
Sound does come out of the output and it DOES seem to be compressing somewhat based on the sound.

Any ideas where I should start to get this thing going?

Thanks,
Chris

 

[dencul]

Regarding recent build of Hairball Rack Revision D. 

Scratching my head here. Calibration steps 1 & 2 seem to go fine. Then, 3rd step I get no movement in the VU meter and no change in VAC (multimeter @ output xlr) when Attack is switched ON/OFF.

I measured all resistors with multimeter upon initial installation and have since double checked every resistor with the color code calculator. All check out fine.

I have inspected and reflowed solder joints, tested continuity of attack switch, and tested transistor voltages against “typical voltages” schematic, and followed many threads here to no avail.

Any help would be much appreciated.

 

[Echo North]

Hi Guys,

I have 2 new Rev A's V1.12
Build was great, however, 
I have a pretty interesting problem here with 3rd Calibration of my 2nd unit ....!!!

With the input at 0.775VAC  @ 1k
All other settings as per 3rd calibration steps

I can only get R44 to about -15db instead of -10db where it is suppose to be. No matter what I do with the R44 and the front panel pot, I cannot get the meter to -10db 

Any ideas
Mike

So you can get a 10dB drop at the output but can not get the meter to calibrate to show the 10dB drop?

Mike

 

[Echo North]

HI there, Rev A v1.12 problem with Q bias adjustment. No reaction of output AV to R59 adjustment. On T18 I measure -1.75V to -1.01V when moved from CCW to CW, howeberoutput remains still the same. Any idea?

What is the DC at the GATE of Q1 when you rotate the Qbias to both sides?

Mike

 

[Echo North]

I have built my 7th FET/RACK Rev A "Blue Stripe" (with Stereo Link), but encountered a problem this time.    In GR mode the needle doesn't go to 0 on the VU meter (just sits motionless on the left), but +4 and +8 DO seem to work properly.    Also, there's a low frequency rumble noise when I rotate the Output knob and more so at the top of the range of the knob.
Sound does come out of the output and it DOES seem to be compressing somewhat based on the sound.

Any ideas where I should start to get this thing going?

Thanks,
Chris

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

 

[Echo North]

Regarding recent build of Hairball Rack Revision D. 

Scratching my head here. Calibration steps 1 & 2 seem to go fine. Then, 3rd step I get no movement in the VU meter and no change in VAC (multimeter @ output xlr) when Attack is switched ON/OFF.

I measured all resistors with multimeter upon initial installation and have since double checked every resistor with the color code calculator. All check out fine.

I have inspected and reflowed solder joints, tested continuity of attack switch, and tested transistor voltages against “typical voltages” schematic, and followed many threads here to no avail.

Any help would be much appreciated.

Sounds like you have an issue with your GR Amp (which also includes the ratio PCB).

1. Set up your unit with a 0dB 1K signal on the input, in/out at 12 o'clock, attack release full CW.
2. Measure the AC at TP22 at each ratio setting
3. Measure the DC at TP21 at each ratio setting

Report here.

Mike

 

[dencul]

Sounds like you have an issue with your GR Amp (which also includes the ratio PCB).

1. Set up your unit with a 0dB 1K signal on the input, in/out at 12 o'clock, attack release full CW.
2. Measure the AC at TP22 at each ratio setting
3. Measure the DC at TP21 at each ratio setting

Report here.

Mike

0dB 1K signal on the input, in/out at 12 o'clock, attack release full CW.

AC at TP22
20 = 0.856 VAC
12 = 0.509 VAC
  8 = 0.339 VAC
  4 = 0.191 VAC

DC at TP21
20 = -6.57 VDC
12 = -3.517 VDC
  8 = -2.379 VDC
  4 = -1.423 VDC

 

[Echo North]

0dB 1K signal on the input, in/out at 12 o'clock, attack release full CW.

AC at TP22
20 = 0.856 VAC
12 = 0.509 VAC
  8 = 0.339 VAC
  4 = 0.191 VAC

DC at TP21
20 = -6.57 VDC
12 = -3.517 VDC
  8 = -2.379 VDC
  4 = -1.423 VDC

Nothing seems too wacky there.

Under the same conditions, what is your ACV with all 4 ratios at the anode (side without the line) of CR2?

Mike

 

[dencul]

Nothing seems too wacky there.

Under the same conditions, what is your ACV with all 4 ratios at the anode (side without the line) of CR2?

Mike

VAC anode of CR2:

20 = 0.002 VAC
12 = 0.001 VAC
  8 = 0 VAC
  4 = 0 VAC

 

[Echo North]

VAC anode of CR2:

20 = 0.002 VAC
12 = 0.001 VAC
  8 = 0 VAC
  4 = 0 VAC

Ya your signal is dying in your GR AMP.

This is the old rev D voltage sheet but it should still apply:
http://mnats.net/files/1176REVD_VOLTS.pdf

Check your DC voltages in your GR AMP section.  Looks for misplaced resistors, bad joints, all that good stuff.

Mike

 

[ratty_7]

So you can get a 10dB drop at the output but can not get the meter to calibrate to show the 10dB drop?

Mike

Ok....  With the Ratio at 20:1 and the meter at +4 and the input at around 11 o'clock and the out put at 9 o'clock attack off/on I get a drop of -10dB from 0db on the meter. After re-calibrating steps 1 & 2 on both units, when I turn the attack on and the meter from +4 to GR, I am now getting a drop of almost -10db. In the pic below the inputs and outputs ended up on both units and they were exactly the same, except the meter is a little out ....?