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

[ccommon]

Calibration has to be done in order. If you can't get the qbias set, you need to stop there and figure that out before moving on.

What is your DC at PAD 18 at each extreme of the qbias pot?

Mike

Looks Like -1.5 with the Q bias cranked .

Also , I noticed Q6 is Getting Pretty hot , Is that normal ?

 

[Echo North]

Looks Like -1.5 with the Q bias cranked .

Also , I noticed Q6 is Getting Pretty hot , Is that normal ?

Need the range.  High and low.

Yes Q6 will burn your hand off. Keep the heat sink on it.

 

[ccommon]

Need the range.  High and low.

Yes Q6 will burn your hand off. Keep the heat sink on it.

At q bias all the way up it is -1.5VDC , half way Down is read -.532VDC
Then it's at O.1 vdc all the way down .

 

[Echo North]

At q bias all the way up it is -1.5VDC , half way Down is read -.532VDC
Then it's at O.1 vdc all the way down .

Seems good.

So when you walk through the calibration steps, starting with the trimmer maxed to -1.5 as you roll towards zero it won't drop the 1db?

You have the new V1.12 Rev A PCB?

Mike

 

[ccommon]

Seems good.

So when you walk through the calibration steps, starting with the trimmer maxed to -1.5 as you roll towards zero it won't drop the 1db?

You have the new V1.12 Rev A PCB?

Mike

Yes it is the new PCB.  I bought two of the kits second hand , un-built.

No, it will not drop . But the meter in the unit drops as I turn down the Q bias , but nothing like how the first one I built . There is no sudden drop .

 

[Echo North]

Yes it is the new PCB.  I bought two of the kits second hand , un-built.

No, it will not drop . But the meter in the unit drops as I turn down the Q bias , but nothing like how the first one I built . There is no sudden drop .

And you're in bypass right?

(this is my last post before bed, I'll check back in the AM).

Mike

 

[ccommon]

And you're in bypass right?

(this is my last post before bed, I'll check back in the AM).

Mike

Yes , it's in by-pass

I'm hitting the hay as well .  I'll bug you tomorrow haha.
  Thanks again
-Chris

 

[mixmasta]

Ya on the rev A that should have something (roughly) like -0.5 to -1.5 VDC.

What is your DC range at pad 18 rotating the pot?

Make sure R60, R83, and the trimmer R59 are all the correct value and properly soldered.

Mike

At pad 18, I get -1.78VDC to about -1.03VDC for the q bias trimmer range.

Checked the resistors and trimmer and they look correct and solder pads are fine.

 

[ccommon]

At pad 18, I get -1.78VDC to about -1.03VDC for the q bias trimmer range.

Checked the resistors and trimmer and they look correct and solder pads are fine.

Yes ,

At TP18 I also Get  -1.784 VDC to -1.02 VDC

( this is all with No Signal, and the Q bias all the way up )

TP19 -1.56 VDC
TP21 -6.04 VDC ?? on my other Rev a its around -1.54 VDC
TP22  0.02
TP7 -1.56 VDC
TP17 0.0
TP15 0.0
TP1 0.0
TP10 12.56
TP11 12.38

ALSO , with It  in Bypass , if i Adjust the release , The front meter drops ?

 

[Echo North]

Yes ,

At TP18 I also Get  -1.784 VDC to -1.02 VDC

( this is all with No Signal, and the Q bias all the way up )

TP19 -1.56 VDC
TP21 -6.04 VDC ?? on my other Rev a its around -1.54 VDC
TP22  0.02
TP7 -1.56 VDC
TP17 0.0
TP15 0.0
TP1 0.0
TP10 12.56
TP11 12.38

ALSO , with It  in Bypass , if i Adjust the release , The front meter drops ?

What's your AC V at TP15 with a 1K 0dB signal w/ GR OFF and input/output midway? What is it at the output XLR pin 2?

Mike

 

[Echo North]

At pad 18, I get -1.78VDC to about -1.03VDC for the q bias trimmer range.

Checked the resistors and trimmer and they look correct and solder pads are fine.

But you still have a constant 0 DC V at the gate of Q1?

 

[ccommon]

What's your AC V at TP15 with a 1K 0dB signal w/ GR OFF and input/output midway? What is it at the output XLR pin 2?

Mike

looks like 16.5 V AC

 

[mixmasta]

But you still have a constant 0 DC V at the gate of Q1?

Yes, I just checked again, 0 DC at the Q1 gate no matter where the q bias trim is.

 

[Echo North]

looks like 16.5 V AC

Where? At pad 15 or the output?

 

[Echo North]

Yes, I just checked again, 0 DC at the Q1 gate no matter where the q bias trim is.

Examine your release pot. Is it soldered well? Are and of the three legs broken off the body?

Mike

 

[ccommon]

Where? At pad 15 or the output?

At TP15 I get 4.8 V AC , and the pin 2 on the out put i get 16.5 V AC

Thanks again for the support
-C

 

[Echo North]

At TP15 I get 4.8 V AC , and the pin 2 on the out put i get 16.5 V AC

Thanks again for the support
-C

Pin 2 seems super hot. What is it measuring between out + and out -?

You have 0.775 VAC between between in + and in -?

Mike

 

[ccommon]

Pin 2 seems super hot. What is it measuring between out + and out -?

You have 0.775 VAC between between in + and in -?

Mike

Yeah , it seems really hot .  and I do have 0.775 at the Input .

 

[Echo North]

Yeah , it seems really hot .  and I do have 0.775 at the Input .

You should have about 2.5 VAC at 15 (using the enclosure as common) and 7.5VAC (20ish dB) between the output + and - if I recall. That's with no GR and the pots midway assuming you have the in/out max position aligned to "0" on the front panel and then set them to "24" for measurement.  0.775 AC V at the input is between + and - input...not the enclosure.

If all that is correct and you're still that hot then you have something off in the signal line or signal preamp. Probably the first one. Visually read and check all of the R values.  Check the schematic w/ voltages in those sections.

http://mnats.net/files/1176REVA_125_VOLTAGES.pdf

Voltatages are always checked using the enclosure as your reference (black probe) except when measuring the input/output AC level. That is always done between input/output +/- also known as pin 2 and pin 3.

Mike

 

[ccommon]

You should have about 2.5 VAC at 15 (using the enclosure as common) and 7.5VAC (20ish dB) between the output + and - if I recall. That's with no GR and the pots midway assuming you have the in/out max position aligned to "0" on the front panel and then set them to "24" for measurement.  0.775 AC V at the input is between + and - input...not the enclosure.

If all that is correct and you're still that hot then you have something off in the signal line or signal preamp. Probably the first one. Visually read and check all of the R values.  Check the schematic w/ voltages in those sections.

http://mnats.net/files/1176REVA_125_VOLTAGES.pdf

Voltatages are always checked using the enclosure as your reference (black probe) except when measuring the input/output AC level. That is always done between input/output +/- also known as pin 2 and pin 3.

Mike

With everything set correct on the front panel and  .775 V ac across the input ,  I am getting 4.8 VAC at tp 15.

I am going to go through the line amp and pre amp now.